Abstract:
In accordance with some embodiments of the present disclosure, a method may include generating a first current equal to a bandgap voltage divided by a resistance selected to approximately match a process resistance integral to a receiver. The method may further include generating a second current equal to temperature-dependent current multiplied by a predetermined scaling factor. The method may also include subtracting the second current from the first current to generate a bias current. The method may additionally include providing the bias current to the receiver.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to wireless communication and, more particularly, to reducing or eliminating temperature dependence of a coherent receiver in a wireless communication device. 
       BACKGROUND 
       [0002]    Wireless communications systems are used in a variety of telecommunications systems, television, radio and other media systems, data communication networks, and other systems to convey information between remote points using wireless transmitters and wireless receivers. A transmitter is an electronic device which, usually with the aid of an antenna, propagates an electromagnetic signal such as radio, television, or other telecommunications. Transmitters often include digital signal processing circuits which encode a data signal, upconverts it to a radio frequency signal, and passes it signal amplifiers which receive the radio-frequency, amplify the signal by a predetermined gain, and transmit the amplified signal through an antenna. On the other hand, a receiver is an electronic device which, also usually with the aid of an antenna, receives and processes a wireless electromagnetic signal. In certain instances, a transmitter and receiver may be combined into a single device called a transceiver. 
         [0003]    A wireless communication device may include, in addition to a transmitter and a receiver, a coherent receiver as part of a feedback control path for monitoring and control of the transmitter. For example, such a feedback control path may provide for monitoring of a phase shift in a transmit path, an output power intensity of a transmit path, and/or other parameters. In addition, based on such monitoring, the control path may control operational parameters in order to provide desired behavior within the transmit path. To ensure accurate monitoring and control, the gain characteristics of the feedback control path must remain substantially constant over temperature. 
       SUMMARY 
       [0004]    In accordance with some embodiments of the present disclosure, a method may include generating a first current equal to a bandgap voltage divided by a resistance selected to approximately match a process resistance integral to a receiver. The method may further include generating a second current equal to temperature-dependent current multiplied by a predetermined scaling factor. The method may also include subtracting the second current from the first current to generate a bias current. The method may additionally include providing the bias current to the receiver. 
         [0005]    Technical advantages of the present disclosure may be readily apparent to one skilled in the art from the figures, description and claims included herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    For a more complete understanding of the present disclosure and its features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
           [0007]      FIG. 1  illustrates a block diagram of an example wireless communication system, in accordance with certain embodiments of the present disclosure; 
           [0008]      FIG. 2  illustrates a block diagram of selected components of an example transmitting and/or receiving element, in accordance with certain embodiments of the present disclosure; 
           [0009]      FIG. 3  illustrates a block diagram of selected components of a feedback control path of the wireless communication element depicted in  FIG. 2 , along with a biasing circuit for certain components of the feedback control path, in accordance with certain embodiments of the present disclosure; and 
           [0010]      FIG. 4  illustrates a block diagram of selected components of an example downconverter/amplifier, in accordance with certain embodiments of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  illustrates a block diagram of an example wireless communication system  100 , in accordance with certain embodiments of the present disclosure. For simplicity, only two terminals  110  and two base stations  120  are shown in  FIG. 1 . A terminal  110  may also be referred to as a remote station, a mobile station, an access terminal, user equipment (UE), a wireless communication device, a cellular phone, or some other terminology. A base station  120  may be a fixed station and may also be referred to as an access point, a Node B, or some other terminology. 
         [0012]    A terminal  110  may or may not be capable of receiving signals from satellites  130 . Satellites  130  may belong to a satellite positioning system such as the well-known Global Positioning System (GPS). Each GPS satellite may transmit a GPS signal encoded with information that allows GPS receivers on earth to measure the time of arrival of the GPS signal. Measurements for a sufficient number of GPS satellites may be used to accurately estimate a three-dimensional position of a GPS receiver. A terminal  110  may also be capable of receiving signals from other types of transmitting sources such as a Bluetooth transmitter, a Wireless Fidelity (Wi-Fi) transmitter, a wireless local area network (WLAN) transmitter, an IEEE 802.11 transmitter, and any other suitable transmitter. 
