Patent Publication Number: US-10770452-B2

Title: Apparatus and methods for electrical overstress protection

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/273,272, filed Dec. 30, 2015 titled “APPARATUS AND METHODS FOR ELECTRICAL OVERSTRESS PROTECTION CIRCUITS,” which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     Embodiments of the invention relate to electronic systems and in particular, to electrical overstress protection circuits. 
     Description of the Related Technology 
     Electrical overstress (EOS) events can arise from a variety of sources, such as external charge sources, supply switching, and/or electromagnetic pulses. EOS events include electrostatic discharge (ESD) events and other transient electrical events associated with high levels of power and/or charge. An EOS event can cause charge build-up in an integrated circuit (IC), leading to high voltage and/or current levels beyond which the IC can reliably tolerate. Absent a protection mechanism, the EOS event can lead to IC damage, such as gate oxide rupture, junction breakdown, and/or metal damage. 
     An IC&#39;s robustness to EOS events can be evaluated in a wide variety of ways. For example, specifications for EOS compliance can be set by various organizations, such as the International Electrotechnical Commission (IEC) and/or Joint Electronic Device Engineering Council (JEDEC). For instance, a human body model (HBM) test can be used to evaluate the IC&#39;s performance with respect to ESD events arising from the sudden release of electrostatic charge from a person to an IC. An IC&#39;s performance with respect to such specifications can be an important performance metric by which the IC is evaluated. 
     SUMMARY 
     In certain embodiments, the present disclosure relates to an integrated circuit with electrical overstress protection. The integrated circuit includes a pad, an internal circuit electrically connected to a signal node, and an overstress protection circuit. The overstress protection circuit includes an overstress sensing circuit electrically connected between the pad and a first supply node, an impedance element electrically connected between the pad and the signal node, a controllable clamp electrically connected between the signal node and the first supply node, and an overshoot limiting circuit electrically connected between the signal node and a second supply node. The overstress sensing circuit is configured to activate the controllable clamp in response to detecting an electrical overstress event at the pad. 
     In some embodiments, the overstress sensing circuit includes a plurality of diodes and a first field-effect transistor configured to activate when the electrical overstress event generates a flow of current through the plurality of diodes. In a number of embodiments, the controllable clamp includes a second field-effect transistor electrically connected with the first field-effect transistor as a current mirror. In various embodiments, the controllable clamp further includes a clamp diode electrically connected in series with the second field-effect transistor between the signal node and the first supply node. 
     In several embodiments, the first supply node is a ground rail and the second supply node is a power supply rail. 
     According to various embodiments, the overshoot limiting circuit includes at least one diode configured to control a trigger voltage of the overshoot limiting circuit. In some embodiments, the overshoot limiting circuit includes two or more diodes electrically connected in series between the signal node and the second supply node. 
     In various embodiments, the impedance element includes a resistor. 
     In accordance with a number of embodiments, the integrated circuit further includes a supply clamp electrically connected between the second supply node and the first supply node. 
     In certain embodiments, the present disclosure relates to an overstress protection circuit for a semiconductor chip. The overstress protection circuit includes an impedance element electrically connected between a pad and a signal node, a controllable clamp electrically connected between the signal node and a first supply node, an overstress sensing circuit electrically connected between the pad and the first supply node, and an overshoot limiting circuit electrically connected between the signal node and a second supply node. The overstress sensing circuit is configured to activate the controllable clamp in response to detecting an electrical overstress event at the pad, and the overstress protection circuit is arranged so as to divert charge associated with the electrical overstress event at the pad away from the signal node to thereby provide overstress protection. 
     In some embodiments, the overstress sensing circuit includes a plurality of diodes and a first field-effect transistor configured to activate when the electrical overstress event generates a flow of current through the plurality of diodes. In a number of embodiments, the controllable clamp includes a second field-effect transistor having a gate voltage that is controlled based on a gate voltage of the first field-effect transistor. In accordance with some embodiments, the controllable clamp further includes a clamp diode electrically connected in series with the second field-effect transistor between the signal node and the first supply node. According to a number of embodiments, the first and second field-effect transistors are electrically connected as a current mirror. 
     In several embodiments, the first supply node is a ground rail and the second supply node is a power supply rail. 
     In various embodiments, the overshoot limiting circuit includes at least one diode configured to control a trigger voltage of the overshoot limiting circuit. 
     In some embodiments, the impedance element includes a resistor. 
