Mixer second order input intercept (IIP2) calibration using single tone generator and / or reverse feedthrough

Abstract

Methods and apparatus for calibrating a second order input intercept point (IIP2) of a mixer, such as a mixer in a wireless receive chain. One example circuit for mixer IIP2 calibration generally includes a first receive chain including a first mixer; and a single tone generator having an output coupled to an input of the first mixer and configured to generate a calibration signal having a single baseband tone. One example method of mixer IIP2 calibration generally includes generating a calibration signal including a single baseband tone; applying the calibration signal to an input of a mixer such that the mixer generates a differential tone at an output of the mixer; and adjusting the mixer to minimize power of the differential tone at the output of the mixer.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. patent application serial number 17 / 934,455 filed on September 22, 2022, which is hereby incorporated by reference into this application. Technical Field

[0003] Certain aspects of the present disclosure relate generally to electronic circuits and, more particularly, to techniques and apparatus for calibrating mixers. Background Art

[0004] Wireless communication devices are widely deployed to provide various communication services, such as telephony, video, data, messaging, broadcasts, etc. Such wireless communication devices may send and / or receive radio frequency (RF) signals via any of a variety of suitable radio access technologies (RATs), including but not limited to fifth generation (5G) New Radio (NR), long term evolution (LTE), code division multiple access (CDMA), time division multiple access (TDMA), wideband CDMA (WCDMA), global system for mobile (GSM), Bluetooth, Bluetooth low energy (BLE), ZigBee, wireless local area network (WLAN) RATs (e.g., WiFi), etc.

[0005] A wireless communication network may include multiple base stations that can support communications for multiple mobile stations. A mobile station (MS) may communicate with a base station (BS) via a downlink and an uplink. A downlink (or forward link) refers to a communication link from a base station to a mobile station, and an uplink (or reverse link) refers to a communication link from a mobile station to a base station. A base station may send data and control information to a mobile station on a downlink, and / or may receive data and control information from a mobile station on an uplink. A base station and / or a mobile station may include a radio receiver with a mixer, which may be used, for example, to down-convert a radio frequency (RF) signal received wirelessly to a baseband signal for signal processing (e.g., filtering, analog-to-digital conversion, and demodulation) before interpreting the signal. Summary of the invention

[0006] The systems, methods, and devices of the present disclosure each have several aspects, no single one of which is solely responsible for its desirable characteristics. Without limiting the scope of the present disclosure as expressed by the claims that follow, some features will now be briefly discussed. After considering this discussion, and particularly after reading the section entitled "Detailed Description of the Invention," it will be understood how the features of the present disclosure provide advantages including reduced mixer second-order input intercept point (IIP2) calibration time and / or reduced circuit lateral area (e.g., footprint) for mixer IIP2 calibration.

[0007] Certain aspects of the present disclosure generally relate to calibration of mixers (eg, in wireless receivers) for IIP2 to reduce second-order intermodulation distortion (IMD2).

[0008] Certain aspects of the present disclosure provide a circuit for mixer IIP2 calibration. The circuit generally includes: a first receive chain, the first receive chain including a first mixer; and a single tone generator having an output coupled to an input of the first mixer and configured to generate a calibration signal having a single baseband tone.

[0009] Certain aspects of the present disclosure provide a wireless device. The wireless device generally includes: a first receive chain, the first receive chain including a first mixer; and a single tone generator, the single tone generator having an output coupled to an input of the first mixer and configured to generate a calibration signal having a single baseband tone. The wireless device also includes: at least one antenna, the at least one antenna coupled to the input of the first receive chain; an analog-to-digital converter (ADC), the analog-to-digital converter (ADC) coupled to the output of the first receive chain; and a processor having an input coupled to the output of the ADC. The first mixer is configured to generate a differential tone when the single tone generator applies the calibration signal to the first mixer. The processor is configured to receive a representation of the differential tone, control the single tone generator, and control the adjustment of the first mixer to minimize the power of the representation of the differential tone.

[0010] Certain aspects of the present disclosure provide a method for mixer IIP2 calibration. The method generally includes: generating a calibration signal including a single baseband tone; applying the calibration signal to an input of a mixer so that the mixer generates a differential tone at an output of the mixer; and adjusting the mixer to minimize the power of the differential tone at the output of the mixer.

[0011] Certain aspects of the present disclosure provide an apparatus for wireless communication capable of mixer IIP2 calibration. The apparatus generally includes: means for generating a calibration signal including a single baseband tone, means for applying the calibration signal to an input of a mixer so that the mixer generates a differential tone at an output of the mixer, and means for adjusting the mixer to minimize the power of the differential tone at the output of the mixer.

[0012] Certain aspects of the present disclosure provide a circuit for mixer IIP2 calibration. The circuit generally includes: a first amplifier; a first receive chain, the first receive chain including a first mixer having an input coupled to an output of the first amplifier; and a second amplifier having an input coupled to the output of the first amplifier.

[0013] Certain aspects of the present disclosure provide a wireless device. The wireless device includes: a first amplifier; a first receiving chain, the first receiving chain including a first mixer having an input coupled to the output of the first amplifier; and a second amplifier, the second amplifier having an input coupled to the output of the first amplifier. The wireless device also includes a single-tone generator, the single-tone generator having an output coupled to the output of the first amplifier, coupled to the input of the first mixer and coupled to the input of the second amplifier, the single-tone generator being configured to generate a calibration signal having a single tone that is the sum of a local oscillator (LO) frequency and a baseband frequency. The wireless device also includes: a frequency synthesizer, the frequency synthesizer being configured to generate an LO signal at the LO frequency and apply the LO signal to the LO port of the first mixer; an analog-to-digital converter, the analog-to-digital converter being coupled to the output of the first receiving chain; and a processor having an input coupled to the output of the analog-to-digital converter. The single tone generator is configured to apply a calibration signal to a radio frequency (RF) port of a first mixer; the first mixer is configured to down-convert the calibration signal based on an LO signal; the second amplifier is configured to amplify second-order intermodulation distortion (IMD2) generated by the first mixer due to the down-conversion; and the processor is configured to control adjustment of the first mixer based on the amplified IMD2 to minimize the amplified IMD2.

[0014] Certain aspects of the present disclosure provide a wireless device. The wireless device includes: a first amplifier; a first receiving chain, the first receiving chain including a first mixer having an input coupled to an output of the first amplifier; and a second amplifier, the second amplifier having an input coupled to the output of the first amplifier. The wireless device also includes: at least one antenna, the at least one antenna coupled to the input of the first receiving chain; an analog-to-digital converter, the analog-to-digital converter coupled to the output of the first receiving chain; and a processor, the processor having an input coupled to the output of the analog-to-digital converter. At least one antenna is configured to receive an RF signal; the first amplifier is configured to amplify the received RF signal; the first mixer is configured to down-convert the amplified RF signal; the second amplifier is configured to amplify IMD2 generated by the first mixer due to the down-conversion; and the processor is configured to control the adjustment of the first mixer based on the amplified IMD2.

[0015] Certain aspects of the present disclosure provide a method for mixer IIP2 calibration. The method generally includes: down-converting an RF signal using a mixer; amplifying IMD2 generated by the mixer due to the down-conversion and fed back from the output port of the mixer to the RF port of the mixer using a first amplifier; and adjusting the mixer based on the amplified IMD2 to minimize the amplified IMD2.

[0016] Certain aspects of the present disclosure provide an apparatus for wireless communication capable of mixer IIP2 calibration. The apparatus generally includes: a component for down-converting an RF signal, a component for amplifying IMD2 generated by the component for down-converting due to the down-conversion and fed back from the output port of the component for down-converting to the RF port of the component for down-converting, and a component for adjusting the component for down-converting based on the amplified IMD2 to minimize the amplified IMD2.

[0017] To achieve the foregoing and related ends, one or more aspects include the features fully described below and particularly pointed out in the claims. The following description and the accompanying drawings set forth in detail some illustrative features of one or more aspects. However, these features are merely indicative of some of the various ways in which the principles of the various aspects may be employed, and this specification is intended to include all such aspects and their equivalents. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to be able to understand in detail the manner in which the above-mentioned features of the present disclosure are achieved, a more specific description briefly summarized above can be obtained by reference to various aspects, some of which are illustrated in the accompanying drawings. However, it should be noted that the accompanying drawings illustrate only certain typical aspects of the present disclosure and are therefore not to be considered as limiting the scope thereof, as the specification may admit to other equally effective aspects.

