JP2713639B2 - Spread spectrum synchronizer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a spread spectrum synchronization signal used in a spread spectrum receiver.

[Conventional technology]

FIG. 4 is a block diagram showing a conventional spread spectrum synchronizer disclosed in, for example, JP-A-1-220542. In the figure, reference numeral 1 denotes an input terminal to which a received signal subjected to spectrum spreading is input, and 2 denotes a despreading code generator for generating a local reference signal for despreading modulation. Reference numeral 3 denotes a correlator that multiplies the local reference signal by the received signal to convert the signal into an intermediate frequency signal. Reference numeral 4 denotes an intermediate frequency filter that performs band-limited filtering of the intermediate frequency signal output from the correlator 3. is there.

Reference numeral 5 denotes an intermediate frequency amplifier that amplifies the intermediate frequency signal band-limited filtered by the intermediate frequency filter 4, and 6 detects the amplified intermediate frequency signal and generates a spread code based on the DC signal. Reference numeral 8 denotes a synchronization determiner for detecting coincidence and determining synchronization, and 8 generates a clock pulse whose phase can be shifted and supplies the clock pulse to the despread code generator 2;
Is a clock generator that stops the clock phase shift by the spread code coincidence detection signal output from the clock generator.

Next, the operation will be described. The received signal input from the input terminal 1 is a signal subjected to spectrum spreading, and is multiplied by the correlator 3 with the local reference signal whose phase is slipping from the despreading code generator 2 to be converted into an intermediate frequency signal. . The intermediate frequency signal converted by the correlator 3 is
When the received signal and the local reference signal are synchronized and their spread codes match, the spectrum becomes sharp as shown by the symbol a in FIG. 3, and when asynchronous, the spectrum shown by the symbol b in FIG. It becomes a gentle thing like.

The band of the intermediate frequency signal output from the correlator 3 is limited by the filtering by the intermediate frequency filter 4 and sent to the intermediate frequency amplifier 5. The intermediate frequency signal amplified by the intermediate frequency amplifier 5 is further sent to a detector 6 where it is detected and converted into a DC signal. Therefore, the level of the DC signal of the detector 6 increases during synchronization as compared to when the synchronization is not performed.

As shown in FIG. 2, the synchronization determination circuit 7
Is compared with a predetermined threshold level to detect that the spread code of the received signal matches the spread code of the local reference signal, and outputs the detected signal to the clock generator 8.
Send to The clock phase shift of the generated clock pulse is stopped by the detection signal of the clock generator 8. As a result, the despreading code generator 2 generates a spreading code synchronized with the received signal.

Here, when the input level of the received signal is large, the energy passing through the intermediate frequency filter 4 is also large,
This is a saturation region where the input / output linearity of the intermediate frequency amplifier 5 and the detector 6 cannot be maintained. Therefore, in such a case,
The output of the detector 6 for detecting the correlation peak may have a noise level higher than the threshold level of the synchronization determiner 7 as shown in FIG.

[Problems to be solved by the invention]

Since the conventional spread spectrum synchronizer is configured as described above, the synchronization is detected based on the presence or absence of the intermediate frequency signal, and therefore, the spread codes of the received signal and the local reference signal do not match. Nevertheless, detector 6
There is a possibility that the noise level of the output may exceed the threshold level of the synchronization determiner 7, and in such a case, there is a problem that even in an asynchronous state, it is erroneously recognized as synchronized.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a spread spectrum synchronizer capable of performing stable detection of spread synchronization regardless of the input level of a received signal.

[Means for solving the problem]

A spread spectrum synchronizer according to the present invention uses a variable gain amplifier whose gain can be controlled by a control signal as an intermediate frequency amplifier for amplifying an intermediate frequency signal band-limited filtered by an intermediate frequency filter. An integrating circuit for integrating the detection output of the detector, and an automatic gain control (hereinafter, referred to as AGC) amplifier for amplifying the integrated output of the integrating circuit and generating a control signal for controlling the gain of the variable gain amplifier. It is provided.

[Action]

An AGC amplifier according to the present invention amplifies an integrated output of an integration circuit that integrates a detection output of a detector to generate a control signal for adjusting a gain of a variable gain amplifier, and the variable gain amplifier corresponds to the control signal. Spread-spectrum synchronization enables stable spread synchronization even when the input level of the received signal is large by amplifying the intermediate frequency signal band-limited filtered by the intermediate frequency filter and sending it to the detector with the gain of the specified value. Implement the device.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is an input terminal, 2 is a despread code generator,
Reference numeral 3 denotes a correlator, 4 denotes an intermediate frequency filter, 6 denotes a detector, 7 denotes a synchronization determiner, and 8 denotes a clock generator. Therefore, detailed description is omitted.

Reference numeral 10 denotes an intermediate frequency amplifier which amplifies an intermediate frequency signal band-limited filtered by the intermediate frequency filter 4 and outputs the amplified intermediate frequency signal to the detector 6, and whose gain can be controlled by a control signal. It is a gain amplifier. Reference numeral 11 denotes an integration circuit that integrates the detection output of the detector 6, and reference numeral 12 denotes an AGC amplifier that amplifies the integration output of the integration circuit 11 and generates a control signal for controlling the gain of the variable gain amplifier 10. .

