Patent Publication Number: US-2016245923-A1

Title: Global navigation satellite system superband processing device and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. patent application Ser. No. 13/545,813, filed Jul. 10, 2012; to U.S. patent application Ser. No. 12/635,527, filed Dec. 10, 2009, now U.S. Pat. No. 8,217,833, issued Jul. 10, 2012; and to U.S. Provisional Patent Application No. 61/121,831, filed Dec. 11, 2008, all of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     Disclosed herein is a global navigation satellite system (GNSS) device, and more specifically a GNSS device for processing GNSS satellite signals from multiple GNSS constellations while mitigating interference from out-of band signals. 
     2. State of the Art 
     Global navigation satellite systems (GNSS) include the Global Positioning System (GPS), which was established by the United States government and employs a constellation of 24 or more satellites in well-defined orbits at an altitude of approximately 26,500 km. These satellites continually transmit microwave L-band radio signals in three frequency bands, centered at 1575.42 MHz, 1227.60 MHz and 1176.45 MHz, denoted as L1, L2 and L5 respectively. All GNSS signals include timing patterns relative to the satellite&#39;s onboard precision clock (which is kept synchronized by a ground station) as well as a navigation message giving the precise orbital positions of the satellites. GPS receivers process the radio signals, computing ranges to the GPS satellites, and by triangulating these ranges, the GPS receiver determines its position and its internal clock error. Different levels of accuracies can be achieved depending on the techniques employed. 
     GNSS also includes the satellite constellations corresponding to the Galileo (Europe) system, the GLObal NAvigation Satellite System (GLONASS, Russia), BeiDou (China), the Indian Regional Navigational Satellite System (IRNSS) and QZSS (Japan, proposed). Galileo will transmit signals centered at 1575.42 MHz, denoted L1 or E1, 1176.45 denoted E5a, 1207.14 MHz, denoted E5b, 1191.795 MHz, denoted E5 and 1278.75 MHz, denoted E6. GLONASS transmits groups of frequency division multiplexed signals centered approximately at 1602 MHz and 1246 MHz, denoted GL1 and GL2 respectively. QZSS will transmit signals centered at L1, L2, L5 and E6. 
     A GNSS receiver that receives and processes GNSS satellite signals from multiple constellations requires a wide bandwidth to accept the wide range of frequencies of the multiple types of GNSS satellite signals. GNSS receivers are highly sensitive devices designed to receive very weak signals transmitted by the source GNSS satellites. As the airwaves become more crowded due to the high demand for radio frequency (RF) signal spectra allocations, reception problems arise from signal interference. Continual improvements in the ability of GNSS receiver devices to mitigate interference from spectrally close signals are desirable. 
     Accordingly, what is needed is a GNSS device which efficiently receives and processes a wide range of GNSS satellite signal frequencies, and yet mitigates the effect of unwanted signals on the operation of the GNSS device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a simplified diagram of a GNSS receiver environment; 
         FIG. 2  shows a block diagram of an embodiment of a GNSS device; 
         FIG. 3  shows a block diagram of an embodiment of a GNSS analog signal processing circuit in the form of a down converter circuit; 
         FIG. 4  shows a block diagram of an embodiment of a GNSS device; 
         FIG. 5  shows a block diagram of an embodiment of a GNSS device; 
         FIG. 6  shows a block diagram of an embodiment of a GNSS analog signal conditioning circuit; 
         FIG. 7  shows a block diagram of an embodiment of a signal transmission path within a GNSS analog signal conditioning circuit; 
         FIG. 8  shows a block diagram of an embodiment of a GNSS digital signal conditioning circuit; 
         FIG. 9  shows a block diagram of an embodiment of a GNSS device; 
         FIG. 10  shows a block diagram of an embodiment of a GNSS analog signal conditioning circuit; 
         FIG. 11  illustrates method  500  of processing radio-frequency (RF) signals received by a GNSS device. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     As discussed above, disclosed herein is a global navigation satellite system (GNSS) device capable of efficient processing of multiple GNSS signal frequencies along with interference mitigation via a combination of analog and digital processing. 
     Disclosed are GNSS devices for capturing and processing GNSS satellite signals and other signals of interest. Also disclosed are methods of processing the GNSS satellite signals and other signals of interest. The disclosed GNSS devices are capable of capturing and processing GNSS satellite signals from more than one GNSS constellation simultaneously. The disclosed GNSS devices and methods group GNSS satellite signals from different GNSS constellations, as well as other signals of interest, into sub-bands, also called ‘superbands’, by frequency, for analog filtering and processing, and then further divides the superbands for additional processing in the digital domain. Each superband is a frequency range that can include GNSS satellite signals from one, two, three, or more than three, GNSS constellations. Using multiple parallel processing channels allows multiple signal frequency bands that cover a wide bandwidth to be divided into narrower superbands for processing. This increases the processing abilities within the superbands, and allows out-of-band interference between superbands to be eliminated. Thus, the GNSS satellite signals are divided for processing according to frequency, not according to the originating GNSS satellite constellation. Dividing the signal processing between the analog and digital domains provides increased processing flexibility and capabilities, while minimizing the size and power consumption of the GNSS device hardware. The disclosed GNSS devices are capable of performing precision signal processing on GNSS signals from multiple GNSS constellations, as well as other signals of interest, while mitigating the interference from other spectrally close signals that are not of interest. 
     The disclosed GNSS devices and methods disclose how other signals of interest can be captured and processed along with the GNSS satellite signals. Other signals of interest can be used by the GNSS device to provide GNSS correction services, remote control, remote configuration of GNSS devices, or other desired features and services that are not provided by GNSS satellite signals. These other signals of interest can be much higher power than GNSS satellite signals, and spectrally close to the GNSS satellite signals. Separating the other signals of interest from the GNSS satellite signals can be difficult because the other signals of interest, such as cellular telephone signals, for example, tend to saturate the GNSS processing circuits due to their high power. Thus, the disclosed GNSS devices both mitigate the influence of the high-powered and spectrally close RF signals of interest on the GNSS satellite signals, as well as capture the other RF signals of interest for use by the GNSS device. 
     Global navigation satellite systems (GNSS) are broadly defined to include the Global Positioning System (GPS), which was established by the United States government and employs a constellation of 24 or more satellites in well-defined orbits at an altitude of approximately 26,500 km. These satellites continually transmit microwave L-band radio signals in three frequency bands, centered at 1575.42 MHz, 1227.60 MHz and 1176.45 MHz, denoted as L1, L2 and L5 respectively. All GNSS signals include timing patterns relative to the satellite&#39;s onboard precision clock (which is kept synchronized by a ground station) as well as a navigation message giving the precise orbital positions of the satellites. GPS receivers process the radio signals, computing ranges to the GPS satellites, and by triangulating these ranges, the GPS receiver determines its position and its internal clock error. Different levels of accuracies can be achieved depending on the techniques employed. 
     GNSS also includes the satellite constellations corresponding to the Galileo (Europe) system, the GLObal NAvigation Satellite System (GLONASS, Russia), Beidou (China), the Indian Regional Navigational Satellite System (IRNSS) and QZSS (Japan, proposed). Galileo will transmit signals centered at 1575.42 MHz, denoted L1 or E1, 1176.45 denoted E5a, 1207.14 MHz, denoted E5b, 1191.795 MHz, denoted E5 and 1278.75 MHz, denoted E6. GLONASS transmits groups of frequency division multiplexed signals centered approximately at 1602 MHz and 1246 MHz, denoted GL1 and GL2 respectively. QZSS will transmit signals centered at L1, L2, L5 and E6. Table 1 provides an example of GNSS frequency channel allocations, which could be received and processed with the GNSS device herein disclosed. 
     GNSS receivers are highly sensitive devices designed to receive very weak signals transmitted by the source GNSS satellites. GNSS receivers process the radio frequency signals, computing ranges to the GNSS satellites, and by triangulating these ranges, the GNSS receiver determines its position and its internal clock error. Different levels of accuracies can be achieved depending on the observed signals used and the correction techniques employed. For example, accuracy within about 2 cm can be achieved using real-time kinematic (RTK) methods with single or dual-frequency (L1 and L2) receivers. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 GNSS System Center Frequencies and Bandwidth 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 F center   
                 Bandwidth 
               
               
                   
                 System (signal) 
                 (MHz) 
                 (MHz) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 SBAS 
                 1575.42 
                 24 
               
               
                   
                 GPS (L1CA) 
                 1575.42 
                 24.0 
               
               
                   
                 GPS (L1C) 
                 1575.42 
                 24.0 
               
               
                   
                 GPS (L1P) 
                 1575.42 
                 24.0 
               
               
                   
                 GLONASS (GL1) 
                 1602.0 
                 16 
               
               
                   
                 Galileo (E1) 
                 1575.42 
                 24.0 
               
               
                   
                 GPS (L2P) 
                 1227.6 
                 24.0 
               
               
                   
                 GPS (L2C) 
                 1227.6 
                 24.0 
               
               
                   
                 GPS (L5) 
                 1176.45 
                 24.0 
               
               
                   
                 GLONASS (GL2) 
                 1246.0 
                 16 
               
               
                   
                 Galileo (E5a) 
                 1176.45 
                 24.0 
               
               
                   
                 Galileo (E5b) 
                 1207.14 
                 24.0 
               
               
                   
                 Galileo (E5ab) 
                 1191.795 
                 51.15 
               
               
                   
                   
               
            
           
         
       