         [0013]    In  FIG. 1 , each terminal  110  is shown as receiving signals from multiple transmitting sources simultaneously, where a transmitting source may be a base station  120  or a satellite  130 . In certain embodiments, a terminal  110  may also be a transmitting source. In general, a terminal  110  may receive signals from zero, one, or multiple transmitting sources at any given moment. 
         [0014]    System  100  may be a Code Division Multiple Access (CDMA) system, a Time Division Multiple Access (TDMA) system, or some other wireless communication system. A CDMA system may implement one or more CDMA standards such as IS-95, IS-2000 (also commonly known as “1x”), IS-856 (also commonly known as “1xEV-DO”), Wideband-CDMA (W-CDMA), and so on. A TDMA system may implement one or more TDMA standards such as Global System for Mobile Communications (GSM). The W-CDMA standard is defined by a consortium known as 3GPP, and the IS-2000 and IS-856 standards are defined by a consortium known as 3GPP2. 
         [0015]      FIG. 2  illustrates a block diagram of selected components of an example transmitting and/or receiving element  200  (e.g., a terminal  110 , a base station  120 , or a satellite  130 ), in accordance with certain embodiments of the present disclosure. Element  200  may include a transmit path  201 , a receive path  221 , and a feedback control path  241 . Depending on the functionality of element  200 , element  200  may be considered a transmitter, a receiver, or a transceiver. 
         [0016]    As depicted in  FIG. 2 , element  200  may include digital circuitry  202 . Digital circuitry  202  may include any system, device, or apparatus configured to process digital signals and information received via receive path  221  and/or feedback control path  241 , and/or configured to process signals and information for transmission via transmit path  201 . Such digital circuitry  202  may include one or more microprocessors, digital signal processors, and/or other suitable devices. As shown in  FIG. 2 , digital circuitry  202  may communicate in-phase (I) channel and quadrature (Q) channel components of a digital signal to transmit path  201 . 
         [0017]    Transmit path  201  may include a digital-to-analog converter (DAC)  204  for each of the I channel and Q channel signals communicated by digital circuitry  202 . Each DAC  204  may be configured to receive its respective I or Q channel component of the digital signal from digital circuitry  202  and convert such digital signal into an analog signal. Such analog signal may then be passed to one or more other components of transmit path  201 , including upconverter  208 . 
         [0018]    Upconverter  208  may be configured to frequency upconvert an analog signal received from DAC  204  to a wireless communication signal at a radio frequency based on an oscillator signal provided by oscillator  210 . Oscillator  210  may be any suitable device, system, or apparatus configured to produce an analog waveform of a particular frequency for modulation or upconversion of an analog signal to a wireless communication signal, or for demodulation or downconversion of a wireless communication signal to an analog signal. In some embodiments, oscillator  210  may be a digitally-controlled crystal oscillator. 
         [0019]    Transmit path  201  may include a variable-gain amplifier (VGA)  214  to amplify an upconverted signal for transmission, and a power amplifier  220  to further amplify the analog upconverted signal for transmission via antenna  218 . The output of power amplifier  220  may be communicated to duplexer  223 . A duplexer  223  may be interfaced between antenna switch  216  and each transmit path  201  and receive path  221 . Accordingly, duplexer  223  may allow bidirectional communication through antenna  218  (e.g., from transmit path  201  to antenna  218 , and from antenna  218  to receive path  221 ). 
         [0020]    Antenna switch  216  may be coupled between duplexer  224  and antenna  218 . Antenna switch  216  may configured to multiplex the output of two or more power amplifiers (e.g., similar to power amplifier  220 ), in which each power amplifier may correspond to a different band or band class. Antenna switch  216  may allow duplexing of signals received by antenna  218  to a plurality of receive paths of different bands or band classes. 
