Abstract:
An electrostatic-discharge/impedance-matching circuit for use in radio frequency (RF) integrated circuits. The electrostatic-discharge/impedance-matching circuit includes at least one shunt circuit operable to shunt current related to an over-voltage condition and at least one series element operably coupled to the shunt element. The shunt element and series element in combination provide electrostatic discharge protection for the RF signal processing circuit elements on the integrated circuit and also provide a matched input impedance for an incoming RF signal. Various alternate embodiments of die electrostatic-discharge/impedance-matching circuit include first and second shunt elements and a series element operably connected in combination to provide optimal electrostatic discharge protection and impedance matching. The electrostatic-discharge/impedance-matching circuit can be placed at various locations on the integrated circuit to provide optimal petformance depending on the particular architecture of the integrated circuit.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a continuation of U.S. Utility application Ser. No. 10/172,913, filed Jun. 17, 2002, which issued on Aug. 3, 2004 as U.S. Utility Pat. No. 6,771,475). 

   FIELD OF THE INVENTION 
   This invention relates generally to communication systems and, more particularly, to circuitry for providing electrostatic protection and impedance matching for radio frequency circuit components in integrated circuits. 
   BACKGROUND OF THE INVENTION 
   Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), wireless application protocols (WAP), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof. 
   Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and share information over that channel. For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the internet, and/or via some other wide area network. 
   For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the receiver receives RF signals, removes the RF carrier frequency from the RF signals via one or more intermediate frequency stages, and demodulates the signals in accordance with a particular wireless communication standard to recapture the transmitted data. The transmitter converts data into RF signals by modulating the data in accordance with the particular wireless communication standard and adds an RF carrier to the modulated data in one or more intermediate frequency stages to produce the RF signals. 
   As the demand for enhanced performance (e.g., reduced interference and/or noise, improved quality of service, compliance with multiple standards, increased broadband applications, et cetera), smaller sizes, lower power consumption, and reduced costs increases, wireless communication device engineers are faced with a very difficult design challenge to develop such a wireless communication device. Typically, an engineer is forced to compromise one or more of these demands to adequately meet the others. 
   Costs of manufacturing a radio frequency integrated circuit (IC) may be reduced by switching from one integrated circuit manufacturing process to another. For example, a CMOS process may be used instead of a bi-CMOS process since it is a more cost effective method of IC manufacture, but the CMOS process increases component mismatches, increases temperature related variations, and increases process variations. 
   Two problems commonly encountered in the design and manufacture of RF signal integrated circuits relate to impedance matching of various RF signal processing components and control of electrostatic discharges to prevent damage to components inside the integrated circuit. Proper impedance matching is important for an efficient transfer of signal and energy from a “source” to a “load.” In an integrated circuit for processing RF signals, impedance matching is especially important to ensure an efficient transfer of an RF signal from the antenna to a receiver filter module or a low-noise amplifier. 
   Electrostatic discharges are well known as a major contributing factor in damaging integrated circuits—both during the manufacturing process and during use of the circuit. Integrated Circuits often come into contact with accumulated static charge on surfaces such as the human body and assembly equipment. The voltage potential that accompanies such built up static charge is often on the order of Kilovolts. When accumulated static charge finds a discharge path through the pins of an integrated circuit, often through contact, electrostatic discharge occurs. These events can result in highly concentrated currents that cause severe heating in the physical circuit devices of an integrated circuit. Severe heating can cause permanent damage to these devices. Therefore, protective circuits or structures must be employed to prevent damage caused by electrostatic discharge. Electrostatic protection circuits must be capable of quickly and efficiently routing electrostatic discharge between any combination of pins of an integrated circuit, eliminating significant voltage differential and preventing damage to circuit devices. 
   Therefore, a need exists for circuit that can be optimized to provide both impedance matching and protection from the damaging effects of electrostatic discharges. 
