Patent Publication Number: US-2019180833-A1

Title: Accidental fuse programming protection circuits

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 15/798,739, filed Oct. 31, 2017, titled “ACCIDENTAL FUSE PROGRAMMING PROTECTION CIRCUITS,” which claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Patent Application No. 62/416,335, filed Nov. 2, 2016 and titled “ACCIDENTAL FUSE PROGRAMMING PROTECTION CIRCUITS,” each of which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Technical Field 
     Embodiments of the invention relate to electronic systems, and in particular, to programmable fuse cells. 
     Description of Related Technology 
     Fuse cells can be used to store data in a semiconductor die. For example, the semiconductor die can be fabricated with one or more programmable fuse cells. Additionally, a particular fuse cell can be programmed using a relatively high programming current that alters the resistivity of the fuse cell, thereby programming or blowing the fuse cell. Additionally, the resistivity of the fuse cell can be sensed to detect a value of the data stored therein. 
     SUMMARY 
     In certain embodiments, the present disclosure relates to a fuse system for a semiconductor die. The fuse system includes a plurality of pads including a first pad and a second pad, a plurality of switches including a first switch and a second switch, a fuse electrically connected in series with the first switch and the second switch between the first pad and the second pad, a biasing circuit configured to bias a control input of the first switch with a fuse programming signal to thereby control a current through the fuse, and a fuse protection capacitor electrically connected between the first pad and a control input of the second switch. The fuse protection capacitor is operable to inhibit unintended programming of the fuse by adjusting a bias of the second switch in response to a change in a voltage of the first pad relative to a voltage of the second pad. 
     In some embodiments, the biasing circuit includes a voltage regulator electrically connected between the first pad and the second pad and configured to generate a regulated voltage, and a programming logic circuit configured to generate the fuse programming signal based on the regulated voltage. 
     In a number of embodiments, the voltage regulator is further configured to bias the control input of the second switch, and the fuse protection capacitor is operable to prevent accidental programming of the fuse arising from a delay of the voltage regulator in providing voltage regulation. 
     In various embodiments, the voltage regulator is a low dropout regulator. 
     According to several embodiments, the programming logic circuit includes a level shifter configured to generate the fuse programming signal by level shifting a control signal. The level shifter is configured to control the fuse programming signal to a first voltage level about equal to the voltage of the first pad in a first state of the control signal, and to control the fuse programming signal to a second voltage level about equal to the regulated voltage in a second state of the control signal. 
     In some embodiments, the fuse system further includes a serial interface configured to provide a control signal to the programming logic circuit to instruct programming of the fuse. 
     In a number of embodiments, the first switch is implemented as a fuse programming field-effect transistor, and the second switch is implemented as a cascode field-effect transistor. 
     According to various embodiments, the first pad is a shared power supply and fuse programming pad and the second pad is a ground pad. 
     In accordance with some embodiments, the fuse system further includes a fuse sensing circuit electrically connected to the fuse and configured to detect a state of the fuse. 
     In several embodiments, the biasing circuit is further configured to bias the control input to the second switch based on a voltage difference between the first pad and the second pad. 
     In certain embodiments, the present disclosure relates to a method of protecting from accidental fuse programming. The method includes biasing a control input of a first switch with a fuse programming signal. The method further includes controlling a current through the fuse based on the fuse programming signal, the fuse electrically connected in series with the first switch and a second switch between a first pad and a second pad. The method further includes inhibiting unintended programming of the fuse by adjusting a bias of the second switch using a fuse protection capacitor in response to a change in a voltage of the first pad relative to a voltage of the second pad, the fuse protection capacitor electrically connected between the first pad and a control input of the second switch. 
     In a number of embodiments, the method further includes biasing the control input of the second switch based on a voltage difference between the first pad and the second pad. 
     In some embodiments, the method further includes generating a regulated voltage using a voltage regulator that is electrically connected between the first pad and the second pad, and generating the fuse programming signal based on the regulated voltage. 
     In several embodiments, the method further includes biasing the control input of the second switch using the voltage regulator, and preventing accidental programming of the fuse arising from a delay of the voltage regulator in providing voltage regulation. 
     In certain embodiments, the present disclosure relates to a packaged module. The packaged module includes a package substrate and a semiconductor die attached to the package substrate. The semiconductor die includes a first switch, a second switch, and a fuse electrically connected in series with one another between a first pad and a second pad. The semiconductor die further includes a biasing circuit configured to bias a control input of the first switch with a fuse programming signal to thereby control a current through the fuse, and a fuse protection capacitor electrically connected between the first pad and a control input of the second switch. The fuse protection capacitor is operable to inhibit unintended programming of the fuse by adjusting a bias of the second switch in response to a change in a voltage of the first pad relative to a voltage of the second pad. 
     In some embodiments, the biasing circuit includes a voltage regulator electrically connected between the first pad and the second pad and configured to generate a regulated voltage, and a programming logic circuit configured to generate the fuse programming signal based on the regulated voltage. 
     In several embodiments, the voltage regulator is further configured to bias the control input of the second switch, and the fuse protection capacitor is operable to prevent accidental programming of the fuse arising from a delay of the voltage regulator in providing voltage regulation. 
     In various embodiments, the programming logic circuit includes a level shifter configured to generate the fuse programming signal by level shifting a control signal. The level shifter is configured to control the fuse programming signal to a first voltage level about equal to the voltage of the first pad in a first state of the control signal, and to control the fuse programming signal to a second voltage level about equal to the regulated voltage in a second state of the control signal. 
     In accordance with a number of embodiments, the first pad is a shared power supply and fuse programming pad and the second pad is a ground pad, and the semiconductor die further includes a core circuit configured to receive power from the first pad and the second pad. 
     In some embodiments, the biasing circuit is further configured to bias the control input to the second switch based on a voltage difference between the first pad and the second pad. 
     In certain embodiments, the present disclosure relates to a fuse system for a semiconductor die. The fuse system includes a plurality of pads including a first pad and a second pad, a fuse programming transistor, a cascode transistor, a fuse cell electrically connected in series with the fuse programming transistor and the cascode transistor between the first pad and the second pad, a bias generator configured to generate a fuse programming voltage that controls a gate of the fuse programming transistor and to generate a cascode bias voltage that controls a gate of the cascode transistor, and a fuse protection capacitor electrically connected between the gate of the cascode transistor and the first pad and operable to inhibit unintended programming of the fuse cell by adjusting the cascode bias voltage in response to a change in a voltage of the first pad relative to a voltage of the second pad. 
     In some embodiments, the fuse system further includes a fuse protection diode in series with the fuse programming transistor, the cascode transistor, and the fuse cell between the first pad and the second pad. 
     In a number of embodiments, the bias generator includes a voltage regulator that generates a regulated voltage, and a programming logic circuit that generates the fuse programming voltage based on the regulated voltage. 
     In several embodiments, the programming logic circuit includes a level shifter that generates the fuse programming voltage. 
     In accordance with some embodiments, the fuse system further includes a serial interface configured to provide a control signal to the programming logic circuit to instruct programming of the fuse cell. 
     In a number of embodiments, the fuse system further includes a fuse sensing circuit electrically connected to the fuse cell and configured to detect a state of the fuse cell. 
     In some embodiments, the fuse programming transistor and the cascode transistor are p-type. 
     In several embodiments, the first pad is a shared power supply and fuse programming pad and the second pad is a ground pad. 
     In accordance with a number of embodiments, the fuse programming transistor and the cascode transistor are n-type. 
     In a number of embodiments, the first pad is a shared power supply and fuse programming pad and the second pad is a ground pad. 
     In certain embodiments, the present disclosure relates to a method of protecting a fuse system of an integrated circuit from accidental programming. The method includes providing a bias generator with a power supply voltage and a ground voltage from a pair of pads including a first pad and a second pad, generating a fuse programming voltage and a cascode bias voltage using the bias generator, providing the fuse programming voltage to a gate of a fuse programming transistor and the cascode bias voltage to a gate of the cascode transistor, the fuse programming transistor and the cascode transistor in series with a fuse cell between the first pad and the second pad, and inhibiting accidental programming of the fuse cell by increasing the cascode bias voltage in response to an increase in a voltage of the first pad relative to a voltage of the second pad using a fuse protection capacitor. 
     In some embodiments, the method further includes inhibiting accidental programming of the fuse cell using a fuse protection diode this is electrically connected in series with the fuse programming transistor, the cascode transistor, and the fuse cell between the first pad and the second pad. 
     In certain embodiments, the present disclosure relates to a packaged module. The packaged module includes a package substrate and a semiconductor die attached to the package substrate. The semiconductor die includes a first pad, a second pad, a fuse programming transistor, a cascode transistor, a fuse cell electrically connected in series with the fuse programming transistor and the cascode transistor between the first pad and the second pad, a bias generator configured to generate a fuse programming voltage that controls a gate of the fuse programming transistor and to generate a cascode bias voltage that controls a gate of the cascode transistor, and a fuse protection capacitor electrically connected between the gate of the cascode transistor and the first pad. The fuse protection capacitor is operable to inhibit unintended programming of the fuse cell by adjusting the cascode bias voltage in response to a change in a voltage of the first pad relative to a voltage of the second pad. 
     In some embodiments, the packaged module further includes a fuse protection diode in series with the fuse programming transistor, the cascode transistor, and the fuse cell between the first pad and the second pad. 
     In a number of embodiments, the bias generator includes a voltage regulator that generates a regulated voltage, and a programming logic circuit that generates the fuse programming voltage based on the regulated voltage. 
     In several embodiments, the programming logic circuit includes a level shifter that generates the fuse programming voltage. 
     In accordance with some embodiments, the packaged module further includes a serial interface configured to provide a control signal to the programming logic circuit to instruct programming of the fuse cell. 
     In some embodiments, the packaged module further includes a fuse sensing circuit electrically connected to the fuse cell and configured to detect a state of the fuse cell. 
     According to a number of embodiments, the fuse programming transistor and the cascode transistor are p-type. 
     In accordance with several embodiments, the first pad is a shared power supply and fuse programming pad and the second pad is a ground pad. 
     In some embodiments, the fuse programming transistor and the cascode transistor are n-type. 
     In a number of embodiments, the first pad is a shared power supply and fuse programming pad and the second pad is a ground pad. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of this disclosure will now be described, by way of non-limiting example, with reference to the accompanying drawings. 
         FIG. 1A  is a schematic diagram of one embodiment of a fuse system for a semiconductor die or integrated circuit (IC). 
         FIG. 1B  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 2  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 3  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 4A  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 4B  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 5  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 6A  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 6B  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 7  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 8  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 9  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 10A  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 10B  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 11A  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 11B  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 11C  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 11D  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 11E  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 11F  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 11G  is a schematic diagram of another embodiment of a fuse system for an IC. 