         [0021]    Antenna  218  may receive the amplified signal from antenna switch  216  (e.g., via RF coupler  242 ) and transmit such signal (e.g., to one or more of a terminal  110 , a base station  120 , and/or a satellite  130 ). As shown in  FIG. 2 , antenna  218  may be coupled to each of transmit path  201  and receive path  221 . 
         [0022]    Receive path  221  may include a low-noise amplifier  234  configured to receive a wireless communication signal (e.g., from a terminal  110 , a base station  120 , and/or a satellite  130 ) via antenna  218 , antenna tuner  217 , and duplexer  223 . LNA  234  may be further configured to amplify the received signal. 
         [0023]    Receive path  221  may also include a downconverter  228 . Downconverter  228  may be configured to frequency downconvert a wireless communication signal received via antenna  218  and amplified by LNA  234  by an oscillator signal provided by oscillator  210  (e.g., downconvert to a baseband signal). Receive path  221  may further include a filter  238 , which may be configured to filter a downconverted wireless communication signal in order to pass the signal components within a radio-frequency channel of interest and/or to remove noise and undesired signals that may be generated by the downconversion process. In addition, receive path  221  may include an analog-to-digital converter (ADC)  224  configured to receive an analog signal from filter  238  and convert such analog signal into a digital signal. Such digital signal may then be passed to digital circuitry  202  for processing. 
         [0024]    Feedback control path  241  may in general be configured to monitor one or more parameters of transmit path  201  (e.g, gain, phase shift, etc.), and transmit a digital signal indicative of such parameters to digital circuitry  202  for analysis and/or control of transmit path  201 . For example, based on monitored parameters, digital circuitry may modify I channel and Q channel signals communicated to transmit path  202 , modify gain parameters of components of transmit path  201 , and/or may take other actions. 
         [0025]    As shown in  FIG. 2 , feedback control path  241  may include a radio frequency (RF) coupler  242 . RF coupler  242  may be any system, device or apparatus configured to couple at least a portion of the transmission power in the transmission line coupling antenna switch  216  to antenna  218  to one or more output ports. As known in the art, one of the output ports may be known as a coupled port (e.g., coupled port  246  as shown in  FIG. 2 ) while the other output port may be known as a terminated or isolated port (e.g., terminated port  247  as shown in  FIG. 2 ). In many cases, each of coupled port  246  and terminated port  247  may be terminated with an internal or external resistance of a particular resistance value (e.g., 50 ohms). Due to the physical properties of RF coupler  242 , during operation of element  200 , coupled port  246  may carry an analog signal (e.g., a voltage) indicative of incident power transmitted to antenna  218  while terminated port  247  may carry an analog signal (e.g., a voltage) indicative of power reflected from antenna  218 . 
         [0026]    Feedback control path  241  may include a variable gain amplifier (VGA)  254  to amplify signals communicated from RF coupler  242 , and communicate such amplified signals to downconverter/amplifier  248 . 
         [0027]    Downconverter/amplifier  248  may be configured to frequency downconvert the analog signal received from VGA  254  by an oscillator signal provided by oscillator  210  (e.g., downconvert to a baseband signal) and output an in-phase (I) channel and quadrature (Q) channel components of for the signal. An example embodiment of downconverter/amplifier  248  is shown in  FIG. 4 . In addition, control path  214  may include an analog-to-digital converter (ADC)  244  for each of the I channel and Q channel, each ADC  244  configured to receive the appropriate component of the baseband signal convert such components of the signal into a digital components of the signal. The digital components of the signal output by ADCs  244  may be communicated to digital circuitry  202  for processing. Together, VGA  254 , downconverter  246 , ADCs  244 , and/or other components may make up a coherent receiver coherent to transmit path  201 . 
         [0028]    For purposes of clarity and exposition, biasing circuits and elements of various components of wireless communication element  200  are not depicted in  FIG. 2 . However,  FIG. 3  illustrates a block diagram of certain components of feedback control path  241 , along with a biasing circuit  302  for certain components of feedback control path  241 . For clarity and exposition,  FIG. 3  depicts a signal path within feedback control path  241  for only one channel of a signal, rather than both the in-phase and quadrature channel. 
