JPH03123222A - Automatic frequency controller - Google Patents

Abstract

PURPOSE:To attain automatic control of a local oscillator frequency with a simpler constitution by implementing the frequency control of the local oscillator while comparing voltages for the local oscillator frequency and a modulated wave frequency. CONSTITUTION:A biphase PSK(phase shift keying) modulation wave is inputted to a frequency conversion circuit 10 and inputted to an automatic frequency controller 40 and the modulated wave inputted to the controller 40 is frequency voltage converted at an FVC(frequency voltage converter) 42, and its voltage is inputted to a subtractor 46. On the other hand, a single resulting from frequency voltage conversion 44 of a local oscillator being the output of a VCO 50 is inputted to the subtractor 46. The subtractor 46 subtracts the output of the FVC 42 and the output voltage of the FVC 44 and the difference voltage between output voltages of the two FVC 42 and 44 is outputted. The difference voltage outputted from the subtractor 46 is fed to the VCO 50 via a loop filter 48. The frequency of the local oscillator is changed in the VCO 50 in response to the inputted voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic frequency control device that adjusts the frequency of a local oscillation signal used for polyphase PSK detection.

BACKGROUND ART Conventionally, a phase shift keying (PSK) method has been known in which the phase of a carrier wave is changed in accordance with a modulated signal.

This PSK method is called an n-phase PSK method when the number of carrier wave phases set according to a modulation signal is n, for example.

Among these, especially in the case of n-2, in the case of two-phase PSK, the carrier wave modulated according to the modulation signal, that is, the modulated wave, is generally expressed as the following equation.

V (t) -ACO8((IJ t+P (t)
l - (1) where A is the amplitude, A≧0, ω is the necessary frequency of the modulated wave, and P (t) is the phase determined by the modulated signal.

In order to detect the two-phase PSK modulated wave expressed in this manner, a method is used in which the frequency of this modulated wave is converted using a local oscillation signal, and the signal is further supplied to a detection circuit for detection.

FIG. 4 particularly shows an example of a circuit configuration in the case of quasi-baseband detection.

In this figure, the two-phase PSK modulated wave is at the station.

Frequency conversion circuit 10 that converts frequency using a partial oscillation signal
Furthermore, the output of the frequency conversion circuit 10 is supplied to a quasi-baseband detection circuit 12.

On the other hand, the two-phase PSK modulated wave is supplied to the automatic frequency control device 14 together with the frequency conversion circuit 10.

The automatic frequency control device 14 is a device that automatically adjusts the frequency of the local oscillation signal supplied to the frequency conversion circuit 10.

The automatic frequency control device 14 shown in this figure has a configuration that mixes a modulated wave and a local oscillation signal and performs feedback control of the frequency of the local oscillation signal.

First, the automatic frequency control device 14 shown in this figure includes:
A doubling circuit 16 that doubles the modulated wave, and the doubling circuit 1
BPF 18 that performs bandpass filtering on the output of BPF 18;
a frequency divider 20 that divides the output of the frequency by 1/2.

That is, the modulated wave input to the automatic frequency control device 14 is first non-modulated in the doubler circuit 16 to become a signal having twice the frequency of the carrier wave, and then noise is removed by the BPF 18 and then sent to the frequency divider 20. The frequency is divided by 1/2 at .

Further, two multipliers 22 are connected in parallel to the latter stage of the frequency divider 20, and an LPF 24 and an A-D converter 26 are further connected in sequence to these two multipliers 22. . These two A-D converters 26 both have C
It is connected to PU28.

On the other hand, the CPU 28 includes a D-A converter 30,
A VCO 34 is connected via the LPF 32, and the output end of the VCO 34 is connected via a phase shifter 36 to one multiplier 22 and directly to the other multiplier 22.

That is, the multiplier 22 is supplied with a signal from the frequency divider 20, and is also supplied with a local oscillation signal output from the frequency divider 34. Here, the phase of one of the two multipliers 22 is shifted by -π/2.

Since the local oscillation signal is supplied via the phase shifter 36,
The output of the frequency divider 20 is multiplied by a local oscillation signal having a phase different by 1π/2 in each multiplier 22.

The outputs of these two multipliers 22, so-called quasi-baseband signals, pass through the LPF 24, are digitized in the A-D converter 26, and are supplied to the CPU 2g. The digital data supplied to the CPU 28 is stored in a memory 38 connected to the CPU 28.

The CPU 28 performs a complex Fourier transform on the thus supplied digital signal and detects frequency components. This frequency component is the VC034
oscillation frequency, that is, the oscillation frequency of the local oscillation signal,
Since this frequency component is a difference component from the frequency of the modulated wave supplied to the device, this frequency component is converted into an analog in the D-A converter 30 and further supplied to the VCO 34 via the LPF 32, thereby changing the oscillation frequency of the VCO 34. As a result, the frequency of the local oscillation signal becomes a frequency that substantially matches the frequency of the modulated wave.

