# Patent

## Title
Radio frequency integrated circuit electro-static discharge circuit

## Abstract

The radio frequency integrated circuit (RFIC) electrostatic discharge (ESD) circuit includes a transformer balun, an impedance matching circuit and a clamping circuit. The balun is operably coupled to transpose a single-ended radio frequency (RF) signal and differential RF signal. The balun includes a 1st winding that is coupled to the single-ended radio frequency signals and a 2nd winding that is coupled for differential RF signals. The impedance matching circuit is coupled to the 1st winding and provides, in conjunction with the impedance of the balun, impedance matching with an antenna coupled to the RFIC. The clamping circuit is operably coupled to the balun and/or to the impedance matching circuit and, in combination with the impedance matching circuit and/or in combination with the balun, provides ESD protection for the receiver section and/or transmitter section of the radio frequency integrated circuit.

## Background
CROSS REFERENCE TO RELATED PATENTS
This patent application is related to co-pending patent application Ser. No. 10/459,985 entitled AN INTEGRATED CIRCUIT RADIO FRONT-END ARCHITECTURE AND APPLICATIONS THEREOF.
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This invention relates generally to electrostatic discharge (ESD) protection and more particularly to ESD protection within a radio frequency integrated circuits.
2. Description of Related Art
As is known, integrated circuits (IC) provide a high degree of functionality in a very small area. Such functionality may include data storage, data processing, radio reception, radio transmission, et cetera. As is also known, integrated circuits include tens-of-thousands to tens-of-millions of transistors (i.e., gates) to implement the desired function or functions. Needless to say, the size of the transistors is very small. For example, a CMOS transistor has a gate oxide thickness of 100 angstroms or less.
As is further known, due to their extremely small size, the gate oxide of CMOS transistors are susceptible to breakdown from static electricity, which is commonly referred to as electrostatic discharge (ESD). If a transistor of an integrated circuit is damaged from ESD while handling of the circuit, the integrated circuit is unusable.
To reduce the risk of damage due to ESD, integrated circuits include ESD protection circuitry. Such ESD protection circuitry includes using silicon-controlled rectifiers (SCR) to clamp ESD voltages and steer related currents away from sensitive transistors, use ESD implanted transistors, which have a higher breakdown voltage, in input/output circuits, use elongated drain structures and larger drain-to-gate spacing, which increase breakdown voltage, and/or other ESD type protection circuitry. While there are numerous ESD protection circuits, none are optimized (i.e., provides desired ESD protection), limit the amount of circuit elements and/or limit the amount of die area, for radio frequency integrated circuits (RFIC).
Therefore, a need exists for a radio frequency integrated circuit ESD protection circuit.
BRIEF SUMMARY OF THE INVENTION
The radio frequency integrated circuit electrostatic discharge circuit of the present invention substantially meets these needs and others. The radio frequency integrated circuit (RFIC) electrostatic discharge (ESD) circuit includes a transformer balun, an impedance matching circuit and a clamping circuit. The balun is operably coupled to transpose a single-ended radio frequency (RF) signal and differential RF signal. The balun includes a 1st winding that is coupled to the single-ended radio frequency signals and a 2nd winding that is coupled for differential RF signals. The impedance matching circuit is coupled to the 1st winding and provides, in conjunction with the impedance of the balun, impedance matching with an antenna coupled to the RFIC. The clamping circuit is operably coupled to the balun and/or to the impedance matching circuit and, in combination with the impedance matching circuit and/or in combination with the balun, provides ESD protection for the receiver section and/or transmitter section of the radio frequency integrated circuit. As such, the circuitry of the impedance matching circuit and/or transformer balun provides a portion of the ESD protection for the RFIC. Thus, minimal additional circuitry (e.g., the clamping circuit) is needed to provide ESD protection for the RFIC and, as a result, additional die area requirements for including ESD protection circuitry is minimized for radio frequency integrated circuits.



BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 is a schematic block diagram of a wireless communication system in accordance with the present invention;
FIG. 2 is a schematic block diagram of a wireless communication device in accordance with the present invention;
FIG. 3 is a schematic block diagram of an RFIC ESD protection circuit in accordance with the present invention;
FIG. 4 is a schematic block diagram of another embodiment of an RFIC ESD protection circuit in accordance with the present invention; and
FIG. 5 is a schematic block diagram of another embodiment of an RFIC ESD protection circuit in accordance with the present invention.