         [0029]    As shown in  FIG. 3 , analog-to-digital converter  244  may be implemented using a summer  302 , a loop filter  304 , and a feedback DAC  306 . Summer  302  may be any system, device, or apparatus configured to sum an analog signal from the output of downconverter/amplifier  248  to an analog signal from the output of feedback DAC  306 . Loop filter  304  may be any system, device, or apparatus configured to, in connection with summer  302  and feedback DAC  306 , convert an analog signal received from downconverter/amplifier  248  into a digital signal indicative of the received analog signal. Loop filter  304  may be implemented as an integrator, delta-sigma modulator, and/or any other suitable circuit. Feedback DAC  306  may be configured to convert the digital output of loop filter  304  into an analog signal to be subtracted by summer  302  from the analog signal received from downconverter  302 . As shown in  FIG. 3 , biasing circuit  302  may provide a bias current to feedback DAC  306 , thus enabling functionality of feedback DAC  306 . As described in greater detail below, biasing circuit  302  may be configured to generate a bias current to offset variations of other components of feedback control path  241  (e.g., downconverter/amplifier  248 ) due to temperature. 
         [0030]      FIG. 4  illustrates a block diagram of selected components of an example downconverter/amplifier  248 , in accordance with certain embodiments of the present disclosure. As shown in  FIG. 4 , downconverter/amplifier  248  may include transistors  402  and resistors  404  having resistance R arranged to form a resistively-generated amplifier. In some embodiments, downconverter/amplifier  248  may include mixers  406  to downconvert an RF signal to baseband. In embodiments in which a baseband signal is received as an input to downconverter/amplifier  248 , downconverter/amplifier  248  may not include mixers  406 . 
         [0031]    As mentioned previously, the performance and/or characteristics of various components of feedback control path  241  may vary with temperature. For example, a signal gain Gm of downconverter/amplifier  248  may be proportional to the quantity Vbg/R−PTAT*k, where Vbg is a bandgap voltage supplied to provide a bias current to downconverter/amplifier  248 , R is a process-dependent resistance present in downconverter/amplifier  248  (e.g., a resistor  404  shown in  FIG. 4 ), PTAT is a temperature-dependent current, and k is a scalar constant based on physical characteristics of downconverter/amplifier  248 . To offset the temperature dependence of the gain of downconverter/amplifier  248  and/or other components of feedbackcontrol path  241 , bias circuit  302  may be configured to generate a temperature-dependent bias current. 
         [0032]    As depicted in  FIG. 3 , bias circuit  302  may include summers  310  and  312 , switches  311 , op amp  314 , mirrored transistors  316  (e.g., transistors  316   a  and  316   b ), resistor  318 , current proportional to ambient temperature circuits (PTATs)  322 , and temperature-independent current circuits (ZTCs)  324 . 
         [0033]    A PTAT  322  may comprise any system, device, or apparatus configured to generate an electrical current proportional to an ambient temperature present proximate to such PTAT  322 , wherein such electrical current is also a function of a predetermined scaling factor n. The scaling factor n may be set by an adjustable trim (e.g., by adjusting a resistance of a variable resistor or potentiometer) based on characterization of feedback control path  241 , as described in greater detail below. A ZTC  324  may comprise any system, device, or apparatus configured to generate an electrical current independent of an ambient temperature present proximate to such ZTC  324 , wherein such electrical current is also a function of a predetermined scaling factor n. 
         [0034]    Each summer  310  may comprise any system, device, or apparatus configured to subtract a current generated by a ZTC  324  from a current generated by a PTAT  322 , thus outputting an electrical current that is dependent upon temperature and the scaling factor n, wherein such electrical current will be approximately zero at a particular temperature. PTATs  322  and/or ZTCs  324  may be configured such that the particular temperature is a desired temperature (e.g., room temperature of approximately 27 degrees Celsius). Switches  311  and summer  312  may be configured such that the output of summer  312  either sources an electrical current output by a summer  310  or sinks an electrical current output by a summer  310 , resulting in an electrical current that may be represented by the quantity PTAT*n. 