   SUMMARY OF THE INVENTION 
   The electrostatic-discharge/impedance-matching circuit disclosed herein for use in radio frequency (RF) integrated circuits substantially meets these needs and others. The electrostatic-discharge/impedance-matching circuit of the present invention is broadly comprised of at least one shunt circuit operable to shunt current related to an over-voltage condition and at least one series element operably coupled to the shunt element. The shunt element and series element in combination provide electrostatic discharge protection for the RF signal processing circuit elements on the integrated circuit and also provide a matched input impedance for an incoming RF signal. Various alternate embodiments of the electrostatic-discharge/impedance-matching circuit include first and second shunt elements and a series element operably connected in combination to provide optimal electrostatic discharge protection and impedance matching. 
   The electrostatic-discharge/impedance-matching circuit can be placed at various locations on the integrated circuit to provide optimal performance depending on the particular architecture of the integrated circuit. In one embodiment, the electrostatic-discharge/impedance-matching circuit it located between a transmitter/receiver switch module and an antenna receiving incoming RF signals. In another embodiment, the electrostatic-discharge/impedance-matching switch is located directly between an antenna and a receiver filter module. In other embodiments, the electrostatic-discharge/impedance-matching circuit is located between a receiver filter module and a low-noise amplifier. 
   Other features and advantages of the present invention will become apparent from the following detailed description of the invention made with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a schematic block diagram of a wireless communication system that supports wireless communication devices in accordance with the present invention. 
       FIG. 2  illustrates a schematic block diagram of a wireless communication device in accordance with the present invention. 
       FIG. 3  illustrates a schematic block diagram of a radio module of a wireless communication device incorporating an electrostatic-discharge/impedance-matching circuit in accordance with the present invention. 
       FIG. 4  illustrates a schematic block diagram of an alternate embodiment radio module of a wireless communication device incorporating an electrostatic-discharge/impedance-matching circuit in accordance with the present invention. 
       FIG. 5  illustrates a schematic block diagram of a second alternate embodiment of a radio module of a wireless communication device incorporating an electrostatic-discharge/impedance-matching circuit in accordance with the present invention. 
       FIG. 6  illustrates a schematic block diagram of a third alternate embodiment radio module of a wireless communication device incorporating an electrostatic-discharge/impedance-matching circuit in accordance with the present invention. 
       FIG. 7  illustrates a schematic block diagram of a fourth alternate embodiment radio module of a wireless communication device incorporating an electrostatic-discharge/impedance-matching circuit in accordance with the present invention. 
       FIG. 8  illustrates a schematic block diagram of the functional components of an electrostatic-discharge/impedance-matching circuit in accordance with the present invention. 
       FIG. 9  illustrates a schematic block diagram of an alternate embodiment of an electrostatic-discharge/impedance-matching circuit in accordance with the present invention. 
       FIG. 10  illustrates a flowchart diagram of a method for using the electrostatic discharge and impedance matching circuit of the present invention to process an incoming radio frequency signal. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a schematic block diagram illustrating a communication system  10  that includes a plurality of base stations and/or access points  12 – 16 , a plurality of wireless communication devices  18 – 32  and a network hardware component  34 . The wireless communication devices  18 – 32  may be laptop host computers  18  and  26 , personal digital assistant hosts  20  and  30 , personal computer hosts  24  and  32  and/or cellular telephone hosts  22  and  28 . The details of the wireless communication devices will be described in greater detail with reference to  FIG. 2 . 
   The base stations or access points  12 – 16  are operably coupled to the network hardware  34  via local area network connections  36 ,  38  and  40 . The network hardware  34 , which may be a router, switch, bridge, modem, system controller, et cetera provides a wide area network connection  42  for the communication system  10 . Each of the base stations or access points  12 – 16  has an associated antenna or antenna array to communicate with the wireless communication devices in its area. Typically, the wireless communication devices register with a particular base station or access point  12 – 14  to receive services from the communication system  10 . For direct connections (i.e., point-to-point communications), wireless communication devices communicate directly via an allocated channel. 