         FIG. 12A  is a schematic diagram of one embodiment of a packaged module. 
         FIG. 12B  is a schematic diagram of a cross-section of the packaged module of  FIG. 12A  taken along the lines  12 B- 12 B. 
         FIG. 13  is a schematic diagram of one embodiment of a mobile device. 
         FIG. 14  is a schematic diagram of one embodiment of a base station. 
         FIG. 15  is a schematic diagram of one embodiment of an RF system. 
         FIG. 16  is a schematic diagram of one example of a power amplifier system. 
         FIG. 17  is a schematic diagram of one embodiment of a semiconductor die with a fuse system. 
         FIG. 18  is a schematic diagram of another embodiment of a semiconductor die with a fuse system. 
         FIG. 19  is a schematic diagram of another embodiment of a mobile device. 
     
    
    
     DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS 
     The following detailed description of certain embodiments presents various descriptions of specific embodiments. However, the innovations described herein can be embodied in a multitude of different ways, for example, as defined and covered by the claims. In this description, reference is made to the drawings where like reference numerals can indicate identical or functionally similar elements. It will be understood that elements illustrated in the figures are not necessarily drawn to scale. Moreover, it will be understood that certain embodiments can include more elements than illustrated in a drawing and/or a subset of the elements illustrated in a drawing. Further, some embodiments can incorporate any suitable combination of features from two or more drawings. 
     Examples of Fuse Systems with a Fuse Protection Capacitor 
     A semiconductor die or integrated circuit (IC) can be implemented with a fuse system that includes one or more fuse cells. A fuse cell is also referred to herein as a fuse. To reduce a cost and/or size of the semiconductor die, it is desirable for the fuse cells to be programmable without needing to use dedicated fuse programming pads. As used herein, pads of an IC can also be referred to as pins or contacts. 
     In certain implementations herein, a fuse system is programmable using a shared power supply and fuse programming pad. Thus, rather than providing programming using a dedicated fuse programming pad, the pad used for fuse programming is shared with a power supply pad of the semiconductor die. Implementing the fuse system in this manner can provide a number of advantages, such as reduced pin count and/or enhanced quality of power supply distribution by increasing the number of power supply pads that provide power during normal operation. 
     Although implementing a fuse system with a shared power supply and fuse programming pad provides certain advantages, implementing the fuse system in this manner also exposes the fuse system to power supply transients. For example, the shared power supply and fuse programming pad is connected to a supply voltage during operation of the IC, and thus the fuse system operates with reduced electrical isolation relative to an implementation using a dedicated fuse programming pad. 
     A shared power supply and fuse programming pad can suffer from power supply transients, such as rapid rising and/or falling edges or glitches. For example, a power supply transients can arise during IC turn-on and/or periods of high chip activity. Moreover, the shared power supply and fuse programming pad can be subjected to electrical overstress, including, but not limited to, electrostatic discharge (ESD) events. 
     Thus, implementing a fuse system using a shared power supply and fuse programming pad advantageously reduces IC pin count, but also exposes the fuse system to power supply transients. Absent a protection scheme, the power supply transients can lead to inadvertent or accidental programming of fuse cells. 
     Apparatus and methods for protection against inadvertent programming of fuse cells are provided herein. In certain configurations, a fuse system includes a fuse programming transistor, a cascode transistor, and a fuse cell electrically connected in series between a first pad (for instance, a power supply pad) and a second pad (for instance, a ground pad). The fuse system further includes a bias generator that controls an amount of current provided to the fuse cell based on biasing a gate of the fuse programming transistor and a gate of the cascode transistor. The fuse system further includes a fuse protection capacitor electrically connected between the first pad and the gate of the cascode transistor to prevent inadvertent programming of the fuse cell in response to an increase in voltage of the first pad relative to the second pad. 
     In contrast, a fuse system that omits the fuse protection capacitor may inadvertently program the fuse cell in response to a transient increase in voltage of the first pad. For example, in response to a rising voltage edge on the first pad, current can flow from the first pad to the second pad through the fuse cell, and thereby cause accidental programming. 
     Accordingly, including the fuse protection capacitor enhances a robustness of the fuse system to voltage transients of the pads. Additionally, the fuse protection capacitor increases chip yield by reducing the likelihood that a particular semiconductor die is defective due to fuse cells that are incorrectly programmed. Thus, the teachings herein can be used to improve fuse yield and/or reduce field returns. 
       FIG. 1A  is a schematic diagram of one embodiment of a fuse system  20  for a semiconductor die or IC. The fuse system  20  includes a fuse cell or fuse  1 , a bias generator or biasing circuit  2 , a fuse sensing circuit  3 , a fuse programming p-type field-effect transistor (PFET)  11 , a cascode PFET  12 , a first pad  15 , a second pad  16 , and a fuse protection capacitor  21 . In the illustrated embodiment, the first pad  15  corresponds to a shared power supply and fuse programming pad, and the second pad  16  corresponds to a ground pad. 
     Although the illustrated fuse system  20  includes one fuse cell, the fuse system  20  can be adapted to include additional fuse cells. 
     As shown in  FIG. 1A , the fuse programming PFET  11 , the cascode PFET  12 , and the fuse cell  1  are electrically connected in series between the first pad  15  and the second pad  16 . Including the cascode PFET  12  enhances the reliability of the fuse system  20  by preventing the fuse programming PFET  11  from being exposed to overvoltage conditions that can lead to transistor damage and/or breakdown. 
     For example, the illustrated FETs may be rated to have a maximum gate-to-drain and/or gate-to-source voltage for a particular process. Including a series combination of two or more FETs can aid in achieving compliance with overstress and/or reliability specifications. Although an example with two transistors in series in shown, the teachings herein are applicable to configurations including more or fewer transistors in series. For example, two or more cascode transistors can be included in series with a fuse programming transistor. 
     In one implementation, the bias generator  2  controls the cascode bias voltage BIAS based on a voltage difference between the first pad  15  and the second pad  16 , for instance, to a voltage level that is about halfway between the voltage of the first pad  15  and the voltage of the second pad  16 . However, other implementations are possible. 
     The bias generator  2  receives a control signal CTL, which is used to instruct the bias generator  2  to program the fuse cell  1 . The bias generator  2  is electrically connected to the first pad  15  and the second pad  16  to receive power. As shown in  FIG. 1A , the bias generator  2  generates a programming control voltage PRG, which is used to control the gate of the fuse programming PFET  11 . Additionally, the bias generator  2  generates a cascode bias voltage BIAS, which is used to control the gate of the cascode PFET  12 . In certain configurations, the fuse programming PFET  11  and the cascode PFET  12  are implemented as metal oxide semiconductor (MOS) transistors. 
     The programming control voltage PRG controls an amount of current flowing through the fuse programming PFET  11  and the cascode PFET  12 , and a corresponding current through the fuse cell  1 . For example, during a fuse programming operation, the programming control voltage PRG controls the gate of the fuse programming PFET  11  to generate a programming current that is sufficiently large to program the fuse cell  1 . 
     In one specific example, the fuse cell  1  is implemented using a polysilicon fuse that has low resistance prior to programming (when the fuse cell is unblown) and a higher resistance after programming (when the fuse cell is blown). Additionally, the polysilicon fuse is programmed by providing a relatively large current for a sufficient period of time. Although one specific example of fuse cell implementation has been described, the fuse cell  1  can be implemented in a wide variety of ways. 
     The fuse sensing circuit  3  is used to sense a state of the fuse cell  1  based on detecting the fuse cell&#39;s resistivity. In the illustrated embodiment, an input to the fuse sensing circuit  3  is electrically connected to a first terminal of the fuse cell  1 . As shown in  FIG. 1A , the fuse sensing circuit  3  generates a data output signal OUT based on reading the state of the fuse cell  1 . 
     Absent a protection scheme, the fuse cell  1  can be accidentally programmed during power supply transients, such as sharp edges of the supply voltage provided to the first pad  15  and/or during an ESD event between the first pad  15  and the second pad  16 . 
     For example, the illustrated fuse system  20  includes the bias generator  2  for controlling programming of the fuse cell  1 . However, during certain power supply transients, such as during an ESD event and/or sharp power supply edges, the bias generator  2  can bias the fuse programming PFET  11  and/or the cascode PFET  12  to an improper bias level. Absent a protection scheme, a current can flow through the fuse cell  1  and lead to inadvertent programming of the fuse cell  1 . The improper transistor biasing can arise from a delay of the bias generator  2  in generating bias voltages, such as the programming control voltage PRG and the cascode bias voltage BIAS. 
     As shown in  FIG. 1A , the fuse protection capacitor  21  is used to provide coupling to the gate of the cascode PFET  12 . Including the fuse protection capacitor  21  compensates for a delay of the bias generator  2  in controlling the voltage level of the cascode bias voltage BIAS. For example, the fuse protection capacitor  21  provides coupling from the shared power supply and fuse programming pad  15  to the gate of the cascode PFET  12 , thereby helping to maintain the cascode PFET  12  turned off in response to a rising edge of the supply voltage. 
     The fuse protection capacitor  21  serves to increase the gate voltage of the cascode PFET  12  in response to a rising edge of the supply voltage received at the first pad  15 . Thus, the gate voltage of the cascode PFET  12  rises in response to a sharp edge of the supply voltage, and thus serves to delay or cut off a current path through the fuse cell  1 . 
     As persons of ordinary skill in the art will appreciate, the impedance of the fuse protection capacitor  21  is frequency dependent, and the fuse protection capacitor  21  passes high frequency signal components while blocking low frequency signal components. For instance, the fuse protection capacitor  21  can behave as a short circuit in response to a voltage signal having a frequency above a high frequency threshold and as an open circuit in response to a voltage signal having a frequency below a low frequency threshold. The high and low frequency thresholds are dependent, in part, on the capacitance value of the fuse protection capacitor  21 . In certain implementations, a capacitance value of the fuse protection capacitor  21  is selected such that the fuse protection capacitor  21  behaves as a short circuit in response to high-frequency events, such as ESD events and/or sharp power supply edges, and otherwise behaves as an open circuit. 
     Accordingly, including the fuse protection capacitor reduces the likelihood that the fuse cell  1  is accidentally programmed or burnt in response to increase in the voltage of the first pad  15  relative to the second pad  16 . 
     In contrast, when the fuse protection capacitor  21  is omitted, the fuse cell  1  may be inadvertently programmed in response to a sudden increase in the voltage of the first pad  15 . For example, after the voltage of the first pad  15  increases, a delay of the bias generator  2  can result in the programming control voltage PRG and/or the cascode bias voltage BIAS may still have a relatively low voltage. Additionally, the bias voltage levels can lead to the presence of a conductive path through which a relatively large current (for instance, a large ESD current) can flow. 