[0019] Figure 1 is an illustration of an example wireless communication network in which aspects of the present disclosure may be practiced.

[0020] Figure 2 is a block diagram conceptually illustrating designs of example base stations (BSs) and user equipment (UEs) in which aspects of the present disclosure may be practiced.

[0021] Figure 3 is a block diagram of an example radio frequency (RF) transceiver in which aspects of the present disclosure may be practiced.

[0022] Figure 4 is a block diagram of an example circuit for mixer second-order input intercept point (IIP2) calibration using a single tone generator in which aspects of the present disclosure may be practiced.

[0023] Figure 5 is a block diagram of an example circuit for mixer IIP2 calibration using a received radio frequency (RF) signal and amplifying second-order intermodulation distortion (IMD2) from backfeedthrough from the mixer in accordance with certain aspects of the present disclosure.

[0024] Figure 6is a block diagram of an example circuit for mixer IIP2 calibration using a single tone generator and amplifying IMD2 from backfeedthrough from the mixer in accordance with certain aspects of the present disclosure.

[0025] Figure 7 is a flow chart of example operations for mixer IIP2 calibration in accordance with certain aspects of the present disclosure.

[0026] Figure 8 is a flow chart of example operations for mixer IIP2 calibration in accordance with certain aspects of the present disclosure.

[0027] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one aspect may be beneficially utilized on other aspects without specific recitation. DETAILED DESCRIPTION

[0028] Certain aspects of the present disclosure relate to techniques and apparatus for mixer second-order input intercept point (IIP2) calibration. One technique involves: applying a single baseband tone to an input of a mixer so that the mixer generates a differential tone; and adjusting the mixer to minimize the power of the differential tone at an output of the mixer. Another technique involves: down-converting a radio frequency (RF) signal using a mixer; amplifying second-order intermodulation distortion (IMD2) products generated by the mixer and fed back from an output port of the mixer to an RF port of the mixer; and adjusting the mixer based on the amplified IMD2 products. The RF signal may be a single RF tone (e.g., including a local oscillator (LO) frequency plus a baseband tone) or a wirelessly received RF signal.

[0029] The various aspects of the present disclosure are described more fully below with reference to the accompanying drawings. However, the present disclosure can be embodied in many different forms, and should not be interpreted as being limited to any specific structure or function presented throughout the present disclosure. Instead, these aspects are provided so that the present disclosure will be thorough and complete, and the scope of the present disclosure will be fully conveyed to those skilled in the art. Based on the teachings of this article, it should be understood by those skilled in the art that the scope of the present disclosure is intended to cover any aspect of the disclosure disclosed herein, whether it is implemented independently or in combination with any other aspect of the present disclosure. For example, any number of aspects set forth herein can be used to implement a device or practice method. In addition, the scope of the present disclosure is intended to cover such a device or method that is practiced using other structures, functionality, or structure and functionality in addition to or different from the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein can be embodied by one or more elements of the present invention.

[0030] The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects.

[0031] As used herein, the term "connected with" in various tenses of the verb "connect" may mean that element A is directly connected to element B or that other elements may be connected between element A and element B (i.e., element A is indirectly connected to element B). In the context of electronic components, the term "connected with" may also be used herein to mean that wires, traces, or other conductive materials are used to electrically connect element A and element B (and any components electrically connected therebetween).

[0032] Example Wireless System

[0033] Figure 1 An example wireless communication network 100 in which aspects of the present disclosure may be practiced is illustrated. For example, the wireless communication network 100 may be a New Radio (NR) system (e.g., a fifth generation (5G) NR network), an Evolved Universal Terrestrial Radio Access (E-UTRA) system (e.g., a fourth generation (4G) network), a Universal Mobile Telecommunications System (UMTS) (e.g., a second generation / third generation (2G / 3G) network), or a Code Division Multiple Access (CDMA) system (e.g., a 2G / 3G network), or may be configured for communication according to IEEE standards such as one or more of the 802.11 standards.

[0034] like Figure 1 As shown in , the wireless communication network 100 may include several base stations (BSs) 110a to 110z (each also individually referred to as BS 110 or collectively referred to as BS 110 herein) and other network entities. A BS may also be referred to as an access point (AP), an evolved Node B (eNodeB or eNB), a next generation Node B (gNodeB or gNB) or some other terminology.

[0035] BS 110 may provide communication coverage for a particular geographic area (sometimes referred to as a "cell"), which may be stationary or may move depending on the location of mobile BS 110. In some examples, BS 110 may be interconnected with each other and / or connected to one or more other BSs or network nodes (not shown) in wireless communication network 100 through various types of backhaul interfaces (e.g., direct physical connections, wireless connections, virtual networks, etc.) using any suitable transport network. Figure 1In the example shown, BSs 110a, 110b, and 110c may be macro BSs for macro cells 102a, 102b, and 102c, respectively. BS 110x may be a pico BS for pico cell 102x. BSs 110y and 110z may be femto BSs for femto cells 102y and 102z, respectively. A BS may support one or more cells.

[0036] The BS 110 communicates with one or more user equipment (UE) 120a to 120y (each also individually or collectively referred to herein as UE 120) in the wireless communication network 100. A UE may be fixed or mobile, and may also be referred to as a user terminal (UT), a mobile station (MS), an access terminal, a station (STA), a client, a wireless device, a mobile device, or some other terminology. A user terminal may be a wireless device such as a cellular phone, a smart phone, a personal digital assistant (PDA), a handheld device, a wearable device, a wireless modem, a laptop computer, a tablet computer, a personal computer, etc.

[0037] BS110 is considered to be a transmitting entity for downlink and a receiving entity for uplink. UE 120 is considered to be a transmitting entity for uplink and a receiving entity for downlink. As used herein, a "transmitting entity" is an independently operated device or equipment capable of sending data via a frequency channel, and a "receiving entity" is an independently operated device or equipment capable of receiving data via a frequency channel. In the following description, the subscript "dn" represents a downlink, and the subscript "up" represents an uplink. Nup UEs can be selected for simultaneous transmission on the uplink, and Ndn UEs can be selected for simultaneous transmission on the downlink. Nup may be equal to or may not be equal to Ndn, and Nup and Ndn may be static values ​​or may change for each scheduling interval. Beam steering or some other spatial processing techniques may be used at BS 110 and UE 120.

[0038] UEs 120 (e.g., 120x, 120y, etc.) may be dispersed throughout the wireless communication network 100, and each UE 120 may be stationary or mobile. The wireless communication network 100 may also include a relay station (e.g., relay station 110r) (also referred to as a repeater, etc.) that receives transmissions of data and / or other information from an upstream station (e.g., BS 110a or UE 120r) and transmits transmissions of data and / or other information to a downstream station (e.g., UE 120 or BS 110), or relays transmissions between UEs 120 to facilitate communication between devices.

[0039] BS 110 may communicate on the downlink and uplink with one or more UEs 120 at any given moment. The downlink (i.e., forward link) is the communication link from BS 110 to UE 120, while the uplink (i.e., reverse link) is the communication link from UE 120 to BS 110. A UE 120 may also communicate peer-to-peer with another UE 120.

[0040] The wireless communication network 100 may use multiple transmit antennas and multiple receive antennas to transmit data on the downlink and uplink. The BS 110 may be equipped with several (Nap) antennas to achieve transmit diversity for downlink transmissions and / or receive diversity for uplink transmissions. A group (Nu) of UEs 120 may receive downlink transmissions and send uplink transmissions. Each UE 120 may send user-specific data to the BS 110 and / or receive user-specific data from the BS. Typically, each UE 120 may be equipped with one or more antennas. The Nu UEs 120 may have the same or different numbers of antennas.

[0041] The wireless communication network 100 may be a time division duplex (TDD) system or a frequency division duplex (FDD) system. For a TDD system, the downlink and uplink share the same frequency band. For an FDD system, the downlink and uplink use different frequency bands. The wireless communication network 100 may also utilize a single carrier or multiple carriers for transmission. Each UE 120 may be equipped with a single antenna (e.g., to reduce costs) or multiple antennas (e.g., where additional costs can be supported).

