JPH0715480A - Automatic frequency controller - Google Patents

Abstract

(57) [Abstract] [Purpose] By using the fixed oscillator of the quasi-synchronous detection type demodulator as the reference frequency for AFC control, it is difficult to set the carrier frequency of the intermediate frequency signal as required by an ordinary digital demodulator. Relaxes frequency stability and high frequency accuracy. [Configuration] The frequency converter 11 and its intermediate frequency signal
After converting into a baseband signal by the quadrature detector 10 and the fixed oscillator 14 input to the quadrature detector 10,
Quasi-synchronous detection type demodulator 13 for digital demodulation, M multiplier 15 for multiplying the frequency of the intermediate frequency signal by M, frequency divider 16 for dividing the output signal of M multiplier 15 by (M × N), and fixed. The frequency divider 11 divides the frequency of the oscillator 14 by N, the phase detector 17 that detects the frequency difference between the output signal of the frequency divider 16 and the output signal of the frequency divider 116, and the frequency converter 11. , And a voltage controlled oscillator 19 whose oscillation frequency is controlled based on the output voltage from the phase detector 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention stabilizes the carrier frequency of a digitally modulated intermediate frequency signal input to a digital demodulation circuit for demodulating a digital modulation signal such as a multilevel QAM modulation signal or a polyphase modulation signal. The present invention relates to an automatic frequency control device for doing so.

[0002]

2. Description of the Related Art At present, an AM modulation method or an FM modulation method is generally used as a modulation method for television broadcasting. However, recently, terrestrial digital broadcasting and satellite digital broadcasting based on the multilevel QAM modulation system and the multiphase phase modulation system have been considered.

Generally, in order to receive a digitally modulated RF signal and demodulate the data with a digital demodulator, it is necessary to stabilize the carrier frequency of the digitally modulated signal input to the digital demodulator.

For example, in a satellite broadcast receiver, the local oscillation frequency of the BS converter may drift about ± several MHz, so when the frequency of the digital modulation signal is converted to an intermediate frequency signal and input to the digital demodulator, An AFC device is required to absorb the drift and stabilize the carrier frequency of the intermediate frequency signal. FIG. 5 shows a conventional automatic frequency control device (see, for example, Japanese Patent Laid-Open No. 63-299526).

In FIG. 5, the digitally modulated high frequency signal is converted into an intermediate frequency signal by a frequency converter 51 and input to a digital demodulator 53 via an intermediate frequency band pass filter 52. In the digital demodulator 53, the carrier wave of the intermediate frequency signal is reproduced by the carrier wave reproduction circuit 54 and the data is demodulated. On the other hand, the carrier wave extraction circuit 55
Then, the carrier of the intermediate frequency signal output from the intermediate frequency band pass filter 52 is extracted and input to the phase detector 56. The phase detector 56 has an intermediate frequency oscillator 57 whose oscillation frequency is equal to the nominal frequency of the carrier frequency of the intermediate frequency signal.
Of the output signal of the carrier wave extraction circuit 55 and the output signal of the carrier wave extraction circuit 55 are detected. Then, the voltage controlled oscillator 5 input to the frequency converter 51 by the output signal of the phase detector 56
The oscillation frequency of 8 is controlled.

[0006]

In the configuration of the conventional example described above, in order for the carrier wave of the intermediate frequency signal to be reproduced by the carrier wave reproducing circuit 54 of the digital demodulator 53, the intermediate frequency signal input to the digital demodulator 53 is to be reproduced. It is necessary to reduce the frequency difference between the carrier frequency of the carrier wave and the operating frequency of the carrier wave reproduction circuit 54. For that purpose, it is necessary to increase the stability of the operating frequency of the carrier wave regenerating circuit 54 together with the temperature stability of the intermediate frequency oscillator 57. Therefore, both the intermediate frequency oscillator 57 and the carrier wave regenerating circuit 54 need an oscillator with high stability. Moreover, when the carrier frequency of the intermediate frequency signal is increased, not only the intermediate frequency oscillator 57 but also the carrier reproducing circuit 54 are required to have temperature stability and strict frequency accuracy.

In addition to the oscillator of the carrier recovery circuit 54 in the digital demodulator 53, an intermediate frequency oscillator 57 is also provided.
Since 2 is used, two oscillators are required.

The present invention has been made in view of the above points, and eliminates the drawbacks of the above-described conventional example, solves the problem of frequency stability of the intermediate frequency signal necessary for the digital demodulator, and provides an intermediate frequency oscillator. It is an object of the present invention to provide an automatic frequency control device that makes it unnecessary.