     In certain embodiments, the present disclosure relates to a method of providing overstress protection. The method includes detecting an electrical overstress event at a pad using an overstress sensing circuit, providing a voltage drop from the pad to a signal node in response to the electrical overstress event using an impedance element, activating a controllable clamp between the signal node and a first supply node in response to detecting the electrical overstress event at the pad using the overstress sensing circuit, and protecting the signal node from overshoot before the controllable clamp is activated using an overshoot limiting circuit. 
     In several embodiments, activating the controllable clamp includes mirroring a current flowing through the overstress sensing circuit. 
     In various embodiments, protecting the signal node from overshoot includes forward biasing at least one diode. 
    
    
     
       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. 1  is a schematic diagram of one example of an integrated circuit that can include one or more electrical overstress (EOS) protection circuits. 
         FIG. 2  is a schematic diagram of an example wireless device that can include one or more EOS protection circuits. 
         FIG. 3A  is a schematic diagram of one example of a module that can include one or more EOS protection circuits. 
         FIG. 3B  is a cross section of the module of  FIG. 3B  taken along the lines  3 B- 3 B. 
         FIG. 3C  is a cross section of a module according to another embodiment. 
         FIG. 4A  is a schematic diagram of an integrated circuit (IC) interface including an EOS protection circuit according to one embodiment. 
         FIG. 4B  is a schematic diagram of an IC interface including an EOS protection circuit according to another embodiment. 
         FIG. 4C  is a schematic diagram of an IC interface including an EOS protection circuit according to another embodiment. 
         FIG. 5  is one example of a graph of voltage versus time for the EOS protection circuit of  FIG. 4A . 
         FIG. 6A  is a schematic diagram of an IC interface including an EOS protection circuit according to another embodiment. 
         FIG. 6B  is a schematic diagram of an IC interface including an EOS protection circuit according to another embodiment. 
         FIG. 7A  is a schematic diagram of a front end system according to one embodiment. 
         FIG. 7B  is a schematic diagram of a front end system according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF 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. 
     To protect a pin or pad of an integrated circuit (IC) from electrical overstress (EOS) events, the IC can include an EOS protection circuit connected between the pad and ground. To prevent the EOS protection circuit from interfering with normal operation of the IC, it is desirable for the EOS protection circuit to be turned off and non-conducting when normal operating conditions or voltage levels are present at the pad, and to turn on and conduct to provide overstress protection in response to an EOS event occurring. 
     Certain EOS protection circuits are implemented using a number of series-connected diodes between a pad and ground. For example, an EOS protection circuit can include a number of diodes in series to provide a trigger voltage sufficiently above normal operating voltage levels of the pad. To prevent the EOS protection circuit from accidentally triggering and conducting in the presence of normal operating voltage levels, the number of series-connected diodes can be selected such that the resulting trigger voltage is safely above the maximum operating voltage of the pad. 
     However, such a protection scheme can limit and/or constrain EOS protection. For example, the trigger voltage of an EOS protection circuit implemented with multiple diodes in series can be based on a sum of the forward voltages of the diodes. For instance, the trigger voltage of an EOS protection circuit with about n identical series-connected diodes can be about n*Vf, where Vf is the forward voltage of each diode. 
     A diode&#39;s forward voltage can reduce with temperature. To prevent unintended activation at high temperatures by normal signaling, the EOS protection circuit should be implemented with a minimum number of diodes sufficient to avoid conduction under normal operating conditions. However, when a sufficient number of diodes are included to accommodate both the maximum pad voltage during normal operation, a desired voltage margin, process variation, and the maximum operating temperature of the IC, EOS protection is reduced at normal temperatures and conditions. 
     For example, when the EOS protection circuit is implemented in this manner, the EOS protection circuit&#39;s trigger voltage can be relatively high at normal operating temperatures, thereby resulting in an increase in peak voltage levels under ESD conditions and a corresponding degradation in overstress protection. 
     Accordingly, providing protection using only series-connected diodes to ground may be insufficient, since too many series-diodes may need to be included to avoid conduction under normal signaling conditions across process and/or temperature variations. 
     In other implementations, a diode is electrically connected between the pad and a power high supply voltage to provide EOS protection. However, during an EOS event, overstress current can flow into the power high supply voltage. Although a clamp circuit can be used to limit a voltage increase of the power high supply rail during an EOS event, the clamp circuit can decrease power performance by generating leakage current, which can be unacceptable in certain low power applications. 