[0042] The network controller 130 (sometimes also referred to as a "system controller") may communicate with a set of BSs 110 and provide coordination and control (e.g., via backhaul) for these BSs 110. In some cases (e.g., in a 5G NR system), the network controller 130 may include a centralized unit (CU) and / or a distributed unit (DU). In some aspects, the network controller 130 may communicate with a core network 132 (e.g., a 5G core network (5GC)), which provides various network functions such as access and mobility management, session management, user plane functions, policy control functions, authentication server functions, unified data management, application functions, network open functions, network repository functions, network slice selection functions, etc.

[0043] In certain aspects of the present disclosure, BS 110 and / or UE 120 may include circuitry for mixer second order input intercept point (IIP2) calibration, as described in more detail herein.

[0044] Figure 21 and 120a (eg, from a BS 110a) in which various aspects of the present disclosure may be implemented. Figure 1 Example components of a wireless communication network 100).

[0045] On the downlink, at BS 110a, the transmit processor 220 may receive data from the data source 212, control information from the controller / processor 240, and / or possibly other data (e.g., from the scheduler 244). Various types of data may be transmitted on different transport channels. For example, control information may be designated for a physical broadcast channel (PBCH), a physical control format indicator channel (PCFICH), a physical hybrid automatic repeat request (HARQ) indicator channel (PHICH), a physical downlink control channel (PDCCH), a group common PDCCH (GC PDCCH), etc. Data may be designated for a physical downlink shared channel (PDSCH), etc. A medium access control (MAC)-control element (MAC-CE) is a MAC layer communication structure that may be used for the exchange of control commands between wireless nodes. The MAC-CE may be carried in a shared channel such as a PDSCH, a physical uplink shared channel (PUSCH), or a physical sidelink shared channel (PSSCH).

[0046] The processor 220 may process (e.g., encode and symbol map) data and control information to obtain data symbols and control symbols, respectively. The transmit processor 220 may also generate reference symbols such as for a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a PBCH demodulation reference signal (DMRS), and a channel state information reference signal (CSI-RS).

[0047] The transmit (TX) multiple-input multiple-output (MIMO) processor 230 may perform spatial processing (e.g., pre-decoding) on ​​data symbols, control symbols, and / or reference symbols where applicable, and may provide an output symbol stream to a modulator (MOD) in a transceiver 232a-232t. Each modulator 232a-232t in the transceiver may process a respective output symbol stream (e.g., for orthogonal frequency division multiplexing (OFDM) or the like) to obtain an output sample stream. Each transceiver 232a-232t may further process (e.g., convert to analog, amplify, filter, and up-convert) the output sample stream to obtain a downlink signal. The downlink signals from the transceivers 232a-232t may be transmitted via antennas 234a-234t, respectively.

[0048] At UE 120a, antennas 252a-252r may receive downlink signals from BS110a and may provide received signals to transceivers 254a-254r, respectively. Transceivers 254a-254r may condition (e.g., filter, amplify, downconvert, and digitize) the corresponding received signals to obtain input samples. Each demodulator (DEMOD) in transceivers 232a-232t may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. MIMO detector 256 may obtain received symbols from all demodulators in transceivers 254a-254r, perform MIMO detection on the received symbols (where applicable), and provide detected symbols. Receive processor 258 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for UE 120a to data sink 260, and provide decoded control information to controller / processor 280.

[0049] On the uplink, at the UE 120a, a transmit processor 264 may receive and process data from a data source 262 (e.g., for a physical uplink shared channel (PUSCH)) and control information from a controller / processor 280 (e.g., for a physical uplink control channel (PUCCH)). The transmit processor 264 may also generate reference symbols for reference signals (e.g., for a sounding reference signal (SRS)). The symbols from the transmit processor 264 may be pre-decoded by a TX MIMO processor 266 (if applicable), further processed by a modulator (MOD) in the transceivers 254a-254r (e.g., for single carrier frequency division multiplexing (SC-FDM), etc.), and transmitted to the BS 110a. At BS 110a, the uplink signal from UE 120a may be received by antenna 234, processed by demodulators in transceivers 232a-232t, detected by MIMO detector 236 (if applicable), and further processed by receive processor 238 to obtain decoded data and control information transmitted by UE 120a. Receive processor 238 may provide the decoded data to a data sink 239 and the decoded control information to controller / processor 240.

[0050] Memories 242 and 282 may store data and program codes for BS 110a and UE 120a, respectively. Memories 242 and 282 may also interface with controllers / processors 240 and 280, respectively. Scheduler 244 may schedule UEs for data transmission on the downlink and / or uplink.

[0051] The antennas 252, processors 258, 264, 266 and / or controller / processor 280 of the UE 120a and / or the antennas 234, processors 220, 230, 238 and / or controller / processor 240 of the BS 110a may be used to perform the various techniques and methods described herein.

[0052] In certain aspects of the present disclosure, transceiver 232 and / or transceiver 254 may include circuitry for mixer second order input intercept point (IIP2) calibration, as described in greater detail herein.

[0053] Example RF Transceiver

[0054] Figure 3 is a block diagram of an example radio frequency (RF) transceiver circuit 300 according to certain aspects of the present disclosure. The RF transceiver circuit 300 includes at least one transmit (TX) path 302 (also referred to as a “transmit chain”) for transmitting signals via one or more antennas 306 and at least one receive (RX) path 304 (also referred to as a “receive chain”) for receiving signals via antenna 306. When TX path 302 and RX path 304 share antenna 306, these paths can be connected to the antenna via interface 308, which can include any of a variety of suitable RF devices, such as switches, duplexers, diplexers, multiplexers, etc.

[0055] Receiving in-phase (I) and / or quadrature (Q) baseband analog signals from a digital-to-analog converter (DAC) 310, the TX path 302 may include a baseband filter (BBF) 312, a mixer 314, a driver amplifier (DA) 316, and a power amplifier (PA) 318. The BBF 312, the mixer 314, the DA 316, and the PA 318 may be included in a radio frequency integrated circuit (RFIC). For certain aspects, the PA 318 may be external to the RFIC.

[0056] The BBF 312 filters the baseband signal received from the DAC 310, and the mixer 314 mixes the filtered baseband signal with a transmit local oscillator (LO) signal to convert the baseband signal of interest to a different frequency (e.g., upconvert from baseband to radio frequency). This frequency conversion process produces sum and difference frequencies between the LO frequency and the frequency of the baseband signal of interest. The sum and difference frequencies are referred to as "beat frequencies." The beat frequencies are typically in the RF range, so that the signal output by the mixer 314 is typically an RF signal, which may be amplified by the DA 316 and / or by the PA 318 before being transmitted by the antenna 306. Although one mixer 314 is illustrated, several mixers may be used to upconvert the filtered baseband signal to one or more intermediate frequencies and thereafter upconvert the intermediate frequency (IF) signal to a frequency for transmission.

[0057] The RX path 304 may include a low noise amplifier (LNA) 324, a mixer 326, and a baseband filter (BBF) 328. The LNA 324, the mixer 326, and the BBF 328 may be included in one or more RFICs, which may be the same RFIC as the RFIC that includes the TX path components, or may be a different RFIC. The RF signal received via the antenna 306 may be amplified by the LNA 324, and the mixer 326 mixes the amplified RF signal with a receive local oscillator (LO) signal to convert the RF signal of interest to a different baseband frequency (e.g., down-convert). The baseband signal output by the mixer 326 may be filtered by the BBF 328 before being converted to a digital I and / or Q signal by an analog-to-digital converter (ADC) 330 for digital signal processing.

[0058] For certain aspects, the mixer 326 may introduce second-order intermodulation distortion (IMD2) in the RX path 304. Therefore, the RF transceiver circuit 300 may also include circuitry for second-order input intercept point (IIP2) calibration of the mixer 326, as described below.

[0059] Some transceivers may employ a frequency synthesizer with a variable frequency oscillator (e.g., a voltage controlled oscillator (VCO) or a digitally controlled oscillator (DCO)) to generate a stable, tunable LO with a specific tuning range. Thus, the transmit LO may be generated by the TX frequency synthesizer 320, which may be buffered or amplified by the amplifier 322 before being mixed with the baseband signal in the mixer 314. Similarly, the receive LO may be generated by the RX frequency synthesizer 332, which may be buffered or amplified by the amplifier 334 before being mixed with the RF signal in the mixer 326. For certain aspects, a single frequency synthesizer may be used for both the TX path 302 and the RX path 304. In certain aspects, the TX frequency synthesizer 320 and / or the RX frequency synthesizer 332 may include a frequency multiplier (such as a doubler) driven by an oscillator (e.g., a VCO) in the frequency synthesizer.