     
     RF signal frequency spectra allocations are highly regulated by the Federal Communications Commission (FCC) in the United States and by other agencies worldwide. As the airwaves become more crowded as a consequence of demand for RF signal spectra allocations, reception problems arise from signal interference. For example, the telecommunications industry has experienced significant growth and increasing wireless traffic levels. Wireless telecommunications via RF signals are becoming increasingly popular among telecommunications service subscribers. To accommodate such demand, telecommunications service providers, through their industry associations, commonly seek FCC allocations of more frequency spectra. 
     The interests of the telecommunications industry are sometimes adverse to that of other RF service providers. For example, GNSS service providers, including the U.S. Department of Defense with its Global Positioning System (GPS), are increasingly likely to encounter interference problems associated with nearby or spectrally-adjacent telecommunications bandwidth usage. 
     With the proliferation of GNSS signals at multiple carrier frequencies, as well as the increased presence of nearby interfering frequencies, it is beneficial for a GNSS device to optimize the distribution of signal processing across the analog and digital domains. Capturing and processing the complete GNSS spectrum would require a bandwidth of approximately 500 MHZ, and would result in excessive power consumption, as well as interference from unwanted signals within the wide band. Alternatively, analog filtering techniques could be used to capture each individual GNSS signal and process each signal optimally. This would result in a relatively large GNSS receiver due to the number of analog filters required, and the resulting GNSS receiver would not be a low power solution. 
     The disclosed system and method addresses the RF-digital signal interference issue with RF receivers. Heretofore, there has not been available an interference-mitigating RF system and method with the advantages and features of the disclosed invention. 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Certain terminology will be used in the following description for convenience in reference only and will not be limiting. The words “first”, “second”, etc., are used to indicated different elements that are the same or similar within a group and are not used to indicate priority or relative importance. 
       FIG. 1  shows a block diagram of a GNSS device  104  in an environment that includes both GNSS satellite signals and other RF signals of interest. GNSS device  104  is used for receiving and processing GNSS satellite signals and other RF signals of interest in order to compute the position, and in some situations the attitude, of GNSS device  104 . GNSS device  104  mitigates the effects of interfering RF signals on the accuracy of GNSS computations performed by GNSS device  104 . 
     GNSS device  104  includes at least one antenna, which in this embodiment is an antenna  108 . GNSS device  104  includes GNSS signal processing circuitry  109 . Antenna  108  receives RF signals  105  and conducts RF signals  105  to GNSS signal processing circuitry  109 .  FIG. 2  through  FIG. 10  show details of example embodiments of GNSS devices, including GNSS device  104 , and other GNSS devices that can be used in place of GNSS device  104 .  FIG. 11  illustrates a method  500  of processing RF signals by a GNSS device. Method  500  can be performed by GNSS device  104  or any other GNSS device described herein. 
     Referring back to  FIG. 1 , antenna  108  receives RF signals  105  and conducts RF signals  105  to GNSS signal processing circuitry  109 . RF signals  105  includes all signals received by antenna  108 . RF signals  105  include both wanted and unwanted RF signals. In the embodiment shown in  FIG. 1 , antenna  108  receives a plurality of GNSS satellite signals  184  from a first GNSS constellation  100 , and a plurality of GNSS satellite signals  185  from a second GNSS constellation  101 . In this embodiment, antenna  108  also receives cellular signals  190  from cellular tower  189 , wanted RF signals  192 , and unwanted RF signals  193 . Wanted RF signals  192  and unwanted RF signals  193  can originate from any of various RF signal sources. In some embodiments, wanted RF signals  192  include INMARSAT satellite signals with frequencies in the range of about 1525 MHz to about 1560 MHz. INMARSAT Company is a satellite phone company. In some embodiments, RF signals  192  include GNSS correction service signals with frequencies in the range of about 400-468 MHz. In some embodiments, RF signals  192  include GNSS correction service signals with frequencies in the range of about 900-928 MHz. In some embodiments, RF signals  192  includes other wanted RF signals that GNSS device  104  will use in its processing. RF signals  193  includes any unwanted RF signals that can interfere with the wanted RF signals  184 ,  185 , and  192  received by GNSS device  104 . 
     In some embodiments, it is desired that GNSS device  104  process only GNSS satellite signals, such as pluralities of GNSS satellite signals  100  and  101 . In some embodiments, it is desired that GNSS device  104  process both GNSS satellite signals, such as pluralities of GNSS satellite signals  100  and  101 , and cellular signals such as cellular telephone signals  190 . In some embodiments, it is desired that GNSS device  104  process GNSS satellite signals, such as pluralities of GNSS satellite signals  100  and  101 , cellular signals such as cellular telephone signals  190 , and other RF signals such as RF signals  192 . GNSS device  104  mitigates the interference effects of unwanted signals  193  on the operation and accuracy of GNSS device  104 . The GNSS devices and methods disclosed herein provide hardware and processes for isolating those signals that are wanted from the spectrum of RF signals received, such as GNSS satellite signals  184  and  185 , for example, and RF signals  190  and  192 , and mitigating the interference from unwanted signals, such as unwanted signals  193 , for example, as well as from adjacent sets of desired signals. 
     Antenna  108  of GNSS device  104  as shown in  FIG. 1  receives GNSS satellite signals that originate from two different GNSS constellations. GNSS device  104  receives plurality of GNSS satellite signals  184  from GNSS constellation  100 . In this embodiment GNSS constellation  100  is the GPS constellation of about 24 GNSS satellites, which includes GNSS satellites  181 ,  182 , and  183 , and may include additional satellites transmitting plurality of GNSS satellite signals  184 . In some embodiments, GNSS constellation  100  is one of the other GNSS constellations in service around the world, now or in the future. 
     Antenna  108  of GNSS device  104  also receives plurality of GNSS satellite signals  185  from GNSS constellation  101 . In this embodiment GNSS constellation  101  is one of the GNSS constellations in service around the world, which includes GNSS satellites  186 ,  187 , and  188 , and which transmit a plurality of GNSS satellite signals  185 . In some embodiments, GNSS constellation  101  is the GPS constellation of about 24 satellites. In some embodiments, GNSS constellation  101  is a GNSS constellation put in service in the future. 
     In some embodiments, antenna  108  of GNSS device  104  receives GNSS satellite signals that originate from additional GNSS constellations. In some embodiments, GNSS device  104  receives GNSS satellite signals that originate from more than two GNSS constellations. In some embodiments, antenna  108  of GNSS device  104  receives GNSS satellite signals that originate from one GNSS constellation. 
     Pluralities of GNSS satellite signals  184  and  185  can include any GNSS satellite signals in any frequency range, including but not limited to these: L1 at 1575.42 MHz; L2 at 1227.60 MHz; L5 at 1176.45 MHz; B1 at 1561.01 MHz; B2 at 1207.14 MHz; B3 at 1268.52 MHz; G1 at 1602 MHz; G2 at 1246 MHz; E1 at 1575.42 MHz; E5 at 1191.795 MHz; E5A at 1176.45 MHz; E5B at 1207.14 MHz; and E6 at 1278.75 MHz. 
       FIG. 2  shows a block diagram of a GNSS device  4  that can be used in place of GNSS device  104  of  FIG. 1 . GNSS device  4  includes active antenna components  6 , and analog signal conditioning circuits  2 , which include down converter application specific integrated circuits (ASICs)  2  as shown. GNSS device  4  also includes a correlator ASIC  12 , and a GPS solution processor  14 . Analog signal conditioning circuits  2  execute multi-frequency down conversion of GNSS satellite signals as explained further below. GNSS device  4  can be employed in a wide range of useful applications, including navigation, guidance and machine control in various industries, such as, for example, precision farming, crop dusting, marine navigation, shipping, transportation, mining and manufacturing. 
     GNSS device  4  includes an antenna subsystem  6 , having at least one antenna. In this embodiment, antenna subsystem  6  includes antenna  8  connected to a low noise amplifier (LNA)  10 . The antenna subsystem  6  receives GNSS signals, amplifies them by means of LNA  10 , and provides the amplified GNSS signals to one or more analog signal conditioning circuits  2 . Analog signal conditioning circuits  2 , which in this embodiment are ASICs  2 , receive RF signals from antenna  8  and digitize at least a portion of the GNSS satellite signals from antenna  8 , as explained herein. The output of each ASIC  2  is provided to a digital signal conditioning circuit  12 , which in this embodiment is a correlator ASIC  12 . Correlator ASIC  12  can include a pseudo-range engine, and provides input to a GNSS solution processor  14 . The GNSS solution processor  14  can be connected to other components, such as graphical user interfaces (GUIs), autosteering devices, etc. GNSS solution processor  14  may also be connected to satellite augmentation systems (SASs) of various types, including free services such as the Wide Area Augmentation System (WAAS) and Omnistar (paid subscription service). These may be used to enhance the accuracy of the system  4  by providing GNSS corrections to GNSS device  4 . 