     Apparatus and methods for EOS protection circuits are provided herein. In certain configurations, an EOS protection circuit includes an overstress sensing circuit electrically connected between a pad and a first supply node, an impedance element electrically connected between the pad and a signal node, a controllable clamp electrically connected between the signal node and the first supply node and selectively activatable by the overstress sensing circuit, and an overshoot limiting circuit electrically connected between the signal node and a second supply node. The overstress sensing circuit activates the controllable clamp when an EOS event is detected at the pad. Thus, the EOS protection circuit is arranged to divert charge associated with the EOS event away from the signal node to provide EOS protection. 
     In certain implementations, the overstress sensing circuit includes a plurality of series-connected diodes and a first field-effect transistor (FET), such as a first metal-oxide-semiconductor (MOS) transistor. Additionally, the controllable clamp includes a second FET, such as a second MOS transistor, having a gate voltage that is controlled based on a gate voltage of the first FET. For example, the first and second FETs can be implemented as a current mirror. Under EOS conditions at the pad, current flows through the overstress sensing circuit&#39;s series-connected diodes, thereby turning on the first and second FETs and activating the controllable clamp. 
     Additionally, the inclusion of the impedance element between the pad and the signal node results in the voltage of the signal node being less than that of the pad in response to a voltage increase at the pad. Additionally, the overshoot limiting circuit holds the voltage at the signal node to a relatively low value until the controllable clamp is activated. Implementing the EOS protection circuit in this manner reduces the peak current injected into the second supply node and reduces voltage overshoot at the signal node. The reduction in peak current leads to a smaller supply clamp (for instance, a more compact circuit layout) between the first and second supply nodes and a corresponding decrease in the IC&#39;s static power dissipation. 
     Accordingly, the teachings herein can be used to provide enhanced EOS protection. Additionally, protecting an IC&#39;s pads using one or more of the EOS protection circuits described herein can lead to a smaller and/or lower leakage supply clamp. 
     In certain configurations, the first supply node corresponds to ground. In such configurations, the EOS protection circuit advantageously shunts charge of the EOS event to a node exhibiting very low impedance and/or enhanced thermal dissipation relative to other supply nodes. 
       FIG. 1  is a schematic diagram of an IC  10 . As shown in  FIG. 1 , the IC  10  can include one or more pins or pads  1  that can be exposed to EOS conditions, such as an ESD event  5 . The IC  10  can include at least one EOS protection circuit  2  implemented in accordance with the teachings herein. 
       FIG. 2  is a schematic diagram of an example wireless or mobile device  11  that can include one or more of the ICs of  FIG. 1 . The wireless device  11  can include EOS protection circuits implementing one or more features of the present disclosure. For example, wireless device  11  can include multiple semiconductor chips or ICs, and one or more of the ICs can include EOS protection circuits implemented in accordance with the teachings herein. 
     The example wireless device  11  depicted in  FIG. 2  can represent a multi-band and/or multi-mode device such as a multi-band/multi-mode mobile phone. In certain embodiments, the wireless device  11  can include a front end  12 , a transceiver  13 , an antenna  14 , a control component  18 , a computer readable medium or memory  19 , a processor  20 , and a battery  21 . 
     The transceiver  13  can generate RF signals for transmission via the antenna  14 . Furthermore, the transceiver  13  can receive incoming RF signals from the antenna  14 . 
     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. 2  as the transceiver  13 . For example, a single component can be configured to provide both transmitting and receiving functionalities. In another example, transmitting and receiving functionalities can be provided by separate components. 
     Similarly, it will be understood that various antenna functionalities associated with the transmission and receiving of RF signals can be achieved by one or more components that are collectively represented in  FIG. 2  as the antenna  14 . For example, a single antenna can be configured to provide both transmitting and receiving functionalities. In another example, transmitting and receiving functionalities can be provided by separate antennas. In yet another example, different bands associated with the wireless device  11  can be provided with different antennas. 
     In  FIG. 2 , one or more output signals from the transceiver  13  are depicted as being provided to the antenna  14  via one or more transmission paths  15 . In the example shown, different transmission paths  15  can represent output paths associated with different bands and/or different power outputs. Although  FIG. 2  illustrates a configuration using two transmission paths  15 , the wireless device  11  can be adapted to include more or fewer transmission paths  15 . 
     In  FIG. 2 , one or more detected signals from the antenna  14  are depicted as being provided to the transceiver  13  via one or more receiving paths  16 . In the example shown, different receiving paths  16  can represent paths associated with different bands. Although  FIG. 2  illustrates a configuration using four receiving paths  16 , the wireless device  11  can be adapted to include more or fewer receiving paths  16 . 