[0009]

To achieve this object, an automatic frequency control device of the present invention comprises a frequency converter for converting an M-phase phase-modulated high-frequency signal into an intermediate-frequency signal, and the intermediate-frequency signal. A quasi-synchronous detection type demodulator that performs digital demodulation after converting to a baseband signal with a quadrature detector and a fixed oscillator input to the quadrature detector,
An M multiplier for multiplying the frequency of the intermediate frequency signal by M, a first divider for dividing the output signal of the M multiplier by (M × N), and a first divider for dividing the frequency of the fixed oscillator by N. 2 frequency divider, a phase detector for detecting a frequency difference between the output signal of the first frequency divider and the output signal of the second frequency divider, and the phase detector which is input to the frequency converter It is composed of a voltage-controlled oscillator whose oscillation frequency is controlled based on the output voltage from the detector.

[0010]

The M-phase phase-modulated high frequency signal is converted into an intermediate frequency signal by the frequency converter. Then, by inputting the intermediate frequency signal to the M multiplier, a non-modulated signal whose frequency is M times as high as the carrier frequency of the intermediate frequency signal and in which the M phase phase modulation component is removed is obtained. Furthermore, this unmodulated signal is
By performing the (M × N) frequency division by the frequency divider of 1, an unmodulated signal having a frequency of 1 / N of the carrier frequency of the intermediate frequency signal can be obtained. On the other hand, by inputting the output signal of the fixed oscillator whose oscillation frequency is substantially equal to the nominal frequency of the intermediate frequency signal to the second frequency divider, the frequency is 1 / N of that of the fixed oscillator.
Signal is obtained. Then, the M-phase phase modulation component is removed, and the frequency difference between the unmodulated signal having a frequency of 1 / N of the carrier frequency of the intermediate frequency signal and the frequency of the signal of 1 / N of the fixed oscillator is the phase detector. Detected in. The output signal detected by the phase detector is averaged by the loop filter and then input to the voltage controlled oscillator to control the oscillation frequency of the voltage controlled oscillator. Moreover, the oscillation frequency of the voltage controlled oscillator is controlled so that the frequency difference between the carrier frequency of the intermediate frequency signal and the frequency of the fixed oscillator of the quasi-synchronous detection demodulator becomes zero.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an automatic frequency control device (hereinafter referred to as an AFC device) according to a first embodiment of the present invention. 11
Is a frequency converter for converting the M-phase phase-modulated high frequency signal into an intermediate frequency signal, 12 is an intermediate frequency band pass filter,
13 is a quasi-synchronous detection type demodulator, 14 is a fixed oscillator whose oscillation frequency is substantially equal to the nominal frequency of the intermediate frequency signal, 10 is a quadrature phase detector of the quasi-synchronous detection type demodulator 13, and 15 is the frequency of the intermediate frequency signal. An M multiplier for multiplying; 16 a divider for dividing the frequency of the output signal of the M multiplier 15 by (M × N);
116 is a frequency divider for dividing the frequency of the fixed oscillator 14 by N,
Reference numeral 17 denotes a phase detector that detects the frequency difference between the output signal of the frequency divider 16 and the output signal of the frequency divider 116. 18 is a loop filter that averages the output signal from the phase detector 17.
Is a voltage controlled oscillator which is input to the frequency converter 11 and whose oscillation frequency is controlled by the output voltage of the loop filter 18.

The operation of the AFC device configured as described above will be described. First, the M-phase phase-modulated high-frequency signal is converted into an intermediate-frequency signal by the frequency converter 11, and an extra spurious signal other than the intermediate-frequency signal is removed by the intermediate-frequency bandpass filter 12, and then the quasi-synchronous detection demodulation is performed. Input to the container 13. In the quasi-synchronous detection demodulator 13, the input intermediate frequency signal is converted into a baseband signal by the quadrature phase detector 10 and the fixed oscillator 14 input to the quadrature phase detector 10, and then the data is demodulated. .

However, if the carrier frequency of the intermediate frequency signal is largely deviated from the frequency of the fixed oscillator 14, the quasi-synchronous detection type demodulator 13 will not be able to achieve phase synchronization with the carrier and data will not be demodulated correctly.