       FIG. 3  shows in block diagram form an embodiment of analog signal conditioning ASIC  2 , configured for operation as a down converter with input from an active antenna  6 . Down conversion as used here designates changing the frequency of a signal to a lower frequency, and a down converter as used herein is a circuit or device that performs the down conversion of a signal. In the embodiment of  FIG. 3 , active antenna  6  has a gain of, for example, +30 dB, and is connected to a band pass diplexer  32  configured to provide GNSS signals for further processing by ASIC  2  via signal paths  18   a,b.  Signal paths  18   a,b  include LNAs  36   a,b,  respectively, each of which is connected to the diplexer  32  and to first stage surface acoustic wave (SAW) band pass filters  19   a,b,  respectively. In the embodiment of  FIG. 3 , SAW band pass filters  19   a,b  are located external to the ASIC  2 . RF amplifiers  40   a,b  (A1) receive signals from the SAW band pass filters  19   a,b  respectively. RF amplifiers  40   a,b  amplify the received signals, and provide the amplified signals to mixers  20   a,b,  respectively. Mixers  20   a,b  are connected to intermediate frequency (IF) amplifiers  42   a,b  (A2), which amplify the signals and provide them to second stage band pass filters  22   a,b,  respectively. Second stage band pass filters  22   a,b  receive signals from the IF amplifiers  42   a,b  and provide signal inputs to variable gain amplifiers (VGAs)  44   a,b,  which are connected to and controlled by automatic gain control (AGC) signals  46   a,b.  The variable gain amplifiers  44   a,b  provide signal inputs to analog-to-digital converters (ADCs)  48   a,b,  which respectively provide digital outputs  72   a,b  from the high and low sides of ASIC  2 , corresponding to high and low signal paths  18   a,b.  Variable gain amplifiers  44   a,b  also provide analog outputs  54   a,b  from high and low sides of ASIC  2  corresponding to high and low signal paths  18   a,b.    
     A common local oscillator/synthesizer (LO/Synth)  50  is coupled to both signal paths  18   a,b.  LO/Synth  50  in this embodiment includes a voltage controlled oscillator (VCO)  52  connected to mixers  20   a,b  and to an external passive loop filter  56 . LO/Synth  50  also includes a Programmable Divide by N Counter (1/N)  58  connected to VCO  52  and a phase/frequency detector  64 . LO/Synth  50  also includes a Programmable Divide by R (1/R)  60  which is connected to phase/frequency detector (P/F Det)  64 . Programmable Divide by R  60  receives signals from an external temperature controlled crystal oscillator (TCXO)  28 . The analog-to-digital clock divider Programmable Divide by Q (1/Q)  68  is connected to mixers  20   a,b  and to analog-to-digital converters (ADCs)  48   a,b.  ADC  48   a,b  perform a second down conversion of the GNSS signals, in response to the input from Programmable Divide by Q  68 . When the input from Programmable Divide by Q  68  undersamples the GNSS signal input to ADC  48   a,b,  multiple digital outputs from ADC  48   a,b  are provided by ADC  48   a,b.  Thus by choosing a digital output from ADC  48   a,b  with a frequency less than the GNSS satellite signal input frequency, an optional second down conversion of the GNSS satellite signal is available at the outputs of ADC  48   a,b.  The value of Q can be chosen to optimize the frequency of the down-converted GNSS satellite signal, and keep the down-converted signal free from interference with other sum and difference frequencies output by ADC  48   a,b.  Thus in analog signal conditioning ASIC  2 , the GNSS satellite signal undergoes two frequency down conversions, a first down conversion from mixer  20   a,b  where the GNSS satellite signal output from mixer  20   a,b  is a frequency lower than the GNSS satellite signal input to mixer  20   a,b,  and a second down conversion from ADC  48   a,b,  where the chosen digitized GNSS satellite signal output from ADC  48   a,b  is at a frequency lower than the GNSS satellite signal input to ADC  48   a,b.    
     A serial peripheral programming interface (SPI)  70  ( FIG. 3 ) is provided for interfacing with external devices whereby the operation of down converter ASIC  2  can be externally controlled by preprogramming such variables as “divide by” values, on/off switching and other components&#39; controls. In the embodiment of  FIG. 3 , band pass filters  19   a,b  and  22   a,b,  are physically mounted exterior to the circuit board that includes the remaining components of down converter ASIC  2 . This enables a relatively “universal” down converter ASIC  2  to be utilized in various GNSS receiver devices, accommodating a wide range of current and future GNSS satellite signals. Such GNSS receiver devices  4  can include multiple band pass filters and other components external to the down converter ASIC  2 , whereby the system can be switched among various filter combinations for multi-frequency operation. Such switching can occur automatically, e.g., via software operation selecting the best available satellite constellations, or manually by an operator based on current satellite availability. Respective high and low side digital outputs  72   a,b  provide digital data that can be processed by digital processing circuitry. In the embodiment of  FIG. 3 , high and low side digital outputs  72   a,b  are output “words,” comprising 4 bit each in the form of digital signals output from the ADCs  48   a,b.  Respective high and low side analog outputs  54   a,b,  provide analog outputs which can be connected to external analog to digital converters that provide higher bit resolution for example, than the on-chip analog-to-digital-converters  48   a,b.  In some embodiments, ADCS  48   a,b  are variable output bit ADCs, where the number of output bits is operator controlled. 
       FIG. 4  shows a simplified block diagram of an embodiment of GNSS device  104  of  FIG. 1  for capturing and processing GNSS satellite signals and other signals of interest. GNSS device  104  includes at least one antenna, which in this embodiment is an antenna  108 . In some embodiments, GNSS device  104  includes more than one antenna. Antenna  108  captures RF signals  105  and conducts RF signals  105  to a signal splitting circuit  132 . In some embodiments, signal splitting circuit  132  is a low-noise amplifier (LNA) circuit. GNSS device  104  also includes an analog signal conditioning circuit  102 , a digital signal conditioning circuit  112 , and a GNSS solution processor  114 . In some embodiments, GNSS device  104  includes an other signal of interest processor  111 , indicated as optional by showing other signal of interest processor  111  in dotted lines. 
     Antenna  108  receives RF signals  105 , which in this embodiment includes pluralities of GNSS satellite signals  184  and  185 , RF signals  190 , which in this embodiment are cellular telephone signals  190 , and RF signals  192 . RF signals  192  are other types and frequencies of RF signals of interest. RF signals  192  can be any kind, type, or frequency of signals of interest to GNSS device  104 . Antenna  108  also receives unwanted RF signals  193 . GNSS device  104  processes RF signals  105 , while mitigating the effects of unwanted signals  193  on the operation of GNSS device  104  as explained below. 
     Signal splitting circuit  132  divides RF signals  105  into two or more superbands of signal frequencies, often using bandpass filters, as explained for signal splitting circuits  232  and  432  below. Signal splitting circuit  123  divides RF signals  105  into superbands of RF signals according to which frequency bands are desired to be collected and processed by GNSS device  104 . In the embodiment shown in  FIG. 4 , signal splitting circuit  132  divides RF signals  105  into three or more superbands of signals, but this is not meant to be limiting. In some embodiments, signal splitting circuit  132  divides RF signals  105  into two bands of signals. In the embodiment shown in  FIG. 4 , signal splitting circuit  132  receives RF signals  105  from antenna  108 , and outputs RF signals  115  in a first frequency range, RF signals  116  in a second frequency range, and RF signals  117  in a third frequency range in response. 
     Analog signal conditioning circuit  102  is electrically coupled to signal splitting circuit  132 , and receives RF signals  115 ,  116 , and  117  from signal splitting circuit  132 . RF signals  115 ,  116 , and  117  can be GNSS satellite signals or other RF signals of interest. Analog signal conditioning circuit  102  performs analog processing on RF signals  115 ,  116 , and  117 . This analog processing can include amplification, filtering, frequency conversion, sampling, and other signal processing. Analog signal conditioning circuit  102  can be replaced with ASIC  2  of  FIG. 2  and  FIG. 3 , analog signal conditioning circuit  202  of  FIG. 5  through  FIG. 7 , or analog signal conditioning circuit  402  of  FIG. 9  and  FIG. 10 . Analog signal conditioning circuit  102  digitizes RF signals  115 ,  116 , and  117 . Digitized RF signals  115 ,  116 , and  117  are labeled RF signals  172 ,  173 , and  174  in this embodiment. Analog signal conditioning circuit  102  digitizes RF signals  115 ,  116 , and  117  and conducts digitized RF signals  172 ,  173 , and  174  to digital signal conditioning circuit  112  in response. In some embodiments, analog signal conditioning circuit  104  digitizes only a portion of RF signals  115 ,  116 , and  117  (see, for example, the discussion of GNSS device  204  of  FIG. 5 ). Analog signal conditioning circuit  102  can include many types of analog signal filtering or processing elements, and can perform many different types of analog filtering and processing operations on RF signals  115 ,  116 , and  117 . 
     Digital signal conditioning circuit  112  is electrically coupled to analog signal conditioning circuit  102 , and receives RF signals  172 ,  173 , and  174  from analog signal conditioning circuit  102 . Digital signal conditioning circuit  112  digitally processes RF signals  172 ,  173 , and  174 , and outputs digitally processed RF signals  123 ,  124 , and  125  in response. In some embodiments, digital signal conditioning circuit  112  conducts RF signals  172 ,  173 ,  174  through one or more correlator circuits, and provides correlator output signals  123 ,  124 , and  125  to GNSS solution processor  114 . In some embodiments, digital signal conditioning circuit  112  is replaced with digital signal conditioning circuit  212  of  FIG. 5  and  FIG. 8 . Digital signal conditioning circuit  112  can include any type of digital signal filtering or processing elements, and can perform many different types of digital filtering and processing operations on RF signals  172 ,  173 , and  174 . 
     Analog signal conditioning circuit  102  and digital signal conditioning circuit  112  perform signal filtering, amplification, frequency shifting, digitization, and channelization in order to capture and clean the GNSS signals of interest and/or other signals of interest, and deliver them to GNSS solution processor  114 . Analog signal conditioning circuit  102  and digital signal conditioning circuit  112  divide the signal filtering and processing of RF signals  115 ,  116 , and  117  among the analog domain and the digital domain in order to minimize power consumption and physical size of GNSS device  104 , and to maximize the noise filtering capabilities of GNSS device  104 . 