[0060] Controller 336 (eg, Figure 2 Controller / processor 280 in the RF transceiver circuit 300A may direct the operation of the RF transceiver circuit 300A, such as transmitting signals via TX path 302 and / or receiving signals via RX path 304. Controller 336 may be a processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic components, discrete hardware components, or any combination thereof. Memory 338 (e.g., Figure 2The memory 282 in the RF transceiver circuit 300 may store data and / or program codes for operating the RF transceiver circuit 300. The controller 336 and / or the memory 338 may include control logic components (eg, complementary metal oxide semiconductor (CMOS) logic components).

[0061] Example Mixer IIP2 Calibration Using a Single Baseband Tone

[0062] Radio receivers (e.g. Figure 3 The RX path 304 of the baseband filter may be designed to meet the specification of the second-order input intercept point (IIP2). IIP2 is a measure of linearity that quantifies the second-order distortion generated by the nonlinearity of circuits such as amplifiers and mixers. In the receiver, second-order intermodulation (IM2) tones may be generated by different types of interference such as out-of-band (OOB) interference or transmit leakage signals (e.g., from the TX path 302), but the mixer may be the main contributor to IM2. IIP2 may be calculated based on the strength of the IM2 tones. The IM2 tone strength (and therefore the IIP2 performance) may depend on the transmit (TX) bandwidth (or the bandwidth of the interference corresponding to the transmit leakage signal) and the TX to RX frequency offset (or the interference to the in-band offset). This is because the down-converted transmit signal (e.g., interference) at the interface between the mixer and the baseband filter may vary depending on the TX bandwidth and the TX to RX offset. Therefore, it may be desirable to perform IIP2 calibration by taking into account the TX bandwidth and the TX to RX offset.

[0063] IIP2 can be measured by: modulating a local oscillator (LO) signal with a modulation signal to generate an amplitude modulated (AM) signal; down-converting the AM signal to baseband; correlating the down-converted signal with the modulation signal; and determining IIP2 based on the correlation result. IIP2 can be improved by adjusting the gate bias voltage of a transistor having nonlinearity that affects IIP2.

[0064] It is well known that zero intermediate frequency (ZIF) systems (also known as direct conversion systems) are susceptible to second-order intermodulation distortion (IMD2). Transmitted interference generates IMD2 products in the ZIF mixer. IMD2 products can fall in-band and cause receiver sensitivity degradation.

[0065] It may be desirable to calibrate the receiver (e.g., during normal operation in the field) to ensure good performance even in the presence of variations in IC process, temperature, supply voltage, etc. It may also be desirable to calibrate the receiver with as little additional hardware as possible to reduce cost, circuit area, etc.

[0066] Some systems use dedicated calibration circuits to correct for IMD2 products at the baseband output. The active mixers in these systems can sense common-mode IMD2 products to provide calibration via calibrated feedforward paths to the in-phase (I) and quadrature (Q) baseband ports. The feedforward calibration "guesses" the effective feedthrough of the mixer (in a feedforward manner).

[0067] Some systems use an IMD2 calibration circuit that attempts to correct the IMD2 mismatch and minimize the mixer's IMD2 feedthrough by adjusting the mixer gate voltage. Unfortunately, the calibration time is band-dependent. Additionally, these systems use two RF tones and port switching, which further increases test time and associated costs.

[0068] Certain aspects of the present disclosure provide techniques and apparatus for mixer IIP2 calibration that reduce test time and / or reduce the lateral area (e.g., footprint) of the system compared to other IIP2 calibration techniques. One technique involves: applying a single baseband tone to an input of a mixer so that the mixer generates a differential tone; and adjusting the mixer to minimize the power of the differential tone at an output of the mixer. Another technique involves: downconverting a radio frequency (RF) signal using a mixer; amplifying an IMD2 product generated by the mixer and back-feeding from an output port of the mixer to an RF port of the mixer; and adjusting the mixer based on the amplified IMD2 product.

[0069] Figure 4 4 is a block diagram of a circuit 400 for mixer IIP2 calibration in which aspects of the present disclosure may be practiced. The circuit 400 includes a tone generator 402 and at least one receive chain (eg, RX path 304). Figure 4 , the first receive chain includes an amplifier 404, a mixer 406, and an amplifier 410. An input of the amplifier 404 may be coupled to at least one antenna (e.g., antenna 306) via an interface (e.g., interface 308). An output of the amplifier 404 may be coupled to a first input of the mixer 406 (e.g., RF port 414), and a frequency synthesizer (e.g., RX frequency synthesizer 332) may be coupled to a second input of the mixer 406 (e.g., local oscillator (LO) port 416). An output of the mixer 406 (e.g., output port 418) may be coupled to an input of the amplifier 410. Although in Figure 4 Certain resistor elements and capacitor elements are shown in FIG. 1 , but it should be understood that at least some of these elements may be optional or may be replaced with other components.

[0070] For certain aspects, circuit 400 may include a second receive chain. The second receive chain includes amplifier 404, mixer 408, and amplifier 412. The output of amplifier 404 may be coupled to a first input of mixer 408, and the same or a different frequency synthesizer may be coupled to a second input of mixer 408. The output of mixer 408 may be coupled to an input of amplifier 412. Although in Figure 4 Two receive chains are illustrated in FIG. 1 , but it should be understood that there may be more or less than two receive chains.

[0071] Each of the mixers 406, 408 may be, for example, a single balanced mixer, a double balanced mixer, an active mixer, or any other suitable type of mixer. Each of the mixers 406, 408 may include an RF port 414, an LO port 416, and an output port 418, and may represent Figure 3 The mixer 326 in FIG. 4 is a mixer 326 in FIG. 400 . For example, the amplifier 404 can be a low noise amplifier (eg, LNA 324). Figure 4 As illustrated in FIG. 4 , amplifier 410 and / or amplifier 412 may be a transimpedance amplifier (TIA).

[0072] The tone generator 402 has an output coupled to an output of the amplifier 404, to an input of the mixer 406, and to an input of the mixer 408. For some aspects, the tone generator 402 may be an on-chip generator included in the same integrated circuit (IC) as the amplifier 404, the mixer 406, and the amplifier 410. For other aspects, the tone generator 402 may be an external generator outside the IC having the amplifier 404, the mixer 406, and the amplifier 410. In this case, the IC may have an input / output (I / O) pin for coupling to the tone generator 402. For some aspects, the input of the tone generator 402 may be coupled to an output of a frequency synthesizer (e.g., the RX frequency synthesizer 332 or the TX frequency synthesizer 320). In this case, the tone generator may include one or more frequency dividers (and other components) for generating an output tone from the frequency synthesizer. For other aspects, the tone generator 402 may be a stand-alone frequency synthesizer.

[0073] The single tone generator 402 can be configured to generate a calibration signal having a single baseband tone. For some aspects, the single baseband tone can have a frequency of no greater than 50 MHz; for other aspects, can have a frequency of no greater than 10 MHz; or for still other aspects, can have a frequency of no greater than 5 MHz. As an example, the single tone generator 402 can be configured to output the calibration tone at 1.2 MHz. For some aspects, the single tone generator 402 is configured to generate a digital calibration tone (e.g., a rail-to-rail square wave having a fundamental frequency at the baseband frequency of the single baseband tone).

[0074] When the baseband tone from the single tone generator 402 is applied to the RF port 414 of the mixer 406 (or the mixer 408) during the IIP2 calibration, the mixer will generate a common mode IMD2 at the RF port and a differential baseband tone at the output port 418. The control logic component (e.g., the controller 336) can control the adjustment of the mixer to minimize or at least reduce the power of the differential baseband tone at the output of the mixer. In other words, the mixer can be calibrated to have zero (or very little) RF feedthrough. For certain aspects, adjusting the mixer may involve changing one or more gate bias voltages of one or more transistors in the mixer. One or more indications of the adjustment for IIP2 calibration made to the mixer (referred to as "IIP2 calibration codes") can be stored in a memory (e.g., memory 338). In this way, the IIP2 of the mixer can be calibrated. Other mixers can be calibrated for IIP2 in the same manner that can be performed concurrently for different mixers. The mixer IIP2 calibration may be repeated for different frequency bands for a given mixer, and the IIP2 calibration codes for these different frequency bands may also be stored.