     To facilitate switching between receive and transmit paths, the front end  12  can be configured to electrically connect the antenna  14  to a selected transmit or receive path. Thus, the front end  12  can provide a number of switching functionalities associated with an operation of the wireless device  11 . In certain embodiments, the front end  12  can provide switching between different bands, switching between different power modes, switching between transmission and receiving modes, or some combination thereof. The front end  12  can also be configured to provide additional functionality, including filtering, amplification, and/or duplexing of signals. 
       FIG. 2  shows that in certain embodiments, a control component  18  can be provided for controlling various control functionalities associated with operations of the wireless device  11 . 
     In certain embodiments, a processor  20  can be configured to facilitate implementation of various processes of the wireless device  11 . For example, the processor  20  can operate using computer program instructions stored in a computer-readable memory  19  that can direct the processor  20  to operate in a particular manner. 
     The battery  21  can be any suitable battery for use in the wireless device  11 , including, for example, a lithium-ion battery. 
       FIG. 3A  is a schematic diagram of one example of a module  60  that can include one or more EOS protection circuits.  FIG. 3B  is a cross section of the module  60  of  FIG. 3B  taken along the lines  3 B- 3 B. The module  60  includes a module substrate or laminate  62 , a silicon on insulator (SOI) die  70 , and bond wires  78 . In certain implementations, the module  60  corresponds to a front end module. 
     The module substrate  62  includes a die attach pad  64  and bond pads  66 . As shown in  FIG. 3A , the SOI die  70  has been attached to the die attach pad  64  of the module substrate  62 . As depicted in  FIG. 3B , the module substrate  62  can include a plurality of conductive and non-conductive layers laminated together, and the die attach pad  64  and the bond pads  66  can be formed from a conductive layer  81  disposed on the surface of the module substrate used to attach the SOI die  70 . 
     The SOI die  70  includes pads  76  that can be exposed to EOS events, such as the ESD event  5 . At least a portion of the pads  76  of the SOI die  70  can include corresponding EOS protection circuits  2  implemented in accordance with the teachings herein. 
       FIG. 3C  is a cross section of a module  80  according to another embodiment. 
     The module  80  of  FIG. 3C  is similar to the module  60  of  FIGS. 3A-3B , except that the module  80  is implemented using a flip-chip configuration. For example, rather than using wire bonds to electrically connect the SOI die  90  to the module substrate  62 , the SOI die  90  of  FIG. 3C  has been flipped upside down and attached to the module substrate  62  using solder bumps  91 . At least a portion of the pads  76  of the SOI die  70  can include EOS protection circuits  2  implemented in accordance with the teachings herein. 
     Accordingly, in certain implementations described herein, EOS protection circuits are included in a die implemented using a flip-chip arrangement. 
     Although  FIGS. 3A-3C  illustrate example modules including an SOI die that includes one or more EOS protection circuits, the teachings herein are applicable to other configurations of modules and/or dies. 
       FIG. 4A  is a schematic diagram of an IC interface  100  including an EOS protection circuit according to one embodiment. The IC interface  100  includes a pad  101 , an internal circuit  103 , and an EOS protection circuit including an overstress sensing circuit  111 , an impedance element  112 , a controllable clamp  113 , and an overshoot protection or limiting circuit  114 . 
     The IC interface  100  can undesirably receive EOS events, such as the ESD event  5  at the pad  101 . Absent a protection mechanism, the EOS event can lead to IC damage, such as gate oxide rupture, junction breakdown, and/or metal damage. For example, the internal circuit  103  can include sensitive transistors and/or structures that can be damaged absent an EOS protection mechanism. 
     As shown in  FIG. 4A , the overstress sensing circuit  111  is electrically connected between the pad  101  and a first supply node or rail V 1 . Additionally, the impedance element  112  is electrically connected between the pad  101  and a signal node  102 . Furthermore, the controllable clamp  113  is electrically connected between the signal node  102  and the first supply node V 1 , and is selectively activatable by the overstress sensing circuit  111 . Additionally, the overshoot limiting circuit  114  is electrically connected between the signal node  102  and a second supply node or rail V 2 . 
     The overstress sensing circuit  111  is electrically connected to the pad  101 , and detects when an EOS event, such as ESD event  5 , is received at the pad  101 . When the EOS event is detected, the overstress sensing circuit  111  activates the controllable clamp  113  to provide a low impedance path between the signal node  102  and the first supply node V 1 . Thus, the EOS protection circuit is arranged to divert charge associated with the EOS event away from the signal node  102  to provide EOS protection. 
     The overstress sensing circuit  111  and the controllable clamp  113  can be implemented in a wide variety of ways. In one embodiment, the overstress sensing circuit  111  includes a plurality of series-connected diodes and a first FET. Additionally, the controllable clamp  113  includes a second FET having a gate voltage controlled based on a gate voltage of the first FET. When an EOS event is received at the pad  101 , current flows through the overstress sensing circuit&#39;s series-connected diodes, thereby activating the first and second FETs. 