Next, the operation will be described. The received signal input from the input terminal 1 is a signal subjected to spectrum spreading, and is multiplied by the correlator 3 with the local reference signal whose phase is slipping from the despreading code generator 2 as in the conventional case. . The intermediate frequency signal output from the correlator 3 is input to the intermediate frequency filter 4, subjected to band-limited filtering, and sent to the variable gain amplifier 10.

The gain of the variable gain amplifier 10 is determined by a control signal from the AGC amplifier 12, and amplifies the signal from the intermediate frequency filter 4 to a predetermined level. The output of the variable gain amplifier 10 is envelope-detected by the detector 6, and the detection output is input to the integration circuit 11 and integrated. This integration circuit
After the integrated output of 11 is amplified to an appropriate level by the AGC amplifier 12, it is sent to the variable gain amplifier 10 as a control signal for controlling the gain of the variable gain amplifier 10.

Here, when the input level of the received signal input to the input terminal 1 is large and synchronization is not achieved, the detector 6 outputs a large noise level. However, since an AGC loop composed of the variable gain amplifier 10 → the detector 6 → the integration circuit 11 → the AGC amplifier 12 is formed, the variable gain amplifier 1
The gain of 0 is controlled by the control signal from the AGC amplifier 12 so that the noise level of the detection output of the detector 6 becomes lower than the threshold level of the synchronization determiner 7. Therefore, when synchronization is not established, the noise energy input to the detector 6 becomes constant regardless of the level of the input level of the received signal, and the noise level output from the detector 6 becomes lower than the threshold. .

When synchronization is achieved, the correlator 3 outputs a sharp spectrum as indicated by the symbol a in FIG. At this time, the waveform output from the detector 6 is a peak waveform having a large level as shown in FIG. Accordingly, the gain of the variable gain amplifier 10 is suppressed, and the same energy as that at the time of the asynchronous operation is applied to the detector 6. In this case, as shown in FIG. 3, the output spectrum from the correlator 3 is such that the spectral density at the time of synchronization indicated by the symbol a is the symbol b
Since it is larger than that at the time of the asynchronous shown in FIG.
Is higher than the noise level or the threshold level, and the synchronization can be detected.

〔The invention's effect〕

As described above, according to the present invention, a control signal obtained by amplifying a signal obtained by integrating a detection output of a detector, and a variable gain amplifier that amplifies an intermediate frequency signal band-limited filtered by an intermediate frequency filter. Since it was configured to control the gain,
Even if the input level of the received signal is high, there is an effect that a spread spectrum synchronizer capable of performing spread synchronization stably can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a spread spectrum synchronizer according to an embodiment of the present invention, FIG. 2 is an explanatory diagram for explaining the operation of the synchronization determiner, and FIG. FIG. 4 is an explanatory diagram showing an output spectrum of a correlator of the device, FIG. 4 is a block diagram showing a conventional spread spectrum synchronizer, and FIG. 5 is an explanatory diagram for explaining an operation of the synchronization determiner. 2 is a despreading code generator, 3 is a correlator, 4 is an intermediate frequency filter, 5 is an intermediate frequency amplifier, 6 is a detector, 7 is a synchronization determiner, 8 is a clock generator, 10 is a variable gain amplifier, 11 is an integrating circuit, 12 is an AGC amplifier. In the drawings, the same reference numerals indicate the same or corresponding parts.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-57036 (JP, A) JP-A-57-73543 (JP, A) JP-A-64-10746 (JP, A) JP-A-1- 220542 (JP, A) JP-A-2-98241 (JP, A) JP-A-63-99440 (JP, U) JP-A-1-100545 (JP, U) JP-A-2-26840 (JP, U)

Claims (1)

(57) [Claims] 1. A despreading code generator for generating a local reference signal for despreading modulation, and an intermediate frequency signal obtained by multiplying a received signal subjected to spectrum spreading by a local reference signal generated by the despreading code generator. A correlator that converts the signal into a signal, an intermediate frequency filter that performs band-limited filtering of the intermediate frequency signal converted by the correlator, and an intermediate frequency signal that is band-limited filtered by the intermediate frequency filter An intermediate frequency amplifier that amplifies the intermediate frequency signal, a detector that detects the intermediate frequency signal amplified by the intermediate frequency amplifier, and a synchronization that detects the coincidence of spread codes based on the detection output of the detector and determines synchronization. A clock generator for generating a clock pulse whose phase can be shifted and supplying the clock pulse to the despread code generator, and stopping the clock phase shift by the spread code coincidence detection signal from the synchronization determiner And a variable gain amplifier whose gain can be controlled by a control signal as the intermediate frequency amplifier, and an integration circuit for integrating the detection output of the detector, and an integration output of the integration circuit. And an automatic gain control amplifier for generating a control signal for controlling the gain of the variable gain amplifier.