JPH08107428A - Automatic frequency controller - Google Patents

Abstract

PURPOSE: To control a voltage controlled oscillator(VCO) and to almost match it with the carrier frequency of an FSK signal in the case of demodulating the FSK signal of a low modulation index or the multi-level FSK signal concerning the automatic frequency controller for the FSK receiver of radio communication. CONSTITUTION: While using an IQ signal provided by the direct conversion and reception of the FSK signal, a frequency deviation modulating means 109 generates the second FSK signal with a fixed frequency signal lower than the received FSK signal, frequency/voltage conversion is respectively performed to the provided second FSK signal and the fixed frequency signal by F/V converting means 110 and 111, and the voltages are compared by a voltage comparator 126. The average voltage due to an averaging means 114 corresponds to the frequency deviation between the carrier wave of the FSK signal 101 and the output of the VCO. Since the VCO is controlled while using the average voltage, the carrier wave of the received FSK signal 101 is almost matched with the frequency of the VCO 105.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to an automatic frequency control device for a frequency shift keying receiver for digital radio communication.

[0002]

2. Description of the Related Art In recent years, frequency shift keying (hereinafter abbreviated as FSK) in digital radio communication is called Frequen.
As a receiver of cy Shift Keying (Frequency Shift Keying) modulation system, a direct conversion receiver is being considered as a configuration suitable for integration into an integrated circuit.
However, in this direct conversion receiver, if the frequency of the local oscillator deviates from the carrier signal frequency, the sensitivity characteristic deteriorates. As a countermeasure for this, for example, Japanese Patent Laid-Open No. 4-4563
An automatic frequency control device (AF
A receiver using C) has been devised. Hereinafter, the conventional automatic frequency control device will be briefly described with reference to FIG. Note that FIG. 12 is a main part waveform diagram in the configuration of FIG.

In FIG. 11, a received wave 1 frequency-shift-modulated with a binary digital signal of a mark or space is shown.
01 is amplified by the amplifier 102, divided into two, and input to the mixers 103 and 104, respectively. The local oscillation signal output from the voltage controlled oscillator 105 is divided into two, one is input to the mixer 103, and the other is input to the 90 ° phase shifter 10.
At 6 the phase is delayed by 90 ° and input to mixer 104.
Then, the outputs of mixers 103 and 104 are band-limited by low-pass filters 107 and 108, respectively, and an in-phase baseband signal (I signal) and a quadrature baseband signal (Q signal) are obtained. The demodulation circuit 801 demodulates using the I and Q signals to obtain a demodulation output 808.

In such a direct conversion receiving circuit, I
Alternatively, the limiter circuit 802 limits the amplitude of the Q signal, the edge detection circuit 803 detects an edge, and the pulse generation circuit 8
After generating a pulse wave with a constant time width at 04, the integrating circuit 8
By performing integration at 05, the F / V (frequency / voltage) conversion of the baseband signal is equivalently performed. By averaging the results by the average value circuit 806, the voltage VD corresponding to the frequency shift FD is obtained. When the frequency of the received carrier signal and the frequency of the output signal of the voltage controlled oscillator are deviated, the output of the integrating circuit 805 is an average value when the data is a mark and when the data is a space, as shown in FIG. It touches big and small compared to VD. Therefore, AFC can be applied by controlling the voltage controlled oscillator 105 by the control circuit 807 so that the output of the integrating circuit substantially matches the average value VD.

[0005]

In recent years, the FS of pagers, etc.
In the K digital radio communication system, for the purpose of coping with an increase in demand and effectively using frequency resources, it is desired to speed up / multi-value the data transmission and narrow the occupied band, that is, the modulation index. It is necessary to demodulate low FSK signals.

Now, when the receiver of FIG. 11 receives an FSK signal having a modulation index of 1 or less,
The number of edges appearing between one data of the I and Q baseband signals is reduced. Then, if the frequency of the carrier signal of the received FSK signal and the frequency of the output signal of the voltage-controlled oscillator 105 are deviated, there is a possibility that an edge will not appear between data in either the mark or the space. The averaging in the average value circuit 806 may not be performed correctly, and the AFC may not operate correctly.

Further, when the receiver of FIG. 11 receives a four-valued FSK signal as shown in FIG. 13, for example, the frequency of the temporarily received carrier signal and the frequency of the output signal of the voltage controlled oscillator 105 are substantially the same. Also, since the output voltage of the integrating circuit 805 is different between the case where the frequency shift frequency is ΔF and the case where the frequency shift frequency is 3ΔF, the output voltage is not constant, so that the AFC does not operate correctly.

Further, when the FSK receiver is used in a portable device such as a pager, it is required to have a simple structure and low power consumption in terms of downsizing and battery life.