   Typically, base stations are used for cellular telephone systems and like-type systems, while access points are used for in-home or in-building wireless networks. Regardless of the particular type of communication system, each wireless communication device includes a built-in radio and/or is coupled to a radio. The radio includes a highly linear amplifier and/or programmable multi-stage amplifier as disclosed herein to enhance performance, reduce costs, reduce size, and/or enhance broadband applications. 
     FIG. 2  is a schematic block diagram illustrating a wireless communication device that includes the host device  18 – 32  and an associated radio  60 . For cellular telephone hosts, the radio  60  is a built-in component. For personal digital assistants hosts, laptop hosts, and/or personal computer hosts, the radio  60  may be built-in or an externally coupled component. 
   As illustrated, the host device  18 – 32  includes a processing module  50 , memory  52 , radio interface  54 , input interface  58  and output interface  56 . The processing module  50  and memory  52  execute the corresponding instructions that are typically done by the host device. For example, for a cellular telephone host device, the processing module  50  performs the corresponding communication functions in accordance with a particular cellular telephone standard. 
   The radio interface  54  allows data to be received from and sent to the radio  60 . For data received from the radio  60  (e.g., inbound data), the radio interface  54  provides the data to the processing module  50  for further processing and/or routing to the output interface  56 . The output interface  56  provides connectivity to an output display device such as a display, monitor, speakers, et cetera such that the received data may be displayed. The radio interface  54  also provides data from the processing module  50  to the radio  60 . The processing module  50  may receive the outbound data from an input device such as a keyboard, keypad, microphone, et cetera via the input interface  58  or generate the data itself. For data received via the input interface  58 , the processing module  50  may perform a corresponding host function on the data and/or route it to the radio  60  via the radio interface  54 . 
   Radio  60  includes a host interface  62 , digital receiver processing module  64 , an analog-to-digital converter  66 , a filtering/attenuation module  68 , an IF mixing down conversion stage  70 , a receiver filter  71 , a low-noise amplifier  72 , a transmitter/receiver switch  73 , a local oscillation module  74 , memory  75 , a digital transmitter processing module  76 , a digital-to-analog converter  78 , a filtering/gain module  80 , an IF mixing up conversion stage  82 , a power amplifier  84 , a transmitter filter module  85 , and an antenna  86 . The antenna  86  may be a single antenna that is shared by the transmit and receive paths as regulated by the Tx/Rx switch  73 , or may include separate antennas for the transmit path and receive path. The antenna implementation will depend on the particular standard to which the wireless communication device is compliant. 
   The digital receiver processing module  64  and the digital transmitter processing module  76 , in combination with operational instructions stored in memory  75 , execute digital receiver functions and digital transmitter functions, respectively. The digital receiver functions include, but are not limited to, digital intermediate frequency to baseband conversion, demodulation, constellation demapping, decoding, and/or descrambling. The digital transmitter functions include, but are not limited to, scrambling, encoding, constellation mapping, modulation, and/or digital baseband to IF conversion. The digital receiver and transmitter processing modules  64  and  76  may be implemented using a shared processing device, individual processing devices, or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions. The memory  75  may be a single memory device or a plurality of memory devices. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, and/or any device that stores digital information. Note that when the processing module  64  and/or  76  implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory storing the corresponding operational instructions is embedded with the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. The memory  75  stores, and the processing module  64  and/or  76  executes, operational instructions corresponding to at least some of the functions illustrated in  FIGS. 3–10 . 
   In operation, the radio  60  receives outbound data  94  from the host device via the host interface  62 . The host interface  62  routes the outbound data  94  to the digital transmitter processing module  76 , which processes the outbound data  94  in accordance with a particular wireless communication standard (e.g., IEEE802.11a, IEEE802.11b, Bluetooth, et cetera) to produce digital transmission formatted data  96 . The digital transmission formatted data  96  will be a digital base-band signal or a digital low IF signal, where the low IF typically will be in the frequency range of one hundred kilohertz to a few megahertz. 