     GNSS solution processor  114  is electrically coupled to digital signal conditioning circuit  112  and receives signals  123 ,  124 , and  125  from digital signal conditioning circuit  112 . GNSS solution processor  114  performs GNSS computations on signals  123 ,  124 , and  125  to compute GNSS location, GNSS attitude, and other desired GNSS outputs. In some embodiments, GNSS solution processor  114  is electrically coupled to, and receives signals from, other signal of interest processor  111 . Other signals of interest can provide correction data, controls, or other types of information, command, and controls to GNSS solution processor  114 . In some embodiments, for example, but not by way of limitation, other signal of interest processor  111  is a cellular telephone modem. In some embodiments, other signal of interest processor  111  receives cellular telephone signals from antenna  108  and provides data and/or signals from the cellular telephone signals to GNSS solution processor  114 . Other signal of interest processor  111  can receive and process many different types of signals for use by GNSS solution processor  114 . 
     It is to be understood that GNSS device  104  can include many other types of circuitry for processing, filtering, and performing signal processing operations on RF signals  115 ,  116 , and  117 . 
       FIG. 5  shows a simplified block diagram of an embodiment of a GNSS device  204 . GNSS device  204  captures and processes GNSS satellite signals from one or more GNSS satellite constellations, as well as other RF signals of interest, as shown with GNSS device  104  in  FIG. 1 . In this embodiment, GNSS device  204  is used in place of GNSS device  104  in  FIG. 1 . 
     GNSS device  204  receives RF signals  205  with at least one antenna, which in the embodiment shown in  FIG. 5  is antenna  208 . RF signals  205  can include any or all of the RF signals shown in  FIG. 1 , as well as other RF signals of any type and frequency. For example, GNSS device  204  in this embodiment receives plurality of GNSS satellite signals  184  from GNSS constellation  100 , and plurality of GNSS satellite signals  185  from GNSS constellation  101 , as shown in  FIG. 1 . In some embodiments, GNSS device  204  receives pluralities of GNSS satellite signals from more than two GNSS constellations. GNSS device  204  also receives cellular telephone signals  190 , wanted RF signals  192  and unwanted RF signals  193 , as shown for GNSS device  104  in  FIG. 1 . 
     GNSS device  204  includes a signal splitting circuit  232  and a GNSS receiver  209 . GNSS receiver  209  is electrically coupled to signal splitting circuit  232 , and receives RF signals  215  and  216  from antenna  205  through signal splitting circuit  232 . GNSS receiver  209  includes an analog signal conditioning circuit  202 , a digital signal conditioning circuit  212 , and a GNSS solution processor  214 . Analog signal conditioning circuit  202  and digital signal conditioning circuit  212  perform signal filtering, frequency shifting, digitization, and channelization in order to capture and clean the GNSS signals of interest and/or other RF signals of interest, and deliver them to GNSS solution processor  214 . GNSS solution processor  214  performs GNSS computations such as location determination and attitude determination, as well as other GNSS computations. 
     Antenna  208  captures RF signals  205  and conducts RF signals  205  to signal splitting circuit  232 . In some embodiments, signal splitting circuit  232  is a LNA circuit. Signal splitting circuit  232  includes two bandpass filters, a bandpass filter  229  and a bandpass filter  230 . However, in some embodiments, signal splitting circuit  232  includes more than two bandpass filters. Each bandpass filter  229  and  230  of signal splitting circuit  232  passes a band of RF signals, and blocks signals outside its passband. Thus, signals outside the passbands of bandpass filters  229  and  230  are blocked from reaching GNSS receiver  209 . Signal splitting circuit  232  includes a plurality of bandpass filters, one bandpass filter to capture each frequency band of interest, either a GNSS satellite signal frequency band, or other RF signal of interest frequency band. GNSS device includes enough bandpass filters in signal splitting circuit  232  to subdivide the frequencies of interest and the GNSS satellite signals received by antenna  208  into frequency bands, so that all signals of interest and GNSS satellite signals are passed through a bandpass filter, and a majority of unwanted signals  193 , signals not of interest, are blocked from passing through signal splitting circuit  232 . 
     Signal splitting circuit  232  receives RF signals  205  from antenna  208 , and outputs RF signals  215  and  216  in response. For example, bandpass filter  229  receives RF signals  205  from antenna  208 , passes RF signals  215  in a first frequency range, and rejects signals of other frequencies. RF signals  215  in the first frequency range are passed by bandpass filter  229  and conducted to analog signal conditioning circuit  202  of GNSS receiver  209 . In this embodiment, RF signals  215  are GNSS satellite signals  215  in the first frequency range, but this is not meant to be limiting. RF signals  215  can be cellular telephone signals, INMARSAT signals, GNSS correction service signals, or other RF signals of interest. In the embodiment of GNSS device shown in  FIG. 5 , the first frequency range is from about 1553 megahertz (MHz) to about 1609 MHz, but this is not meant to be limiting. In some embodiments, the first frequency range is from about 1217 MHz to about 1289 MHz. In some embodiments, the first frequency range is from about 1165 MHz to about 1217 MHz. In some embodiments, the first frequency range is from about 1525 MHz to about 1560 MHz. In some embodiments, the first frequency range is from about 400 MHz to about 468 MHz. In some embodiments, the first frequency range is from about 900 MHz to about 928 MHz. In some embodiments, the first frequency range is a different frequency range. 
     Bandpass filter  230  receives RF signals  205  from antenna  208 , passes RF signals  216  in a second frequency range, and rejects signals of other frequencies. RF signals  216  in the second frequency range are passed by bandpass filter  230  and conducted to analog signal conditioning circuit  202  of GNSS receiver  209 . RF signals  216  can be GNSS satellite signals, cellular telephone signals, INMARSAT signals, GNSS correction service signals, or other RF signals of interest. RF signals  216  can be any of the RF signal frequency ranges discussed above for RF signals  215 , or other signal frequency ranges. 
     Analog signal conditioning circuit  202  receives RF signals  215  and  216  from signal splitting circuit  232 , and outputs digitized RF signals  272 , digitized RF signals  273  and/or analog RF signals  254  in response, as explained herein. 
     In this embodiment, RF signals  215  are GNSS satellite signals, and RF signals  216  are either GNSS satellite signals or other RF signals such as cellular telephone signals, GNSS correction service signals, satellite telephone signals, or other types of RF signals. In some embodiments, both RF signals  215  and RF signals  216  are GNSS satellite signals. In some embodiments, both RF signals  215  and RF signals  216  are other RF signals. Analog signal conditioning circuit  202  receives and processes RF signals  215  and  216 . The processing that analog signal conditioning circuit  202  performs on RF signals  215  and  216  includes digitizing at least a portion of RF signals  215  and  216 , as explained further below. Digitized GNSS satellite signals  215  are labeled  272  in  FIG. 5 , and are conducted to digital signal conditioning circuit  212  as shown. Digitized RF signals  216  are labeled  273  in  FIG. 5 , and are conducted to digital signal conditioning circuit  212 . In some applications, at least a portion of RF signals  216  remain analog signals. The portion of RF signals  216  that remain analog are labelled as signals  254  in  FIG. 5 , and are conducted to GNSS solution processor  214 . 
     Referring concurrently to  FIG. 5  and  FIG. 6 ,  FIG. 6  shows one example embodiment of analog signal conditioning circuit  202  of  FIG. 5 . Analog signal conditioning circuit  202  includes two signal filtering/processing channels, also called signal transmission paths, but this is not meant to be limiting. In some embodiments, analog signal conditioning circuit  202  includes more than two signal transmission paths. In this embodiment analog signal conditioning circuit  202  includes a signal transmission path  226  and a signal transmission path  227 . Analog signal conditioning circuit  202  is electrically coupled to signal splitting circuit  232 , and receives GNSS satellite signals  215  and RF signals  216  from signal splitting circuit  232 . Analog signal conditioning circuit  202  digitizes at least a portion of signals  215  and  216 , but not necessarily all of signals  215  and  216 . GNSS satellite signals  215  are digitized by an ADC circuit  248  before they are conducted to digital signal conditioning circuit  212 . In this embodiment, analog signal conditioning circuit  202  includes a switch  241 , which delivers RF signals  216  to either an analog-to-digital converter (ADC) circuit  249 , or to a frequency mixer  279  and an amplifier  247 , as shown in  FIG. 6 . When RF signals  216  are conducted through frequency mixer  279  instead of ADC circuit  249 , RF signals  216  are not digitized, but are instead conducted to GNSS solution processor  214  as analog signals  254  as shown in  FIG. 5  and  FIG. 6 . 
     Analog signal conditioning circuit  202  receives GNSS satellite signals  215  at an input node  295 . Signal transmission path  226  of analog signal conditioning circuit  202  conducts GNSS satellite signals  215  from input node  295  to output node  297  through the electrical components of signal transmission path  226 , which includes ADC circuit  248 . Digitized GNSS satellite signals  215  are output from ADC circuit  248 , and are labeled  272  in  FIG. 5  and  FIG. 6 . 
     Signal transmission path  226  includes variable gain amplifiers  236  and  244 , analog bandpass filters  219  and  222 , a frequency mixer  220 , and analog-to-digital converter circuit  248 . Variable gain amplifier (VGA)  236  is electrically coupled to input node  295 , and receives GNSS satellite signals  215  in the first frequency range from antenna  208  and signal splitting circuit  232 , through first input node  295 , and outputs amplified GNSS satellite signals  215  in the first frequency range in response. Bandpass filter  219  is electrically coupled to input node  295  through variable gain amplifier  236 , and receives GNSS satellite signals  215  from variable gain amplifier  236 . Bandpass filter  219  filters amplified GNSS satellite signals  215  in the first frequency range, passing GNSS satellite signals  215  in the first frequency range, and blocking other frequencies. In some embodiments, filter  219  is a SAW bandpass filter. In some embodiments, filter  219  is mounted remote from the circuit board that includes most of the circuitry of analog signal conditioning circuit  202 . This facilitates replacing filter  219  for the purpose of changing the pass band characteristics of filter  219 , for example. 