The present invention has been made to solve the above problems, and controls the output frequency of the voltage controlled oscillator when demodulating an FSK signal having a low modulation index or a multi-valued FSK signal. However, the object is to make the carrier frequency of the received FSK signal approximately the same and to have a low power consumption and a simple device.

[0010]

In order to achieve the above object, an automatic frequency control device of the present invention comprises an FSK wave signal frequency-shift keyed with a digital signal, an amplifier for amplifying the FSK signal, and the FSK signal. A voltage controlled oscillator that generates a frequency substantially equal to the carrier signal of the signal, a phase shifter that shifts the phase of the output signal of the voltage controlled oscillator by 90 °, an output signal of the amplifier and an output signal of the voltage controlled oscillator. A first mixer for mixing, a second mixer for mixing the output signal of the amplifier and an output signal of the phase shifter, and an output signal of the first mixer for band limiting, and an in-phase baseband signal. A first low-pass filter for extracting the (I signal); a second low-pass filter for extracting the quadrature baseband signal (Q signal) by band limiting the output signal of the second mixer; signal From the Q signal, a frequency shift keying means for frequency shift keying with a fixed frequency signal lower than the carrier wave signal and a signal frequency shift keyed by the frequency shift keying means are converted into a voltage substantially proportional to the frequency. First frequency-voltage conversion (F / V conversion) means, second F / V conversion means for converting to a voltage substantially proportional to the frequency of the fixed frequency signal, and output of the first F / V conversion means A voltage comparator that outputs the result of comparing the voltage and the output voltage of the second F / V conversion means as a demodulation signal;
The output of the voltage comparator is averaged for a time sufficiently longer than the data rate, and the averaging means for controlling the voltage controlled oscillator using the output,
The automatic frequency control may be always performed, or a control means for controlling the automatic frequency control to be performed at regular intervals may be provided.

Further, instead of the second F / V conversion means, a holding means and first and second switching means may be provided, or a third low pass filter may be provided at the output of the voltage comparator. The configuration may be provided, or the fourth low pass filter may be provided between the frequency conversion unit and the first F / V conversion unit.

[0012]

According to the present invention, after the received FSK signal is directly converted into the I and Q baseband signals, the second FSK signal is converted into the second FSK signal with a fixed frequency signal lower than the carrier signal of the received FSK signal. / V conversion is performed. As a result, the frequency shift between the first FSK signal and the output signal of the voltage controlled oscillator is determined by the average of the signal voltages F / V converted by the first F / V conversion means and the frequency of the fixed frequency signal. Appears as a difference from the voltage corresponding to. By controlling the voltage-controlled oscillator using this voltage difference, automatic frequency control is possible. In particular, automatic frequency control is possible even for FSK signals with a low modulation index and multilevel FSK signals.

[0013]

【Example】

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described with reference to FIG. 1 is a circuit diagram of an automatic frequency control device according to a first embodiment of the present invention.

In FIG. 1, 101 is a frequency shift keying modulated FSK signal, 102 is an amplifier, and 103 and 104 are 2 signals.
Mixer for mixing and outputting two input signals, 105 a voltage controlled oscillator for controlling the output frequency by voltage, 106 a phase shifter for shifting the phase of the signal by 90 °, 107 and 108 for I and Q baseband signals A low-pass filter for passing the component, 109 outputs the I and Q signals subjected to frequency shift modulation by quadrature modulation at a fixed frequency lower than the carrier frequency of the FSK signal 101, and also outputs a fixed frequency signal. The frequency shift keying means 110, 111 for outputting outputs F each for converting an input signal into a voltage substantially proportional to its frequency.
/ V conversion means, 112 is a voltage comparator that outputs a voltage comparison result of two input voltages, and 113 is an averaging means that averages the input signals. The frequency shift keying means 109
Is an oscillator 114 for generating a fixed frequency signal lower than the carrier of the FSK signal 101, and a phase shift of the signal by 90
The phase shifter 115 for shifting the phase, the mixers 116 and 117,
It is assumed to be configured with a subtractor 118 that outputs a difference voltage between two inputs. Further, the F / V conversion means 110, 111
Is, for example, a limiter circuit 119 that limits the amplitude, a delay circuit 120 that delays a signal by a minute time, and an edge detection circuit 127 that includes an exclusive OR circuit 121 that outputs an exclusive OR of two input signals, It is composed of a pulse generation circuit 122 for generating a pulse wave having a constant time width and a low pass filter 123.

In the automatic frequency control device configured as described above, the operation of directly converting the received FSK signal at a frequency substantially equal to its carrier frequency to obtain I and Q signals has been described in the prior art. Since it is the same, it is omitted and the operation thereafter is described below.