     With continuing reference to  FIG. 4A , the impedance element  112  is electrically connected between the pad  101  and the signal node  102 . Thus, when an EOS event increases the voltage of the pad  101  relative to the first supply node V 1 , the impedance element  112  provides a voltage drop that results in the voltage of the signal node  102  being less than that of the pad  101 . The illustrated EOS protection circuit further includes the overshoot limiting circuit  114 , which transitions from high to low impedance when the voltage of the signal node  102  increases above the voltage of the second supply node V 2  by a trigger voltage of the overshoot limiting circuit  114 . 
     Including the impedance element  112  and the overshoot limiting circuit  114  maintains the voltage level of the signal node  102  relatively low when an EOS event is present. In particular, the overshoot limiting circuit  114  holds or limits the voltage at the signal node  102  to a relatively low level until the overstress sensing circuit  111  activates the controllable clamp  113 . Additionally, the impedance element  112  provides a voltage drop that allows the overshoot limiting circuit  114  to maintain the signal node&#39;s voltage to a relatively low voltage level even when the EOS event causes the voltage of the pad  101  to increase to a relatively high voltage level. 
     Accordingly, the illustrated configuration of the impedance element  112  and the overshoot limiting circuit  114  aids in maintaining the signal node  102  at a relatively low voltage level. Furthermore, the inclusion of the impedance element  112  reduces the amount of charge that is injected into the second supply node V 2  via the overshoot limiting circuit  114  relative to a configuration in which the signal node  102  is directly connected to the pad  101 . Accordingly, the illustrated configuration exhibits a relatively small amount of peak current injection into the second supply node V 2  and reduces voltage overshoot of the signal node  102  during an EOS event. In certain implementations, the reduction in peak current leads to a smaller supply clamp (for example, the supply clamp  157  of  FIG. 4C ) between the first and second supply nodes V 1 , V 2  and a corresponding decrease in the IC&#39;s static power dissipation. 
     Additional details of the IC interface  100  can be as described earlier. 
       FIG. 4B  is a schematic diagram of an IC interface  130  including an EOS protection circuit according to another embodiment. The IC interface  130  includes a pad  101 , an internal circuit  103 , and an EOS protection circuit including an overstress sensing circuit  111 , an impedance element  112 , a controllable clamp  113 , an overshoot limiting circuit  114 , a first reverse protection circuit  131 , and a second reverse protection circuit  132 . 
     The IC interface  130  of  FIG. 4B  is similar to the IC interface  100  of  FIG. 4A , except that the IC interface  130  further includes the first reverse protection circuit  131  and the second reverse protection circuit  132 . In certain implementations, the overstress sensing circuit  111  is implemented to activate the controllable clamp  113  in response to detecting a positive polarity EOS event that increases the voltage of the pad  101  relative to the first supply node V 1 . 
     In the illustrated embodiment, the first reverse protection circuit  131  and the second reverse protection circuit  132  have been included to protect the IC interface  130  against a negative EOS event that decreases the voltage of the pad  101  relative to the first supply node V 1 . The first reverse protection circuit  131  is electrically connected between the pad  101  and the first supply node V 1 , and transitions from high to low impedance when the voltage of the pad  101  falls below the voltage of the first supply node V 1  by a trigger voltage of the first reverse protection circuit  131 . Additionally, the second reverse protection circuit  132  is electrically connected between the signal node  102  and the first supply node V 1 , and transitions from high to low impedance when the voltage of the signal node  102  falls below the voltage of the first supply node V 1  by a trigger voltage of the second reverse protection circuit  132 . 
     Although the illustrated IC interface  130  of  FIG. 4B  includes two reverse protection circuits, more or fewer reverse protection circuits can be included. In one embodiment, the first reverse protection circuit  131  is included and the second reverse protection circuit  132  is omitted. In another embodiment, the first reverse protection circuit  131  is omitted and the second reverse protection circuit  132  is included. 
     Additional details of the IC interface  130  can be as described earlier. 
       FIG. 4C  is a schematic diagram of an IC interface  150  including an EOS protection circuit according to another embodiment. The IC interface  150  includes a pad  101 , an internal circuit  103 , and an EOS protection circuit including an overstress sensing circuit  111 , an impedance element  112 , a controllable clamp  113 , an overshoot limiting circuit  114 , and a supply clamp  157 . 
