JP4665501B2 - Temperature compensated piezoelectric oscillator and receiver using the same - Google Patents

Description

The present invention relates to a satellite receiver that receives positioning information, and more particularly to a temperature-compensated piezoelectric oscillator that enables shortening of satellite acquisition time and stable tracking of the satellite and a satellite receiver using the same.

A positioning satellite system, such as GPS (Global Positioning System), is a global positioning system using satellites, and can be continuously and independently positioned in any region on the earth regardless of land or sea. It is.
The GPS receiver receives a signal related to positioning information transmitted from a GPS satellite, performs demodulation processing, performs a positioning calculation based on the data obtained as a result, and performs the position of the GPS receiver (latitude, longitude and Information on altitude) is output.
This GPS receiving device has been reduced in size year by year, and not only a stationary type such as a car navigation system but also a device incorporated in a mobile terminal for mobile communication has been put into practical use.

In order to extract data related to positioning information from the GPS received signal, the signal corresponding to the carrier wave of the received signal is multiplied by the pseudo-spread signal of the GPS system synchronized with this signal, and the correlation value is integrated. A “satellite acquisition process” is performed in which the point that becomes stronger is determined as a synchronization point and data is extracted.

Furthermore, since the frequency of the signal corresponding to the carrier of the received signal fluctuates due to Doppler shift due to the high-speed movement of the satellite even after the satellite is acquired, the frequency of the received signal that fluctuates the frequency of the pseudo spread signal to be multiplied Therefore, it is necessary to perform “satellite tracking processing” for continuously extracting data.
Positioning information can be obtained by performing calculation processing of data obtained while the satellite acquisition processing is completed and the tracking processing is performed.

FIG. 3 is a schematic configuration diagram illustrating an example of a conventional GPS receiver. As shown in the figure, the GPS receiver 100 includes a temperature-compensated crystal oscillator (hereinafter referred to as TCXO) including an antenna 1, a frequency converting unit 2 including a frequency mixing unit 21 and a PLL / VCO circuit 22, and a memory 32. 3, a primary demodulation unit 4, a spread spectrum (hereinafter referred to as SS) demodulation unit (SS demodulation unit) 5, and a CPU 6 including a positioning calculation unit 61.

The primary demodulation unit 4 includes a multiplication unit 41 and a carrier wave reproduction unit 42 including a fractional synthesizer unit 42b.
The SS demodulator 5 is provided with a number of SS demodulator units corresponding to the number of satellite channels set in the receiving system. Each SS demodulator unit includes a correlator 51 and a PN code generator 52. , A correlation integration / determination unit 53, a DPLL 56 and a frequency divider 55. However, FIG. 3 shows only the SS demodulator 5 for one channel for the sake of simplicity.

In the figure, the GPS signal (center frequency: fGPS) from the satellite received by the antenna 1 is BPSK (Binary Phase Shift Keying) modulated on the transmission data, and further spread spectrum modulated (SS modulated) by the pseudo spread signal. Signal. This signal is input to one input terminal of the frequency mixing unit 21 of the frequency conversion unit 2.
On the other hand, an output signal (frequency: fXO) of a temperature-compensated crystal oscillator (hereinafter referred to as TCXO) 3 that has been temperature-compensated based on compensation data stored in the memory 32 is sent to the PLL / VCO circuit 22 of the frequency converter 2. The frequency is multiplied to a predetermined local oscillation frequency (fLO) and input to the other input terminal of the frequency mixing unit 21.
In the frequency mixing unit 21, the GPS signal (fGPS) is mixed with the local oscillation frequency (fLO), converted into an intermediate frequency signal (IFGPS), and output to the primary demodulation unit 4.

The intermediate frequency signal (IFGPS) input to the primary demodulator 4 is input to one input terminal of the multiplier 41 and supplied to the carrier recovery circuit 42. The carrier recovery circuit 42 recovers a carrier synchronized with the intermediate frequency reception signal (IFGPS) based on the output signal of the fractional synthesizer unit 42b using TCXO3 as a reference signal source. Output to the input terminal.
As a result, a BPSK demodulated wave is extracted from the intermediate frequency signal (IFGPS) and output to the SS demodulator 5.
The output signal of the primary demodulator 4 is a signal whose transmission data is SS-modulated, and this signal is input to the SS demodulator 5 provided for each satellite channel, and SS is demodulated as described below, respectively. Transmission data (orbit information) is obtained.