DETAILED DESCRIPTION OF THE INVENTION
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, an RF interface module with RFIC ESD protection circuit 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 RF interface module 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.
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., IEEE 802.11a, IEEE 802.11b, 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 provided to the antenna via the RF interface module 73. 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 RF interface module 73, which provides the RF signal to low noise amplifier 72. The LNA 72 amplifies the signal 88 to produce an amplified inbound RF signal and 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/gain module 68. The filtering/gain module 68 filters and/or gains 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 of average skill 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.
FIG. 3 is a schematic block diagram of a radio frequency (RFIC) electrostatic discharge (ESD) protection circuit 100 that may be incorporated in the RF interface module 73. The circuit 100 includes a balun 102, impedance matching circuit 104 and clamping circuit 106. The impedance matching circuit 104 and the impedance of balun 102 match, at frequencies of a radio frequency signal, the impedance of the antenna providing the single-ended RF signal 110. As configured, the transformer balun 102 converts single-ended RF signals 110 into differential RF signals 108 or conversely converts differential RF signals 108 into single-ended RF signals 110.
The clamping circuit 106 may be coupled to the impedance matching circuit 104 and/or to first winding the transformer balun 102 to provide ESD protection for the radio frequency integrated circuit. Alternatively, the clamping circuit 106 may be tied to the secondary of balun 102.
FIG. 4 is a schematic block diagram of an alternative radio frequency integrated circuit electrostatic discharge protection circuit 120 that may comprise the RF interface module 73. As shown, an integrated circuit pad of the RFIC is coupled to antenna 86. The balun 122 includes a 1st winding coupled to the integrated circuit pad and to capacitor C3, and a 2nd winding. The 2nd winding includes a 1st pair of taps coupled to the input of the low noise amplifier and a 2nd pair of taps coupled to the output of power amplifier 84. In this embodiment, capacitor C1 and C2 provide the impedance matching, in combination with the input impedance of balun 122. The clamping circuit may include one or more of diodes D1–D4 and inductor L1. The diodes D1–D4 may be transistors, diodes, and/or silicon-controlled rectifiers.
In one embodiment, the clamping circuit may include only diodes D1 and D2, where, when a static charge is received at the integrated circuit pad, one of the diodes D1 or D3 becomes active and, in combination with capacitors C1, C2 and C3, absorb the energy provided by the static discharge. The absorption of the energy provided by the static discharge may also be dissipated within the transformer balun 122. Further dissipation of the energy may be achieved by including inductor L1. Note that the size of inductor L1 corresponds to the rate of electrostatic discharge but is of such a size that provides negligible effect on processing of single-ended RF signals.
In another configuration of the ESD protection circuit 120 of FIG. 4, diodes D3 and D4 may be included with the omission of D1 and D2. When an ESD event occurs, the voltage corresponding to the ESD event is divided between capacitors C1, C2 and C3. The voltage across capacitor C2 is transposed to the 2nd winding of balun 122 and is clamped to VDD via diode D3 and/or D4. Accordingly, the sensitive input transistors of LNA 72 are protected.
FIG. 5 is a schematic block diagram of another embodiment of a RFIC ESD protection circuit 130 that may comprise the RF interface module 73. In this embodiment, the RFIC ESD protection circuit 130 includes balun 132 that is coupled to a transmit/receive switch module 77. The transmit/receive switch module 77 couples the balun 132 either to the LNA 72 and receiver filter module 71 or couples the balun 132 to the power amplifier 84 and transmit filter module 85. In this embodiment, the protection circuitry includes one or more of diodes D1–D4 and inductor L1. As described with reference to FIGS. 4, the protection circuitry may be implemented in a variety of combinations of the elements L1 and D1–D4.
The preceding discussion has presented an electrostatic discharge protection circuit for use in a radio frequency integrated circuit. By utilizing existing components of the radio frequency integrated circuit as part of the ESD protection circuit, ESD protection for radio frequency integrated circuits is optimized. As one of average 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.

## Claims

1. A radio frequency integrated circuit (RFIC) electro-static discharge (ESD) circuit comprises:
balun operably coupled to transpose a single-ended radio frequency (RF) signal and differential RF signal, wherein the balun includes a first winding and a second winding, wherein the first winding provides the single-ended RF signal and the second winding provides the differential RF signal;
impedance matching circuit operably coupled to first winding, wherein impedance of the impedance matching circuit in conjunction with impedance of the balun at frequencies in a range of the RF substantially match an impedance of an antenna; and
clamping circuit operably coupled to at least one of the balun and the impedance matching circuit, wherein the clamping circuit in combination with at least the impedance matching circuit provide ESD protection for at least one of a receiver section and a transmitter section of the RFIC.