     The IC interface  150  of  FIG. 4C  is similar to the IC interface  100  of  FIG. 4A , except that the IC interface  150  further includes the supply clamp  157 . In certain implementations, the supply clamp  157  is included to help limit a voltage difference between the second supply node V 2  and the first supply node V 1  during an overstress event. 
     Additional details of the IC interface  150  can be as described earlier. 
       FIG. 5  is one example of a graph  190  of voltage versus time for the EOS protection circuit of  FIG. 4A . The graph  190  includes a plot  191  of the voltage of the signal node  102  of  FIG. 4A  versus time. 
     The graph  190  begins at time zero, in which an EOS event is received at the pad  101 . The graph  190  has been annotated to show an activation time t ACTIVATION , corresponding to a time at which the controllable clamp  113  is activated or turned on by the overstress sensing circuit  111 . The activation time t ACTIVATION  can be associated with a delay in detecting the EOS event and in providing a control voltage and/or current of sufficient magnitude to activate the controllable clamp  113 . 
     As shown in  FIG. 5 , the voltage of the signal node  102  can increase during a period of time in which the controllable clamp  113  is not activated. By including the impedance element  112  and the overshoot limiting circuit  114 , the voltage overshoot V OVERSHOOT  of signal node  102  can be decreased. Reducing voltage overshoot can provide enhanced protection to the internal circuit  103  and/or reduce charge injection to the second supply node V 2  via the overshoot limiting circuit  114 . 
     Although  FIG. 5  illustrates one example of a graph of voltage versus time for the EOS protection circuit of  FIG. 4A , other results are possible. For example, simulated and/or measured results can vary based on implementation and/or application. 
       FIG. 6A  is a schematic diagram of an IC interface  200  including an EOS protection circuit according to another embodiment. The IC interface  200  includes an input pad  201 , an input logic circuit  203 , and an EOS protection circuit including an overstress sensing circuit  211 , a resistor  212 , a controllable clamp  213 , an overshoot limiting circuit  214 , a first reverse protection circuit  215 , a second reverse protection circuit  216 , and a supply clamp  217 . 
     The IC interface  200  can receive EOS events such as the ESD event  5  at the input pad  201 . Absent a protection mechanism, the EOS event can lead to IC damage, such as damage to the input logic circuit  203  that is electrically connected to the signal node  202 . 
     The illustrated EOS protection circuit provides bidirectional EOS protection against both positive polarity EOS events that increase the voltage of the input pad  201  relative to the first supply node V 1  and against negative polarity EOS events that decrease the voltage of the input pad  201  relative to the first supply node V 1 . 
     As shown in  FIG. 6A , the overstress sensing circuit  211  is electrically connected between the input pad  201  and a first supply node V 1 . The overstress sensing circuit  211  includes first to seventh diodes  221 - 227 , respectively, and a first n-type metal oxide semiconductor (NMOS) transistor  230 . As shown in  FIG. 6A , the first to sixth diodes  221 - 226  are electrically connected in series from anode to cathode between the input pad  201  and a drain of the first NMOS transistor  230 . Additionally, the seventh diode  227  includes an anode electrically connected to a source of the first NMOS transistor  230  and a cathode electrically connected to the first supply node V 1 . The first NMOS transistor  230  is diode-connected, and includes a gate and drain electrically connected to one another. 
     The illustrated controllable clamp  213  includes a second NMOS transistor  231  and a clamp diode  232 . The second NMOS transistor  231  includes a drain electrically connected to the signal node  202 , and a source electrically connected to the first supply node V 1  via the clamp diode  232 . Including the clamp diode  232  in the controllable clamp  213  can aid in reducing the clamp&#39;s leakage current when normal signaling conditions are present and the controllable clamp  213  is turned off. As shown in  FIG. 6A , the gate of the second NMOS transistor  231  of the controllable clamp  213  is electrically connected to the gate of the first NMOS transistor  230  of the overstress sensing circuit  211 . 
     In the illustrated embodiment, the first NMOS transistor  230  of the overstress sensing circuit  211  and the second NMOS transistor  231  of the controllable clamp  213  are connected as a current mirror. Although a specific implementation of overstress sensing circuit and controllable clamp are shown, the teachings herein are applicable to a wide variety of overstress sensing circuits and controllable clamps. 
     The overstress sensing circuit  211  activates the controllable clamp  213  when a positive polarity EOS event is detected at the input pad  201 . For example, when the voltage at the input pad  201  is sufficiently high, a current can flow through the first to seventh diodes  221 - 227  and the first NMOS transistor  230 , thereby controlling the gate voltage of the first NMOS transistor  230  to a sufficient voltage to turn on the second NMOS transistor  231 . The activation voltage of the overstress sensing circuit  211  can be based on a forward voltage of the diodes  221 - 227  and a threshold voltage of the first NMOS transistor  230 . 