The local oscillation signal whose frequency has been controlled in this way is supplied to the frequency conversion circuit 10, and the frequency conversion circuit 1
Used for frequency conversion operation at 0.

In this way, conventionally, the automatic frequency control device 14
Accordingly, the frequency of the local oscillation signal used for detecting the modulated wave is automatically adjusted, and it is possible to generate a local oscillation signal of a desired frequency.

[Problems to be Solved by the Invention] However, the conventional automatic frequency control device having such a configuration requires a configuration that performs operations such as mixing of modulated waves and digitization, and the configuration of the device is complicated. Another problem was that it was large-scale. Furthermore, in order to improve the resolution of the frequency difference between the local oscillation signal and the modulated wave, a memory with a large storage capacity is required, which also causes the problem of prolonging the calculation time.

The present invention aims to solve these problems.

The purpose of this invention is to obtain an automatic frequency control device that can automatically control the frequency of a local oscillation signal used for detecting a modulated wave of polyphase PSK with a simpler configuration.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a first frequency-voltage converter that converts a modulated wave into a frequency-voltage, and a second frequency-voltage converter that converts a local oscillation signal into a frequency-voltage. a converter;
and a comparison section that compares the output voltages of the second frequency-voltage converter; and a comparison section that compares the output voltages of the second frequency-voltage converter; An oscillator that generates an oscillation signal.

Furthermore, the apparatus according to claim (2) of the present invention is characterized in that the comparison section includes a subtracter that outputs a difference voltage between the output voltages of the first and second frequency-voltage converters.

Further, in the automatic frequency control device according to claim (3), the oscillator is a voltage controlled oscillator whose oscillation frequency is changed according to the differential voltage output from the subtracter.

[Operation] In the automatic frequency control device according to claim (1) of the present invention, the modulated wave is frequency-voltage converted in the first frequency-voltage converter. On the other hand, the local oscillation signal is frequency-voltage converted in the second frequency-voltage converter, and the output of the first frequency-voltage converter and the output of the second frequency-voltage converter are compared in the comparison section. The oscillation frequency of the oscillator is controlled according to the comparison result in the comparison section.

This control is performed so that the frequency of the local oscillation signal matches the center frequency of the modulated wave, and therefore the frequency of the local oscillation signal output from the device matches the center frequency of the modulated wave. Control will be realized by a device with a simple configuration.

Furthermore, in the apparatus according to claim (2), the output voltages of the first and second frequency-voltage converters are compared by determining the difference voltage between these output voltages using a subtracter.

Furthermore, in the automatic frequency control device according to claim (3), since the oscillator is a voltage controlled oscillator, so-called vCO, the oscillation frequency of this vCO is changed according to the differential voltage output from the subtracter, and local oscillation is performed. Automatic control of the signal frequency will be easily realized.

[Embodiments] Preferred embodiments of the present invention will be described below with reference to the drawings.

Note that the same components as those of the conventional example shown in FIG. 4 are designated by the same reference numerals, and the description thereof will be omitted.

FIG. 1 shows the configuration of an automatic frequency control device according to an embodiment of the present invention.

The automatic frequency control device 40 shown in this figure includes a frequency-voltage converter (hereinafter referred to as FVC) 42 that converts a modulated wave into frequency and voltage, and an FVC that converts a local oscillation signal into frequency and voltage.
C44, a subtracter 46 that outputs the difference voltage between the outputs of the FVCs 42 and 44, a loop filter 48 that determines a control time constant according to the output of the subtracter 46, and a The oscillation frequency is determined by V
Cσ50, and the output of the VCO50 is FVC4
It is connected to the input terminal of 4.

That is, in this figure, the two-phase PSK modulated wave is
The modulated wave that is input to the frequency conversion circuit 10 and to the automatic frequency control device 40 according to this embodiment, and further input to the automatic frequency control device 40, is frequency-voltage converted in the FVC 42. That is, the modulated wave input to the FVC 42 is converted into a voltage signal according to its frequency and input to the subtracter 46. On the other hand, a signal obtained by frequency-voltage conversion of the local oscillation signal, which is the output of the VCO 50, is input to the subtracter 46. That is, the local oscillation signal output from the VCO 50 undergoes frequency-voltage conversion in the FVC 44 and is supplied to the subtracter 46. In the subtracter 46, the output voltage of the FVC 42 and the output voltage of the FVC 44 are subtracted, and the difference voltage between the output voltages of these two FVCs 42 and 44 is output.

The differential voltage output from the subtracter 46 is supplied to the VCO 50 via a loop filter 48. Said VC
At O50, the frequency of the local oscillation signal is changed according to the input voltage.