2. The RFIC ESD circuit of claim 1 further comprises:
the second winding of the balun coupled to a differential input of a low noise amplifier of the receiver section, wherein the impedance matching circuit receives an inbound single-ended RF signal via the antenna, and wherein the balun converts the inbound single-ended RF signal into an inbound differential RF signal.

3. The RFIC ESD circuit of claim 1 further comprises:
the second winding of the balun coupled to a differential output of a power amplifier of the transmitter section, wherein the balun converts an outbound differential RF signal into an outbound single-ended RF signal, and wherein the impedance matching circuit provides the outbound single-ended RF to the antenna.

4. The RFIC ESD circuit of claim 1, wherein the second winding of the balun further comprises:
a first pair of differential taps coupled to a differential input of a low noise amplifier of the receiver section, wherein the impedance matching circuit receives an inbound single-ended RF signal via the antenna, and wherein the balun converts the inbound single-ended RF signal into an inbound differential RF signal; and
a second pair of differential taps coupled to a differential output of a power amplifier of the transmitter section, wherein the balun converts an outbound differential RF signal into an outbound single-ended RF signal, and wherein the impedance matching circuit provides the outbound single-ended RF to the antenna.

5. The RFC ESD circuit of claim 1 further comprises:
grounding circuit operably coupled to the balun to provide a low impedance ground at frequencies in the range of the RF, wherein the grounding circuit in combination with the clamping circuit and the impedance matching circuit provide ESD protection for at least one of the receiver section and the transmitter section.

6. The RFIC ESD circuit of claim 1, wherein the clamping circuit further comprises:
a reversed biased diode element coupled between the first winding of the balun and a positive supply of the RFIC.

7. The RFIC ESD circuit of claim 1, wherein the clamping circuit further comprises:
a pair of reversed biased diode elements coupled between the second winding of the balun and a positive supply of the RFIC.

8. A radio frequency integrated circuit (RFIC) comprises:
transmitter section operably coupled to convert differential outbound low intermediate frequency (IF) signals into differential outbound radio frequency (RF) signals;
receiver section operably coupled to convert differential inbound RF signals into differential inbound low IF signals;
balun operably coupled to at least one of the receiver section and the transmitter section, wherein the balun converts inbound single-ended RF signals into the differential inbound RF signals when the RFIC is in a receive mode and converts the differential outbound RF signals into outbound single-ended signals when the RFIC is in a transmit mode, and wherein the balun includes a first winding and a second winding, wherein the first winding is operably coupled for single-ended signals and the second winding is operably coupled for differential signals;
impedance matching circuit operably coupled to first winding, wherein impedance of the impedance matching circuit in conjunction with impedance of the balun at frequencies in a range of the RF substantially match an impedance of an antenna; and
clamping circuit operably coupled to at least one of the balun and the impedance matching circuit, wherein the clamping circuit in combination with at least the impedance matching circuit provide ESD protection for at least one of a receiver section and a transmitter section of the RFIC.

9. The RFIC of claim 8 further comprises:
a transmit/receive switch operable to couple the second winding of the balun to a differential input of a low noise amplifier of the receiver section when the RFIC is in the receive mode and to couple the second winding to a differential output of a power amplifier of the transmitter section when the RFIC is in the transmit mode.

10. The RFIC of claim 8, wherein the second winding of the balun further comprises:
a first pair of differential taps coupled to a differential input of a low noise amplifier of the receiver section, wherein the impedance matching circuit receives an inbound single-ended RF signal via the antenna, and wherein the balun converts the inbound single-ended RF signal into an inbound differential RF signal; and
a second pair of differential taps coupled to a differential output of a power amplifier of the transmitter section, wherein the balun converts an outbound differential RF signal into an outbound single-ended RF signal, and wherein the impedance matching circuit provides the outbound single-ended RF to the antenna.

11. The RFC of claim 8 further comprises:
grounding circuit operably coupled to the balun to provide a low impedance ground at frequencies in the range of the RF, wherein the grounding circuit in combination with the clamping circuit and the impedance matching circuit provide ESD protection for the RFIC.

12. The RFIC of claim 8, wherein the clamping circuit further comprises:
a reversed biased diode element coupled between the first winding of the balun and a positive supply of the RFIC.

13. The RFIC of claim 8, wherein the clamping circuit further comprises:
a pair of reversed biased diode elements coupled between the second winding of the balun and a positive supply of the RFIC.