   The digital-to-analog converter  78  converts the digital transmission formatted data  96  from the digital domain to the analog domain. The filtering/gain module  80  filters and/or adjusts the gain of the analog signal prior to providing it to the IF mixing stage  82 . The IF mixing stage  82  directly converts the analog baseband or low IF signal into an RF signal based on a transmitter local oscillation  83  provided by local oscillation module  74 . The power amplifier  84  amplifies the RF signal to produce outbound RF signal  98 , which is filtered by the transmitter filter module  85 . The antenna  86  transmits the outbound RF signal  98  to a targeted device such as a base station, an access point and/or another wireless communication device. 
   The radio  60  also receives an inbound RF signal  88  via the antenna  86 , which was transmitted by a base station, an access point, or another wireless communication device. The antenna  86  provides the inbound RF signal  88  to the receiver filter module  71  via the Tx/Rx switch  77 , where the Rx filter  71  bandpass filters the inbound RF signal  88 . The Rx filter  71  provides the filtered RF signal to low-noise amplifier  72 , which amplifies the signal  88  to produce an amplified inbound RF signal. The low-noise amplifier  72  provides the amplified inbound RF signal to the IF mixing module  70 , which directly converts the amplified inbound RF signal into an inbound low IF signal or baseband signal based on a receiver local oscillation  81  provided by local oscillation module  74 . The down conversion module  70  provides the inbound low IF signal or baseband signal to the filtering/attenuation module  68 . The filtering/attenuation module  68  may be implemented in accordance with the teachings of the present invention to filter and/or attenuate the inbound low IF signal or the inbound baseband signal to produce a filtered inbound signal. 
   The analog-to-digital converter  66  converts the filtered inbound signal from the analog domain to the digital domain to produce digital reception formatted data  90 . The digital receiver processing module  64  decodes, descrambles, demaps, and/or demodulates the digital reception formatted data  90  to recapture inbound data  92  in accordance with the particular wireless communication standard being implemented by radio  60 . The host interface  62  provides the recaptured inbound data  92  to the host device  18 – 32  via the radio interface  54 . 
   As one skilled in the art will appreciate, the wireless communication device of  FIG. 2  may be implemented using one or more integrated circuits. For example, the host device may be implemented on one integrated circuit, the digital receiver processing module  64 , the digital transmitter processing module  76  and memory  75  may be implemented on a second integrated circuit, and the remaining components of the radio  60 , less the antenna  86 , may be implemented on a third integrated circuit. As an alternate example, the radio  60  may be implemented on a single integrated circuit. As yet another example, the processing module  50  of the host device and the digital receiver and transmitter processing modules  64  and  76  may be a common processing device implemented on a single integrated circuit. Further, the memory  52  and memory  75  may be implemented on a single integrated circuit and/or on the same integrated circuit as the common processing modules of processing module  50  and the digital receiver and transmitter processing module  64  and  76 . 
   It will be understood by those skilled in the art that the various circuit components illustrated in  FIG. 2  can be constructed on a monolithic integrated circuit. The individual integrated circuit components can be damaged by electrostatic discharge over-voltage conditions that are often created on the boundary of the integrated circuit and conducted through the integrated circuit connecting pins. While the advantages of the electrostatic-discharge/impedance-matching circuit of the present invention can be obtained by placing the circuit in a multitude of locations on the integrated circuit, there are particular advantages associated with locating it at the boundary of the integrated circuit to prevent damage associated with electrostatic discharges transmitted through the integrated circuit connecting pins. In each of the embodiments described herein, the electrostatic-discharge/impedance-matching circuit may be formed upon an integrated circuit at a boundary of the integrated circuit. Formed at the boundary of the integrated circuit, the electrostatic-discharge/impedance-matching circuit provides protection from electrostatic-discharge at a respective input and also impedance-matching at the respective input. 