The SS modulated wave input to the SS demodulator 5 is a GPS pseudo spread code generated by the PN code generator 52 using the output signal of the DPLL 56 using the output of the TCXO 3 as a reference signal source in the correlator 51 as a clock signal. Correlation with (PN code) is taken.
Since the synchronization point is unknown at the satellite acquisition stage, the synchronization point is searched while changing the frequency of the output signal of the DPLL 56 at a predetermined rate.
The output signal (correlation value) of the correlator 51 is sequentially integrated for each period by the correlation integration / determination unit 53, and the point with the maximum integrated value at which the correlation is strongest is determined as the synchronization point, and the search is stopped there. Reception data (satellite orbit information, etc.) can be obtained with the output frequency of the DPLL 56 fixed. In this way, the SS modulated wave is demodulated.

The frequency of the SS modulated wave input to the correlator 51 changes every moment due to the Doppler effect of the satellite moving at high speed. In the satellite tracking stage in which data is obtained while following the variation in the frequency of the SS modulated wave after capturing the satellite, the frequency of the output signal generated by the DPLL 56 is changed in response to the frequency variation in the SS modulated wave. Thus, the correlation integration / determination unit 53 keeps the synchronization by performing the same synchronization point determination as described above.
From the correlation integration / determination unit 53, automatic frequency control information on how to adjust (increase, decrease, or maintain) the output frequency of the DPLL 56 to obtain the synchronization point is sent to the DPLL 56. Supplied.

The respective orbit information obtained for each satellite channel as described above is input to the positioning calculation unit 61 of the CPU 6 and is processed in the positioning calculation unit 6 to obtain the positioning information of the receiving device 100.
JP 2002-228737 A

As described above, when the GPS reception signal is demodulated, the primary demodulation unit 4 supplies the output frequency fXO from the TCXO 3 to the fractional synthesizer unit 42b at the start of the operation of the reception device 100 for BPSK demodulation.
However, the output frequency fXO of the TCXO 3 oscillates with a frequency deviation with respect to the temperature inherent to the TCXO even after temperature compensation. Therefore, for example, when the center frequency f0 of the TCXO3 is 24.5 MHz, the maximum deviation of the oscillation frequency is ± 2 ppm, and the reference output frequency of the fractional synthesizer unit 42b is 64.5 MHz, the operation of the fractional synthesizer unit 42b At the start, the output frequency starts to search for an intermediate frequency signal (IFgps) including the Doppler frequency from a point where the output frequency is shifted from the reference frequency (64.5 MHz) by a maximum of 64.5 MHz × 2 ppm = 129 Hz. Therefore, there is a problem that it takes time for the primary demodulation of the intermediate frequency signal (IFgps).

Further, in the SS demodulator 5, in order to synchronize the GPS reception signal whose frequency fluctuates due to Doppler shift and the code sequence generated by the PN code generator 52, the output frequency of the DPLL 56 is in the range of 1.023 MHz ± 5 kHz. Over a period of time, the frequency is adjusted at a predetermined synchronization pull-in speed to track and capture the fluctuating reception frequency for synchronization.
Conventionally, this synchronization pull-in speed is generally set to, for example, about 100 Hz / sec in consideration of the initial oscillation frequency stability of the TCXO.
In this way, since the synchronization point is searched by tracking the frequency of the SS modulation wave that fluctuates due to the Doppler shift at a coarse synchronization pull-in speed of 100 Hz / sec, the correlation becomes weak and out of synchronization occurs, and the search for the synchronization point is performed. There was a problem that the case where it redoed occurred.
Due to the above-described problems, there is a problem that it takes a long time, for example, 40 to 60 seconds to demodulate the trajectory information to obtain positioning information after the reception operation of the receiving apparatus is started.
The present invention has been made to solve the above-described problems, and shortens the demodulation time of the SS modulation wave in the GPS receiver using the temperature-compensated crystal oscillator as a reference signal source, thereby providing excellent reception sensitivity characteristics. It is an object of the present invention to provide a GPS receiving device having the above.