     Thus, a fuse cell can be programmed (for instance, burnt) by accident during ESD or other sharp voltage edges on the supply voltage VDD. By including the fuse protection capacitor  21 , the likelihood of accidental programming of the fuse cell  1  can be reduced. 
     The fuse protection capacitor  21  corresponds to an explicit capacitor, rather than mere parasitic capacitance. In one embodiment, the fuse protection capacitor  21  has a capacitance of at least 1 pF. 
       FIG. 1B  is a schematic diagram of another embodiment of a fuse system  25  for an IC. The fuse system  25  includes a fuse cell or fuse  1 , a biasing circuit  2 , a fuse sensing circuit  3 , a first switch  4 , a second switch  5 , a first pad  15 , a second pad  16 , and a fuse protection capacitor  21 . In the illustrated embodiment, the first pad  15  corresponds to a shared power supply and fuse programming pad, and the second pad  16  corresponds to a ground pad. 
     The fuse system  25  of  FIG. 1B  is similar to the fuse system  20  of  FIG. 1A , except that the fuse system  25  illustrates an embodiment in which the biasing circuit  2  biases a control input of the first switch  4  with a fuse programming signal PRG (which can be a voltage and/or current) to thereby control a current through the fuse  1 . Additionally, the biasing circuit  2  biases a control input of the second switch  4  with a bias signal BIAS (which can be a voltage and/or current). As shown in  FIG. 1B , the fuse protection capacitor  21  is connected between the first pad  15  and the control input to the second switch  5 . In certain implementations, the first switch  4  and the second switch  5  are implemented as FETs, such as PFETs as in the embodiment of  FIG. 1A . However, the first switch  4  and the second switch  5  can correspond to any suitable type of switches for controlling the current through the fuse  1 . 
     Although various embodiments are depicted herein in the context of FET implementations, the fuse systems herein can be implemented using a wide variety of types of switches, including, but not limited to, voltage-controlled switches. 
       FIG. 2  is a schematic diagram of another embodiment of a fuse system  30  for an IC. The fuse system  30  includes a fuse cell  1 , a bias generator  2 , a fuse sensing circuit  3 , a fuse programming n-type field-effect transistor (NFET)  51 , a cascode NFET  52 , a first pad  15 , a second pad  16 , and a fuse protection capacitor  21 . 
     The fuse system  30  of  FIG. 2  is similar to the fuse system  20  of  FIG. 1A , except that the fuse system  30  of  FIG. 2  illustrates a complementary implementation using an n-type transistors rather than p-type transistors. The fuse systems herein are applicable to a wide variety of configurations, including implementations using p-type transistors, n-type transistors, or a combination of p-type and n-type transistors. 
     As shown in  FIG. 2 , the fuse cell  1 , the cascode NFET  52 , and the fuse programming NFET  51  are electrically connected in series between the first pad  15  and the second pad  16 . Additionally, the fuse sensing circuit  3  includes an input electrically connected to a first terminal of the fuse cell  1 . Furthermore, the bias generator  2  is electrically connected between the first pad  15  and the second pad  16  to receive power. As shown in  FIG. 2 , the bias generator  2  generates a programming control voltage PRG for a gate of the fuse programming NFET  51  and a cascode bias voltage BIAS for the cascode NFET  52 . 
     As shown in  FIG. 2 , the fuse protection capacitor  21  is electrically connected between the gate of the cascode NFET  52  and the ground pad  16 . Thus, in response to a sudden decrease of the voltage of the ground pad  16  (for instance, during a negative polarity ESD event), the gate voltage of the cascode NFET  52  is coupled downward to inhibit undesired current from flowing through the fuse cell  1 . 
     Additional details of the fuse system  30  can be similar to those described earlier. 
       FIG. 3  is a schematic diagram of another embodiment of a fuse system  70  for an IC. The fuse system  70  includes a fuse cell  1 , a fuse sensing circuit  3 , a fuse programming PFET  11 , a cascode PFET  12 , a first pad  15 , a second pad  16 , a serial interface  71 , a bias generator  72 , and a fuse protection capacitor  21 . 
     The fuse system  70  of  FIG. 3  is similar to the fuse system  20  of  FIG. 1A , except that the fuse system  70  of  FIG. 3  illustrates a specific implementation of a bias generator. In particular, the bias generator  72  of  FIG. 3  includes a bandgap reference circuit  81 , a low dropout (LDO) regulator  82 , and a programming logic circuit  83  that includes a level-shifter  84 . Additionally, the bias generator  72  of  FIG. 3  receives a control signal CTL over the serial interface  71 , which can be, for example, a mobile industry processor interface (MIPI) radio frequency front end (RFFE) bus, an inter integrated circuit (I 2 C) bus, or a serial peripheral interface (SPI) bus. 
     The bandgap reference circuit  81  is electrically connected between the first pad  15  and the second pad  16  to receive power. The bandgap reference circuit  81  generates a bandgap reference voltage V BG , which is substantially independent of temperature. The bandgap reference voltage V BG  serves as a reference voltage to the LDO regulator  82 , which generates one or more regulated voltages based on the supply voltage received on the first pad  15  and the bandgap reference voltage V BG . In the illustrated embodiment, the LDO regulator  82  generates the cascode bias voltage BIAS for the cascode PFET  12  and an LDO voltage V LDO  for the level shifter  84  of the programming logic circuit  83 . 
     In certain implementations, the level shifter  84  level shifts the control signal CTL received from the serial interface  71  to generate the fuse programming voltage PRG. In certain implementations, an output of the level shifter  84  is controllable between a high voltage about equal to the power supply voltage received on the first pad  15  and a low voltage about equal to the LDO voltage V LDO . The LDO voltage V LDO  can be selected based on a variety of factors, for instance to control an amount of current during programming and/or based on a maximum gate-to-source voltage of the fuse programming PFET  11  permitted for a particular process. 
     During certain power supply transients, such as during an ESD event and/or sharp power supply edges, the bias generator  72  can bias the fuse programming PFET  11  and/or the cascode PFET  12  to an improper bias level. The improper transistor biasing can arise from a delay of the bias generator  72  in generating bias voltages, such as a delay of the LDO regulator  82  in providing voltage regulation. Accordingly, after a change in voltage of the first pad  15 , the bias voltage levels of the programming control voltage PRG and/or the cascode bias voltage BIAS can temporarily operate with incorrect voltage levels. This in turn can expose the fuse cell  1  to a programming current that can cause accidental fuse programming. 
     The fuse protection capacitor  21  aids in preventing current from flowing through the fuse cell  1  in response to a sudden increase in the voltage of the first pad  15 . In particular, the fuse protection capacitor  21  serves to increase the gate voltage of the cascode PFET  12  in response to a rising edge of the supply voltage received at the first pad  15 . Thus, the gate voltage of the cascode PFET  12  rises in response to a sharp edge of the supply voltage, and thus delays or cut offs a current path through the fuse cell  1 . 
     Accordingly, including the fuse protection capacitor  21  reduces the likelihood that the fuse cell  1  is accidentally programmed or burnt in response to increase in the voltage of the first pad  15  relative to the second pad  16 . 
     Additional details of the fuse system  70  can be similar to those described earlier. 
       FIG. 4A  is a schematic diagram of another embodiment of a fuse system  100  for an IC. The fuse system  100  includes a first fuse cell  1   a , a second fuse cell  1   b , a third fuse cell  1   c , a bias generator  102 , a fuse sensing circuit  103 , a first fuse programming PFET  11   a , a second fuse programming PFET  11   b , a third fuse programming PFET  11   c , a first cascode PFET  12   a , a second cascode PFET  12   b , a third cascode PFET  12   c , a first pad  15 , a second pad  16 , and a shared fuse protection capacitor  21 . 
     The fuse system  100  of  FIG. 4A  illustrates one example of a multi-cell fuse system including multiple fuse cells. Although the illustrated fuse system  100  of  FIG. 4A  includes three fuse cells, the teachings herein are applicable to configurations including more or fewer fuse cells. Furthermore, although  FIG. 4A  illustrates an example in which biasing circuitry and fuse sensing circuitry is shared across multiple fuse cells, the teachings herein are applicable to implementations using multiple bias generators and/or multiple fuse sensing circuits. 
     As shown in  FIG. 4A , the first fuse programming PFET  11   a , the first cascode PFET  12   a , and the first fuse cell  1   a  are connected in series in a first electrical path between the first pad  15  and the second pad  16 . Additionally, the second fuse programming PFET  11   b , the second cascode PFET  12   b , and the second fuse cell  1   b  are connected in series in a second electrical path between the first pad  15  and the second pad  16 . Furthermore, the third fuse programming PFET  11   c , the third cascode PFET  12   c , and the third fuse cell  1   c  are connected in series in a third electrical path between the first pad  15  and the second pad  16 . 
     The data stored in the fuse cells can correspond to a wide variety of types of data, including, but not limited to, manufacturing identification data and/or data indicating parameters after device fabrication. For example, the fuse cells can include data used to compensate a semiconductor die for variation arising from manufacturing. 
     The fuse sensing circuit  103  includes multiple inputs connected to each of the fuse cells  11   a - 11   c . The fuse sensing circuit  103  can be used to read the state of one or more of the fuse cells and to provide output data OUT corresponding to the read data. 
     The bias generator  102  generates a first programming control voltage PRG 1  for the gate of the first fuse programming PFET  11   a , a second programming control voltage PRG 2  for the gate of the second fuse programming PFET  11   b , and a third programming control voltage PRG 3  for the gate of the third fuse programming PFET  11   c . The bias generator  102  also receives a control signal CTL, which instructs programming of the first fuse cell  1   a , the second fuse cell  1   b , and/or the third fuse cell  1   c . The bias generator  102  further generates a cascode bias voltage BIAS for the first cascode PFET  12   a , the second cascode PFET  12   b , and the third cascode PFET  12   c.    
     As shown in  FIG. 4A , the shared fuse protection capacitor  21  is electrically connected between the cascode bias voltage BIAS and the first pad  15 . Accordingly, the illustrated embodiment uses a shared fuse protection capacitor  21  to provide protection to multiple fuse cells  11   a - 11   c . Providing protection against accidental programming of fuse cells using a shared or common fuse protection capacitor  21  reduces a number of components and provides a compact layout. 