     Frequency mixer  220  is electrically coupled to bandpass filter  219  and receives filtered and amplified GNSS satellite signals  215  in the first frequency from bandpass filter  219 , and outputs analog GNSS satellite signals  217  in a third frequency range in response. Frequency mixer  220  shifts the frequency of filtered GNSS satellite signals  215 . GNSS satellite signals  215  that are frequency-shifted are labeled GNSS satellite signals  217  in  FIG. 6 . In this embodiment, frequency mixer  220  downconverts the frequency of GNSS satellite signals  215 , in other words, frequency mixer shifts the frequency of GNSS satellite signals  215  to a lower frequency. The third frequency range is a frequency range lower than the first frequency range, and GNSS satellite signals  217  have a lower frequency than GNSS satellite signals  215 . 
     Bandpass filter  222  is electrically coupled to frequency mixer  220  and receives GNSS satellite signals  217  in the third frequency range from frequency mixer  220 . Bandpass filter  222  performs further analog filtering on GNSS satellite signals  217 , passing frequency-shifted GNSS satellite signals  217  in the third frequency range, and blocking signals of other frequencies. In some embodiments, filter  222  is a SAW bandpass filter. In some embodiments, filter  222  is mounted remote from the circuit board that includes most of the circuitry of analog signal conditioning circuit  202 , as with bandpass filter  219 . This facilitates replacing filter  222  for the purpose of changing the pass band characteristics of filter  222 , for example. 
     Variable gain amplifier (VGA)  244  is electrically coupled to bandpass filter  222 , and receives GNSS satellite signals  217  from bandpass filter  222 . ADC  248  is electrically coupled to VGA  244  and receives GNSS satellite signals  217  from VGA  244 . ADC circuit  248  digitizes GNSS satellite signals  217 , and frequency-shifts GNSS satellite signal  217 , as described earlier with regard to ADC  48   a,b  of  FIG. 3 . ADC circuit  248  receives analog GNSS satellite signals  217  in the third frequency range, and outputs digital GNSS satellite signals  272  in a fourth frequency range in response. In this embodiment ADC downconverts GNSS satellite signals  217  such that the fourth frequency range is a lower frequency range than the third frequency range. Thus, digital GNSS satellite signals  272  of the fourth frequency range have been down-converted twice. Digitized and twice frequency-shifted (once by mixer  220  and once by ADC  248 ) GNSS satellite signals  215 , labeled GNSS satellite signals  272 , exit analog signal conditioning circuit  202  at output node  297 . GNSS satellite signals  272  are conducted from output node  297  to digital signal conditioning circuit  212 . 
     Analog signal conditioning circuit  202  conducts RF signals  216  through signal transmission path  227 . Signal transmission path  227  includes switch  241 , which conducts RF signals  216  from an input node  296  to either an output node  298  or an output node  299 , depending on the state, or position, of switch  241 . Switch  241  is used to bypass ADC circuit  249  when it is desired that RF signals  216  remain as analog signals. It may be desired to have RF signals  216  remain in analog form when RF signals  216  are not GNSS satellite signals, for example, but this is just one of many reasons why it may be desired that RF signals  216  remain in analog form. 
     Signal input node  296  is electrically coupled to signal splitting circuit  232 , and receives RF signals  216  from antenna  208  through signal splitting circuit  232 . Signal output node  298  is electrically coupled to signal input node  296  through switch  241 . Signal output node  299  is also electrically coupled to signal input node  296  through switch  241 . Signal transmission path  227  conducts RF signals  216  from signal input node  296  through ADC circuit  249  to signal output node  298  when switch  241  is in a first position. Signal output node  298  is electrically coupled to digital signal conditioning circuit  212 . Digitized RF signals  216 , labeled  273  in the figures, are conducted from signal output node  298  to digital signal conditioning circuit  212  as shown in  FIG. 6 . 
     Signal transmission path  227 , alternatively, conducts RF signals  216  from signal input node  296  to signal output node  299  when switch  241  is in a second position. Signal transmission path  227  conducts RF signals  216  from signal input node  296  to signal output node  299  through a frequency mixer  279  when switch  241  is in the second position. Signal output node  299  is electrically coupled to GNSS solution processor  214 . Frequency-shifted analog RF signals  216 , labeled signals  254  in the figures, are conducted from signal output node  299  to GNSS solution processor  214  as shown in  FIG. 6 . Switch  241  is controlled by the user, or by computer or electronic control according to decisions programmed by the user of GNSS device  204 . 
     Signal transmission path  227  includes variable gain amplifiers  237 ,  245 , and  247 , analog bandpass filters  221  and  294 , frequency mixers  280  and  279 , switch  241 , and analog-to-digital converter circuit  249 . Variable gain amplifier (VGA)  237  is electrically coupled to input node  296 , and receives analog RF signals  216  in the second frequency range from signal splitting circuit  232  through signal input node  296 . Bandpass filter  221  is electrically coupled to input node  296  through variable gain amplifier  237 , and receives RF signals  216  from signal splitting circuit  232  through signal input node  296  and variable gain amplifier  237 . Bandpass filter  221  further filters RF signals  216 , passing RF signals  216  in the second frequency range and blocking other frequencies. Frequency mixer  280  is electrically coupled to bandpass filter  221  and receives RF signals  216  from bandpass filter  221 . Frequency mixer  280  shifts the frequency of RF signals  216 . In this embodiment, frequency mixer  280  downconverts the frequency of RF signals  216  from the second frequency range to a fifth frequency range. 
     Bandpass filter  294  is electrically coupled to frequency shifter  280  and receives frequency-shifted RF signals  216  from frequency shifter  280 . Bandpass filter  294  performs further analog filtering on RF signals  216 , passing frequency-shifted RF signals  216  and blocking other signals. In some embodiments, filters  221  and/or  294  are SAW bandpass filters. In some embodiments, filters  221  and/or  294  are mounted remote from the circuit board that includes most of the circuitry of analog signal conditioning circuit  202 , similar to filters  219  and  222 . This facilitates replacing filters  221  and/or  294  for the purpose of changing the pass band characteristics of filters  221  and/or  294 , for example. 
     Switch  241  controls whether frequency-shifted RF signals  216  are conducted to signal output node  298  through VGA  245  and ADC circuit  249 , or to signal output node  299  through frequency mixer  279  and VGA  247 . When switch  241  is in a first position, switch  241  electrically couples bandpass filter  294  and VGA  245 , and electrically isolates frequency mixer  279  from bandpass filter  294 . When switch  241  is in the first position, frequency-shifted RF signals  216  are conducted from bandpass filter  294  through switch  241 , through VGA  245 , through ADC circuit  249 , to signal output node  298 . In this embodiment ADC  249  performs a further frequency downconversion, but this is not meant to be limiting. The digitized and twice frequency-shifted RF signals  216  are labeled RF signals  273  in  FIG. 5  and  FIG. 6 , and are conducted from signal output node  298  to digital signal conditioning circuit  212 . 
     When switch  241  is in a second position, switch  596  electrically couples bandpass filter  294  and frequency mixer  279 , and electrically isolates VGA  245  from bandpass filter  294 . When switch  241  is in the second position, frequency-shifted RF signals  216  are conducted from bandpass filter  294  through switch  241 , through frequency mixer  279  and VGA  247  to signal output node  299 . Frequency mixer  279  shifts the frequency of analog RF signals  216  a second time. The twice frequency-shifted analog RF signals  216  are labeled RF signals  254  in  FIG. 5  and  FIG. 6 , and are conducted from signal output node  299  to GNSS solution processor  214 . Switch  241 , frequency mixer  279 , and VGA  247  are used, for example but not by way of limitation, when RF signals  216  are not GNSS signals, but instead are remote control, correction, or other informational signals such as INMARSAT signals, cellular or satellite cellular telephone signals, or correction service signals. In these situations, it is not desired to digitize RF signals  216 , but instead to filter and frequency shift RF signals  216  and deliver them to GNSS solution processor  214  as analog RF signals  254 . 
     Thus switch  241  is used in signal transmission path  227  to direct RF signals  216  through different processing paths based on the type of processing desired for RF signals  216 . When it is desired to digitize RF signals  216 , switch  241  can be put in the first position, where signal transmission path  227  conducts RF signals  216  through a signal filtering and processing channel similar to that contained in signal transmission path  226 , with RF signals  216  being digitized, downconverted in frequency by ADC  249 , and conducted to digital signal conditioning circuit  212 . When it is desired to not digitize RF signals  216 , switch  241  can be put in the second position, where signal  216  are not digitized, but instead shifted in frequency by mixer  279  and conducted to GNSS solution processor  214  as analog RF signals  254 . 
     RF signal transmission paths  226  and  227  can include many other elements. In some embodiments, signal transmission path  226  includes an anti-aliasing filter between AGC  244  and ADC circuit  248 . An anti-aliasing filter removes frequencies that can cause interference modulations in the desired signal. In some embodiments, signal transmission path  227  includes an anti-aliasing filter between AGC  245  and ADC circuit  249 . 