On the other hand, the intermediate frequency signal that has passed through the intermediate frequency band pass filter 12 is input to the M multiplier 15, and the frequency of the intermediate frequency signal is multiplied by M so that the frequency is M times the carrier frequency of the intermediate frequency signal. Thus, an unmodulated signal from which the M-phase phase modulation component has been removed is obtained. Further, by dividing this unmodulated signal by (M × N) by the frequency divider 16, an unmodulated signal having a frequency of 1 / N of the carrier frequency of the intermediate frequency signal can be obtained.

On the other hand, by inputting the frequency of the fixed oscillator 14 of the quasi-synchronous detection type demodulator 13 to the frequency divider 116,
A signal whose frequency is 1 / N of the fixed oscillator 14 is obtained.
Then, the phase detector 17 detects the frequency difference between the 1 / N frequency of the carrier frequency of the intermediate frequency signal and the 1 / N frequency of the oscillation frequency of the fixed oscillator 14. In the loop filter 18, the output signal of the phase detector 17 is averaged and input to the voltage controlled oscillator 19 to control the oscillation frequency of the voltage controlled oscillator 19.

Here, the frequency of the output signal of the frequency divider 16 and the frequency of the output signal of the frequency divider 116 are made equal to each other.
That is, the carrier frequency of the intermediate frequency signal and the fixed oscillator 1
Voltage controlled oscillator 1 so that the oscillation frequency of 4 becomes equal.
Since the oscillation frequency of 9 is controlled via the loop filter 18, the quasi-synchronous detection type demodulator 1 is used when the carrier frequency of the intermediate frequency signal is within the frequency pull-in range of the AFC control loop.
The carrier frequency of the intermediate frequency signal input to 3 and the oscillation frequency of the fixed oscillator 14 match.

As described above, according to the first embodiment, M
Quasi-synchronous detection demodulator 1 even if the carrier frequency of the phase-phase modulated high-frequency signal drifts from the nominal frequency
Since the carrier frequency of the intermediate frequency signal M-phase-phase-modulated with the oscillation frequency of the fixed oscillator 14 of No. 3 is stabilized, it is fixed to the carrier frequency of the intermediate frequency signal input to the quasi-synchronous detection type demodulator 13. It matches the oscillation frequency of the oscillator 14, and the demodulation operation of the quasi-synchronous detection type demodulator 13 is extremely stabilized.

Further, the carrier frequency of the intermediate frequency signal input to the quasi-synchronous detection type demodulator 13 is always the fixed oscillator 14.
Since AFC control is performed to match the oscillation frequency of
There is no need to tighten the precision and stability of the oscillation frequency of the fixed oscillator 14, and at the same time, even if the carrier frequency of the intermediate frequency signal is increased, the precision and stability of the oscillation frequency of the fixed oscillator 14 are proportionally increased. No need.

Further, since one fixed oscillator 14 has both a function as a reference frequency for AFC control and a function as a local oscillator input to the quadrature phase detector 10, an intermediate frequency oscillator as in the conventional example is omitted. There is an effect that can be done.

In this embodiment, the frequency dividers 16 and 116 are used.
Since the frequency difference is detected by the phase comparator 17 after the frequency is lowered by, the phase comparator 17 may have a low operating frequency.

FIG. 2 shows an AFC according to the second embodiment of the present invention.
It is a block block diagram of an apparatus. Reference numeral 21 is a frequency converter for converting a high frequency signal phase-modulated by M phase into an intermediate frequency signal,
22 is an intermediate frequency band pass filter, 23 is a quasi-synchronous detection type demodulator, 24 is a fixed oscillator whose oscillation frequency is substantially equal to the nominal frequency of the intermediate frequency signal, 20 is a quasi-synchronous detection type demodulator 2
3 is a quadrature phase detector, 25 is the frequency of the intermediate frequency signal
M is a multiplier for multiplying, 26 is a divider for dividing the frequency of the output signal of the M multiplier 25 by (M × N), 226 is a divider for dividing the frequency of the fixed oscillator 24 by N, and 27 is a divider. The phase detector that detects the frequency difference between the output signal of the frequency detector 26 and the output signal of the frequency divider 226, 28 is a loop filter that averages the output signal from the phase detector 27, and 29 is the frequency converter 21.
Voltage controlled oscillator whose oscillation frequency is controlled by the output voltage of the loop filter 28, 201 is a synchronous determiner that determines whether the quasi-synchronous detection type demodulator 23 is correctly demodulating data, and 202 is a voltage. A sweep signal generator for forcibly sweeping the oscillation frequency of the controlled oscillator 29, 203
Is the output voltage of the loop filter 28 and the sweep signal generator 20.
It is an adder for adding the output voltages of 2 and inputting to the voltage controlled oscillator 29.