       FIG. 4B  is a schematic diagram of another embodiment of a fuse system  110  for an IC. The fuse system  110  includes a first fuse cell  1   a , a second fuse cell  1   b , a third fuse cell  1   c , a bias generator  102 , a fuse sensing circuit  103 , a first fuse programming PFET  11   a , a second fuse programming PFET  11   b , a third fuse programming PFET  11   c , a first cascode PFET  12   a , a second cascode PFET  12   b , a third cascode PFET  12   c , a first pad  15 , a second pad  16 , a first fuse protection capacitor  21   a , a second fuse protection capacitor  21   b , and a third fuse protection capacitor  21   c.    
     The fuse system  110  of  FIG. 4B  is similar to the fuse system  100  of  FIG. 4A , except that the fuse system  110  of  FIG. 4B  includes separate fuse protection capacitors for each fuse cell. 
     For example, the bias generator  102  generates a first cascode bias voltage BIAS 1  for the first cascode PFET  12   a , a second cascode bias voltage BIAS  2  for the second cascode PFET  12   b , and a third cascode bias voltage BIAS 3  for the third cascode PFET  12   c . Additionally, the first fuse protection capacitor  21   a  is connected between the first cascode bias voltage BIAS 1  and the first pad  15 , the second fuse protection capacitor  21   b  is connected between the second cascode bias voltage BIAS 2  and the first pad  15 , and the third fuse protection capacitor  21   c  is connected between the third cascode bias voltage BIAS 3  and the first pad  15 . 
     Examples of Fuse Systems with a Fuse Protection Diode 
     Apparatus and methods for protection against inadvertent programming of fuse cells are provided herein. In certain configurations, a fuse system includes a fuse protection diode, a fuse programming transistor, and a fuse cell electrically connected in series between a first pad (for instance, a power supply pad) and a second pad (for instance, a ground pad). The fuse system further includes a bias generator that biases a gate of the fuse programming transistor to control an amount of current provided to the fuse cell. The fuse protection diode helps prevent inadvertent programming of the fuse cell by blocking current from flowing through the fuse cell in response to a decrease in voltage of the first pad relative to the second pad. 
     In contrast, a fuse system that omits the fuse protection diode may inadvertently program the fuse cell in response to a transient decrease in the first pad&#39;s voltage. For example, in response to a falling voltage edge on the first pad, current can flow from the second pad to the first pad through the fuse cell, and thereby cause accidental programming. 
     Accordingly, including the fuse protection diode enhances a robustness of the fuse system to voltage transients of the pads. Additionally, the fuse protection diode increases chip yield by reducing the likelihood that a particular semiconductor die is defective due to fuse cells that are incorrectly programmed. Thus, the teachings herein can be used to improve fuse yield and/or reduce field returns. 
       FIG. 5  is a schematic diagram of another embodiment of a fuse system  120  for a semiconductor die. The fuse system  120  includes a fuse cell  1 , a bias generator  2 , a fuse sensing circuit  3 , a fuse programming PFET  11 , a first pad  15 , a second pad  16 , and a fuse protection diode  18 . In the illustrated embodiment, the first pad  15  corresponds to a shared power supply and fuse programming pad, and the second pad  16  corresponds to a ground pad. 
     Although the illustrated fuse system  120  includes one fuse cell, the fuse system  120  can be adapted to include additional fuse cells. 
     The fuse system  120  is included on a semiconductor die or IC, which includes additional pads and circuitry. For example, the semiconductor die can include a variety of other circuits, such as amplifiers, switches, and/or other circuitry, including, but not limited to, radio frequency circuits. 
     The bias generator  2  receives a control signal CTL, which is used to instruct the bias generator  2  to selectively program the fuse cell  1 . The bias generator  2  is electrically connected to the first pad  15  and the second pad  16  to receive power. As shown in  FIG. 5 , the bias generator  2  generates a programming control voltage PRG, which is used to control the gate of the fuse programming PFET  11 . In certain configurations, the fuse programming PFET  11  is implemented as a MOS transistor. Although an example with a field-effect transistor is shown, other types of switches can be used for fuse programming. For example, the bias generator  2  can bias a control input to any suitable fuse programming switch to thereby control a current through the fuse cell  1 . 
     The programming control voltage PRG controls an amount of current flowing through the fuse programming PFET  11  and a corresponding current through the fuse cell  1 . For example, during a fuse programming operation, the programming control voltage PRG controls the gate of the fuse programming PFET  11  to generate a programming current that is sufficiently large to program the fuse cell  1 . 
     The fuse sensing circuit  3  is used to sense a state of the fuse cell  1  based on detecting the fuse cell&#39;s resistivity. In the illustrated embodiment, an input to the fuse sensing circuit  3  is electrically connected to a first terminal of the fuse cell  1 . As persons having skill in the art will appreciate, the fuse sensing circuit  3  can be implemented in a wide variety of ways. As shown in  FIG. 5 , the fuse sensing circuit  3  generates a data output signal OUT based on reading the state of the fuse cell  1 . 
     Absent a protection scheme, the fuse cell  1  can be accidentally programmed during power supply transients, such as sharp edges of the supply voltage provided to the first pad  15  and/or during an ESD event between the first pad  15  and the second pad  16 . 
     For example, the illustrated fuse system  120  includes the bias generator  2  for controlling programming of the fuse cell  1 . However, during certain power supply transients, such as during an ESD event and/or sharp power supply edges, the bias generator  2  can bias the fuse programming PFET  11  to an improper bias level. Absent a protection scheme, a current can flow through the fuse cell  1  and lead to inadvertent programming of the fuse cell  1 . The improper transistor biasing can arise from a delay of the bias generator  2  in generating bias voltages, such as the programming control voltage PRG. 
     As shown in  FIG. 5 , the fuse protection diode  18 , the fuse programming PFET  11 , and the fuse cell  1  are electrically connected in series between the first pad  15  and the second pad  16 . As shown in  FIG. 5 , an anode of the fuse protection diode  18  is electrically connected to the first pad  15 , and a cathode of the fuse protection diode  18  is electrically connected to a source of the fuse programming PFET  11 . 
     Including the fuse protection diode  18  enhances the robustness of the fuse system  120  to inadvertent programming of the fuse cell  1 . 
     For example, in the illustrated embodiment, the first pad  15  corresponds to a shared power supply and fuse programming pad. Implementing the fuse system  120  in this manner advantageously reduces a pad count of a semiconductor die or IC by avoiding a need for a dedicated fuse programming pad. 
     However, implementing the fuse system  120  in this manner also increases the exposure of the fuse cell  1  to power supply transients, including, but not limited to, ESD events. 
     For example, a negative polarity ESD event and/or falling power supply edge can cause the voltage of the first pad  15  to decrease relative to the second pad  16 . Additionally, the fuse protection diode  18  inhibits the flow of current from ground pad  16  to the shared power supply and fuse programming pad  15 , thereby protecting the fuse cell  1  from current that may otherwise inadvertently program the fuse cell  1 . Thus, the fuse protection diode  18  serves to cut off a negative edge of the supply voltage. 
       FIG. 6A  is a schematic diagram of another embodiment of a fuse system  130  for an IC. The fuse system  130  includes a fuse cell  1 , a bias generator  2 , a fuse sensing circuit  3 , a fuse programming PFET  11 , a cascode PFET  12 , a first pad  15 , a second pad  16 , and a fuse protection diode  18 . 
     The fuse system  130  of  FIG. 6A  is similar to the fuse system  120  of  FIG. 5 , except that the fuse system  130  further includes the cascode PFET  12 . Additionally, as shown in  FIG. 6A , the bias generator  2  generates a cascode bias voltage BIAS for a gate of the cascode PFET  12 . In certain configurations, the fuse programming PFET  11  and the cascode PFET  12  are implemented as MOS transistors. 
     Including the cascode PFET  12  enhances the reliability of the fuse system  130  by preventing the fuse programming PFET  11  from being exposed to overvoltage conditions that can lead to transistor damage and/or breakdown. 
     For example, the fuse programming PFET  11  may be rated to have a maximum gate-to-drain and/or gate-to-source voltage for a particular process. Including a series combination of two or more FETs can aid in achieving compliance with overstress and/or reliability specifications. Although an example with two transistors in series in shown, the teachings herein are applicable to configurations including more or fewer transistors in series. For example, two or more cascode transistors can be included in series with a fuse programming transistor. 
     A delay of the bias generator  2  can lead to inappropriate bias voltage levels of the programming control voltage PRG and/or the cascode bias voltage BIAS in response to a sudden decrease in a voltage of the first pad  15  relative to a voltage of the second pad  16 . When the fuse protection diode  18  is omitted, incorrect bias voltage levels can lead to a flow of current that can inadvertently program the fuse cell  1 . 
     By adding the fuse protection diode  18 , a reverse current from the second pad  16  to the first pad  15  through the fuse cell  1  can be blocked. However, the fuse protection diode  18  still permits a programming current to flow from the first pad  15  to the second pad  16  through the fuse cell  1  when programming of the fuse cell  1  is desired. Accordingly, the fuse protection diode  18  does not inhibit the flow of a regular programming current. 
       FIG. 6B  is a schematic diagram of another embodiment of a fuse system  140  for an IC. The fuse system  140  includes a fuse cell  1 , a bias generator  2 , a fuse sensing circuit  3 , a fuse programming PFET  11 , a cascode PFET  12 , a first pad  15 , a second pad  16 , and a fuse protection diode  18 . 
     The fuse system  140  of  FIG. 6B  is similar to the fuse system  130  of  FIG. 6A , except that the fuse system  140  illustrates a different component order in the series combination of the fuse programming PFET  11 , the cascode PFET  12 , the fuse protection diode  18 , and the fuse cell  1 . In particular, in contrast to the fuse system  130  of  FIG. 6A  in which the fuse protection diode  18  is between the first pad  15  and the fuse programming PFET  11 , the fuse system  140  of  FIG. 6B  illustrates an implementation in which the fuse protection diode  18  is between the cascode PFET  12  and the fuse cell  1 . 
     Thus, the fuse protection diode  18  can be positioned in a wide variety of locations along an electrical path between the first pad  15  and the second pad  16 . Although two examples are shown, the fuse protection diode  18  can be positioned in any suitable location between the first pad  15  and the second pad  16 . 
       FIG. 7  is a schematic diagram of another embodiment of a fuse system  150  for an IC. The fuse system  150  includes a fuse cell  1 , a bias generator  2 , a fuse sensing circuit  3 , a fuse programming NFET  51 , a first pad  15 , a second pad  16 , and a fuse protection diode  18 . 
     The fuse system  150  of  FIG. 7  is similar to the fuse system  120  of  FIG. 5 , except that the fuse system  150  of  FIG. 7  illustrates a complementary implementation using an n-type fuse programming transistor rather than a p-type fuse programming transistor. The fuse systems herein are applicable to a wide variety of configurations of switches for controlling fuse programming, including, but not limited to, implementations using p-type transistors, n-type transistors, or a combination of p-type and n-type transistors. 