In order to solve the above-mentioned problem, in claim 1, a temperature compensation piezoelectric oscillator having storage means for storing temperature compensation data is provided, and the storage means has an oscillation frequency at a reference temperature with respect to a center oscillation frequency of the temperature compensation piezoelectric oscillator. The offset amount and the maximum frequency change rate when the temperature is changed at a predetermined speed are stored, and an output signal from a DPLL (Digital Phase Lock Loop) using the output of the temperature compensated piezoelectric oscillator as a reference signal is stored. Spread spectrum demodulation is performed by obtaining a synchronization point based on the correlation between the pseudo-spread code generated as a clock signal and the received signal, and the maximum frequency stored in the storage means is the synchronization pull-in speed when obtaining the synchronization point. The receiving apparatus is characterized in that the value of the rate of change is used.
According to a second aspect of the present invention, a temperature compensated piezoelectric oscillator having storage means for storing temperature compensation data is provided, and the storage means has an oscillation frequency offset amount at a reference temperature with respect to a center oscillation frequency of the temperature compensated piezoelectric oscillator, and a temperature The maximum frequency change rate when the frequency is changed at a predetermined speed is stored, and the carrier wave is reproduced based on the signal output from the fractional synthesizer using the output of the temperature compensated piezoelectric oscillator as a reference signal. A BPSK (Binary Phase Shift Keying) demodulation is performed by multiplying the circuit output signal and the received signal, and a DPLL (Digital PLL) using the spread spectrum modulated wave extracted by the BPSK demodulation and the output of the temperature compensated piezoelectric oscillator as a reference signal By the correlation with the pseudo spread code generated using the output signal from Phase Lock Loop) as the clock signal A receiving apparatus for performing spread spectrum demodulation by obtaining an epoch, wherein when the operation of the receiving apparatus starts, the offset amount stored in the storage unit is set in the fractional synthesizer, and an output signal of the fractional synthesizer is The reception signal is configured to have a predetermined center frequency, and the synchronization pull-in speed when obtaining the synchronization point is the value of the maximum frequency change rate stored in the storage unit.

In the positioning satellite receiver of the present invention, the memory of the temperature-compensated crystal oscillator (TCXO) serving as the reference signal source of the fractional synthesizer of the primary demodulator and the DPLL of the spread spectrum demodulator (SS demodulator) is stored in the TCXO. The center frequency of the oscillation output, the amount of offset of the oscillation frequency at the reference temperature, and the maximum frequency change rate of the TCXO when the temperature is changed at 1 ° C./sec are stored.
Then, when the receiver is turned on, the TCXO center frequency and the amount of offset of the oscillation frequency at the reference temperature are set in the fractional synthesizer so that the output frequency of the fractional synthesizer becomes the predetermined center frequency of the reception intermediate frequency signal. To control. As a result, a received signal from a satellite deviated from the center frequency by Doppler shift can be captured more quickly than before.

Further, the value of the maximum frequency change rate of the TCXO stored in the memory of the TCXO is set as the clock synchronization pull-in speed when the synchronization point in the spread spectrum demodulation is obtained by changing the frequency by the DPLL. Since this speed is smaller than the conventional synchronization pull-in speed, the correlation between the received signal for SS demodulation and the output of the PN code generator appears strongly, so that synchronization loss is prevented and the synchronization point is reliably captured. Is possible. In addition, since it is easy to synchronize even a weak radio wave, the reception sensitivity is improved.
Therefore, according to the present invention, the satellite reception radio wave is quickly and surely captured to shorten the positioning time, and at the same time, the present invention is very effective in providing an excellent positioning satellite receiver capable of capturing a satellite signal with low reception sensitivity.

The present invention will be described based on the embodiments shown in the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of a GPS receiver using a temperature compensated crystal oscillator according to the present invention.
As shown in the figure, the GPS receiver 10 includes a temperature-compensated crystal oscillator (hereinafter referred to as TCXO) including an antenna 1, a frequency converting unit 2 including a frequency mixing unit 21 and a PLL / VCO circuit 22, and a memory 31. 3, a primary demodulation unit 4, a spread spectrum demodulation unit (SS demodulation unit) 5, a CPU 6 including a positioning calculation unit 61, and a memory 7.

The primary demodulator 4 includes a multiplier 41 and a carrier recovery unit 42 including a fractional synthesizer unit 42a.
The SS demodulator 5 is provided with a number of SS demodulator units corresponding to the number of satellite channels set in the receiving system. Each SS demodulator unit includes a correlator 51 and a PN code generator 52. , A correlation integration / determination unit 53, a DPLL 54 and a frequency divider 55. However, FIG. 1 shows only the SS demodulator 5 for one channel for the sake of simplicity.