The frequency shift keying means 109 includes the I, Q
The signal is frequency shift-modulated with a fixed frequency signal lower than the carrier frequency of the FSK signal 101, for example, 20 kHz, and a second FSK signal 124 is obtained. The FSK signal 124 is converted by the F / V conversion means 110 into a voltage VF that is substantially proportional to the frequency.

Further, the F / V conversion means 111 obtains the voltage Vo corresponding to the fixed frequency signal 125 of the frequency shift modulation means 109. Then, the voltage comparator 112 outputs the VF.
And a Vo voltage comparison result (VF-Vo) are output. This voltage difference becomes 0 V when the instantaneous frequency of the second FSK signal 123 is equal to the fixed frequency signal, and takes a positive or negative value almost in proportion to the frequency change of the second FSK signal 124.
The demodulation result 126 is output.

The demodulation result is averaged by the averaging means 113.
Then, the average value is calculated for a time sufficiently longer than the data rate. Assuming that the transmission data is random, the average value is a voltage corresponding to the center frequency of the second FSK signal. If the frequency of the carrier signal of the first FSK signal and the frequency of the output signal of the voltage controlled oscillator match, then the second
The center frequency of the FSK signal and the frequency of the fixed frequency signal are the same, and the average value voltage is 0V. On the other hand, if the carrier frequency of the first FSK signal 101 and the output frequency of the voltage controlled oscillator 105 are deviated, this frequency deviation corresponds to the average value voltage. Therefore, using this average value voltage, the voltage controlled oscillator 1
Control 05.

When the F / V converting means 110 and 111 are constructed as shown in FIG. 1C, the operation will be described below. The input signal is the limiter circuit 11
9, the amplitude is limited, one is input to the exclusive OR circuit 121, and the other is delayed by a delay time by the delay circuit 120 and then input to the exclusive OR circuit 121.
Then, the exclusive OR is calculated, and the rising and falling portions of the signal are detected. At the detected edge portion, a pulse wave having a constant time width is generated by the pulse generation circuit 122, and the obtained pulse train is the low-pass filter 12
Integrated at 3.

As described above, according to the present embodiment, the frequency shift between the carrier signal of the first FSK signal and the voltage controlled oscillator appears as the output voltage of the averaging means 113. Therefore, using this voltage, Automatic frequency control becomes possible by controlling the frequency of the voltage controlled oscillator in the direction in which the frequency shift decreases.

The configurations of the frequency shift modulation means 109 and the F / V conversion means 110 and 111 shown in the present embodiment are not limited to this, and for example, the frequency shift modulation means 1
As shown in FIG. 1D, a phase shifter 126 may be provided instead of the phase shifter 115 and an adder 127 may be provided instead of the subtractor 118.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to FIG. FIG. 3 is a circuit system diagram of an automatic frequency control device according to the second embodiment of the present invention.

In FIG. 3, each of the constituent elements 101 to 113 is shown.
Is similar to the configuration of FIG. In FIG. 3, FIG.
The configuration is different from that of the holding means 201 for holding the output of the averaging means 113, the averaging means 113 and the holding means 20.
This is the point that a control means 202 for controlling 1 is newly provided.

The operation of the automatic frequency control device configured as described above will be described below. First, the control means 2
In the demodulation result 02 demodulated in the same manner as in the first embodiment, for example, as shown in FIG. 4, an average value of only a specific section such as an even number of bit synchronization data in which marks and spaces are alternately repeated. Is calculated by the averaging means 113, and the mean value is held by the holding means 201 and supplied to the voltage controlled oscillator 105 until the mean value is calculated again. The averaging means 113 keeps the power off while averaging is not performed.

As described above, according to this embodiment, if the section in which an even number of data strings in which marks and spaces are alternately repeated appears is known, only that section is averaged and the result is calculated as a voltage. By using it as the control voltage of the controlled oscillator 105, more accurate automatic frequency control becomes possible.

In this embodiment, an even number of bit synchronization data in which marks and spaces are alternately repeated is used as the averaging section, but the present invention is not limited to this, and the output of the averaging means 113 is used. The voltage is the second FSK signal 1
It suffices if it is a section where it is known that the voltage corresponds to the center frequency of 24. Therefore, for example, the FSK signal may be multi-valued, and an even number of data strings in which the symbol corresponding to the maximum frequency deviation on the positive side and the symbol corresponding to the maximum frequency deviation on the negative side are alternately repeated are used. Good. Further, the control unit 202 may be controlled by the CPU.

(Embodiment 3) A third embodiment of the present invention will be described below with reference to FIG. FIG. 5 is a circuit system diagram of an automatic frequency control device according to the third embodiment of the present invention.