[0075] Therefore, instead of trying to measure IIP2, mixer IIP2 calibration is performed by balancing the mixer, which will result in better IIP2 performance. In other words, the purpose of the baseband tone is to sense the imbalance of the mixer at the output of the mixer, and then directly balance the mixer, rather than trying to offset some frequencies translated by IIP2. Performing mixer IIP2 calibration using a single baseband tone in this way avoids RF mismatch effects and actually involves optimizing the common-mode to differential-mode conversion of the mixer. In addition, the mixer has common-mode rejection, and therefore, a large amplitude baseband tone can be applied to the input of the mixer. In contrast, a large amplitude in-band RF signal can saturate the baseband filter (e.g., BBF 328), so that the IMD2 product may not be measured, and large out-of-band signals will be filtered out.

[0076] Using the on-chip tone generator, mixer IIP2 calibration can be performed in the lab, in the factory, or in the field. Mixer IIP2 calibration in the field can permit adjustment of the mixer due to changes in ambient temperature, drift, or voltage. For example, threshold voltage (Vth) mismatch in mixer transistors can be temperature dependent.

[0077] For certain aspects, after storing the IIP2 calibration code for the mixer, an RF tone (e.g., an in-band tone) may be applied to test the receive path to confirm that the IIP2 performance meets the specification. The RF tone may be applied at the input of the amplifier 404 or at the input of the mixers 406, 408. In the latter case, the RF tone may be applied by the single tone generator 402 or by a different signal generator on-chip or external to the IC having the receive chain.

[0078] Example mixer IIP2 calibration using backfeedthrough based on received RF signal

[0079] Figure 5 FIG. 5 is a block diagram of another circuit 500 for mixer IIP2 calibration according to certain aspects of the present disclosure. The circuit 500 includes a number of Figure 4 The same components of circuit 400 and many of the descriptions of circuit 400 are also applicable to circuit 500 and will not be repeated here.

[0080] Compared to circuit 400, the tone generator may be removed, but amplifier 502 may be added to circuit 500, thereby forming a calibration path in addition to the normal receive chain. Figure 5 4. The amplifier 502 may have an input coupled to the output of the amplifier 404. However, there may be no mixer coupled between the output of the amplifier 404 and the input of the amplifier 502 (and no active components). In fact, the input of the amplifier 502 may be coupled directly to the output of the amplifier 404, rather than a trace (and in some cases a passive component, such as a resistor, as shown) therebetween. Figure 5 ). In this manner, unlike amplifiers 410 and 412, amplifier 502 can receive a radio frequency (RF) signal from amplifier 404 without down-converting the RF signal. For certain aspects, amplifier 502 can be a TIA, such as Figure 5 Although Figure 5 Certain resistor elements and capacitor elements are shown in FIG. 1 , but it should be understood that at least some of these elements may be optional or may be replaced with other components.

[0081] The circuit 500 provides mixer IIP2 calibration by using a wirelessly received RF signal and amplifying the second-order intermodulation distortion (IMD2) from the reverse feedthrough (i.e., baseband to RF) from the mixer 406 (and / or the mixer 408). For example, a strong in-band RF signal may be received by an antenna (e.g., antenna 306) coupled to the input of the amplifier 404 (in the absence of a transmit signal from the same device). The amplified RF signal may be down-converted by the mixer, thereby generating IMD2 at the RF port 414 of the mixer. The IMD2 at the RF port 414 of the mixer is considered to be reverse feedthrough (from the output port 418 of the mixer to the RF port 414). The IMD2 at the RF port of the mixer may be sensed and amplified by the amplifier 502 (without down-conversion). The signal that is not down-converted will be highly correlated with the down-converted signal in the normal receive chain (with a mixer), although there may be some phase offset. Calibration may be performed in a "walking algorithm" by adjusting the mixer, determining whether IMD2 is increasing or decreasing, and adjusting the mixer to minimize or at least reduce the amplified IMD2 (e.g., minimize the power of the amplified signal output by amplifier 502). Other mixers may be calibrated for IIP2 in the same manner that may be performed concurrently for different mixers.

[0082] As described above, adjusting the mixer may involve changing one or more gate bias voltages of one or more transistors in the mixer. One or more indications of adjustments made to the mixer for IIP2 calibration may be stored in a memory (e.g., memory 338). In this way, the IIP2 of the mixer may be calibrated online in the field. The mixer IIP2 calibration in the field may allow the mixer to be adjusted due to changes in ambient temperature, drift, or voltage. Online calibration may provide better IIP2 performance than such changes.

[0083] For certain aspects, after storing the IIP2 calibration code for the mixer, an RF tone (eg, an in-band tone) may be applied to test the receive path to confirm that the IIP2 performance meets specifications. The RF tone may be applied at the input of the amplifier 404 .

[0084] Example Mixer IIP2 Calibration Using Backfeedthrough Based on a Single RF Tone

[0085] Figure 6 6 is a block diagram of another circuit 600 for mixer IIP2 calibration according to certain aspects of the present disclosure. Circuit 600 can be viewed as a combination of circuit 500 with a tone generator 602 added. Circuit 600 includes a number of Figure 4 and Figure 5The circuits 400 and 500 have the same components, and many of the descriptions of the circuits 400 and 500 also apply to the circuit 600 and will not be repeated here. Figure 6 Certain resistor elements and capacitor elements are shown in FIG. 1 , but it should be understood that at least some of these elements may be optional or may be replaced with other components.

[0086] The tone generator 602 has an output coupled to the output of the amplifier 404, to the input of the mixer 406, to the input of the mixer 408, and to the input of the amplifier 502. For some aspects, the tone generator 602 may be an on-chip generator included in the same integrated circuit (IC) as the amplifier 404, the receive chain, and the amplifier 502. For other aspects, the tone generator 602 may be an external generator outside the IC having the amplifier 404, the receive chain, and the amplifier 502. In the latter case, the IC may have an input / output (I / O) pin for coupling to the tone generator 602. For some aspects, the input of the tone generator 602 may be coupled to the output of a frequency synthesizer (e.g., the RX frequency synthesizer 332 or the TX frequency synthesizer 320). In this case, the tone generator may include one or more frequency dividers (and other components) for generating an output tone from the frequency synthesizer. For other aspects, the tone generator 602 may be a stand-alone frequency synthesizer.

[0087] The single tone generator 602 can be configured to generate a calibration signal having a single RF tone. The single RF tone can have a frequency that is the sum of a local oscillator (LO) frequency and a baseband frequency. The LO frequency can be the frequency of an LO signal for a mixer. For certain aspects, the baseband frequency can be no greater than 50 MHz; for other aspects, no greater than 10 MHz; or for still other aspects, no greater than 5 MHz. As an example, the single tone generator 602 can be configured to output the calibration tone at LO+1.2 MHz. For certain aspects, the single tone generator 602 is configured to generate a digital calibration tone (e.g., a rail-to-rail square wave having a fundamental frequency at the frequency of the single RF tone).

[0088] The mixer IIP2 calibration performed using circuit 600 may be similar to the mixer IIP2 calibration performed using circuit 500, except that a single RF tone from a single tone generator 602 is applied to the input of the mixer instead of a wirelessly received RF signal. In other words, the single RF tone is down-converted by the mixer (using an LO signal at the LO frequency applied to the LO port 416 of the mixer), thereby generating IMD2 at the RF port 414 of the mixer, and the reverse feed-through signal is sensed and amplified by the amplifier 502 (without down-conversion). The signal that is not down-converted will be highly correlated with the down-converted signal in the receive chain (with the mixer). The calibration may be performed with a "walking algorithm" by the following operations: adjusting the mixer; determining whether IMD2 is increasing or decreasing; and having each of the mixers have an adjustment that minimizes the amplified IMD2. Other mixers may be calibrated for IIP2 in the same manner that may be performed concurrently for different mixers.

[0089] For certain aspects, after the IIP2 calibration code for the mixer is stored, an RF tone (e.g., an in-band tone) may be applied to test the receive path to confirm that the IIP2 performance meets the specification. The RF tone may be applied at the input of the amplifier 404 or at the input of the mixers 406, 408. In the latter case, the RF tone may be applied by the single tone generator 602 or by a different signal generator on-chip or external to the IC having the receive chain.

[0090] Example Mixer IIP2 Calibration Operation

[0091] Figure 7 7 is a flow diagram of example operations 700 for calibrating a mixer (eg, for second order input intercept point (IIP2)) according to certain aspects of the present disclosure. Operations 700 may be performed, for example, by a circuit for mixer IIP2 calibration (eg, Figure 4 400) to execute.