     As shown in  FIG. 6A , the resistor  212  is electrically connected between the input pad  201  and the signal node  202 . Additionally, the overshoot limiting circuit  214  is electrically connected between the signal node  202  and the second supply node V 2 . In the illustrated configuration, the overshoot limiting circuit  214  includes an overshoot limiting diode  241  including an anode electrically connected to the signal node  202  and a cathode electrically connected to the second supply node V 2 . Implementing the overshoot limiting circuit  214  in this manner can provide the overshoot limiting circuit  214  with a relatively low trigger voltage that is about equal to a forward voltage of the overshoot limiting diode  241 . However, other configurations are possible, such as implementations selected based on signaling levels and/or processing constraints. 
     When an EOS event increases the voltage of the input pad  201  relative to the first supply node V 1 , the resistor  212  provides a voltage drop that results in the voltage of the signal node  202  being less than that of the input pad  201 . Including the resistor  212  and the overshoot limiting circuit  214  maintains the voltage level of the signal node  202  relatively low when an EOS event is present. In particular, the overshoot limiting circuit  214  holds the voltage at the signal node  202  to a relatively low level until the overstress sensing circuit  211  activates the controllable clamp  213 . Additionally, the resistor  212  provides a voltage drop that allows the overshoot limiting circuit  214  to maintain the signal node&#39;s voltage to a relatively low voltage level even when the EOS event causes the voltage of the input pad  201  to increase to a relatively high voltage level. 
     Furthermore, the inclusion of the resistor  212  reduces the amount of charge that is injected into the second supply node V 2  via the overshoot limiting circuit  214  relative to a configuration in which the signal node  202  is directly connected to the input pad  201 . Accordingly, the illustrated configuration exhibits a relatively small amount of peak current injection into the second supply node V 2  and reduces voltage overshoot of the signal node  202  during an EOS event. The reduction in peak current leads to a reduction in a size of the supply clamp  217  and a corresponding decrease in leakage current. 
     In the illustrated embodiment, the resistor  212  is an explicit resistor (for instance, a thin-film resistor), and corresponds to more than mere parasitic resistance. 
     The illustrated EOS protection circuit further includes the first reverse protection circuit  215  and the second reverse protection circuit  216 , which aid in providing protection against negative polarity EOS events that decrease the voltage of the input pad  201  relative to the first supply node V 1 . In the illustrated embodiment, the first reverse protection circuit  215  includes a diode  251  including an anode electrically connected to the first supply node V 1  and a cathode electrically connected to the input pad  201 . Additionally, the second reverse protection circuit  216  includes a diode  252  including an anode electrically connected to the first supply node V 1  and a cathode electrically connected to the signal node  202 . However, other configurations are possible. 
     Additional details of the IC interface  200  can be as described earlier. 
       FIG. 6B  is a schematic diagram of an IC interface  300  including an EOS protection circuit according to another embodiment. The IC interface  300  includes an input pad  201 , an input logic circuit  203 , and an EOS protection circuit including an overstress sensing circuit  311 , a resistor  212 , a controllable clamp  313 , an overshoot limiting circuit  314 , a first reverse protection circuit  315 , a second reverse protection circuit  216 , and a supply clamp  217 . 
     The EOS protection circuit of  FIG. 6B  is similar to the EOS protection circuit of  FIG. 6A , except that the EOS protection circuit of  FIG. 6B  includes different implementations of certain circuits. 
     For example, in the embodiment illustrated in  FIG. 6B , the overstress sensing circuit  311  includes first to eight diodes  321 - 328 , respectively, and a first NMOS transistor  330 . The first to eight diodes  321 - 328  are electrically connected in series from anode to cathode between the input pad  201  and the first supply node V 1 , and control a voltage at which the overstress sensing circuit  311  detects overstress. Additionally, the first NMOS transistor includes a drain and gate electrically connected to the anode of the seventh diode  327 , and a source electrically connected to a cathode of the seventh diode  327 . 
     The illustrated controllable clamp  313  of  FIG. 6B  includes the second NMOS transistor  331  and clamp diode  332 , which can be similar to the second NMOS transistor  231  and clamp diode  232  described earlier with respect to  FIG. 6A . The controllable clamp  313  of  FIG. 6B  further includes the capacitor  333 , which is electrically connected between the gate of the second NMOS transistor  331  and the first supply node V 1 . The capacitor  333  can aid in stabilizing a control voltage used to activate the controllable clamp  313 , thereby helping to prevent unintended activation. 