In FIG. 5, each constituent element 101-113
Is similar to the configuration of FIG. The difference from the configuration of FIG. 1 is that the holding means 301 that holds the output voltage of the F / V conversion means 111, the F / V conversion means 111 and the holding means 301.
This is the point that a control means 302 for controlling the is newly provided.

The operation of the automatic frequency control device configured as described above, which is different from that of the first embodiment, will be described below.
The control unit 302 includes the F / V conversion unit 111 and the holding unit 30.
The following control is performed for 1. That is, the F / V converting means 111 converts the voltage into a voltage corresponding to the frequency of the fixed frequency signal 125 at regular time intervals, and the voltage is held by the holding means 301 and supplied to the voltage comparator 112. Also,
The F / V conversion means 111 keeps the power off while the F / V conversion is not performed.

As described above, according to this embodiment, the F / V conversion of the carrier signal 125 is performed every certain time, and the power of the F / V conversion means 111 is turned off while the F / V conversion is not performed. As a result, power consumption can be reduced. Further, even if the frequency of the carrier signal 125 fluctuates due to temperature characteristics or the passage of time, the F / V conversion is performed at intervals such that the fluctuation does not increase, so that it is possible to sufficiently follow the frequency fluctuation.

In the present embodiment, the interval for performing the F / V conversion is fixed, but the interval is not limited to this, and the frequency fluctuation of the fixed frequency signal 125 and the fluctuation of the holding voltage of the holding means 301 do not become large. The following F / V conversion may be performed. Further, the control means 302 is C
It may be controlled by the PU.

(Embodiment 4) A fourth embodiment of the present invention will be described below with reference to FIG. FIG. 6 is a circuit system diagram of an automatic frequency control device according to the fourth embodiment of the present invention.

6 is different from the configuration of FIG. 1 in that the frequency shift modulation means 109 of FIG. 1 uses a digital oscillator 401 for generating a double fixed frequency signal twice the fixed frequency signal 125 and an input signal of 1 Divider 40 that divides by 2
2, an exclusive OR circuit 403, inverting amplifiers 404 and 405 that invert the sign of the signal, and 2 according to the control signal.
Switching means 406, 40 for switching between two input terminals
7 and a subtractor 408 that outputs a difference voltage between two inputs are provided, and the output of the digital oscillator 401 is output as a double fixed frequency signal 412. Further, as the F / V conversion means 110, a limiter circuit 119 for limiting the amplitude is provided.
And a delay circuit 120 for delaying the signal by a minute time and an exclusive OR circuit 1 for outputting an exclusive OR of two input signals.
An edge detection circuit configured by 21, a pulse generation circuit 122 that generates a pulse wave having a constant time width, and a low pass filter 123 are provided. Furthermore, the F / V conversion means 1
A pulse generation circuit 409 for generating a pulse wave having a constant time width at the rising edge of the input signal and a low-pass filter 410 for integrating the pulse train are provided as 11, and the frequency shift modulation means 109 and the F / V conversion means are provided. A low-pass filter 411 is provided between the low-pass filter 110 and 110.

In the automatic frequency control device configured as described above, a portion that operates differently from the first embodiment shown in FIG. 1 will be described below.

First, the double fixed frequency signal generated by the digital oscillator 401 shown in FIG.
The frequency is divided by 2 by the frequency divider 402, and the switching means 407 is performed.
Is supplied to. On the other hand, the exclusive OR circuit 403
At, the exclusive OR is calculated with the 1/2 frequency-divided signal and is supplied to the switching means 406.

Here, the signals supplied to the switching means 406 and 407 are signals (FIGS. 7 (b) and 7 (c)) whose phases are shifted by 90 ° as shown in FIG. The switching means 406 and 407 switch between the output signal of the inverting amplifier and the signal bypassing the inverting amplifier according to the input signal.

The subtractor 408 switches the switching means 40.
By calculating the difference between the output signals of 6 and 407, the FSK signal 124 of the double fixed frequency signal is equivalently obtained. However, since this signal is a digital signal, the low-pass filter 411 removes the harmonic components to perform waveform shaping, and is input to the F / V conversion circuit 110. Further, the double fixed frequency signal 412 is input to the pulse generation circuit 409, a pulse wave having a constant time width is output at the rising edge of the signal, and the obtained pulse train is integrated by the low-pass filter 410.

As described above, according to the present embodiment, by using the digital oscillator 401, the 1/2 frequency divider and the mixer can be configured by a digital circuit, which facilitates IC integration. Also, the F / V conversion means 111
By inputting a double fixed frequency signal having a frequency twice as high as the fixed frequency signal to the pulse generator, it suffices to generate a pulse width only at the rising edge of the signal, and a limiter circuit and an edge detection circuit for detecting an edge are unnecessary, It is possible to reduce the number of parts and power consumption.