[0092] Operations 700 may begin at block 702 by generating a calibration signal including a single baseband tone (e.g., using an (on-chip) tone generator or frequency synthesizer). For some aspects, the single baseband tone may have a frequency of no greater than 50 MHz; for other aspects may have a frequency of no greater than 10 MHz; or for still other aspects may have a frequency of no greater than 5 MHz. At block 704, the calibration signal is applied to an input (e.g., RF port 414) of a mixer (e.g., mixer 406 or 408), and the mixer generates a differential tone at an output (e.g., output port 418) of the mixer. At block 706, the mixer is adjusted (e.g., by control logic, such as controller 336) to, for example, attempt to minimize the power of the differential tone at the output of the mixer.

[0093] According to certain aspects, the calibration signal is generated by a tone generator, such as tone generator 402. For certain aspects, the mixer and the tone generator are part of the same integrated circuit (IC).

[0094] According to certain aspects, the calibration signal is a square wave (eg, a rail-to-rail square wave) having a fundamental frequency that is a single baseband tone.

[0095] According to certain aspects, operations 700 further involve testing the adjustment of the mixer at optional block 708. In this case, the testing may include: applying a test signal including a single radio frequency (RF) tone to an input of the mixer or to an input of an amplifier (e.g., amplifier 404 or LNA 324) having an output coupled to the input of the mixer (e.g., using an (on-chip) single tone generator or frequency synthesizer); and determining (e.g., using a processor such as controller 336) whether second-order intermodulation distortion (IMD2) performance meets predefined specifications for the single RF tone case.

[0096] According to certain aspects, adjusting the mixer at block 706 includes adjusting at least one gate bias voltage of at least one transistor in the mixer.

[0097] According to certain aspects, adjusting the mixer at block 706 involves adjusting the mixer to not have significant feedthrough of the single baseband tone at an output of the mixer.

[0098] According to certain aspects, the mixer is a single balanced mixer or a double balanced mixer. For other aspects, the mixer is an active mixer.

[0099] According to certain aspects, operations 700 further involve storing (eg, in a memory, such as memory 338 ) one or more indications (eg, IIP2 calibration codes) based on the adjustment of the mixer at block 706 .

[0100] Figure 8 8 is a flow chart of example operations 800 for calibrating a mixer (eg, for second order input intercept point (IIP2)) according to certain aspects of the present disclosure. Operations 800 may be performed, for example, by a circuit for mixer IIP2 calibration (eg, Figure 5 The circuit 500 or Figure 6 600) to perform.

[0101] Operations 800 may generally begin at block 802 with a mixer (e.g., mixer 406 or mixer 408) down-converting a radio frequency (RF) signal. At block 804, a first amplifier (e.g., amplifier 502) may amplify second-order intermodulation distortion (IMD2) generated by the mixer and fed back from an output port (e.g., output port 418) of the mixer to an RF port (e.g., RF port 414) of the mixer due to the down-conversion at block 802. At block 806, a circuit (e.g., a control logic component such as controller 336) may adjust the mixer based on the amplified IMD2 (e.g., in an effort to minimize the amplified IMD2).

[0102] According to certain aspects, operations 800 also include: an antenna (e.g., antenna 306) receiving an RF signal (e.g., a strong received signal); and a second amplifier (e.g., amplifier 404) amplifying the RF signal prior to down-conversion at block 802. In this manner, an online calibration of the mixer may be performed so that the mixer may be adjusted for temperature variations during regular operation in the field.

[0103] According to certain aspects, the operation further involves: generating a calibration signal including a single tone that is the sum of a local oscillator (LO) frequency and a baseband frequency (e.g., with an (on-chip) single tone generator or divider); and applying the calibration signal to an RF port of the mixer (e.g., RF port 414) and applying an LO signal at the LO frequency to an LO port of the mixer (e.g., LO port 416). In this case, the calibration signal is an RF signal used for down-conversion with the mixer at block 802. For certain aspects, the calibration signal is generated by a single tone generator (e.g., single tone generator 602). In this case, the mixer and the single tone generator can be part of the same integrated circuit (IC). The calibration signal can be a square wave (e.g., a rail-to-rail square wave) having a baseband frequency as the single tone. For certain aspects, the baseband frequency can be no greater than 50 MHz; for other aspects, no greater than 10 MHz; or for still other aspects, no greater than 5 MHz.

[0104] According to certain aspects, the adjustment at block 806 includes adjusting the mixer for changes in temperature.

[0105] According to certain aspects, the adjusting at block 806 involves adjusting at least one gate bias voltage of at least one transistor in the mixer.

[0106] According to certain aspects, operations 800 also include testing the adjustment of the mixer at optional block 808. In this case, testing the adjustment of the mixer may involve: applying a test signal including a single RF tone to an RF port of the mixer or to an input of a second amplifier (e.g., amplifier 404 or LNA 324) having an output coupled to the RF port of the mixer (e.g., using an (on-chip) single tone generator or frequency synthesizer); and determining (e.g., using a processor such as controller 336) whether the IMD2 performance of the single RF tone meets a predefined specification.

[0107] According to certain aspects, the mixer is a single balanced mixer or a double balanced mixer.

[0108] According to certain aspects, operations 800 further involve storing (eg, in a memory, such as memory 338 ) one or more indications (eg, IIP2 calibration codes) based on the adjustment of the mixer at block 806 .

[0109] Example aspects

[0110] In addition to the above-mentioned aspects, specific combinations of the aspects are also within the scope of the present disclosure, and the details of some of the specific combinations are as follows:

[0111] Aspect 1: A circuit for mixer second-order input intercept point (IIP2) calibration, the circuit comprising: a first receive chain, the first receive chain comprising a first mixer; and a single tone generator, the single tone generator having an output coupled to an input of the first mixer and configured to generate a calibration signal having a single baseband tone.

[0112] Aspect 2: The circuit of aspect 1, wherein the circuit is an integrated circuit (IC), and wherein the IC comprises the first receive chain and the tone generator.

[0113] Aspect 3: The circuit according to aspect 1 or 2, wherein the first receive chain further comprises a first amplifier having an output coupled to the input of the first mixer and to the output of the single tone generator.

[0114] Aspect 4: The circuit of aspect 3, wherein the first receive chain further comprises a second amplifier having an input coupled to an output of the first mixer.

[0115] Aspect 5: The circuit according to aspect 3 or 4 further includes a second receiving chain, the second receiving chain includes the first amplifier and a second mixer, wherein the input of the second mixer is coupled to the output of the first amplifier and to the output of the single tone generator.

[0116] Aspect 6: The circuit according to any one of aspects 1 to 5, wherein the first mixer comprises a single balanced mixer or a double balanced mixer.

[0117] Aspect 7: The circuit according to any one of aspects 1 to 6, wherein the single tone generator is configured to generate a rail-to-rail square wave having a fundamental frequency of the single baseband tone as the calibration signal.

[0118] Aspect 8: The method according to any one of aspects 1 to 7, wherein the single tone generator comprises a frequency divider.

[0119] Aspect 9: The circuit of any one of aspects 1 to 8, wherein the single baseband tone has a frequency no greater than 5 MHz.

[0120] Aspect 10: A wireless device comprising a circuit according to any one of Aspects 1 to 9, the wireless device further comprising: at least one antenna, the at least one antenna coupled to an input of the first receive chain; an analog-to-digital converter, the analog-to-digital converter coupled to an output of the first receive chain; and a processor having an input coupled to the output of the analog-to-digital converter, wherein the first mixer is configured to generate a differential tone when the single tone generator applies the calibration signal to the first mixer, and wherein the processor is configured to: receive a representation of the differential tone, control the single tone generator, and control adjustment of the first mixer to minimize the power of the representation of the differential tone.

[0121] Aspect 11: A method for calibrating a mixer second-order input intercept point (IIP2), the method comprising: generating a calibration signal comprising a single baseband tone; applying the calibration signal to the input of the mixer so that the mixer generates a differential tone at the output of the mixer; and adjusting the mixer to minimize the power of the differential tone at the output of the mixer.

[0122] Aspect 12: The method of aspect 11, wherein the calibration signal is generated by a single tone generator, and wherein the mixer and the single tone generator are part of the same integrated circuit (IC).