The operation of the AFC device configured as above will be described. First, the M-phase phase-modulated high-frequency signal is converted into an intermediate-frequency signal by the frequency converter 21, the extra spurious signal other than the intermediate-frequency signal is removed by the intermediate-frequency bandpass filter 22, and then the quasi-synchronous detection demodulation is performed. Input to the container 23. The quasi-coherent detection demodulator 23 converts the input intermediate frequency signal into a baseband signal by the quadrature detector 20 and the fixed oscillator 24 input to the quadrature detector 20, and then demodulates the data. . However, if the carrier frequency of the intermediate frequency signal deviates greatly from the frequency of the fixed oscillator 24, the quasi-synchronous detection type demodulator 23
In that case, the phase synchronization with the carrier wave is lost, and the data is not demodulated correctly.

On the other hand, the intermediate frequency signal passed through the intermediate frequency band pass filter 22 is input to the M multiplier 25. By multiplying the frequency of the intermediate frequency signal by M, a non-modulated signal whose frequency is M times the carrier frequency of the intermediate frequency signal and in which the M-phase phase modulation component is removed can be obtained. Further, by dividing this non-modulated signal by (M × N) by the frequency divider 26, a non-modulated signal having a frequency of 1 / N of the carrier frequency of the intermediate frequency signal can be obtained.

On the other hand, by inputting the frequency of the fixed oscillator 24 of the quasi-synchronous detection type demodulator 23 to the frequency divider 226,
A signal whose frequency is 1 / N of the fixed oscillator 24 is obtained.
Then, the phase detector 27 detects the frequency difference between the 1 / N frequency of the carrier frequency of the intermediate frequency signal and the 1 / N frequency of the oscillation frequency of the fixed oscillator 24. In the loop filter 28, the output signal of the phase detector 27 is averaged and input to the voltage controlled oscillator 29 to control the oscillation frequency of the voltage controlled oscillator 29.

Here, the frequency of the output signal of the frequency divider 26 and the frequency of the output signal of the frequency divider 226 are made equal to each other.
That is, the carrier frequency of the intermediate frequency signal and the fixed oscillator 2
Voltage controlled oscillator 2 so that the oscillation frequency of 4 becomes equal.
Since the oscillation frequency of 9 is controlled via the loop filter 28, the quasi-synchronous detection type demodulator 2 is operated when the carrier frequency of the intermediate frequency signal is within the frequency pull-in range of the AFC control loop.
The carrier frequency of the intermediate frequency signal input to 3 and the oscillation frequency of the fixed oscillator 24 match.

The synchronization decision unit 201 is a quasi-synchronization detection type demodulator 2
3 determines whether the data is correctly demodulated, and when the data is not correctly demodulated, the synchronization determiner 201 sends a sweep control signal to the sweep signal generator 202, and the sweep signal generator 202 causes the sweep control to be performed. A sweep signal is generated based on the signal, and the voltage-controlled oscillator 2 is generated via the adder 203.
Forcibly sweep the oscillation frequency of 9.

If, in the initial state, the carrier frequency of the intermediate frequency signal is outside the frequency pull-in range of the AFC control loop, and the carrier frequency of the intermediate frequency signal deviates greatly from the frequency of the fixed oscillator 24, the quasi-synchronization occurs. In the detection type demodulator 23, the phase synchronization with the carrier wave is lost, and the data is not demodulated correctly. At this time, the synchronization determiner 20
1, a sweep control signal is sent to the sweep signal generator 202, the sweep signal generator 202 generates a sweep signal based on the sweep control signal, and the oscillation frequency of the voltage controlled oscillator 29 is forcedly switched via the adder 203. Then, the oscillation frequency of the voltage controlled oscillator 29 is forcibly swept until the intermediate frequency signal is phase-synchronized with the carrier in the quasi-synchronous detection type demodulator 23 and the data is correctly demodulated.

As described above, according to the second embodiment, M
Quasi-synchronous detection demodulator 2 even if the carrier frequency of the phase-phase modulated high-frequency signal drifts from the nominal frequency
Since the carrier frequency of the intermediate frequency signal M-phase-phase-modulated with the oscillation frequency of the fixed oscillator 24 of No. 3 is stabilized, the carrier frequency of the intermediate frequency signal input to the quasi-synchronous detection demodulator 23 is fixed. It matches the oscillation frequency of the oscillator 24, and the demodulation operation of the quasi-synchronous detection type demodulator 23 is extremely stabilized.