     Analog signal conditioning circuit  202  also includes amplifier  213 ,  261 , and  262 , oscillators  234  and  235 , and ADC clock  260 . Oscillators  234  and  235  receive a reference frequency input signal  233  through amplifier  213 . Oscillator  234  outputs a frequency signal LO 1  to frequency mixer  220 . Oscillator  235  outputs a frequency signal LO 2  to frequency mixer  280 . ADC clock  260  receives ADC clock input signal  263  through VGA  261 . ADC clock  260  provides ADC clock output signal  264  through VGA  262 , as well as clock frequency signal F 1  to ADC  248 , clock frequency signal F 2  to mixer  279 , and clock frequency signal F 3  to ADC  249 . The schematic elements, and interconnects shown for analog signal conditioning circuit  202  are exemplary only, and other interconnects and elements are possible. 
     It is desired that the total gain through signal transmission paths  226  and  227  is variable over a wide range. In some embodiments, VGA  244  is implemented as two VGAs in series to increase the gain range and gain level flexibility of signal transmission path  226 . In some embodiments, VGA  245  is implemented as two VGAs in series to increase the gain range and gain level flexibility of signal transmission path  227 . In some embodiments, VGA  247  is implemented as two VGAs in series to increase the gain range and gain level flexibility of signal transmission path  227 . 
       FIG. 7  shows a simplified schematic drawing of a signal transmission path  326 . Signal transmission path  326  can be used in place of signal transmission path  226  of  FIG. 6 , for example, but this is not mean to be limiting. Signal transmission path  326  can be used in many different places in GNSS device  204  and analog signal conditioning circuit  202 . 
     In the embodiment shown in  FIG. 7 , signal transmission path  326  is used in analog signal conditioning circuit  202  of  FIG. 5  and  FIG. 6 , in place of signal transmission path  226  of  FIG. 6 . Signal transmission path  326  of analog signal conditioning circuit  202  conducts GNSS satellite signals  215  from input node  295  to output node  297  through the electrical components of signal transmission path  326 . Digitized GNSS satellite signals  215  are output from ADC circuit  348 , and are labeled  272  in  FIG. 5 ,  FIG. 6 , and  FIG. 7 . Signal transmission path  326  is similar to signal transmission path  226  and includes some of the same components. 
     Signal transmission path  326  includes variable gain amplifiers  336  and  344 , analog bandpass filters  219  and  222 , frequency mixer  220 , and analog-to-digital converter circuit  348 . Signal transmission path  326  also includes interference detector circuit  338  and bias control circuit  339 . Variable gain amplifier (VGA)  336  is electrically coupled to input node  295 , and receives GNSS satellite signals  215  in the first frequency range from antenna  208  and signal splitting circuit  232 , through first input node  295 , and outputs amplified GNSS satellite signals  337  in the first frequency range. GNSS satellite signals  337  are amplified GNSS satellite signals  215 . Bandpass filter  219  is electrically coupled to input node  295  through variable gain amplifier  336 , and receives GNSS satellite signals  337  from variable gain amplifier  336 . Bandpass filter  219  filters amplified GNSS satellite signals  337  in the first frequency range, passing GNSS satellite signals  337  in the first frequency range, and blocking other frequencies. Frequency mixer  220  is electrically coupled to bandpass filter  219  and receives filtered GNSS satellite signals  337  in the first frequency from bandpass filter  219 , and outputs analog GNSS satellite signals  347  in the third frequency range in response. Frequency mixer  220  shifts the frequency of filtered GNSS satellite signals  337  from a first frequency in the first frequency range to a second frequency in the third frequency range, in this embodiment. GNSS satellite signals  337  that are frequency-shifted are labeled GNSS satellite signals  347  in  FIG. 7 . In this embodiment, frequency mixer  220  downconverts the frequency of GNSS satellite signals  337 . In other words, the second frequency is less than the first frequency, the third frequency range is a frequency range lower than the first frequency range, and GNSS satellite signals  347  have a lower frequency than GNSS satellite signals  337 . 
     Bandpass filter  222  is electrically coupled to frequency shifter  220  and receives GNSS satellite signals  347  in the third frequency range from frequency shifter  220 . Bandpass filter  222  performs further analog filtering on GNSS satellite signals  347 , passing frequency-shifted GNSS satellite signals  347  in the third frequency range, and blocking signals of other frequencies. Variable gain amplifier (VGA)  344  is electrically coupled to bandpass filter  222 , and receives GNSS satellite signals  347  from bandpass filter  222 . ADC  348  is electrically coupled to VGA  344  and receives GNSS satellite signals  337  from VGA  344 . ADC circuit  348  digitizes GNSS satellite signals  347  and frequency-shifts GNSS satellite signal  347 , as described earlier with regard to ADC  48   a,b  of  FIG. 3 . ADC circuit  348  receives analog GNSS satellite signals  347  in the third frequency range, and outputs digital GNSS satellite signals  272  in the fourth frequency range in response. In this embodiment the fourth frequency range is lower than the third frequency range. Digitized and twice frequency-shifted (once by mixer  220  and once by ADC  348 ) GNSS satellite signals  215 , labeled GNSS satellite signals  272 , exit analog signal conditioning circuit  202  at output node  297 . GNSS satellite signals  272  are conducted from output node  297  to digital signal conditioning circuit  212 . 
     Signal transmission path  326  includes interference detector circuit  338 . Interference detector circuit  338  compares the power level of received signals  215  against the background noise of the signals as they enter signal transmission path  326 . Interference detector circuit  338  uses the detected power level of the background noise to determine when there are interfering signals present. In some embodiments, interfering signals are determined to be present when the power level of the background noise is higher than a predetermined threshold power level. In some embodiments, interfering signals are detected using other methods. When interfering signals are detected, bias control circuit  339  adjusts the bias current of amplifiers  336  and  344 , and the number of digitization bits of ADC circuit  348 , to counteract the effects of the interfering signals. In this embodiment, ADC  348  is a variable bit ADC. In a signal environment free from interfering signals, GNSS device  204  yields acceptable performance with a two-bit digital output from ADC  348 . However, when GNSS device  204  is in an interfering environment, interfering signals and the resulting background noise have a high power level, and this high power level of interfering signals will force amplifiers  336  and  344  into a lower gain state. When this occurs, increasing the number of bits of the ADC output will act to keep GNSS satellite signals  347  from being pushed beneath the quantization noise floor of ADC  348 . In addition, increasing the bias current of AGCs  336  and  344  ensures that the one decibel compression point of GNSS device  204  is increased in response to the interfering signals. Thus, interference detector circuit  338  and bias control circuit  339  provide circuit corrections that counteract the effect of the interfering signals. When the power level of the interfering signals detected by interference detector circuit  338  is above a predetermined threshold power level, interference detector circuit  338  causes bias control circuit  339  to increase a bias current of amplifier  336 , or amplifier  344 , or both amplifier  336  and  344 , in response. When the power level of the interfering signals detected by interference detector circuit  338  is above the predetermined threshold power level, interference detector circuit  338  causes bias control circuit  339  to increase the number of digitization bits of ADC  348  in response. Thus signal transmission path  326  includes interference detector circuit  338  and bias control circuit  339 , which mitigate the effects of interfering signals on the performance of ADC  348 , analog signal conditioning circuit  202 , and GNSS device  204 . 
     Referring concurrently to  FIG. 5  and  FIG. 8 ,  FIG. 8  shows a block diagram of a portion of an embodiment of digital signal conditioning circuit  212  of  FIG. 5  and  FIG. 8 . Digital signal conditioning circuit  212  is electrically coupled to analog signal conditioning circuit  202 , and receives digitized GNSS satellite signals  272  and  273  from analog signal conditioning circuit  202 . Digital signal conditioning circuit  212  digitally processes GNSS satellite signals  272  and  273 , and outputs digitally processed signals  223  and  224  in response. 
     Digital signal conditioning circuit  212  includes a digital channelizer. A portion  362  of the digital channelizer is shown in  FIG. 8 . A digital channelizer as used herein is an electrical circuit that divides an input digital signal into a plurality of subsets of the input digital signal, where each subset is conducted through its own chain, or channel, of signal processing/filtering circuitry. In some digital channelizers, the input signal is divided multiple times into subsets. 
     In the illustrated embodiment, digital channelizer portion  362  is the portion of the digital channelizer of digital signal conditioning circuit  212  that channelizes GNSS satellite signal  272 . “Channelizes” as used herein means to divide a signal into multiple subsets and conduct each subset through a parallel signal processing channel, in this case parallel digital signal processing channels. Only portion  362  is shown in  FIG. 8  for clarity, but it is to be understood that digital signal conditioning circuit  212  includes a further portion of the digital channelizer that channelizes and processes GNSS satellite signals  273 , and can contain other digital channelizer portions in some embodiments. Portion  362  includes digital signal processing channels  374  and  375  as shown in  FIG. 8 . Digital channelizer portion  362  channelizes and processes GNSS satellite signals  272 . Digital channelizer portion  362  receives GNSS satellite signals  272  and outputs signals  223  in response, where signals  223  is the output of plurality of correlator circuits  390  and  391 . Digital channelizer portion  362  receives GNSS satellite signals  272  and divides GNSS satellite signals  272  into subset  376  of GNSS satellite signals  272 , and subset  377  of GNSS satellite signals  272 . Digital signal processing channel  374  receives subset  376  of GNSS satellite signals  272 . Channel  375  receives subset  377  of GNSS satellite signals  272 . 