That is, if there is no difference between the center frequency of the modulated wave and the frequency of the local oscillation signal, there is no difference between the output voltages of the FVCs 42 and 44, and the voltage output from the subtracter 46 is zero. When there is a difference between the modulated wave and the local oscillation signal, a difference occurs between the output voltages of the FVCs 42 and 44, and the subtracter 46 outputs a voltage corresponding to this difference. In the VCO 50, the loop filter 48
The oscillation frequency is adjusted according to the output voltage of the subtracter 46 supplied via the subtracter 46, that is, the difference voltage between the modulated wave and the local oscillation signal, and the frequency is adjusted so that the frequency of the local oscillation signal matches the center frequency of the modulated wave. controlled.

FIG. 2 shows the configuration of the FVCs 42 and 44 shown in FIG. 1.

The FVCs 42 and 44 shown in the diagram are circuits that apply the zero-crossing of the two-phase PSK modulated wave shown by equation (1).

That is, the FVCs 42 and 44 shown in this figure include a zero-cross detection circuit 52 that generates a zero-cross pulse in response to a zero-cross of an input signal that is a modulated wave or a local oscillation signal, and a zero-cross pulse output from the zero-cross detection circuit 52. A one-shot multivibrator 54 that is triggered and outputs a one-shot pulse.
and an integrator 56 that integrates the one-shot pulse that is the output of the one-shot multivibrator 54. That is, the frequency of the input modulated wave or local oscillation signal is detected based on the output cycle of the zero-cross pulse output from the zero-cross detection circuit 52, and furthermore, the frequency of the input modulated wave or local oscillation signal is detected according to the zero-cross pulse output from the zero-cross detection circuit 52. By integrating the triggered output of the one-shot multivibrator 54, the signals output from the FVCs 42 and 44 become voltages obtained by frequency-voltage conversion of the input signal, that is, the modulated wave or the local oscillation signal.

Further, as another configuration of the FVCs 42 and 44 shown in FIG. 1, there is a configuration as shown in FIG. 3, for example.

The FVCs 42 and 44 shown in this figure include a counter 60 instead of the integrating circuit 56 shown in FIG.

That is, in the FVCs 42 and 44 shown in this figure, the output of the one-shot multivibrator 54 is counted by the counter 60, and from the counter 60,
A value corresponding to the frequency is output. Those two numbers are
A subtracter 46 calculates the difference, and a DA converter 47 outputs a voltage according to the frequency difference.

In this way, the automatic frequency control device according to this embodiment can automatically control the frequency of the local oscillation signal for detecting the two-phase PSK modulated wave. Furthermore, compared to the conventional device shown in FIG. 4, for example, the device shown in this embodiment does not require devices for multiplying a local oscillation signal and a modulated wave, digitizing a quasi-baseband signal, etc., and has a simpler configuration. Miniaturized. In addition, resolution improvement can be achieved without using a memory with a large storage capacity.

In this embodiment, the modulated wave supplied to the automatic frequency control device 40 is a two-phase PSK modulated wave, but it may generally be a polyphase PSK modulated wave. In this case as well, the operation is similar to the embodiment described above.

[Effects of the Invention] As explained above, according to the present invention, the frequency control of the local oscillation signal used for detecting the modulated wave of polyphase PSK is
Since the frequencies of the local oscillation signal and the modulated wave are compared using voltages, complicated configurations such as digitization of quasi-baseband signals are omitted, and the frequency of the local oscillation signal can be automatically controlled with a simpler configuration. It becomes possible to do so.

In addition, the comparison section for comparing the frequencies of the modulated wave and the local oscillation signal, each converted into a voltage, is configured by a subtracter that subtracts the voltage, so that this comparison can be easily realized.

Further, by using a voltage controlled oscillator whose oscillation frequency is changed according to the differential voltage output from the subtracter, automatic frequency adjustment can be more easily realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an automatic frequency control device according to an embodiment of the present invention, FIG. 2 is a block diagram showing a first configuration example of the FVC shown in FIG. 1, and FIG. , a block diagram showing a second configuration example of the FVC shown in FIG. 1, and FIG. 4 is a block diagram showing a configuration example of a conventional automatic frequency control device. 40... Automatic frequency control device 42.44-FVC 46... Subtractor 50... vCO

Claims (3)

[Claims] (1) In an automatic frequency control device that takes in a modulated wave of a polyphase PSK and generates a local oscillation signal while controlling the frequency to be equal to the center frequency of this modulated wave, a step that converts the modulated wave into frequency and voltage. a second frequency-voltage converter that converts the local oscillation signal into a frequency-voltage; a comparison section that compares the output voltages of the first and second frequency-voltage converters; and the comparison section. an oscillator that generates a local oscillation signal while controlling the frequency so that the frequency of the local oscillation signal matches the center frequency of the modulated wave according to the comparison result of the automatic frequency control. Device. (2) The automatic frequency control device according to claim (1), wherein the comparison section includes a subtracter that outputs a difference voltage between the output voltages of the first and second frequency-voltage converters. (3) The automatic frequency control device according to claim (2), wherein the oscillator is a voltage controlled oscillator whose oscillation frequency is changed according to the differential voltage output from the subtracter.