Note that the digital oscillator 401 for generating the double fixed frequency signal may be used by dividing the frequency of, for example, the clock source of the CPU other than the receiving circuit. Further, instead of the low-pass filter 411, a band-pass filter may be used to remove a low-frequency component including a DC component as well as a harmonic component.

(Fifth Embodiment) A fifth embodiment of the present invention will be described below with reference to FIG. FIG. 8 is a circuit system diagram of an automatic frequency control device according to the fifth embodiment of the present invention. 8 is different from the configuration of FIG. 7 in that FIG.
As the F / V conversion means 110 of the fourth embodiment, the pulse generation circuit 501 that generates a pulse wave having a time width twice that of the pulse generation circuit 409 only when the input signal rises.
And a low-pass filter 502 for integrating the pulse train.

In the automatic frequency control device configured as described above, the operation other than the F / V conversion circuit 110 is the same as that of the fourth embodiment. Therefore, the operation of the F / V conversion circuit 110 will be described below. To do. Low pass filter 411
In the pulse generation circuit 501, the second FSK signal 124 band-limited by is generated a pulse wave having a time width double that of the pulse generation circuit 409 only at the rising edge of the signal. Then, the obtained pulse train is integrated by the low pass filter 502.

As described above, according to this embodiment, F / V
The number of pulse waves generated in the conversion circuit 110 is half that in the case of the fourth embodiment, but since the time width of the pulse waves generated is doubled, the result of integration by the low-pass filter 502. Is almost the same as that of the fourth embodiment. Therefore, the limiter circuit and the edge detection circuit are not required, and the number of parts and power consumption can be reduced.

(Sixth Embodiment) A sixth embodiment of the present invention will be described below with reference to FIG. FIG. 9 is a circuit system diagram of an automatic frequency control device according to the sixth embodiment of the present invention.

In FIG. 9, each constituent element 101 to 10
Reference numerals 9, 112, and 113 have the same configuration as that of FIG.
9 is different from the configuration of FIG. 1 in that the low-pass filter 123 among the elements configuring the F / V conversion means 110 and 111 is removed and the voltage comparator 112 and the averaging means 113 are provided. This is the point where a low pass filter 601 is newly provided.

In the automatic frequency control device configured as described above, the received FSK signal 101 is directly converted at a frequency substantially equal to its carrier frequency to obtain I and Q signals, and then the carrier of the received FSK signal 101 is obtained. The operation of obtaining the second FSK signal 124 at a fixed frequency lower than that of the signal will be omitted as described in the first embodiment, and the operation thereafter will be described below.

Second obtained by frequency conversion means 109
The amplitude of the FSK signal 124 is limited by the limiter circuit 119, and the edge detection circuit 120 detects rising and falling edges of the signal. Then, at the rising edge of the obtained edge, the pulse generation circuit 122 generates a pulse wave having a constant time width, and a pulse train having a density approximately proportional to the second FSK signal is obtained. Further, also in one of the F / V conversion means 111, similar processing is performed on the fixed frequency signal output 124 from the frequency shift modulation means 109, and a pulse train having a density corresponding to the frequency of the fixed frequency signal is obtained. . Then, in the voltage comparator 112, F /
Subtraction between the pulse trains of the V conversion means 110 and 111 is performed. Then, the obtained difference voltage is passed through the low pass filter 6
By inputting 01, the demodulation result 126 is obtained. The operation of obtaining the average value by the averaging means 113 using this result and controlling the voltage controlled oscillator 105 is as described in the first embodiment.

As described above, according to this embodiment, the F / V
Both the F / V conversion means 110 and 111 are obtained by obtaining pulse trains having a density substantially proportional to the frequency of each input signal by the conversion means 110 and 111, performing subtraction between these pulse trains, and then performing filtering. The low-pass filter required for the above can be completed with one of the latter stages of the voltage comparator.

(Embodiment 7) Hereinafter, a seventh embodiment of the present invention will be described with reference to FIG. FIG. 10 is a circuit system diagram of an automatic frequency control device according to the seventh embodiment of the present invention.

In FIG. 10, each constituent element 101 to 10
Reference numerals 9, 112, and 113 have the same configuration as that of FIG.
10 is different from the configuration of FIG. 1 in that the F / V conversion means 111 is removed and the holding means 701 that holds the voltage in the preceding stage of the voltage comparator 112 and the input of the F / V conversion means 110 are connected to the second input. First switching means 702 for switching between the FSK signal output 124 and the fixed frequency signal output 125.
And the output of the F / V conversion means 110 to the voltage comparator 1
Second switching means 703 for switching between 12 and the holding means 701, the holding means 701 and the switching means 7
02, 703 and a control means 704 for controlling.