[0123] Aspect 13: The method according to Aspect 11 or 12 further includes testing the adjustment of the mixer, wherein the test includes: applying a test signal including a single radio frequency (RF) tone to the input of the mixer or to the input of an amplifier having an output coupled to the input of the mixer; and determining whether the second-order intermodulation distortion (IMD2) performance in the single RF tone case meets predefined specifications.

[0124] Aspect 14: The method according to any one of aspects 11 to 13, wherein the calibration signal is a rail-to-rail square wave having a fundamental frequency as the single baseband tone.

[0125] Aspect 15: The method according to any one of aspects 11 to 14, wherein the single baseband tone has a frequency no greater than 5 MHz.

[0126] Aspect 16: The method according to any one of aspects 11 to 15, wherein adjusting the mixer comprises adjusting at least one gate bias voltage of at least one transistor in the mixer.

[0127] Aspect 17: The method of any one of aspects 11 to 16, wherein adjusting the mixer comprises adjusting the mixer to have no significant feedthrough of the single baseband tone at the output of the mixer.

[0128] Aspect 18: A circuit for mixer second-order input intercept point (IIP2) calibration, the circuit comprising: a first amplifier; a first receiving chain, the first receiving chain comprising a first mixer, the first mixer having an input coupled to the output of the first amplifier; and a second amplifier, the second amplifier having an input coupled to the output of the first amplifier.

[0129] Aspect 19: The circuit of aspect 18, wherein the circuit does not include a mixer coupled between the first amplifier and the second amplifier.

[0130] Aspect 20: The circuit according to aspect 18 or 19, wherein the first mixer is configured to down-convert a radio frequency (RF) signal to a baseband signal, and wherein the second amplifier is configured to receive a backfeedthrough signal from the input terminal of the first mixer.

[0131] Aspect 21: A circuit according to any one of Aspects 18 to 20, wherein the circuit further comprises a single-tone generator having an output coupled to the output of the first amplifier, coupled to the input of the first mixer and coupled to the input of the second amplifier, the single-tone generator being configured to generate a calibration signal having a single tone that is the sum of a local oscillator (LO) frequency and a baseband frequency.

[0132] Aspect 22: The circuit of aspect 21, wherein the circuit is an integrated circuit (IC), and wherein the IC comprises the first amplifier, the first receive chain, the second amplifier, and the tone generator.

[0133] Aspect 23: The circuit according to Aspect 21 or 22 further includes a second receiving chain, the second receiving chain including: the first amplifier; and a second mixer, the second mixer having an input coupled to the output of the first amplifier, coupled to the input of the second amplifier and coupled to the output of the single tone generator.

[0134] Aspect 24: The circuit according to any one of aspects 21 to 23, wherein the single tone generator is configured to generate a rail-to-rail square wave having a fundamental frequency of the single tone as the calibration signal.

[0135] Aspect 25: The circuit of any one of aspects 21 to 24, wherein the LO frequency is a radio frequency, and wherein the baseband frequency is no greater than 5 MHz.

[0136] Aspect 26: A wireless device comprising a circuit according to any one of Aspects 21 to 25, the wireless device further comprising: a frequency synthesizer, the frequency synthesizer being configured to generate an LO signal at the LO frequency and apply the LO signal to the LO port of the first mixer; an analog-to-digital converter, the analog-to-digital converter being coupled to the output of the first receive chain; and a processor having an input coupled to the output of the analog-to-digital converter, wherein: the single tone generator is configured to apply the calibration signal to a radio frequency (RF) port of the first mixer; the first mixer is configured to down-convert the calibration signal based on the LO signal; the second amplifier is configured to amplify second-order intermodulation distortion (IMD2) generated by the first mixer due to the down-conversion; and the processor is configured to control adjustment of the first mixer based on the amplified IMD2 to minimize the amplified IMD2.

[0137] Aspect 27: A wireless device comprising a circuit according to any one of Aspects 18 to 20, the wireless device further comprising: at least one antenna, the at least one antenna coupled to an input of the first receiving chain; an analog-to-digital converter, the analog-to-digital converter coupled to an output of the first receiving chain; and a processor having an input coupled to the output of the analog-to-digital converter, wherein: the at least one antenna is configured to receive a radio frequency (RF) signal; the first amplifier is configured to amplify the received RF signal; the first mixer is configured to down-convert the amplified RF signal; the second amplifier is configured to amplify second-order intermodulation distortion (IMD2) generated by the first mixer due to the down-conversion; and the processor is configured to control adjustment of the first mixer based on the amplified IMD2.

[0138] Aspect 28: The circuit of any one of Aspects 18 to 27, wherein the first mixer comprises a single balanced mixer or a double balanced mixer.

[0139] Aspect 29: A method for calibrating a mixer second-order input intercept point (IIP2), the method comprising: using a mixer to down-convert a radio frequency (RF) signal; using a first amplifier to amplify second-order intermodulation distortion (IMD2) generated by the mixer due to the down-conversion and fed back from the output port of the mixer to the RF port of the mixer; and adjusting the mixer based on the amplified IMD2 to minimize the amplified IMD2.

[0140] Aspect 30: The method according to aspect 29, the method further comprising: receiving the RF signaling using an antenna; and amplifying the RF signal using a second amplifier before the down-conversion.

[0141] Aspect 31: According to the method according to Aspect 29, the method also includes: generating a calibration signal, the calibration signal includes a single tone that is the sum of a local oscillator (LO) frequency and a baseband frequency; and applying the calibration signal to the RF port of the mixer and applying an LO signal at the LO frequency to the LO port of the mixer, wherein the calibration signal is the RF signal used for the down-conversion using the mixer.

[0142] Aspect 32: The method of aspect 31, wherein the calibration signal is generated by a single tone generator, and wherein the mixer and the single tone generator are part of the same integrated circuit (IC).

[0143] Aspect 33: The method according to aspect 31 or 32, wherein the calibration signal is a rail-to-rail square wave having a fundamental frequency as the single tone.

[0144] Aspect 34: A method according to any one of Aspects 31 to 33, wherein the baseband frequency is no greater than 5 MHz.

[0145] Aspect 35: The method according to any one of aspects 29 to 34, wherein the adjusting comprises adjusting the mixer for temperature changes.

[0146] Aspect 36: The method according to any one of aspects 29 to 35, wherein the adjusting comprises adjusting at least one gate bias voltage of at least one transistor in the mixer.

[0147] Aspect 37: According to a method described in any one of Aspects 29 to 36, the method further includes testing the adjustment of the mixer, wherein the test includes: applying a test signal including a single RF tone to the RF port of the mixer or to an input of a second amplifier having an output coupled to the RF port of the mixer; and determining whether the IMD2 performance meets predefined specifications in the single RF tone case.

[0148] Additional considerations

[0149] The above description provides examples, but does not limit the scope, applicability or examples set forth in the claims. Without departing from the scope of the present disclosure, the functions and arrangements of the elements discussed may be changed. Various procedures or components may be omitted, replaced or added to each example as appropriate. For example, the method described may be performed in a different order from that described, and various steps may be added, omitted or combined. In addition, the features described for some examples may be combined in some other examples. For example, any number of aspects set forth herein may be used to implement a device or practice method. In addition, the scope of the present disclosure is intended to cover such devices or methods practiced using other structures, functional functions or structures and functionality in addition to or different from the various aspects of the present disclosure given herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of the present invention. The word "exemplary" is used herein to mean "used as an example, instance, or illustration". Any aspect described as "exemplary" herein is not necessarily interpreted as being preferred or having advantages over other aspects.

[0150] The various operations of the above methods may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and / or software components and / or modules, including but not limited to circuits, application specific integrated circuits (ASICs), or processors. In general, where there are operations illustrated in the figures, these operations may have corresponding corresponding means plus functional components. For example, the means for generating the calibration signal may include a frequency synthesizer, such as Figure 3 The TX frequency synthesizer 320 or RX frequency synthesizer 332, or a single tone generator, such as Figure 4 or Figure 6 The single tone generator 402 or 602 of FIG. 4 may include one or more traces, connectors, cables, resistors, and / or RF ports, such as Figure 4 , Figure 5 or Figure 6 RF port 414. The means for adjusting may include control logic means such as Figure 3 Controller 336. The components for down-conversion may include mixers such as Figure 4 , Figure 5 or Figure 6 The mixer 406 or 408. The means for amplifying may include an amplifier such as Figure 5 or Figure 6 Amplifier 502.