Further, the carrier frequency of the intermediate frequency signal input to the quasi-synchronous detection type demodulator 23 is always the fixed oscillator 24.
Since AFC control is performed to match the oscillation frequency of
There is no need to tighten the precision and stability of the oscillation frequency of the fixed oscillator 24, and at the same time, even if the carrier frequency of the intermediate frequency signal is increased, the precision and stability of the oscillation frequency of the fixed oscillator 24 are increased in proportion thereto. No need.

Moreover, since one fixed oscillator 24 has both a function as a reference frequency for AFC control and a function as a local oscillator input to the quadrature detector 20, an intermediate frequency oscillator as in the conventional example is omitted. There is an effect that can be done.
Further, by providing the sweep signal generator 202 which outputs the sweep signal according to the synchronization determination, the pull-in range of the AFC can be expanded.

In the present embodiment, the frequency dividers 26, 226 are used.
Since the frequency difference is detected by the phase detector 27 after the frequency is lowered by, the phase detector 27 may have a low operating frequency.

FIG. 3 shows an AFC according to the third embodiment of the present invention.
FIG. 3 is an explanatory diagram of the apparatus, and particularly a diagram showing a synchronization determination method by the synchronization determiner 201 of the quasi-synchronous detection type demodulator 23 shown in FIG. 2. Reference numeral 33 is a quasi-synchronous detection type demodulator, 34 is a fixed oscillator of the quasi-synchronous detection type demodulator 33, 30 is a quadrature phase detector of the quasi-synchronous detection type demodulator 33, and 300 is an error for detecting an error rate of demodulated data. A rate detector 301 is a synchronization determiner that determines whether or not the quasi-synchronization detection type demodulator 33 is demodulating data correctly.

A synchronization determination method of the AFC device configured as above will be described. The intermediate frequency signal input to the quasi-coherent detection type demodulator 33 is converted into a baseband signal by the quadrature phase detector 30 and the fixed oscillator 34, and then data demodulated. The error rate of the demodulated data is detected by the error rate detector 300 in the process of correcting the error of the demodulated data by a known error correction decoder (not shown), and the detected error rate is synchronized as error rate information. It is sent to the determiner 301. The synchronization determiner 301 compares the error rate information with a predetermined reference value, and if the error rate exceeds this reference value, the quasi-synchronous detection type demodulator 33 determines that the data is not correctly demodulated, and the sweep is performed. The sweep control signal is sent to the signal generator 202.

FIG. 4 shows an AFC according to the fourth embodiment of the present invention.
FIG. 3 is an explanatory diagram of the apparatus, and particularly a diagram showing a synchronization determination method by the synchronization determiner 201 of the quasi-synchronous detection type demodulator 23 shown in FIG. 2. 43 is a quasi-synchronous detection type demodulator, 44 is a fixed oscillator of the quasi-synchronous detection type demodulator 43, 40 is a quadrature phase detector of the quasi-synchronous detection type demodulator 43, and 400 is a phase-locked loop of the quasi-synchronous detection type demodulator 43. The circuit 401 is based on the phase error signal output from the phase-locked loop circuit 400,
The quasi-coherent detection type demodulator 43 is a synchronism decision device for deciding whether or not data is correctly demodulated.

The synchronization determination method of the AFC device configured as above will be described. The intermediate frequency signal input to the quasi-synchronous detection demodulator 43 is converted by the quadrature detector 40 and the fixed oscillator 44 into I-axis and Q-axis baseband signals. This baseband signal includes an error (frequency error and phase error) between the frequency / phase of the carrier of the intermediate frequency signal and the frequency / phase of the fixed oscillator 44, and these errors are removed from the baseband signal. A circuit is generally included in the quasi-coherent detection type demodulator 43. And
The circuit that removes the phase error is the phase locked loop circuit 400.

Therefore, the phase locked loop circuit 400 includes a phase detector (not shown), the phase error is detected by this phase detector, and this phase error is averaged by a loop filter (not shown). It is converted into a phase error signal and provided to the synchronization decision unit 401. In the synchronism determiner 401, based on the provided phase error signal, the phase lock loop circuit 4
At 00, it is determined whether the phase error is removed from the baseband signal, that is, whether the phase locked loop circuit 400 is synchronized. If the phase error signal exceeds a predetermined reference level, the phase locked loop is detected. Since it is determined that the circuit 400 is not synchronized, it is also determined that the quasi-coherent detection type demodulator 43 is not correctly demodulating data,
A sweep control signal is sent to the sweep signal generator 202.