In the automatic frequency control device configured as described above, the received FSK signal 101 is directly converted at a frequency substantially equal to its carrier frequency to obtain I and Q signals, and then the carrier of the received FSK signal 101 is obtained. The operation of obtaining the second FSK signal 124 with a fixed frequency signal lower than the signal will be omitted as described in the first embodiment, and the operation thereafter will be described below.

The normal switching means 702 and 703 are respectively connected to the second FSK signal 124 and the voltage comparator 112. The control unit 704 controls, for example, the switching units 702 and 703 at fixed intervals, connects the fixed frequency signal 125 and the holding unit 701, respectively, and corresponds to the frequency of the fixed frequency signal 125 in the F / V conversion unit 110. The voltage is supplied to the holding means 701 and held. Hereinafter, the operation of performing the voltage comparison between the F / V conversion output of the second FSK signal 124 and the holding voltage of the holding means 701 and controlling the voltage controlled oscillator using the average value thereof will be described in the first embodiment. As I did.

As described above, according to the present embodiment, F / V conversion of the fixed frequency signal 125 is performed in the F / V conversion means 110 at a certain fixed cycle and the fixed frequency signal 125 is held in the holding means 701, whereby F / V conversion is performed. V conversion means 111 becomes unnecessary,
It is possible to reduce the number of parts and power consumption.

In this embodiment, the switching means 70
The timing of switching 2, 703 to the fixed frequency signal 125 and the holding circuit 701 is set at a certain fixed cycle, but the timing is not limited to this. For example, this switching may be performed while unnecessary data is being sent to the receiver itself. You may make it control. Further, the control unit 704 may be controlled by the CPU.

Further, the present invention is not limited to the above-mentioned embodiments, and for example, the low pass filters 107, 1
A limiter circuit may be provided between the 08 and the frequency shift keying means 109.

[0055]

As described above, according to the present invention, after the received FSK signal is directly converted into the baseband signal, the fixed frequency signal lower than the carrier signal of the received FSK signal is used as the second FSK signal. Since the F / V conversion is performed, the frequency difference between the carrier wave signal and the voltage controlled oscillator can be detected more accurately even for the FSK signal having a low modulation index. Also, in the multi-valued FSK signal, if each symbol is arranged symmetrically with respect to the carrier signal, the average value voltage of the F / V conversion result is also constant at the voltage corresponding to the center frequency. , Automatic frequency control becomes possible. Further, according to the configuration of the present invention, it is only necessary to add a few circuits in addition to the configuration required to obtain the demodulation result, and it is possible to realize an automatic frequency control device with low power consumption and a simple configuration.

[Brief description of drawings]

FIG. 1 is a circuit system diagram of an automatic frequency control device according to a first embodiment of the present invention.

FIG. 2 is a control voltage vs. output frequency characteristic diagram of a voltage controlled oscillator, which is a main part of the embodiment.

FIG. 3 is a circuit system diagram of an automatic frequency control device according to a second embodiment of the present invention.

FIG. 4 is a waveform chart showing data for bit synchronization in the embodiment.

FIG. 5 is a circuit system diagram of an automatic frequency control device according to a third embodiment of the present invention.

FIG. 6 is a circuit system diagram of an automatic frequency control device according to a fourth embodiment of the present invention.

FIG. 7 is a waveform diagram showing an output signal of a main part in the embodiment.

FIG. 8 is a circuit system diagram of an automatic frequency control device according to a fifth embodiment of the present invention.

FIG. 9 is a circuit system diagram of an automatic frequency control device according to a sixth embodiment of the present invention.

FIG. 10 is a circuit system diagram of an automatic frequency control device according to a seventh embodiment of the present invention.

FIG. 11 is a circuit system diagram of a conventional automatic frequency control device.

FIG. 12 is a waveform diagram showing an output signal of a main part in an example of a conventional automatic frequency control device.

FIG. 13: 4 in an example of a conventional automatic frequency control device
Value FSK signal component diagram

[Explanation of symbols]

 102 Amplifier 103, 104 Mixer 105 Voltage Controlled Oscillator 106 Phase Shifter 107, 108 Low Pass Filter 109 Frequency Shift Modulation Means 110, 111 F / V Conversion Means 112 Voltage Comparator 113 Averaging Means 114 Oscillator 115 Phase Shifter 116, 117 mixer 118 subtractor 119 limiter circuit 120 delay circuit 121 exclusive OR circuit 122 pulse generation circuit 123 low-pass filter 126 phase shifter 127 adder 201 holding means 202 control means 301 holding means 302 control means 401 digital Oscillator 402 Frequency divider 403 Exclusive OR circuit 404, 405 Inverting amplifier 406, 407 Switching means 408 Subtractor 409 Pulse generation circuit 410 Low pass filter 411 Low pass filter 501 Pulse generation circuit 502 Low pass Over filter 601 low-pass filter 701 holding means 702, 703 switching unit 704 control unit 801 demodulating circuit 802 a limiter circuit 803 edge detection circuit 804 pulse generating circuit 805 integrating circuit 806 averaging circuit 807 control circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsushi Yokozaki 4-3-1 Tsunashima, Kohoku-ku, Yokohama-shi, Kanagawa Matsushita Communication Industrial Co., Ltd.