[0151] As used herein, a phrase referring to "at least one of" a list of items refers to any combination of those items (including single members). As an example, "at least one of a, b, or c" is intended to cover: a, b, c, ab, ac, bc, and abc, as well as any combination with multiple identical elements (e.g., aa, aaa, aab, aac, abb, acc, bb, bbb, bbc, cc, and ccc, or any other ordering of a, b, and c).

[0152] The methods disclosed herein include one or more steps or actions for implementing the described methods. The steps and / or actions of the methods may be interchangeable with each other without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and / or use of specific steps and / or actions may be modified without departing from the scope of the claims.

[0153] It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims.

Claims

1. A circuit for calibrating a mixer second-order input intercept point (IIP2), the circuit comprising: a first receive chain, the first receive chain comprising a first mixer; as well as A single tone generator has an output coupled to the input of the first mixer and is configured to generate a calibration signal having a single baseband tone.

2. The circuit of claim 1, wherein the circuit is an integrated circuit (IC), and wherein the IC includes the first receive chain and the tone generator.

3. The circuit of claim 1, wherein the first receive chain further comprises a first amplifier having an output coupled to the input of the first mixer and to the output of the tone generator. 4 . The circuit of claim 3 , wherein the first receive chain further comprises a second amplifier having an input coupled to the output of the first mixer.

5. The circuit of claim 3, further comprising a second receive chain comprising the first amplifier and a second mixer, wherein an input of the second mixer is coupled to the output of the first amplifier and to the output of the tone generator.

6. The circuit of claim 1, wherein the first mixer comprises a single-balanced mixer or a double-balanced mixer.

7. The circuit of claim 1, wherein the single tone generator is configured to generate a rail-to-rail square wave having a fundamental frequency of the single baseband tone as the calibration signal.

8. The circuit of claim 1 wherein the tone generator comprises a frequency divider.

9. The circuit of claim 1 wherein the single baseband tone has a frequency no greater than 5 MHz.

10. A wireless device comprising the circuit according to claim 1, the wireless device further comprising: at least one antenna, the at least one antenna coupled to an input of the first receive chain; an analog-to-digital converter coupled to an output of the first receive chain; as well as a processor having an input coupled to an output of the analog-to-digital converter, wherein the first mixer is configured to generate a differential tone when the single tone generator applies the calibration signal to the first mixer, and wherein the processor is configured to: receive a representation of the differential tone, control the single tone generator, and control adjustment of the first mixer to minimize the power of the representation of the differential tone.

11. A method for calibrating a mixer second-order input intercept point (IIP2), the method comprising: generating a calibration signal comprising a single baseband tone; applying the calibration signal to an input of a mixer so that the mixer generates a differential tone at an output of the mixer; as well as The mixer is adjusted to minimize the power of the differential tone at the output of the mixer.

12. The method of claim 11, wherein the calibration signal is generated by a tone generator, and wherein the mixer and the tone generator are part of the same integrated circuit (IC).

13. The method of claim 11, further comprising testing the adjustment of the mixer, wherein the testing comprises: applying a test signal comprising a single radio frequency (RF) tone to the input of the mixer or to an input of an amplifier having an output coupled to the input of the mixer; and A determination is made as to whether second order intermodulation distortion (IMD2) performance for the single RF tone case meets predefined specifications.

14. The method of claim 11, wherein the calibration signal is a rail-to-rail square wave having a fundamental frequency as the single baseband tone.

15. The method of claim 11, wherein the single baseband tone has a frequency no greater than 5 MHz.

16. The method of claim 11, wherein adjusting the mixer comprises adjusting at least one gate bias voltage of at least one transistor in the mixer.

17. The method of claim 11, wherein adjusting the mixer comprises adjusting the mixer to not have significant feedthrough of the single baseband tone at the output of the mixer.

18. A circuit for mixer second-order input intercept point (IIP2) calibration, the circuit comprising: First amplifier; a first receive chain comprising a first mixer having an input coupled to an output of the first amplifier; as well as A second amplifier has an input coupled to the output of the first amplifier.

19. The circuit of claim 18, wherein the circuit is free of a mixer coupled between the first amplifier and the second amplifier.

20. The circuit of claim 18, wherein the first mixer is configured to down-convert a radio frequency (RF) signal to a baseband signal, and wherein the second amplifier is configured to receive a backfeedthrough signal from the input of the first mixer.

21. The circuit of claim 18, further comprising a single tone generator having an output coupled to the output of the first amplifier, to the input of the first mixer, and to the input of the second amplifier, the single tone generator being configured to generate a calibration signal having a single tone that is a sum of a local oscillator (LO) frequency and a baseband frequency.

22. The circuit of claim 21, wherein the circuit is an integrated circuit (IC), and wherein the IC includes the first amplifier, the first receive chain, the second amplifier, and the tone generator.

23. The circuit of claim 21 , further comprising a second receive chain, the second receive chain comprising: the first amplifier; as well as A second mixer has an input coupled to the output of the first amplifier, to the input of the second amplifier, and to the output of the tone generator.

24. The circuit of claim 21, wherein the tone generator is configured to generate a rail-to-rail square wave having a fundamental frequency of the tone as the calibration signal.

25. The circuit of claim 21, wherein the LO frequency is a radio frequency, and wherein the baseband frequency is no greater than 5 MHz.

26. A wireless device comprising the circuit of claim 21, the wireless device further comprising: a frequency synthesizer configured to generate an LO signal at the LO frequency and apply the LO signal to the LO port of the first mixer; an analog-to-digital converter coupled to an output of the first receive chain; as well as a processor having an input coupled to an output of the analog-to-digital converter, wherein: The tone generator is configured to apply the calibration signal to a radio frequency (RF) port of the first mixer; The first mixer is configured to down-convert the calibration signal based on the LO signal; The second amplifier is configured to amplify second-order intermodulation distortion (IMD2) generated by the first mixer due to the down-conversion; and The processor is configured to control adjustment of the first mixer based on the amplified IMD2 to minimize the amplified IMD2.

27. A wireless device comprising the circuit of claim 18, the wireless device further comprising: at least one antenna, the at least one antenna coupled to an input of the first receive chain; an analog-to-digital converter coupled to an output of the first receive chain; as well as a processor having an input coupled to an output of the analog-to-digital converter, wherein: The at least one antenna is configured to receive a radio frequency (RF) signal; The first amplifier is configured to amplify the received RF signal; The first mixer is configured to down-convert the amplified RF signal; The second amplifier is configured to amplify second-order intermodulation distortion (IMD2) generated by the first mixer due to the down-conversion; and The processor is configured to control adjustment of the first mixer based on the amplified IMD2.

28. The circuit of claim 18, wherein the first mixer comprises a single-balanced mixer or a double-balanced mixer.

29. A method for calibrating a mixer second-order input intercept point (IIP2), the method comprising: Down-converting a radio frequency (RF) signal using a mixer; amplifying, using a first amplifier, second order intermodulation distortion (IMD2) generated by the mixer as a result of the down-conversion and fed back from an output port of the mixer to an RF port of the mixer; and The mixer is adjusted based on the amplified IMD2 to minimize the amplified IMD2.

30. The method according to claim 29, further comprising: receiving the RF signal using an antenna; as well as The RF signal is amplified using a second amplifier prior to the down-conversion.

31. The method of claim 29, further comprising: generating a calibration signal comprising a single tone at a sum of a local oscillator (LO) frequency and a baseband frequency; as well as The calibration signal is applied to an RF port of the mixer and an LO signal at the LO frequency is applied to the LO port of the mixer, wherein the calibration signal is the RF signal used for the down-conversion using the mixer.

32. The method of claim 31, wherein the calibration signal is generated by a tone generator, and wherein the mixer and the tone generator are part of the same integrated circuit (IC).

33. The method of claim 31, wherein the calibration signal is a rail-to-rail square wave having a fundamental frequency as the single tone.

34. The method of claim 31, wherein the baseband frequency is no greater than 5 MHz.

35. The method of claim 29, wherein the adjusting comprises adjusting the mixer for temperature changes.

36. The method of claim 29, wherein the adjusting comprises adjusting at least one gate bias voltage of at least one transistor in the mixer.

37. The method of claim 29, further comprising testing the adjustment of the mixer, wherein the testing comprises: applying a test signal comprising a single RF tone to the RF port of the mixer or to an input of a second amplifier having an output coupled to the RF port of the mixer; as well as A determination is made as to whether the IMD2 performance meets predefined specifications for the single RF tone case.

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