[0038]

As described above, according to the present invention, the following effects are exhibited.

(1) Since the carrier frequency of the M-phase phase-modulated intermediate frequency signal is stabilized with reference to the oscillation frequency of the fixed oscillator of the quasi-synchronous detection type demodulator, the demodulation operation of the quasi-synchronous detection type demodulator is stabilized. Is extremely stable.

(2) Since the carrier frequency of the intermediate frequency signal and the oscillation frequency of the fixed oscillator of the quasi-synchronous detection type demodulator are AFC controlled, the frequency accuracy and frequency stability required for the fixed oscillator are It doesn't have to be strict.

(3) Since the frequency difference is detected by the phase detector after lowering the frequency by the frequency divider, a phase detector with a low operating frequency may be used.

(4) Since the fixed oscillator of the quasi-synchronous detection type demodulator is the reference oscillator, the intermediate frequency oscillator can be omitted.

(5) By providing the sweep signal generator for sending the sweep control signal from the synchronization determiner and sweeping the center frequency of the voltage controlled oscillator, the pull-in range of the AFC can be expanded.

[Brief description of drawings]

FIG. 1 is a block diagram of an AFC device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of an AFC device according to a second embodiment of the present invention.

FIG. 3 is a diagram showing an AFC device according to a third embodiment of the present invention, and particularly a diagram showing a synchronization determination method of a synchronization determiner in the embodiment of FIG.

FIG. 4 is a diagram showing an AFC device according to a fourth embodiment of the present invention, and in particular, a diagram showing a synchronization determination method of a synchronization determiner in the embodiment of FIG. 2;

FIG. 5 is a block diagram of an AFC device in a conventional example.

[Explanation of symbols]

 10, 20, 30, 40 Quadrature phase detector 11, 21 Frequency converter 12, 22 Intermediate frequency band pass filter 13, 23, 33, 43 Quasi-synchronous detection type demodulator 14, 24, 34, 44 Fixed oscillator 15, 25 M multiplier 16, 26, 116, 226 frequency divider 17, 27 phase detector 18, 28 loop filter 19, 29 voltage controlled oscillator 201, 301, 401 synchronization decision unit 202 sweep signal generator 203 adder 300 error rate detection 400 Phase locked loop circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisaya Kato 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A frequency converter for converting a M-phase phase-modulated high-frequency signal into an intermediate-frequency signal, and the intermediate-frequency signal,
A quasi-synchronous detection type demodulator that performs digital demodulation after converting to a baseband signal by a quadrature phase detector and a fixed oscillator that is input to the quadrature phase detector, and an M multiplier that multiplies the frequency of the intermediate frequency signal by M A first divider that divides the output signal of the M multiplier by (M × N), a second divider that divides the frequency of the fixed oscillator by N, and the first divider. Detector for detecting the frequency difference between the output signal of the frequency divider and the output signal of the second frequency divider, and the oscillation frequency is controlled based on the output voltage from the phase detector which is input to the frequency converter. Automatic frequency control device comprising: 2. A frequency converter for converting an M-phase phase-modulated high frequency signal into an intermediate frequency signal, and the intermediate frequency signal,
A quasi-synchronous detection type demodulator that performs digital demodulation after converting to a baseband signal by a quadrature phase detector and a fixed oscillator that is input to the quadrature phase detector, and an M multiplier that multiplies the frequency of the intermediate frequency signal by M A first divider that divides the output signal of the M multiplier by (M × N), a second divider that divides the frequency of the fixed oscillator by N, and the first divider. Detector for detecting the frequency difference between the output signal of the frequency divider and the output signal of the second frequency divider, and the oscillation frequency is controlled based on the output voltage from the phase detector which is input to the frequency converter. A voltage controlled oscillator, a quasi-synchronous detection type demodulator, which determines whether or not the data is correctly demodulated, and which outputs a sweep control signal corresponding to the determination result, and the sweep control signal. Sweep the center frequency of the voltage controlled oscillator based on Automatic frequency control device of the sweep signal that has been characterized to consist of a sweep signal generator for outputting to the voltage controlled oscillator. 3. The automatic frequency control device according to claim 2, wherein the synchronism judging device judges synchronism based on error rate information of data demodulated by the quasi-coherent detection type demodulator. 4. A synchronization judging device judges whether or not the phase locking loop circuit is phase locked based on a phase error signal output from a phase locking loop circuit which constitutes the quasi-synchronization detection type demodulator. 3. The automatic frequency control device according to claim 2, wherein the synchronization is determined.