     As shown in  FIG. 7 , the first pad  15  corresponds to a shared power supply and fuse programming pad, and the second pad  16  corresponds to a ground pad. Additionally, the fuse programming NFET  51 , the fuse cell  1 , and the fuse protection diode  18  are electrically connected in series between the first pad  15  and the second pad  16 . Additionally, the fuse sensing circuit  3  includes an input electrically connected to a first terminal of the fuse cell  1  and to a source of the fuse programming NFET  51 . Furthermore, the bias generator  2  is electrically connected between the first pad  15  and the second pad  16  to receive power. As shown in  FIG. 7 , the bias generator  2  generates a programming control voltage PRG for a gate of the fuse programming NFET  51 . 
     Additional details of the fuse system  150  can be similar to those described earlier. 
       FIG. 8  is a schematic diagram of another embodiment of a fuse system  160  for an IC. The fuse system  160  includes a fuse cell  1 , a bias generator  2 , a fuse sensing circuit  3 , a fuse programming PFET  11 , a first pad  15 , a second pad  16 , and a fuse protection diode-connected NFET  68 . 
     The fuse system  160  of  FIG. 8  is similar to the fuse system  120  of  FIG. 5 , except that the fuse system  160  of  FIG. 8  illustrates an implementation in which the diode  18  is implemented using the diode-connected transistor. The fuse protection diode  18  of  FIG. 5  can be implemented in a variety of ways, including, but not limited to, as a p-n junction diode or a diode-connected transistor. 
     Additional details of the fuse system  160  can be similar to those described earlier. 
       FIG. 9  is a schematic diagram of another embodiment of a fuse system  170  for an IC. The fuse system  170  includes a fuse cell  1 , a fuse sensing circuit  3 , a fuse programming PFET  11 , a cascode PFET  12 , a first pad  15 , a second pad  16 , a fuse protection diode  18 , a serial interface  71 , and a bias generator  72 . 
     The fuse system  170  of  FIG. 9  is similar to the fuse system  130  of  FIG. 6A , except that the fuse system  170  illustrates a specific implementation of a bias generator. In particular, the bias generator  72  of  FIG. 9  includes a bandgap reference circuit  81 , an LDO regulator  82 , and a programming logic circuit  83  that includes a level-shifter  84 . Additionally, the bias generator  72  of  FIG. 9  receives a control signal CTL over the serial interface  71 . 
     During certain power supply transients, such as during an ESD event and/or sharp power supply edges, the bias generator  72  can bias the fuse programming PFET  11  and/or the cascode PFET  12  to an improper bias level. The improper transistor biasing can arise from a delay of the bias generator  72  in generating bias voltages, such as a delay of the LDO regulator  82  in providing voltage regulation. 
     The fuse protection diode  18  aids in preventing current from flowing through the fuse cell  1  in response to a sudden decrease in the voltage of the first pad  15  relative to the voltage of the second pad  16 . 
     Additional details of the fuse system  170  can be similar to those described earlier. 
       FIG. 10A  is a schematic diagram of another embodiment of a fuse system  200  for an IC. The fuse system  200  includes a first fuse cell  1   a , a second fuse cell  1   b , a third fuse cell  1   c , a bias generator  102 , a fuse sensing circuit  103 , a first fuse programming PFET  11   a , a second fuse programming PFET  11   b , a third fuse programming PFET  11   c , a first cascode PFET  12   a , a second cascode PFET  12   b , a third cascode PFET  12   c , a first pad  15 , a second pad  16 , and a shared fuse protection diode  118 . 
     The fuse system  200  of  FIG. 10A  illustrates one example of a multi-cell fuse system including multiple fuse cells. Although the illustrated fuse system  200  includes three fuse cells, the teachings herein are applicable to configurations including more or fewer fuse cells. 
     The bias generator  102  generates a first programming control voltage PRG 1  for the gate of the first fuse programming PFET  11   a , a second programming control voltage PRG 2  for the gate of the second fuse programming PFET  11   b , and a third programming control voltage PRG 3  for the gate of the third fuse programming PFET  11   c . The bias generator  102  further generates a cascode bias voltage BIAS for the gates of the first cascode PFET  12   a , the second cascode PFET  12   b , and the third cascode PFET  12   c . The bias generator  102  also receives a control signal CTL, which instructs programming of the first fuse cell  1   a , the second fuse cell  1   b , and/or the third fuse cell  1   c.    
     The fuse sensing circuit  103  includes multiple inputs connected to each of the fuse cells  11   a - 11   c . The fuse sensing circuit  103  can be used to read the state of one or more of the fuse cells and to provide output data OUT corresponding to the read data. 
     As shown in  FIG. 10A , the shared fuse protection diode  118 , the first fuse programming PFET  11   a , the first cascode PFET  12   a , and the first fuse cell  1   a  are connected in series in a first electrical path between the first pad  15  and the second pad  16 . Additionally, the shared fuse protection diode  118 , the second fuse programming PFET  11   b , the second cascode PFET  12   b , and the second fuse cell  1   b  are connected in series in a second electrical path between the first pad  15  and the second pad  16 . Furthermore, the shared fuse protection diode  118 , the third fuse programming PFET  11   c , the third cascode PFET  12   c , and the third fuse cell  1   c  are connected in series in a third electrical path between the first pad  15  and the second pad  16 . 
     Accordingly, the illustrated embodiment uses a shared fuse protection diode  118  to provide protection to multiple fuse cells  11   a - 11   c . Providing protection against accidental programming of fuse cells using a shared or common fuse protection diode  118  reduces a number of components and provides a compact layout. 
       FIG. 10B  is a schematic diagram of another embodiment of a fuse system  210  for an IC. The fuse system  210  includes a first fuse cell  1   a , a second fuse cell  1   b , a third fuse cell  1   c , a bias generator  102 , a fuse sensing circuit  103 , a first fuse programming PFET  11   a , a second fuse programming PFET  11   b , a third fuse programming PFET  11   c , a first cascode PFET  12   a , a second cascode PFET  12   b , a third cascode PFET  12   c , a first pad  15 , a second pad  16 , a first fuse protection diode  18   a , a second fuse protection diode  18   b , and a third fuse protection diode  18   c.    
     The fuse system  210  of  FIG. 10B  is similar to the fuse system  200  of  FIG. 10A , except that the fuse system  210  of  FIG. 10B  includes separate fuse protection diodes for each fuse cell. 
     Examples of Fuse Systems with a Fuse Protection Diode and a Fuse Protection Capacitor 
     A programmable fuse system can include a combination of a fuse protection diode and a fuse protection capacitor. Implementing a programmable fuse system in this manner can provide enhanced resilience to inadvertent fuse programming in the presence of a wide range of power supply transients, including, but not limited to positive and negative polarity ESD events and/or rising and falling power supply edges. 
     Although various embodiments of fuse systems including a combination of a fuse protection diode and a fuse protection capacitor are illustrated, the teachings herein are applicable to a wide variety of configurations. For example, although the fuse protection systems of  FIGS. 1A-4B  are illustrated with a fuse protection capacitor but without a fuse protection diode, any of the fuse protection systems of  FIGS. 1A-4B  can also include a fuse protection diode. Likewise, although the fuse protection systems of  FIGS. 5-10B  are illustrated with a fuse protection diode but without a fuse protection capacitor, any of the fuse protection systems of  FIGS. 5-10B  can also include a fuse protection capacitor. 
       FIG. 11A  is a schematic diagram of another embodiment of a fuse system  250  for an IC. The illustrated fuse system  250  includes a fuse cell  1 , a bias generator  2 , a fuse sensing circuit  3 , a fuse programming PFET  11 , a cascode PFET  12 , a shared power supply and fuse programming pad  15 , a ground pad  16 , a fuse protection diode  18 , and a fuse protection capacitor  21 . In the illustrated embodiment, the fuse protection diode  18 , the fuse programming PFET  11 , the cascade PFET  12 , and the fuse cell  1  are electrically connected in series between the shared power supply and fuse programming pad  15  and the ground pad  16 . Additionally, the fuse protection capacitor  21  is electrically connected between the gate of the cascode PFET  12  and the shared power supply and fuse programming pad  15 . 
     The fuse system  250  of  FIG. 11A  illustrates one example of a fuse system  250  including a combination of a fuse protection diode and a fuse protection capacitor. Additional details of the fuse system  250  can be similar to those described earlier. 
       FIG. 11B  is a schematic diagram of another embodiment of a fuse system  260  for an IC. The illustrated fuse system  260  includes a fuse cell  1 , a bias generator  2 , a fuse sensing circuit  3 , a fuse programming PFET  11 , a cascode PFET  12 , a shared power supply and fuse programming pad  15 , a ground pad  16 , a fuse protection diode  18 , and a fuse protection capacitor  21 . 
     The fuse system  260  of  FIG. 11B  is similar to the fuse system  250  of  FIG. 11A , except that  FIG. 11B  illustrates a configuration with different connectivity for the fuse protection capacitor  21 . In particular, in contrast to the fuse system  250  of  FIG. 11A  in which the fuse protection capacitor  21  is directly connected to the shared power supply and fuse programming pad  15 , the fuse system  260  of  FIG. 11B  illustrates a configuration in which the fuse protection capacitor  21  is electrically connected to the shared power supply and fuse programming pad  15  via the fuse protection diode  18 . 
     The fuse system  260  of  FIG. 11B  illustrates another example of a fuse system including a combination of a fuse protection diode and a fuse protection capacitor. Additional details of the fuse system  260  can be similar to those described earlier. 
       FIG. 11C  is a schematic diagram of another embodiment of a fuse system  270  for an IC. The fuse system  270  includes a first fuse cell  1   a , a second fuse cell  1   b , a third fuse cell  1   c , a bias generator  102 , a fuse sensing circuit  103 , a first fuse programming PFET  11   a , a second fuse programming PFET  11   b , a third fuse programming PFET  11   c , a first cascode PFET  12   a , a second cascode PFET  12   b , a third cascode PFET  12   c , a first pad  15 , a second pad  16 , a shared fuse protection diode  118 , and a shared fuse protection capacitor  21 . 
     The fuse system  270  of  FIG. 11C  illustrates one example of a multi-cell fuse system including multiple fuse cells. Although the illustrated fuse system  270  includes three fuse cells, the teachings herein are applicable to configurations including more or fewer fuse cells. Furthermore, although  FIG. 11C  illustrates an example in which biasing circuitry and fuse sensing circuitry is shared across multiple fuse cells, the teachings herein are applicable to implementations using multiple bias generators and/or multiple fuse sensing circuits. 