     Digital signal processing channel  374  includes a digital mixer circuit  378 , a digital bandpass filter  380 , a downsampler circuit  382 , a requantizer circuit  384 , and plurality of correlator circuits  390 . Plurality of correlator circuits  390  includes correlator  392 , correlator  393 , and additional correlator circuits not shown for simplicity. Digital mixer circuit  378  receives subset  376  of GNSS satellite signals  272 , and shifts the frequency of subset  376  of GNSS satellite signals  272 . Changing the frequency of subset  376  of GNSS satellite signals  272  for processing allows digital signal conditioning circuit  212  to isolate the desired GNSS satellite signals  272  from other nearby signals and minimize the cost, size, bandwidth, and power consumption of GNSS device  204 . Digital filter  380  passes the frequency band that includes the frequency-shifted subset  376  of GNSS satellite signals  272 , and blocks other frequencies. In some embodiments, digital filter  380  has a programmable passband. In some embodiments, each of the digital filters included in digital signal conditioning circuit  212  have a programmable passband. Using digital filters with programmable passbands allows GNSS device  204  to be programmed to capture different frequency bands at different times, depending on the needs of the application. 
     Downsampler circuit  382  and requantizer circuit  384  adjust the sampling of the frequency-shifted subset  376  of GNSS satellite signal  272 . Downsampling and requantizing optimize the sampling of subset  376  of GNSS satellite signals  272 , in order to obtain a maximum amount of information with a minimum frequency bandwidth. Downsampling as used herein means to reduce the sampling frequency of the signal. Frequency shifted, downsampled, and requantized subset  376  of GNSS satellite signal  272  is then divided into further subsets  386 ,  387 , and additional subsets (not shown for simplicity of  FIG. 8 ). Each subset  386 ,  387 , and others not shown, are conducted through one of plurality of correlator circuits  390 , which includes correlator circuit  392 , correlator circuit  393 , and other correlator circuits not shown for simplicity. 
     Digital signal processing channel  375  includes a digital mixer circuit  379 , a digital bandpass filter  381 , a downsampler circuit  383 , a requantizer circuit  385 , and plurality of correlator circuits  391 . Plurality of correlator circuits  391  includes a correlator circuit  394 , a correlator circuit  395 , and additional correlator circuits not shown for simplicity. Digital signal processing channel  375  channelizes and processes portion  377  of GNSS satellite signals  272 , as explained earlier for channel  374 . 
     The collective outputs of plurality of correlator circuits  390  and plurality of correlator circuits  391  comprise correlated signals  223 , which are conducted to GNSS solution processor  214  for GNSS processing such as location determination, attitude determination, or other GNSS computations. 
     Digital signal conditioning circuit  212  as described herein divides digitized GNSS satellite signals  272  into a plurality of subsets of digitized GNSS satellite signal  272 . The subsets of digitized GNSS satellite signal  272  includes subsets  376 ,  377 ,  386 ,  387 ,  388 , and  389 . Each of subsets  386 ,  387 ,  388 , and  389  are conducted through a respective correlator circuit  392 ,  393 ,  394 , and  395 . The plurality of correlator outputs  223  of each of the plurality of correlator circuits  390  and  391  are conducted to GNSS solution processor  214 . 
     GNSS satellite signal  273  is conducted through a similar channelizer portion by digital signal conditioning circuit  212 , which detail is not shown for simplicity of  FIG. 8 . Digital signal conditioning circuit  212  as described herein divides digitized GNSS satellite signals  273  into a plurality of subsets of digitized GNSS satellite signal  273 . Each of the subsets of digitized GNSS satellite signals  273  are conducted through one of a plurality of correlator circuits. The outputs  224  ( FIG. 5 ) of each of the plurality of correlator circuits are conducted to GNSS solution processor  214 . 
     It is to be understood that digital signal conditioning circuit  212  can have other components, elements, signal paths, and connections in some embodiments. 
     Referring particularly to  FIG. 5 , analog signal conditioning circuit  202  and digital signal conditioning circuit  212  perform signal filtering, frequency shifting, digitization, and channelization in order to capture and clean the GNSS signals of interest and/or other signals of interest, and deliver them to GNSS solution processor  214 . Analog signal conditioning circuit  202  and digital signal conditioning circuit  212  divide the signal filtering and processing of RF signals  215 , and  216  among the analog domain and the digital domain in order to minimize power consumption and physical size of GNSS device  204 , and to maximize the noise filtering capabilities of GNSS device  104 . GNSS solution processor  214  receives signals  223  and  224  from digital signal conditioning circuit  212 , and performs GNSS processing on signals  223  and  224  to compute GNSS location, GNSS attitude, and perform any other desired GNSS calculations. The GNSS location, attitude and other GNSS calculations are precise because GNSS device  204  has captured and isolated GNSS satellite signals  215  and  216 , creating clean signals  223  and  224 , without interference from nearby out-of-band signals or other undesirable frequencies. 
       FIG. 9  shows a block diagram of an embodiment of GNSS device  404 . GNSS device  404  is similar to GNSS device  204  of  FIG. 5 , except that GNSS device  404  divides the RF signals  405  received into three initial portions as compared to two for GNSS device  204 . It is to be understood that GNSS device  204  and  404  can, in some embodiments, divide the received RF signals into two, three, four, or more portions of the received RF signals. GNSS device  404  captures and processes GNSS satellite signals from one or more GNSS satellite constellations, as well as other RF signals of interest, as shown with GNSS device  104  in  FIG. 1 . In this embodiment, GNSS device  404  is used in place of GNSS device  104  in  FIG. 1 . 
     GNSS device  404  receives RF signals  405  with at least one antenna, which in the embodiment shown in  FIG. 9  is antenna  408 . RF signals  405  can include any or all of the RF signals shown in  FIG. 1 , as well as other RF signals of any type and frequency. For example, GNSS device  404  in this embodiment receives a plurality of GNSS satellite signals  184  from GNSS constellation  100 , and a plurality of GNSS satellite signals  185  from GNSS constellation  101 , as shown in  FIG. 1 . In some embodiments, GNSS device  404  receives pluralities of GNSS satellite signals from more than two GNSS constellations. GNSS device  404  also receives cellular telephone signals  190 , wanted RF signals  192  and unwanted RF signals  193 , as shown for GNSS device  104  in  FIG. 1 . 
     GNSS device  404  includes a signal splitting circuit  432 , an analog signal conditioning circuit  402 , a digital signal conditioning circuit  412 , and a GNSS solutions processor  414 . Antenna  408  captures RF signals  405  and conducts RF signals  405  to signal splitting circuit  432 . In some embodiments, signal splitting circuit  432  is a LNA circuit. Signal splitting circuit  432  includes three bandpass filters, a bandpass filter  429 , a bandpass filter  430 , and a bandpass filter  431 . 
     Each bandpass filter  429 ,  430 , and  431  of signal splitting circuit  432  passes a band of RF signals, and blocks signals outside its passband, as explained for signal splitting circuit  232  except for the fact that the present embodiment employs three passband filters. Thus, signals outside the passbands of bandpass filters  429 ,  430 , and  431  are blocked from reaching GNSS receiver  409 . 
     Signal splitting circuit  432  receives RF signals  405  from antenna  408 , and outputs RF signals  415 ,  416 , and  417 . In this embodiment, bandpass filters  429 ,  430 , and  431  receive RF signals  405  from antenna  408 , pass RF signals  415 ,  416 , and  417  in a first frequency range, a second frequency range, and a third frequency range respectively in response, and reject signals of other frequencies. RF signals  415  in the first frequency range, RF signals  416  in the second frequency range, and RF signals  417  in the third frequency range are conducted to analog signal conditioning circuit  402  of GNSS receiver  409 . RF signals  415 ,  416 , and  417  can be GNSS satellite signals, cellular telephone signals, INMARSAT signals, GNSS correction service signals, or other RF signals of interest. In the embodiment of GNSS device shown in  FIG. 9 , the first frequency range is from about 1553 megahertz (MHz) to about 1609 MHz, the second frequency range is from about 1217 MHz to about 1289 MHz, and the third frequency range is from about 1165 MHz to about 1217 MHz. In some embodiment the first, second, or third frequency ranges are other frequency ranges. 
     Analog signal conditioning circuit  402  and digital signal conditioning circuit  412  perform signal filtering, frequency shifting, digitization, and channelization in order to capture and clean the GNSS signals of interest and/or other RF signals of interest, and deliver them to GNSS solution processor  414 . GNSS solution processor  414  performs GNSS computations such as location determination and attitude determination, as well as other GNSS computations. 
     Referring concurrently to  FIG. 9  and  FIG. 10 ,  FIG. 10  shows a simplified block diagram of one example embodiment of analog signal conditioning circuit  402  of  FIG. 9 . Analog signal conditioning circuit  402  includes a plurality of signal filtering/processing channels. In this embodiment analog signal conditioning circuit  402  includes three signal processing and filtering channels  426 ,  427 , and  418 , but this is not meant to be limiting. In this embodiment channels  426 ,  427 , and  418  are each similar to signal processing and filtering channel  226  described earlier. GNSS satellite signals  415 ,  416 , and  417  received at analog signal conditioning circuit  402  from signal splitting circuit  432  are the GNSS satellite signal sub-bands subdivided from RF satellite signal  405  by signal splitting circuit  432 . Analog signal conditioning circuit  402  digitizes each of GNSS satellite signals  415 ,  416 , and  417  before they are conducted to digital signal conditioning circuit  412 . 