     FIG. 3  illustrates an embodiment of the present invention wherein the electrostatic-discharge/impedance-matching circuit  100  is connected between the Tx/Rx switch module  73  and the antenna  86 . The electrostatic-discharge/impedance-matching circuit  100 ′, shown in phantom, illustrates a connection of the circuit  100  to the Rx filter module  71  during operation when the Tx/Rx switch module  73  connects the antenna  86  to the Rx filter module  71 . In the illustration shown in  FIG. 3 , all of the circuit components of the radio  60  are formed (“on-chip”) on a single integrated circuit and the electrostatic-discharge/impedance-matching circuit  100  is located on the boundary of the chip to protect against damage from static discharges at the input connection where the an inbound RF signal is received from the antenna  86 . 
   As will be discussed in greater detail below, the electrostatic-discharge/impedance-matching circuit  100  comprises a combination of circuit components that provide matched input impedance to the antenna  86 . Further, the electrostatic-discharge/impedance-matching circuit  100  may also provide desired output impedance to the RF filter module  71 . While the components of the electrostatic-discharge/impedance-matching circuit  100  can be selected to provide a wide range of matching impedances, depending on the specific application, typical matched impedance as presented to the antenna  86  is 50 ohms. 
     FIG. 4  illustrates an embodiment of the present invention wherein the electrostatic-discharge/impedance-matching circuit  100  is connected between the Rx filter module  71  and the low-noise amplifier  72 . In the illustration shown in  FIG. 4 , the circuit components for the Tx/Rx switch module  73 , the Tx filter module  85  and the Rx filter module are formed “off-chip,” while all of the other circuit components of the radio  60  are formed on a single integrated circuit. The electrostatic-discharge/impedance-matching circuit  100  is, therefore, located on the boundary of the chip to protect against damage from static discharges at the input connection where an inbound RF signal is received from the Rx filer module  71 . The electrostatic-discharge/impedance-matching circuit  100  comprises a combination of circuit components that provide matched input impedance to the Rx filter  71 . The electrostatic-discharge/impedance-matching circuit  100  may also provide a desired output impedance to the low-noise amplifier  72 . 
     FIG. 5  illustrates an embodiment of the present invention in a radio  60  that does not comprise a Tx/Rx switch module. In this embodiment, the outbound RF signal  98  from Rx filter module  85  is transmitted on antenna  86 , while the inbound RF signal  88  is received on a separate antenna  86   a . The electrostatic-discharge/impedance-matching circuit  100  is connected between the antenna  86   a  and the input to the Rx filter module  71 . In the illustration shown in  FIG. 5 , all of the circuit components of the radio  60  are formed on a single integrated circuit and, therefore, the electrostatic-discharge/impedance-matching circuit  100  is located on the boundary of the chip to protect against damage from static discharges at the input connection where the an inbound RF signal is received from the antenna  86   a.    
     FIG. 6  illustrates another embodiment of the present invention wherein the electrostatic-discharge/impedance-matching circuit  100  is incorporated into a radio  60  that utilizes separate transmit and receive antennas  86  and  86   a , respectively. In this embodiment, the electrostatic-discharge/impedance-matching circuit  100  is connected between the Rx filter module  71  and the low-noise amplifier  72 . In the illustration shown in  FIG. 6 , the circuit components for the Tx filter module  85  and the Rx filter module are formed “off-chip,” while all of the other circuit components of the radio  60  are formed on a single integrated circuit. The electrostatic-discharge/impedance-matching circuit  100  is, therefore, located on the boundary of the chip to protect against damage from static discharges at the input connection where an inbound RF signal is received from the Rx filer module  71 . Again, as discussed in connection with previous embodiments, the electrostatic-discharge/impedance-matching circuit  100  comprises a combination of circuit components that provide a predetermined impedance that provides a matched impedance between the output of the Rx filter  71  and the input to the low-noise amplifier  72 . 