Claims (17)

[Claims] 1. An amplifier for amplifying a frequency shift keyed first frequency shift keying signal, a voltage controlled oscillator for generating a frequency substantially equal to a carrier signal of the first frequency shift keying signal, and A phase shifter that shifts the phase of the output signal of the voltage controlled oscillator by 90 °; a first mixer that mixes the output signal of the amplifier and the output signal of the voltage controlled oscillator;
A second mixer for mixing the output signal of the amplifier and the output signal of the phase shifter, and a first low-pass filter for band-limiting the output signal of the first mixer to extract an in-phase baseband signal. A second low-pass filter for band-limiting the output signal of the second mixer to extract a quadrature baseband signal, and the first frequency deviation from the in-phase baseband signal and the quadrature baseband signal. Frequency shift keying means for frequency shift keying a fixed frequency signal lower than the carrier signal of the transmodulation signal, and outputting the obtained second frequency shift keying signal and the fixed frequency signal, and the frequency shift keying First frequency-voltage conversion means for converting the signal frequency-shift-modulated by the means into a voltage substantially proportional to frequency,
A second frequency voltage conversion means for converting the fixed frequency signal into a voltage substantially proportional to the frequency, and an output voltage of the first frequency voltage conversion means and an output voltage of the second frequency voltage conversion means were compared. It has a voltage comparator for outputting the result as a demodulation signal, and an averaging means for averaging the output of the voltage comparator in a time sufficiently longer than the data rate and controlling the voltage controlled oscillator using the output. An automatic frequency control device characterized in that 2. A frequency shift keying means for generating a fixed frequency signal, a fixed frequency oscillator, a second phase shifter for shifting a phase of an output signal of the oscillator by 90 °, an in-phase baseband signal and the in-phase baseband signal. A third mixer that mixes the output signals of the second phase shifter, a fourth mixer that mixes the quadrature baseband signal and the output signal of the fixed frequency oscillator, the third mixer and the fourth mixer. The difference between the output signals of the mixer of
A subtractor for obtaining the frequency shift keying signal of
2. The automatic frequency control device according to claim 1, wherein the frequency shift keying signal of 1 and the fixed frequency signal are output. 3. A first limiter circuit as the first frequency-voltage converting means for limiting the amplitude of the output signal of the frequency shift keying means, and a first limiter circuit for detecting rising / falling edges of the amplitude-limited signal. No. 1 edge detection circuit, a first pulse generation circuit that generates a pulse wave having a constant time width at the rising edge of the edge detected by the first edge detection circuit, and the first pulse generation circuit. An automatic frequency control device according to claim 1, further comprising a third low-pass filter for integrating the pulse train. 4. A second limiter circuit as the second frequency-voltage converting means for limiting the amplitude of the output signal of the frequency shift modulation means, and a second limiter circuit for detecting the rising and falling edges of the amplitude-limited signal. A second edge detection circuit, a second pulse generation circuit that generates a pulse wave having a constant time width at the rising edge of the edge detected by the second edge detection circuit, and a second pulse generation circuit that is generated by the second pulse generation circuit. An automatic frequency control device according to claim 1, further comprising a fourth low-pass filter for integrating the pulse train, and having the same frequency-voltage characteristic as the first frequency-voltage converting means. 5. The first frequency shift keying signal is a binary frequency shift keying signal in which an even number of data strings in which marks and spaces are alternately repeated are inserted at regular intervals, and the averaging means. Is provided, and first control means for controlling the averaging means and the first holding means are provided, and the first control means is provided in the section of the data string. The averaging means averages the demodulation results, the obtained value is held by the first holding means and supplied to the voltage controlled oscillator, and the power of the averaging means is turned off except for the section of the data string. The automatic frequency control device according to claim 1, wherein the automatic frequency control device is controlled as follows. 6. As the first frequency shift keying signal, a symbol corresponding to the maximum frequency shift on the positive side and a symbol corresponding to the maximum frequency shift on the negative side are used instead of the binary frequency shift keying signal. 6. The automatic frequency control device according to claim 5, wherein the multi-valued frequency shift keying signal has an even number of data strings which are alternately repeated. 7. A second holding means for holding the output of the second frequency-voltage converting means and supplying it to a voltage comparator, and the second holding means.