     Analog signal conditioning circuit  402  conducts GNSS satellite signals  415  through signal filtering/processing channel  426  comprising VGAs  436  and  444 , analog bandpass filters  419  and  422 , frequency mixer  420 , and analog-to-digital converter  448 . VGAs  436  and  444  provide a distributed and adjustable amount of gain to GNSS satellite signals  415 . Bandpass filters  419  and  422  block undesirable frequencies from passing through channel  426 . Frequency mixer  420  shifts the frequency of GNSS satellite signals  415 . In this embodiment, frequency mixer  420  downconverts the frequency of GNSS satellite signals  415 . Shifting the frequency provides for moving GNSS satellite signals  415  away from interfering frequencies, as well as minimizing the power consumption of the signal processing elements. ADC  448  digitizes GNSS satellite signal  415 , as well as performing a second downconversion on GNSS satellite signals  415 . 
     Analog signal conditioning circuit  402  conducts GNSS satellite signals  416  and  417  through parallel signal filtering/processing channels  427  and  418 , which are similar to channel  426 . Analog signal conditioning circuit  402  conducts GNSS satellite signals  416  through signal filtering/processing channel  427  comprising VGA  437  and  445 , analog bandpass filters  421  and  492 , frequency mixer  479 , and analog-to-digital converter  449 . GNSS satellite signals  417  are conducted through signal filtering/processing channel  418  comprising VGAs  438  and  443 , analog bandpass filters  491  and  493 , frequency mixer  480 , and analog-to-digital converter  451 . Analog signal conditioning circuit  202  also includes a frequency synthesizer  450  and a crystal oscillator  428 . Frequency synthesizer  450  receives a clock signal from crystal oscillator  428 , which it uses to create clock frequency signals LO 1 , LO 2 , and LO 3  for frequency mixers  420 ,  479 , and  480  respectively, and frequency signals F 1 , F 2 , and F 3 , for ADC circuits  448 ,  449 , and  451 . 
     Each of GNSS satellite signals  415 ,  416 , and  417  are filtered, shifted in frequency twice (once by mixers  420 ,  479 , and  480 , and once by ADCs  448 ,  449 , and  451 ), and digitized by analog signal conditioning circuit  402 . In this embodiment all the frequency shifting downconverts the signal frequencies to lower frequencies. Filtered, downconverted, and digitized GNSS satellite signals  415  are labeled  472  in  FIG. 9  and  FIG. 10 , and are conducted to digital signal conditioning circuit  412  for digital signal filtering/processing. Filtered, downconverted, and digitized GNSS satellite signals  416  are labeled  473  in  FIG. 9  and  FIG. 10 , and are conducted to digital signal conditioning circuit  412  for digital signal filtering/processing. Filtered, downconverted, and digitized GNSS satellite signals  417  are labeled  474  in  FIG. 9  and  FIG. 10 , and are conducted to digital signal conditioning circuit  414  for digital signal filtering/processing. 
     Signal processing channels  426 ,  427 , and  418  can include many different configurations. Signal processing channels  426 ,  427 , or  418  can be the same or similar to signal processing channels  18   a  or  18   b  of  FIG. 3 , or channel  227  of  FIG. 6 , or channel  326  of  FIG. 7 , for example but not by way of limitation. 
     Digital signal conditioning circuit  412  is electrically coupled to analog signal conditioning circuit  402 , and receives digitized GNSS satellite signals  472 ,  473 , and  474  from analog signal conditioning circuit  402 . Digital signal conditioning circuit  412  further digitally processes GNSS satellite signals  472 ,  473 , and  474 , and outputs digitally processed signals  423 ,  424 , and  425  in response. 
     Digital signal conditioning circuit  412  in this embodiment includes a digital channelizer, similar to digital signal conditioning circuit  212  of  FIG. 8 . Digital signal conditioning circuit  412  channelizes, processes, subdivides, and correlates GNSS signals  472 ,  473 , and  474 , and outputs correlator outputs signals  423 ,  424 , and  425  in response. Signals  423 ,  424 , and  425  are conducted to GNSS solution processor  414  for GNSS processing such as location determination, attitude determination, or other GNSS computations. 
     Referring again to  FIG. 9 , analog signal conditioning circuit  402  and digital signal conditioning circuit  412  perform signal filtering, frequency shifting, digitization, and channelization in order to capture and clean the GNSS signals of interest and/or other signals of interest, and deliver them to GNSS solution processor  414 . Analog signal conditioning circuit  402  and digital signal conditioning circuit  412  divide the signal filtering and processing of RF signals  415 ,  416 , and  417  among the analog domain and the digital domain in order to minimize power consumption and physical size of GNSS device  404 , and to maximize the noise filtering capabilities of GNSS device  404 . GNSS solution processor  414  receives signals  423 ,  424 , and  425  from digital signal conditioning circuit  412 , and performs GNSS processing on signals  423 ,  424 , and  425  to compute GNSS location, GNSS attitude, and perform any other desired GNSS calculations. The GNSS location, attitude and other GNSS calculations are precise because GNSS device  404  has captured and isolated GNSS satellite signals  415 ,  416 , and  417 , creating clean signals  423 ,  424 , and  425 , without interference from nearby out-of-band signals or other undesirable frequencies. 
       FIG. 11  illustrates method  500  of processing RF signals received by a GNSS device. Method  500  includes element  510  of conducting a first portion of RF signals received by an antenna through a first analog filter, wherein the first analog filter passes GNSS satellite signals in a first frequency range and rejects signals of other frequencies. Method  500  of processing RF signals received by a GNSS device also includes element  520  of digitizing the GNSS satellite signals passed through the first analog filter. In some embodiments, an ADC circuit is used to digitize the GNSS satellite signals. 
     Method  500  of processing RF signals received by a GNSS device also includes element  530  of conducting a second portion of the RF signals received by the antenna through a second analog filter, wherein the second analog filter passes RF signals in a second frequency range and rejects signals of other frequencies. Method  500  also includes element  540  of dividing the digitized GNSS satellite signals passed through the first analog filter into a plurality of subsets of the digitized GNSS satellite signals passed through the first analog filter, and element  550  of conducting each of the plurality of subsets of the digitized GNSS satellite signals passed through the first analog filter through a corresponding one of a plurality of correlator circuits. 
     In some embodiments, the GNSS satellite signals passed through the first analog filter circuit include GNSS satellite signals from at least two GNSS constellations. In some embodiments, the GNSS satellite signals passed through the first analog filter circuit include GNSS satellite signals from at least three GNSS constellations. In some embodiments, the GNSS satellite signals passed through the first analog filter circuit include GNSS satellite signals from more than three GNSS constellations. In some embodiments, the second portion of the RF signals includes GNSS satellite signals in the second frequency range from at least two GNSS constellations. In some embodiments, the second portion of the RF signals includes GNSS satellite signals in the second frequency range from more than two GNSS constellations. 
     Method  500  can include many other elements. In some embodiments, method  500  includes digitally filtering each one of the plurality of subsets of the digitized GNSS satellite signals passed through the first analog filter with a corresponding one of a plurality of digital filters, wherein each of the plurality of digital filters has a programmable passband. In some embodiments, method  500  includes downsampling each of the digitally filtered plurality of subsets of the digitized GNSS satellite signals before correlation. In some embodiments, method  500  includes re-quantizing each of the downsampled plurality of subsets of the digitized GNSS satellite signals before correlation. 
     In some embodiments, method  500  includes amplifying the first portion of the RF signals with a first amplifier. In some embodiments, method  500  includes shifting the frequency of the amplified first portion of the RF signals from a first frequency in the first frequency range to a second frequency. In some embodiments, method  500  includes amplifying the RF signals of the second frequency with a second amplifier. In some embodiments, method  500  includes detecting a power level of the first portion of the RF signals. In some embodiments, method  500  includes increasing a bias current of the first and the second amplifier in response to a detected power level of the first portion of the RF signals being greater than a predetermined threshold power level. In some embodiments, method  500  includes increasing a number of bits of the analog-to-digital converter in response to the detected power level of the first portion of the RF signals being greater than a predetermined threshold power level. 
     In some embodiments, element  520  of digitizing the GNSS satellite signals passed through the first analog filter includes shifting the frequency of the RF signals of the second frequency from the second frequency to a third frequency using the analog-to-digital converter. In some embodiments, the third frequency is less than the second frequency and the second frequency is less than the first frequency. 
     In some embodiments, element  550  of conducting each of the plurality of subsets of the digitized GNSS satellite signals through a corresponding one of a plurality of correlator circuits includes subdividing each of the re-quantized plurality of subsets of the GNSS satellite signals into a plurality of re-quantized GNSS satellite signals. In some embodiments, element  500  of conducting each of the plurality of subsets of the digitized GNSS satellite signals through a corresponding one of a plurality of correlator circuits includes conducting each one of the plurality of re-quantized GNSS satellite signals through a corresponding one of a plurality of correlator circuits. 
     The embodiments and examples set forth herein were presented in order to best explain the present invention and its practical application and to thereby enable those of ordinary skill in the art to make and use the invention. However, those of ordinary skill in the art will recognize that the foregoing description and examples have been presented for the purposes of illustration and example only. The description as set forth is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the teachings above.