         [0035]    Operational amplifier  314  may comprise any system, device, or apparatus with a differential input and either a single-ended or differential output (a single-ended output is depicted in  FIG. 3 ), which is a multiple of the voltage difference between the input terminals. As shown in  FIG. 3 , the negative input terminal of operational amplifier  314  may be supplied with a bandgap voltage Vbg, while the positive input terminal may be coupled to the output of summer  312 , a resistor  318 , and an active-region terminal (e.g., source, drain, emitter, collector) of a mirrored transistor  316   a . The output terminal may be coupled to gates of each of mirrored transistors  316 . 
         [0036]    Mirrored transistors  316  may include any suitable transistor. Transistors  316  are depicted in the specific embodiment of  FIG. 3  as n-type metal-oxide semiconductor field-effect transistors (MOSFETs). As shown in  FIG. 3 , transistors  316  may be coupled to each other and to a rail voltage (e.g., VDD) at one of their active-region terminals (e.g., source, drain, emitter, collector) and coupled to each other and the output of operational amplifier  314  at their non-active-region terminals (e.g., base, collector). Those of skill in the art may appreciate that, as so configured, mirrored transistors  316  form a current mirror, such that a current sourced by and flowing through the various terminals of transistor  316   b  is approximately equal to the current sourced by and flowing through the various terminals of transistor  316   a.    
         [0037]    Resistor  318  may include any suitable resistive circuit element. In some embodiments, resistor  318  may be selected to have a resistance R based on a process resistance present in downconverter/amplifier  248  and/or other components of feedback control path  241 . As shown in  FIG. 3 , resistor  318  may be coupled between the positive input terminal of operational amplifier  316  and a rail voltage (e.g., VSS). Those of skill in the art may appreciate that, as so configured, the voltage present at the positive input terminal of operational amplifier  314 , and thus the voltage present at node A, will be approximately equal to Vbg. Accordingly, an electrical current flowing through resistor  318  will be approximately equal to Vbg/R. Accordingly, to satisfy Kirchoff&#39;s current law, the current flowing through transistor  316   a  may be approximately equal to Vbg/R−PTAT*n. Transistor  316   b  may mirror the current of transistor  316   a , and such current may be provided as a bias current to ADC  244  (e.g., as a bias current to feedback DAC  306 ). Thus, the bias current provided to feedback DAC  306  and/or other components of ADC  244  may be approximately centered about Vbg/R, and vary linearly with temperature as a function of the scaling factor n. 
         [0038]    As shown in  FIG. 3 , the output current of feedback DAC  306  may be proportional to the bias current, and thus, is a function of temperature, as given in the PTAT*n term of the bias current. As discussed earlier, performance of other components of feedback control path  241  may vary with temperature. For example, a gain Gm of downconverter/amplifier  248  may have temperature dependence and may be proportional to the quantity Vbg/R−PTAT*k, where k is a constant scaling factor based on physical properties of downconverter/amplifier  248 . Accordingly, an output current generated by downconverter/amplifier  248  may also have temperature dependence and may be proportional to the quantity Vbg/R−PTAT*k. Because the output current of feedback DAC  306  is subtracted from downconverter/amplifier  248  at summer  302 , temperature variance of downconverter/amplifier  248  and/or other components of feedback control path  241  may be offset, reduced, or eliminated if a suitable value for scaling factor n is selected. Thus, by characterizing the temperature-based performance of feedback control path  241 , a manufacturer or other individual may select an appropriate value of n, such that feedback control path  241  may operate with little or no temperature dependence. 
         [0039]    Modifications, additions, or omissions may be made to system  100  from the scope of the disclosure. The components of system  100  may be integrated or separated. Moreover, the operations of system  100  may be performed by more, fewer, or other components. As used in this document, “each” refers to each member of a set or each member of a subset of a set. 
         [0040]    Although the present disclosure has been described with several embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.