     The illustrated overshoot limiting circuit  314  of  FIG. 6B  includes a first diode  341  and a second diode  342  electrically connected in series from anode to cathode between the signal node  202  and the second supply node V 2 . Although the overshoot limiting circuit  314  includes two diodes in series, more or fewer diodes can be included. Moreover, other implementations of overshoot limiting circuits are possible, such as implementations selected based on signaling levels and/or processing constraints. 
     The illustrated first reverse protection circuit  315  includes first to fourth diodes  351 - 354  electrically connected in series from anode to cathode between the first supply node V 1  and the input pad  201 . However, other configurations are possible, including, but not limited to, implementations with more or fewer diodes in series. 
     Additional details of the IC interface  300  can be as described earlier. 
       FIG. 7A  is a schematic diagram of a front end system  630  according to one embodiment.  FIG. 7B  is a schematic diagram of a front end system  640  according to another embodiment. 
     The front end systems of  7 A and  7 B can include EOS protection circuits implementing one or more features of the present disclosure. For example, the front end systems of  7 A and  7 B can include one or more semiconductor chips or ICs that include EOS protection circuits implemented in accordance with the teachings herein. 
     An RF front end system can include circuits in a signal path between an antennas and a baseband system. Some RF front ends can include circuits in signal paths between one or more antennas and a mixer configured to modulate a signal to RF or to demodulate an RF signal. 
     The front end systems of  7 A and  7 B can be implemented in a packaged module. Such packaged modules can include relatively low cost laminate based front end modules that combine power amplifiers with low noise amplifiers and/or switch functions. Some such packaged modules can be multi-chip modules. In certain implementations, some or the all of the illustrated components in any of the front end systems in  FIGS. 7A and/or 7B  can be embodied on a single integrated circuit or die. Such a die can be manufactured using any suitable process technology. As one example, the die can be a semiconductor-on-insulator die, such as a silicon-on-insulator (SOI) die. According to some implementations, one or more antennas can be integrated with any of the front end systems discussed herein. 
     With reference to  FIG. 7A , the RF front end system  630  is configured to receive RF signals from an antenna  641  and to transmit RF signals by way of the antenna  641 . The illustrated front end system  630  includes a first multi-throw switch  642 , a second multi-throw switch  643 , a receive signal path that includes an LNA  646 , a bypass signal path that includes a bypass network  644 , and a transmit signal path that includes a power amplifier  645 . The low noise amplifier  646  can be implemented by any suitable low noise amplifier. The bypass network  644  can include any suitable network for matching and/or bypassing the receive signal path and the transmit signal path. The bypass network  644  can be implemented by a passive impedance network or by a conductive trace or wire. 
     The first multi-throw switch  642  can selectively connect a particular signal path to the antenna  641 . The first multi-throw switch  642  can electrically connect the transmit signal path to the antenna  641  in a first state, electrically connect the receive signal path to the antenna  641  in a second state, and electrically connect the bypass signal path to the antenna  641  in a third state. The second multi-throw switch  643  can selectively connect a particular signal path to an input/output port of the front end system  630 , in which the particular signal path is the same signal path electrically connected to the antenna  641  by way of the first multi-throw switch  642 . Accordingly, the second multi-throw switch  643  together with the first multi-throw switch  642  can selectively connect a particular signal path between the antenna  641  and the input/output port of the front end system  630 . 
     The control and biasing circuit  647  can be used to control and bias circuitry of the RF front end system  630 . In certain configurations, the control and biasing circuit  647  receives a mode signal indicating a mode of operation of the power amplifier  645 . The mode signal can be provided to the control and biasing circuit  647  in a variety of ways, such as over a serial interface. The control and biasing circuit  647  can use the mode signal for a variety of purposes, including, for example, controlling a voltage level of a supply voltage used to power an output stage of the power amplifier  645 . 
     The RF front end system  640  of  FIG. 7B  is similar to the RF front end system  630  of  FIG. 7A , except that the first multi-throw switch  649  is configured to selectively connect a particular signal path to either a first antenna  641  or a second antenna  648 . The multi-throw switch  649  can be a multi-throw, multi-pole switch. 
     Applications 
     Some of the embodiments described above have provided examples in connection with communications devices, such as mobile phones and wireless devices. However, the principles and advantages of the embodiments can be used for any other systems or apparatus that have needs for EOS protection circuits. 
     For example, EOS protection circuits can be included 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.