     FIG. 7  illustrates another embodiment of the present invention wherein the electrostatic-discharge/impedance-matching circuit  100  is incorporated into a radio  60  that utilizes separate transmit and receive antennas  86  and  86   a , respectively. In this embodiment, the electrostatic-discharge/impedance-matching circuit  100  is connected between the low-noise amplifier  72  and the down-conversion module  70 . In the illustration shown in  FIG. 7 , the circuit components for the power amplifier module  84 , the Tx filter module  85 , the Rx filter module  71  and the low-noise amplifier  72  are formed “off-chip,” while all of the other circuit components of the radio  60  are formed on a single integrated circuit. The electrostatic-discharge/impedance-matching circuit  100  is, therefore, located on the boundary of the chip to protect against damage from static discharges at the input connection where an inbound RF signal is received from the low-noise amplifier  72 . Again, as discussed in connection with previous embodiments, the electrostatic-discharge/impedance-matching circuit  100  comprises a combination of circuit components that provide a matched input impedance to the low-noise amplifier  72 . 
     FIG. 8  is a schematic block diagram illustration of an embodiment of the electrostatic-discharge/impedance-matching circuit  100  comprising a shunt impedance  102  and a series impedance  104 . As will be appreciated by those of skill in the art, the impedance values of the shunt impedance  102  and the series impedance  104  can be selected to optimize the dissipation of electrostatic discharges at the RF input through the shunt impedance  102  to the ground line  105 . Moreover, the combined impedance of the shunt and series impedance elements  102  and  104 , can also be optimized to provide impedance matching between the RF input and the RF circuit component  107 , which can be an Rx filter module  71 , low-noise amplifier  72  or other RF circuit component on the boundary of the integrated circuit module. 
     FIG. 9  is a schematic block diagram illustration of another embodiment of the electrostatic-discharge/impedance-matching circuit  100  comprising a first and second shunt impedance elements  102  and  106 , respectively, and a series impedance  104 . The first shunt element  102  is connected between the RF input and Vss and the second shunt element  106  is connected between the RF input and Vdd. As discussed above, it will be appreciated by those of skill in the art that the impedance values of the first and second shunt impedances  102 ,  106  and the series impedance  104  can be selected to optimize the dissipation of electrostatic discharges at the RF input. Furthermore, the combined impedance of the first and second shunt impedances and series impedance can also be optimized to provide impedance matching between the RF input and the RF circuit component  107 , which can be an Rx filter module  71 , low-noise amplifier  72  or other RF circuit component on the boundary of the integrated circuit module. Various discrete circuit components, known to those skilled in the art, can be combined to obtain the desired impedances for each of the shunt and series impedance elements discussed above. By was of illustration, shunt element  102  is shown to comprise a diode and resistor combination, while shunt element  106  is shown to comprise a resistor, inductor and capacitor combination. 
     FIG. 10  is a flowchart illustration of the processing steps for using the electrostatic-discharge/impedance-matching circuit of the present invention to process an incoming RF signal. In step  200 , an incoming RF signal at a first impedance is obtained from an antenna, such as antenna  86  or from an RF circuit component, such as Rx filter  71 . In step  202  the incoming RF signal is processed using the electrostatic-discharge/impedance-matching circuit  100  to generate an RF signal at a second impedance that is matched to the input impedance of an RF circuit element. In step  204 , the RF signal at the second impedance is provided to an RF circuit element in the wireless receiver for further signal processing. 
   The preceding discussion has presented a circuit for providing electrostatic discharge and impedance matching that may be used in a radio transmitter or radio transceiver. As one of skill in the art will appreciate, other embodiments may be derived from the teaching of the present invention, without deviating from the scope of the claims.