     The bias generator  102  generates a first programming control voltage PRG 1  for the gate of the first fuse programming PFET  11   a , a second programming control voltage PRG 2  for the gate of the second fuse programming PFET  11   b , and a third programming control voltage PRG 3  for the gate of the third fuse programming PFET  11   c . The bias generator  102  further generates a cascode bias voltage BIAS for the gates of the first cascode PFET  12   a , the second cascode PFET  12   b , and the third cascode PFET  12   c . The bias generator  102  also receives a control signal CTL, which instructs programming of the first fuse cell  1   a , the second fuse cell  1   b , and/or the third fuse cell  1   c.    
     The fuse sensing circuit  103  includes multiple inputs connected to each of the fuse cells  11   a - 11   c . The fuse sensing circuit  103  can be used to read the state of one or more of the fuse cells and to provide output data OUT corresponding to the read data. 
     As shown in  FIG. 11C , the shared fuse protection diode  118 , the first fuse programming PFET  11   a , the first cascode PFET  12   a , and the first fuse cell  1   a  are connected in series in a first electrical path between the first pad  15  and the second pad  16 . Additionally, the shared fuse protection diode  118 , the second fuse programming PFET  11   b , the second cascode PFET  12   b , and the second fuse cell  1   b  are connected in series in a second electrical path between the first pad  15  and the second pad  16 . Furthermore, the shared fuse protection diode  118 , the third fuse programming PFET  11   c,  the third cascode PFET  12   c , and the third fuse cell  1   c  are connected in series in a third electrical path between the first pad  15  and the second pad  16 . 
     Accordingly, the illustrated embodiment uses a shared fuse protection diode  118  to provide protection to multiple fuse cells  11   a - 11   c . Providing protection against accidental programming of fuse cells using a shared or common fuse protection diode  118  reduces a number of components and provides a compact layout. 
     Furthermore, as shown in  FIG. 11C , the shared fuse protection capacitor  21  is electrically connected between the cascode bias voltage BIAS and the first pad  15 . Accordingly, the illustrated embodiment uses a shared fuse protection capacitor  21  to provide protection to multiple fuse cells  11   a - 11   c . Providing protection against accidental programming of fuse cells using a shared or common fuse protection capacitor  21  reduces a number of components and provides a compact layout. 
       FIG. 11D  is a schematic diagram of another embodiment of a fuse system  280  for an IC. The fuse system  280  includes a first fuse cell  1   a , a second fuse cell  1   b , a third fuse cell  1   c , a bias generator  102 , a fuse sensing circuit  103 , a first fuse programming PFET  11   a , a second fuse programming PFET  11   b , a third fuse programming PFET  11   c , a first cascode PFET  12   a , a second cascode PFET  12   b , a third cascode PFET  12   c , a first pad  15 , a second pad  16 , a first fuse protection diode  18   a , a second fuse protection diode  18   b , a third fuse protection diode  18   c , and a shared fuse protection capacitor  21 . 
     The fuse system  280  of  FIG. 11D  is similar to the fuse system  270  of  FIG. 11C , except that the fuse system  280  of  FIG. 11D  includes separate fuse protection diodes for each fuse cell. 
       FIG. 11E  is a schematic diagram of another embodiment of a fuse system  290  for an IC. The fuse system  290  includes a first fuse cell  1   a , a second fuse cell  1   b , a third fuse cell  1   c , a bias generator  102 , a fuse sensing circuit  103 , a first fuse programming PFET  11   a , a second fuse programming PFET  11   b , a third fuse programming PFET  11   c,  a first cascode PFET  12   a , a second cascode PFET  12   b , a third cascode PFET  12   c , a first pad  15 , a second pad  16 , a shared fuse protection diode  118 , a first fuse protection capacitor  21   a , a second fuse protection capacitor  21   b , and a third fuse protection capacitor  21   c.    
     The fuse system  290  of  FIG. 11E  is similar to the fuse system  270  of  FIG. 11C , except that the fuse system  290  of  FIG. 11E  includes separate fuse protection capacitors for each fuse cell. 
     For example, the bias generator  102  generates a first cascode bias voltage BIAS 1  for the first cascode PFET  12   a , a second cascode bias voltage BIAS  2  for the second cascode PFET  12   b , and a third cascode bias voltage BIAS 3  for the third cascode PFET  12   c . Additionally, the first fuse protection capacitor  21   a  is connected between the first cascode bias voltage BIAS 1  and the first pad  15 , the second fuse protection capacitor  21   b  is connected between the second cascode bias voltage BIAS 2  and the first pad  15 , and the third fuse protection capacitor  21   c  is connected between the third cascode bias voltage BIAS 3  and the first pad  15 . 
       FIG. 1  IF is a schematic diagram of another embodiment of a fuse system  291  for an IC. The illustrated fuse system  291  includes a fuse cell  1 , a biasing circuit  2 , a fuse sensing circuit  3 , a first switch  4 , a second switch  5 , a shared power supply and fuse programming pad  15 , a ground pad  16 , a fuse protection diode  18 , and a fuse protection capacitor  21 . 
     The fuse system  291  of  FIG. 11F  is similar to the fuse system  250  of  FIG. 11A , except that the fuse system  291  of  FIG. 11F  illustrates an embodiment including the first switch  4  and the second switch  5  rather than the fuse programming PFET  11  and the cascode PFET  12 . As shown in  FIG. 11F , the biasing circuit  2  biases a control input of the first switch  4  with a fuse programming signal PRG (which can be a voltage and/or current) to thereby control a current through the fuse  1 . Additionally, the biasing circuit  2  biases a control input of the second switch  5  with a bias signal BIAS (which can be a voltage and/or current). In certain implementations, the first switch  4  and the second switch  5  are implemented as FETs, such as PFETs as in the embodiment of  FIG. 11A . However, the first switch  4  and the second switch  5  can correspond to any suitable type of switches. 
     Although various embodiments are depicted herein in the context of FET implementations, the fuse systems herein can be implemented using a wide variety of types of switches, including, but not limited to, voltage-controlled switches. 
       FIG. 11G  is a schematic diagram of another embodiment of a fuse system  292  for an IC. The illustrated fuse system  292  includes a first fuse cell  1   a , a second fuse cell  1   b , a third fuse cell  1   c , a bias generator  102 , a fuse sensing circuit  103 , a first group of switches  4   a - 4   c , a second group of switches  5   a - 5   c , a first pad  15 , a second pad  16 , a shared fuse protection diode  118 , and a shared fuse protection capacitor  21 . 
     The fuse system  292  of  FIG. 11G  is similar to the fuse system  270  of  FIG. 11C , except that the fuse system  292  of  FIG. 11G  illustrates an embodiment including the first group of switches  4   a - 4   c  and the group of switches  5   a - 5   c  rather than the fuse programming PFETs  11   a - 11   c  and the cascode PFETs  12   a - 12   c.    
     Examples of Electronic Systems Including ICs Implemented with a Fuse System 
     A fuse system can be integrated on a semiconductor die, which in turn can be included in a wide variety of electronic systems. 
       FIG. 12A  is a schematic diagram of one embodiment of a packaged module  300 .  FIG. 12B  is a schematic diagram of a cross-section of the packaged module  300  of  FIG. 12A  taken along the lines  12 B- 12 B. 
     The packaged module  300  includes a semiconductor die  302 , surface mount components  303 , wirebonds  308 , a package substrate  320 , and encapsulation structure  340 . The package substrate  320  includes pads  306  formed from conductors disposed therein. Additionally, the semiconductor die  302  includes pins or pads  304 , and the wirebonds  308  have been used to connect the pads  304  of the die  302  to the pads  306  of the package substrate  320 . 
     The semiconductor die  302  includes a programmable fuse system  650  that includes at least one of a fuse protection diode  18  or a fuse protection capacitor  21 , which can be as described earlier. 
     The packaging substrate  320  can be configured to receive a plurality of components such as the semiconductor die  302  and the surface mount components  303 , which can include, for example, surface mount capacitors and/or inductors. 
     As shown in  FIG. 12B , the packaged module  300  is shown to include a plurality of contact pads  332  disposed on the side of the packaged module  300  opposite the side used to mount the semiconductor die  302 . Configuring the packaged module  300  in this manner can aid in connecting the packaged module  300  to a circuit board, such as a phone board of a wireless device. The example contact pads  332  can be configured to provide radio frequency signals, bias signals, and/or power (for example, a power supply voltage and ground) to the semiconductor die  302  and/or the surface mount components  303 . As shown in  FIG. 12B , the electrical connections between the contact pads  332  and the semiconductor die  302  can be facilitated by connections  333  through the package substrate  320 . The connections  333  can represent electrical paths formed through the package substrate  320 , such as connections associated with vias and conductors of a multilayer laminated package substrate. 
     In some embodiments, the packaged module  300  can also include one or more packaging structures to, for example, provide protection and/or facilitate handling. Such a packaging structure can include overmold or encapsulation structure  340  formed over the packaging substrate  320  and the components and die(s) disposed thereon. 
     It will be understood that although the packaged module  300  is described in the context of electrical connections based on wirebonds, one or more features of the present disclosure can also be implemented in other packaging configurations, including, for example, flip-chip configurations. 
       FIG. 13  is a schematic diagram of one embodiment of a mobile device  600 . The mobile device  600  includes a semiconductor die  601  including a programmable fuse system  650 . The programmable fuse system  650  includes at least one of a fuse protection diode or a fuse protection capacitor. Although not illustrated in  FIG. 13  for clarity, the mobile device  600  includes additional components and structures. 
       FIG. 14  is a schematic diagram of one embodiment of a base station  700 . The base station  700  includes a semiconductor die  601  including a programmable fuse system  650 . The programmable fuse system  650  includes at least one of a fuse protection diode or a fuse protection capacitor. Although not illustrated in  FIG. 14  for clarity, the base station  700  includes additional components and structures. 
       FIG. 15  is a schematic diagram of one embodiment of an RF system  730 . The RF system  730  includes a baseband processor  735 , a receive path  742 , a transmit path  746 , a T/R switch  731 , and an antenna  759 . The RF system  700  illustrates one example implementation of radio frequency circuitry suitable for operation in the mobile device  600  of  FIG. 13  and/or the base station  700  of  FIG. 14 . However, other implementations are possible. 
     The RF system  730  can be used for transmitting and/or receiving RF signals using a variety of communication standards, including, for example, Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA), wideband CDMA (W-CDMA), Long Term Evolution (LTE), Advanced LTE, 3G (including 3GPP), 4G, Enhanced Data Rates for GSM Evolution (EDGE), wireless local loop (WLL), and/or Worldwide Interoperability for Microwave Access (WiMax), as well as other proprietary and non-proprietary communications standards. 