Second frequency control means for controlling the frequency voltage conversion means and the second holding means are provided, and the second control means turns on the second frequency voltage conversion means at regular intervals. 2. The automatic frequency control device according to claim 1, wherein frequency conversion is performed on the fixed frequency signal, and the obtained voltage is held by the second holding means and supplied to the voltage comparator. 8. Instead of the fixed frequency oscillator and the second phase shifter, a double fixed frequency signal having a frequency twice as high as the fixed frequency signal, and ½ of the frequency of the double fixed frequency signal. A frequency divider and an exclusive OR circuit for outputting an exclusive OR of the double fixed frequency signal and the output signal of the 1/2 frequency divider, and the output of the exclusive OR circuit is combined with the third mixing circuit. 3. The automatic frequency control device according to claim 2, wherein the automatic frequency control device supplies the output of the 1/2 frequency divider to the fourth mixer. 9. A fifth low-pass filter that passes the signal band of the second frequency shift keying signal is provided between the frequency shift keying means and the first frequency voltage converting means, and a harmonic component is provided. 9. The automatic frequency control device according to claim 8, wherein the waveform of the second frequency shift keying signal is shaped by removing the. 10. A band pass filter for passing a signal band of a second frequency shift keying signal is provided between the frequency shift keying unit and the first frequency voltage converting unit, and a harmonic component and a low frequency component are provided. 9. The automatic frequency control device according to claim 8, wherein the waveform of the second frequency shift keying signal is shaped by removing the. 11. The third mixer comprises an inverting amplifier that inverts a sign of an input signal, and an output signal of the inverting amplifier and a device that bypasses the inverting amplifier according to an output signal of the exclusive OR circuit. A fourth mixer for inverting the sign of the input signal, and a first mixer for switching the output between the inverting amplifier and the output of the inverting amplifier according to the output signal of the 1/2 frequency divider. 9. The automatic frequency control device according to claim 8, further comprising second switching means for switching an output between a signal and a signal bypassing the inverting amplifier. 12. The frequency shift keying means outputs a double fixed frequency signal instead of outputting a fixed frequency signal, and the second frequency voltage converting means outputs a pulse width of a constant time width at the rising of the input signal. 9. The automatic frequency control device according to claim 8, further comprising a third pulse generating circuit for generating and a sixth low pass filter for integrating an output of the third pulse generating circuit. 13. A fourth pulse generating circuit as the first frequency-voltage converting means, which generates a pulse wave having a time width twice that of the third pulse generating circuit when the input signal rises,
13. The automatic frequency control device according to claim 12, further comprising a seventh low pass filter that integrates the output of the pulse generation circuit. 14. A third limiter circuit as the first frequency-voltage converting means for limiting the amplitude of the frequency shift keying signal, and a third edge for detecting the rising and falling edges of the amplitude limited signal. A detection circuit, and the third
And a fifth pulse generation circuit for generating a pulse wave having a constant time width at the rising edge of the edge detected by the edge detection circuit, and as a second F / V conversion means, a fixed frequency signal is amplitude limited. 4 limiter circuit, a fourth edge detection circuit for detecting rising and falling edges of the amplitude-limited signal, and a pulse having a constant time width at the rising edge of the edge detected by the fourth edge detection circuit. A sixth pulse generating circuit for generating a wave, and further an eighth low pass filter for integrating the output of the voltage comparator is provided, with respect to the output pulse trains of the first and second frequency-voltage converting means. 2. The automatic frequency control device according to claim 1, wherein the voltage comparator takes a difference and the output is integrated by the eighth low pass filter. 15. Instead of the second frequency-voltage converting means, the third holding means and the input of the first frequency-voltage converting means are switched between the output of the frequency-converting means and the fixed frequency signal output. And a fourth switching means for switching the output of the first frequency-voltage conversion means between the input of the voltage comparator and the third holding means, and usually the third switching means. And the fourth switching means are respectively connected to the frequency converting means and the voltage comparing means, but the third switching means and the fourth switching means are respectively provided with a fixed frequency signal output and 3. The automatic frequency control according to claim 1, wherein the third holding means holds the frequency-voltage conversion result of the frequency of the carrier signal of the second frequency shift keying signal by switching to the third holding means. apparatus. 16. A fifth limiter circuit is provided between the first low-pass filter and the frequency conversion means, and a sixth limiter circuit is provided between the second low-pass filter and the frequency conversion means. The automatic frequency control device according to claim 1, wherein 17. The automatic frequency controller according to claim 1, wherein the averaging means is a ninth low pass filter having a cutoff frequency sufficiently lower than the data rate.