The functions and operations of the components of the GPS receiver 10 are the same as those in FIG. 3 except for the memory 31 of the TCXO 3, the fractional synthesizer 42a of the primary demodulator 4, the DPLL 54 of the SS demodulator, and the memory 7. This is the same as the functional operation of the constituent parts represented by reference numerals, and the basic demodulation operations of BPSK demodulation and SS demodulation in the receiving apparatus 10 are the same as those in the GPS receiving apparatus 100 of FIG. Detailed description of the portion is omitted.

The TCXO 3 including the memory 31 attached to the receiving apparatus 10 is configured as follows in the manufacturing / inspection stage.
(B) Measure the deviation (frequency offset) from the center frequency of the oscillation frequency at the reference temperature (25 ° C).
(B) The oscillation frequency when the temperature is changed at a predetermined speed (for example, a rate of 1 ° C. per second) is measured.
(C) Calculate the frequency change rate (ppm / ° C) at each temperature based on the measurement result.
(D) The maximum value (hereinafter referred to as the maximum frequency change rate (ppm / ° C)) of the center frequency of TCXO, the frequency offset of (b), and the frequency change rate (ppm / ° C) obtained by (c) ) Are stored in the memory 31.
Note that the center frequency of the TCXO 3 is an arbitrarily determined reference frequency, and a so-called nominal frequency is generally used.

FIG. 2 shows the fractional synthesizer 42a and the SS demodulator of the primary demodulator 4 based on the data stored in the memory 31 of the TCXO3 with respect to the GPS receiver 10 having the TCXO3 constructed as described above. 5 is a control flowchart for controlling the operation of the DPLL 54 in FIG.
The demodulation operation of the GPS receiver 10 will be described with reference to FIG.

When the GPS receiver 10 is powered on (S1 in FIG. 2), the TCXO 3 outputs an oscillation frequency that has been subjected to temperature compensation based on the temperature compensation data in the memory 31, and also from the memory 31 via the CPU 6 to the memory. The data of the center frequency of the TCXO 3, the frequency offset at the reference temperature, and the maximum frequency change rate (ppm / ° C.) are read into 7 (S 2 in FIG. 2).
The CPU 6 which has read these data controls the fractional synthesizer unit 42a based on the center frequency and frequency offset data, and the output frequency of the fractional synthesizer unit 42a is determined from the center frequency (IF0) of the predetermined reception intermediate frequency signal. Setting is made so as to start outputting (S3 and S4 in FIG. 2).
In this way, the output of the fractional synthesizer unit 42 a whose frequency changes from the center frequency (IF 0) of the predetermined intermediate frequency signal is output to the carrier wave reproduction circuit 42.
In the carrier recovery circuit 42, the output signal of the fractional synthesizer 42a and the received signal (IFGPS) are synchronized to recover the carrier, and the multiplier 41 multiplies the recovered carrier and the received signal (IFGPS) to perform primary modulation (BPSK). Demodulate the modulated wave.

Further, the CPU 6 sets the clock synchronization pull-in speed in the DPLL 54 of the SS demodulator 5 to the value of the maximum frequency change rate (ppm / ° C.) of the TCXO 3 read into the memory 7 (S5 in FIG. 2).
For example, when the maximum frequency change rate (ppm / ° C.) of TCXO3 is 0.02 ppm / ° C., the clock synchronization pull-in speed is GPS frequency × maximum frequency change rate (ppm / ° C.) = 1575.42 (MHz) × 0.4. 02 (ppm / ° C.) = 31.5 Hz / ° C. That is, the clock synchronous pull-in speed is set to 31.5 Hz / sec.
The correlator 51 correlates the output signal of the primary demodulator 4 input to the SS demodulator 5 with the GPS PN code generated by the PN code generator 52. This PN code is a clock signal that is output from the DPLL 54 whose oscillation frequency is adjusted at a rate of 31.5 Hz / sec set based on the maximum frequency change rate (ppm / ° C.) of the TCXO 3 as described above. Is generated by the PN code generator 52. Of course, the clock synchronization pull-in speed may be an approximate value (for example, 30 Hz / sec) based on the calculated value.
The output signal (correlation value) of the correlator 51 is sequentially integrated for each cycle by the correlation integration / determination unit 53, and the point with the maximum integrated value is determined as the synchronization point with the strongest correlation, and the received data (satellite orbit information, etc. ) Can be obtained.