     The transmit path  746  and the receive path  742  can be used for transmitting and receiving signals over the antenna  759 . Although one implementation of the RF system  730  is illustrated in  FIG. 15 , the RF system  730  can be modified in any suitable manner. For example, the base station  730  can be modified to include additional transmit paths, receive paths, and/or antennas. 
     In the illustrated configuration, the receive path  742  includes a low noise amplifier (LNA)  747 , a digital step attenuator (DSA)  732 , a local oscillator  722 , a first mixer  723   a , a second mixer  723   b , a first programmable gain amplifier (PGA)  725   a , a second PGA  725   b , a first filter  727   a , a second filter  727   b , a first analog-to-digital converter (ADC)  729   a , and a second ADC  729   b . Although one implementation of a receive path is illustrated in  FIG. 15 , a receive path can include more or fewer components and/or a different arrangement of components. 
     An RF signal can be received on the antenna  759  and provided to the receive path  742  using the T/R switch  731 . For example, the T/R switch  731  can be controlled to electrically couple the antenna  759  to an input of the LNA  747 , thereby providing the received RF signal to the LNA&#39;s input. The LNA  747  provides low noise amplification such that the LNA  747  amplifies the received RF signal while adding or introducing a relatively small amount of noise. As shown in  FIG. 15 , the amplified RF signal generated by the LNA  747  is provided to the DSA  732 . In the illustrated embodiment, an amount of attenuation provided by the DSA  732  is digitally-controllable, and can be set to achieve a desired signal power level. 
     The first and second mixers  723   a ,  723   b  receive first and second local oscillator clock signals, respectively, from the local oscillator  722 . The first and second local oscillator clock signals can have about the same frequency and a phase difference equal to about a quarter of a period, or about 90°. The first and second mixers  723   a ,  723   b  downconvert the output of the DSA  732  using the first and second local oscillator clock signals, respectively, thereby generating first and second demodulated signals. The first and second demodulated signals can have a relative phase difference of about a quarter of a period, or about 90°, and can correspond to an in-phase (I) receive signal and a quadrature-phase (Q) signal, respectively. In certain implementations, one of the first or second oscillator clock signals is generated by phase shifting from the other. 
     The first and second local oscillator clock signals can have a frequency selected to achieve a desired intermediate frequency and/or baseband frequency for the first and second demodulated signals. For example, multiplying the output of the DSA  732  by a sinusoidal signal from the local oscillator  722  can produce a mixed signal having a frequency content centered about the sum and difference frequencies of the carrier frequency of the DSA output signal and the oscillation frequency of the local oscillator  722 . 
     In the illustrated configuration, the first and second demodulated signals are amplified using the first and second programmable gain amplifiers  725   a ,  725   b , respectively. To aid in reducing output noise, the outputs of the first and second programmable gain amplifiers  725   a ,  725   b  can be filtered using the first and second filters  727   a ,  727   b , which can be any suitable filter, including, for example, low pass, band pass, or high pass filters. The outputs of the first and second filters  727   a ,  727   b  can be provided to the first and second ADCs  729   a ,  729   b , respectively. The first and second ADCs  729   a ,  729   b  can have any suitable resolution. In the illustrated configuration, the outputs of the first and second ADCs  729   a ,  729   b  are provided to the baseband processor  735  for processing. 
     The baseband processor  735  can be implemented in a variety of ways. For instance, the baseband processor  735  can include a digital signal processor, a microprocessor, a programmable core, the like, or any combination thereof. Moreover, in some implementations, two or more baseband processors can be included in the RF system  730 . 
     As shown in  FIG. 15 , the transmit path  746  receives data from the baseband processor  735  and is used to transmit RF signals via the antenna  759 . The transmit path  746  and the receive path  742  both operate using the antenna  759 , and access to the antenna  759  is controlled using the T/R switch  731 . The illustrated transmit path  746  includes first and second digital-to-analog converters (DACs)  737   a ,  737   b , first and second filters  739   a ,  739   b , first and second mixers  741   a ,  741   b , a local oscillator  743 , a combiner  745 , a DSA  732 , an output filter  751 , and a power amplifier  758 . Although one implementation of a transmit path is illustrated in  FIG. 15 , a transmit path can include more or fewer components and/or a different arrangement of components. 
     The baseband processor  735  can output a digital in-phase (I) signal and a digital quadrature-phase (Q) signal, which can be separately processed until they are combined using the combiner  745 . The first DAC  737   a  converts the digital I signal into an analog I signal, and the second DAC  737   b  converts the digital Q signal into an analog Q signal. The first and second DACs  737   a ,  737   b  can have any suitable precision. The analog I signal and the analog Q signal can be filtered using the first and second filters  739   a ,  739   b , respectively. The outputs of the first and second filters  739   a ,  739   b  can be upconverted using the first and second mixers  741   a ,  741   b , respectively. For example, the first mixer  741   a  is used to upconvert the output of the first filter  739   a  based on an oscillation frequency of the local oscillator  743 , and the second mixer  741   b  is used to upconvert the output of the second filter  739   b  based on the oscillation frequency of the local oscillator  743 . 
     The combiner  743  combines the outputs of the first and second mixers  741   a ,  741   b  to generate a combined RF signal. The combined RF signal is provided to an input of the DSA  732 , which is used to control a signal power level of the combined RF signal. 
     The output of the DSA  732  can be filtered using the output filter  751 , which can be, for example, a low pass, band pass, or high pass filter configured to remove noise and/or unwanted frequency components from the signal. The output of the output filter  751  can be amplified by a power amplifier  758 . In some implementations, the power amplifier  758  includes a plurality of stages cascaded to achieve a target gain. The power amplifier  758  can provide an amplified RF signal to the antenna  759  through the T/R switch  731 . 
     The programmable fuse systems described herein can be used in the RF system of  FIG. 15 . For example, the RF system  730  can be implemented using one or more semiconductor dies that include a programmable fuse system. Although  FIG. 15  illustrates an example of an RF system that can include a programmable fuse system implemented in accordance with the teachings herein, programmable fuse systems can be used in other configurations of electronics. 
       FIG. 16  is a schematic diagram of one example of a power amplifier system  800 . The illustrated power amplifier system  800  includes the switches  812 , the antenna  814 , the battery  821 , a directional coupler  824 , the envelope tracker  830 , a power amplifier  832 , and a transceiver  833 . The illustrated transceiver  833  includes a baseband processor  834 , an envelope shaping block  835 , a digital-to-analog converter (DAC)  836 , an I/Q modulator  837 , a mixer  838 , and an analog-to-digital converter (ADC)  839 . Although not illustrated in  FIG. 16  for clarity, the transceiver  833  can include circuitry associated with receiving signals over one or more receive paths. The power amplifier system  800  illustrates one example implementation of a power amplifier circuity suitable for operation in the mobile device  600  of  FIG. 13  and/or the base station  700  of  FIG. 14 . However, other implementations are possible. 
     The baseband processor  834  can be used to generate an I signal and a Q signal, which correspond to signal components of a sinusoidal wave or signal of a desired amplitude, frequency, and phase. For example, the I signal can be used to represent an in-phase component of the sinusoidal wave and the Q signal can be used to represent a quadrature component of the sinusoidal wave, which can be an equivalent representation of the sinusoidal wave. In certain implementations, the I and Q signals can be provided to the I/Q modulator  837  in a digital format. The baseband processor  834  can be any suitable processor configured to process a baseband signal. For instance, the baseband processor  834  can include a digital signal processor, a microprocessor, a programmable core, or any combination thereof. Moreover, in some implementations, two or more baseband processors  834  can be included in the power amplifier system  800 . 
     The I/Q modulator  837  can be configured to receive the I and Q signals from the baseband processor  834  and to process the I and Q signals to generate an RF signal. For example, the I/Q modulator  837  can include DACs configured to convert the I and Q signals into an analog format, mixers for upconverting the I and Q signals to radio frequency, and a signal combiner for combining the upconverted I and Q signals into an RF signal suitable for amplification by the power amplifier  832 . In certain implementations, the I/Q modulator  837  can include one or more filters configured to filter frequency content of signals processed therein. 
     The envelope shaping block  835  can be used to convert envelope or amplitude data associated with the I and Q signals into shaped envelope data. Shaping the envelope data from the baseband processor  834  can aid in enhancing performance of the power amplifier system  800  by, for example, adjusting the envelope signal to optimize linearity of the power amplifier  32  and/or to achieve a desired gain compression of the power amplifier  832 . In certain implementations, the envelope shaping block  835  is a digital block, and the DAC  836  is used to convert the shaped envelope data into an analog envelope signal suitable for use by the envelope tracker  830 . However, in other implementations, the DAC  836  can be omitted in favor of providing the envelope tracker  830  with a digital envelope signal to aid the envelope tracker  830  in further processing of the envelope signal. 
     The envelope tracker  830  can receive the envelope signal from the transceiver  833  and a battery voltage V BATT  from the battery  821 , and can use the envelope signal to generate a power amplifier supply voltage V CC   _   PA  for the power amplifier  832  that changes in relation to the envelope. The power amplifier  832  can receive the RF signal from the I/Q modulator  837  of the transceiver  833 , and can provide an amplified RF signal to the antenna  814  through the switches  812 . 
     The directional coupler  824  can be positioned between the output of the power amplifier  832  and an input of the switches  812 , thereby allowing an output power measurement of the power amplifier  832  that does not include insertion loss of the switches  812 . The sensed output signal from the directional coupler  824  can be provided to the mixer  838 , which can multiply the sensed output signal by a reference signal of a controlled frequency so as to downshift the frequency spectrum of the sensed output signal. The downshifted signal can be provided to the ADC  839 , which can convert the downshifted signal to a digital format suitable for processing by the baseband processor  834 . 
     By including a feedback path between the output of the power amplifier  832  and an input of the baseband processor  834 , the baseband processor  834  can be configured to dynamically adjust the I and Q signals and/or envelope data associated with the I and Q signals to optimize the operation of the power amplifier system  800 . For example, configuring the power amplifier system  800  in this manner can aid in controlling the power added efficiency (PAE) and/or linearity of the power amplifier  832 . 
     The programmable fuse systems described herein can be used in the power amplifier system  800  of  FIG. 16 . For example, the power amplifier system  800  can be implemented using one or more semiconductor dies that include a programmable fuse system. Although  FIG. 16  illustrates an example of a power amplifier system that can include a programmable fuse system implemented in accordance with the teachings herein, programmable fuse systems can be used in other configurations of electronics. 