The frequency of the SS modulated wave input to the correlator 51 changes due to the Doppler effect of the satellite. Following the variation in the frequency of the SS modulation wave, the frequency of the output signal generated by the DPLL 54 is adjusted to change the chip rate of the PN code, and keep the synchronization.
From the correlation integration / determination unit 53, automatic frequency control information is supplied to the DPLL 54, and an instruction to adjust the output frequency of the DPLL 54 for maintaining a synchronization point is issued.

By configuring the GPS receiver 10 as described above, the carrier wave recovery circuit 42 of the primary demodulator 4 can quickly reproduce the carrier wave and perform BPSK demodulation.
In addition, since the synchronous pull-in speed is the value of the maximum frequency change rate (ppm / ° C.) of each TCXO 3, considering the variation of TCXO, a value corresponding to the capability of each TCXO without setting the synchronous pull-in speed large Therefore, since the correlation in the correlator 51 of the SS demodulator 5 becomes stronger than when the synchronization pull-in speed is set to a large value, it becomes easier to synchronize with the satellite reception wave, and the satellite tracking Operation will be reliable.

1 is a schematic configuration diagram showing an embodiment of a GPS receiver using a temperature-compensated crystal oscillator according to the present invention. The control flowchart figure which controls operation | movement with the fractional synthesizer of a primary demodulation part, and DPLL of SS demodulation part 5. FIG. The structure schematic diagram which shows an example of the conventional GPS receiver.

Explanation of symbols

1 .... Antenna, 2 .... Frequency converter, 3 .... Temperature compensated crystal oscillator (TCXO),
4 .... primary demodulation unit, 5 .... spread spectrum demodulation unit (SS demodulation unit), 6 .... CPU,
7 .... Memory 10 .... GPS receiver, 21 ... Frequency mixing unit 22, ... PLL
VCO circuit,
31, 32 ... Memory 41 ... Multiplying unit 42 ... Carrier recovery unit,
42a, 42b, a fractional synthesizer section, 51, a correlator,
52 .. PN code generator, 53 .. Correlation integration / determination unit, 54, 56.
55..Division circuit, 61..Positioning calculation unit, 100..GPS receiver,

Claims (2)

  A temperature compensated piezoelectric oscillator having storage means for storing temperature compensation data;
  The storage means stores an offset amount of an oscillation frequency at a reference temperature with respect to a center oscillation frequency of the temperature compensated piezoelectric oscillator, and a maximum frequency change rate when the temperature is changed at a predetermined speed,
  Spread spectrum demodulation is performed by obtaining a synchronization point based on a correlation between a pseudo spread code generated by using an output signal from a digital phase lock loop (DPLL) using the output of the temperature compensated piezoelectric oscillator as a reference signal and a received signal as a clock signal. ,
  5. A receiving apparatus according to claim 1, wherein the synchronization pull-in speed when obtaining the synchronization point is a value of the maximum frequency change rate stored in the storage means.   A temperature compensated piezoelectric oscillator having storage means for storing temperature compensation data;
  The storage means stores an offset amount of an oscillation frequency at a reference temperature with respect to a center oscillation frequency of the temperature compensated piezoelectric oscillator, and a maximum frequency change rate when the temperature is changed at a predetermined speed,
  BPSK (Binary Phase Shift Keying) demodulation is performed by multiplying the received signal with the carrier signal recovery circuit output signal that reproduces the carrier wave based on the signal output from the fractional synthesizer using the output of the temperature compensated piezoelectric oscillator as a reference signal. ,
  Based on the correlation between the spread spectrum modulated wave extracted by the BPSK demodulation and the pseudo spread code generated using the output signal from the digital phase lock loop (DPLL) using the output of the temperature compensated piezoelectric oscillator as a reference signal A receiver that performs spread spectrum demodulation to obtain a synchronization point,
  At the start of the operation of the receiving device, the offset amount stored in the storage means is set in the fractional synthesizer so that the output signal of the fractional synthesizer becomes a predetermined center frequency of the received signal, and 5. A receiving apparatus according to claim 1, wherein a synchronization pull-in speed when obtaining a synchronization point is a value of the maximum frequency change rate stored in the storage means.

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