       FIG. 17  is a schematic diagram of one embodiment of a semiconductor die  900  with a fuse system  901 . As shown in  FIG. 17  the fuse system  901  includes a dedicated fuse programming pad  910 , fuse circuitry  914 , and a ground pad  921 . The fuse circuitry  914  includes fuses  1   a - 1   c  (three, in this example), which can be protected using any of the fuse protection schemes disclosed herein. Additionally, the semiconductor die  900  further includes power supply pads  912 - 913  (two, in this example), core circuits  915 - 917  (three, in this example), and ground pads  922 - 924  (three, in this example). 
     Although one example of a semiconductor die is shown in  FIG. 17 , other implementations of semiconductor dies are possible, including, but not limited to, dies including more or fewer pads, more or fewer core circuits, and/or more or fewer fuses. 
     The core circuits  915 - 917  correspond to circuitry used during normal operation of the semiconductor die  900 , for instance, digital, analog, and/or RF circuits that operate to provide a desired function of the chip or die  900 . As shown in  FIG. 17 , the core circuits  915 - 917  are powered using the power supply pads  912 - 913  and ground pads  922 - 924 . 
     The chip&#39;s power supply can experience a power supply transient  925 , which can be, for example, a relatively rapid voltage transition or glitch. For instance, the power supply transient  925  can arise during turn-on of the semiconductor die  900 , during periods of high circuit activity, and/or when the semiconductor die  900  is subjected to electrical overstress, such as an ESD event. 
     The fuse system  901  operates using a dedicated fuse programming pad  910  that is electrically disconnected from the power supply pads  912 - 913 . Thus, the fuse system  901  is isolated from the power supply transient  925 , and thus operates with higher robustness against inadvertent or accidental fuse programming. 
       FIG. 18  is a schematic diagram of another embodiment of a semiconductor die  930  with a fuse system  931 . As shown in  FIG. 18  the fuse system  931  includes a shared power supply and fuse programming pad  911 , fuse circuitry  914 , and a ground pad  921 . 
     The semiconductor die  930  of  FIG. 18  is similar to the semiconductor die  900  of  FIG. 17 , except that the semiconductor die  930  of  FIG. 18  includes a fuse system  931  that is programmable using a shared power supply and fuse programming pad  911 . Thus, rather than providing programming using a dedicated fuse programming pad  910 , the pad  911  is used for both fuse programming and for receiving a power supply voltage. 
     Using a shared power supply and fuse programming pad reduces pin count (for instance, a shared power supply and fuse programming pad can replace a power supply pad and separate fuse programming pad) and/or enhances the quality of power supply distribution by increasing the number of power supply pads that provide power during normal operation. For instance, in comparison to the semiconductor die  900  of  FIG. 17 , the semiconductor die  930  of  FIG. 18  includes an additional power supply pad for powering the core circuits  915 - 917 , and thus can operate with superior power supply distribution. 
     Although implementing a fuse system with a shared power supply and fuse programming pad advantageously reduces pin count and/or enhances power supply distribution, implementing the fuse system in this manner also exposes the fuse system to power supply transients. For example, the shared power supply and fuse programming pad is connected to a supply voltage during operation of the IC, and thus the fuse system operates with reduced electrical isolation relative to an implementation using a dedicated fuse programming pad. For instance, with respect to the examples shown in  FIGS. 17 and 18 , the fuse system  931  of  FIG. 18  is exposed to the power supply transient  925  while the fuse system  901  of  FIG. 17  is isolated from the power supply transient  925 . 
     The fuse protection schemes described herein can provide enhanced robustness against accidental programming of fuses, including, but not limited to, in fuse system implementations using a shared power supply and fuse programming pad. 
       FIG. 19  is a schematic diagram of another embodiment of a mobile device  1000 . The mobile device  1000  includes a baseband system  1001 , a transceiver  1002 , a front end system  1003 , antennas  1004 , a power management system  1005 , a memory  1006 , a user interface  1007 , and a battery  1008 . 
     The mobile device  1000  of  FIG. 19  can include one or more fuse systems implemented in accordance with the teachings herein. For example, in the illustrated embodiment, the baseband processor  1001  includes a fuse system  1021 , the transceiver  1002  includes a fuse system  1022 , the front end system  1003  includes a fuse system  1023 , the memory  1006  includes a fuse system  1024 , and the power management system  1005  includes a fuse system  1025 . One or more of the fuse systems  1021 - 1025  can be implemented in accordance with the teachings herein. 
     The mobile device  1000  can be used communicate using a wide variety of communications technologies, including, but not limited to, 2G, 3G, 4G (including LTE, LTE-Advanced, and LTE-Advanced Pro), 5G NR, WLAN (for instance, Wi-Fi), WPAN (for instance, Bluetooth and ZigBee), WMAN (for instance, WiMax), and/or GPS technologies. 
     The transceiver  1002  generates RF signals for transmission and processes incoming RF signals received from the antennas  1004 . It will be understood that various functionalities associated with the transmission and receiving of RF signals can be achieved by one or more components that are collectively represented in  FIG. 19  as the transceiver  1002 . In one example, separate components (for instance, separate circuits or dies) can be provided for handling certain types of RF signals. 
     The front end system  1003  aids is conditioning signals transmitted to and/or received from the antennas  1004 . In the illustrated embodiment, the front end system  1003  includes power amplifiers (PAs)  1011 , low noise amplifiers (LNAs)  1012 , filters  1013 , switches  1014 , and duplexers  1015 . However, other implementations are possible. 
     For example, the front end system  1003  can provide a number of functionalities, including, but not limited to, amplifying signals for transmission, amplifying received signals, filtering signals, switching between different bands, switching between different power modes, switching between transmission and receiving modes, duplexing of signals, multiplexing of signals (for instance, diplexing or triplexing), or some combination thereof. 
     In certain implementations, the mobile device  1000  supports carrier aggregation, thereby providing flexibility to increase peak data rates. Carrier aggregation can be used for both Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD), and may be used to aggregate a plurality of carriers or channels. Carrier aggregation includes contiguous aggregation, in which contiguous carriers within the same operating frequency band are aggregated. Carrier aggregation can also be non-contiguous, and can include carriers separated in frequency within a common band or in different bands. 
     The antennas  1004  can include antennas used for a wide variety of types of communications. For example, the antennas  1004  can include antennas for transmitting and/or receiving signals associated with a wide variety of frequencies and communications standards. 
     In certain implementations, the antennas  1004  support MIMO communications and/or switched diversity communications. For example, MIMO communications use multiple antennas for communicating multiple data streams over a single radio frequency channel. MIMO communications benefit from higher signal to noise ratio, improved coding, and/or reduced signal interference due to spatial multiplexing differences of the radio environment. Switched diversity refers to communications in which a particular antenna is selected for operation at a particular time. For example, a switch can be used to select a particular antenna from a group of antennas based on a variety of factors, such as an observed bit error rate and/or a signal strength indicator. 
     The mobile device  1000  can operate with beamforming in certain implementations. For example, the front end system  1003  can include phase shifters having variable phase controlled by the transceiver  1002 . Additionally, the phase shifters are controlled to provide beam formation and directivity for transmission and/or reception of signals using the antennas  1004 . For example, in the context of signal transmission, the phases of the transmit signals provided to the antennas  1004  are controlled such that radiated signals from the antennas  1004  combine using constructive and destructive interference to generate an aggregate transmit signal exhibiting beam-like qualities with more signal strength propagating in a given direction. In the context of signal reception, the phases are controlled such that more signal energy is received when the signal is arriving to the antennas  1004  from a particular direction. In certain implementations, the antennas  1004  include one or more arrays of antenna elements to enhance beamforming. 
     The baseband system  1001  is coupled to the user interface  1007  to facilitate processing of various user input and output (I/O), such as voice and data. The baseband system  1001  provides the transceiver  1002  with digital representations of transmit signals, which the transceiver  1002  processes to generate RF signals for transmission. The baseband system  1001  also processes digital representations of received signals provided by the transceiver  1002 . As shown in  FIG. 19 , the baseband system  1001  is coupled to the memory  1006  of facilitate operation of the mobile device  1000 . 
     The memory  1006  can be used for a wide variety of purposes, such as storing data and/or instructions to facilitate the operation of the mobile device  1000  and/or to provide storage of user information. 
     The power management system  1005  provides a number of power management functions of the mobile device  1000 . In certain implementations, the power management system  1005  includes a PA supply control circuit that controls the supply voltages of the power amplifiers  1011 . For example, the power management system  1005  can be configured to change the supply voltage(s) provided to one or more of the power amplifiers  1011  to improve efficiency, such as power added efficiency (PAE). 
     As shown in  FIG. 19 , the power management system  1005  receives a battery voltage from the battery  1008 . The battery  1008  can be any suitable battery for use in the mobile device  1000 , including, for example, a lithium-ion battery. 
     Applications 
     Some of the embodiments described above have provided examples in connection with a fuse system integrated on a semiconductor die of an RF system. However, the principles and advantages of the embodiments can be used for any other systems or apparatus that benefit from any of the circuits described herein. 
     For example, fuse systems can be included in ICs used in various electronic devices, including, but not limited to consumer electronic products, parts of the consumer electronic products, electronic test equipment, etc. Examples of the electronic devices can also include, but are not limited to, memory chips, memory modules, circuits of optical networks or other communication networks, and disk driver circuits. The consumer electronic products can include, but are not limited to, a mobile phone, a telephone, a television, a computer monitor, a computer, a hand-held computer, a personal digital assistant (PDA), a microwave, a refrigerator, an automobile, a stereo system, a cassette recorder or player, a DVD player, a CD player, a VCR, an MP3 player, a radio, a camcorder, a camera, a digital camera, a portable memory chip, a washer, a dryer, a washer/dryer, a copier, a facsimile machine, a scanner, a multi-functional peripheral device, a wrist watch, a clock, etc. Further, the electronic devices can include unfinished products. 
     CONCLUSION 
     Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to.” The word “coupled”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Likewise, the word “connected”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Additionally, the words “herein,” “above,” “below,” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the above Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word “or” in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. 
     Moreover, conditional language used herein, such as, among others, “can,” “could,” “might,” “can,” “e.g.,” “for example,” “such as” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment. 
     The above detailed description of embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise form disclosed above. While specific embodiments of, and examples for, the invention are described above for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. For example, while processes or blocks are presented in a given order, alternative embodiments may perform routines having steps, or employ systems having blocks, in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and/or modified. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks are at times shown as being performed in series, these processes or blocks may instead be performed in parallel, or may be performed at different times. 
     The teachings of the invention provided herein can be applied to other systems, not necessarily the system described above. The elements and acts of the various embodiments described above can be combined to provide further embodiments. 
     While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure. cm What is claimed is: