JPS62224145A - Dpsk demodulation circuit - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution by constituting a carrier signal generating circuit by a both-edge extraction circuit of a modulated signal, a conversion circuit converting a pulse signal into a rectangular wave signal whose duty is 1/2 and a frequency division circuit doubling the period. CONSTITUTION:A modulated carrier signal A is fed to one input terminal of an Ex-OR circuit 7 for demodulation and also fed to one input of an Ex-OR circuit 3, then inputted to a delay circuit 4, where both leading/trailing edges of the signal A are extracted. A PLL 5 consists of a phase comparator, a low pass filter and a voltage controlled oscillation circuit to obtain a rectangular wave signal D whose duty is 1/2. The rectangular wave signal D is inputted to a 1/2 frequency division circuit 6, where the signal is converted into a carrier signal E, the Ex-OR circuit 7 uses the carrier signal E to demodulate the signal A.

Description

DETAILED DESCRIPTION OF THE INVENTION Summary of the Invention The data signal is demodulated by an exclusive OR (Ex-OR) operation between a signal modulated by data and a carrier signal. The carrier signal can be obtained by simple circuit processing of the modulated data signal.

BACKGROUND OF THE INVENTION This invention is based on
ntlal PhaseShift Keying:
Differential phase shift change, il! The present invention relates to a circuit for demodulating a data signal modulated by a method.

In this DPSK system, for example, a video signal that is FM modulated by a magnetic head is recorded on a magnetic disk that rotates once. Or, in a magnetic recording and reproducing device that reads and reproduces video signals from a magnetic disk, it is used to convert data other than the video signal into a video signal by frequency multiplexing and write the TIrHk to the magnetic disk or read it from the magnetic disk. .

Recently, imaging devices such as solid-state image sensors and image pickup tubes have been combined with recording devices that use magnetic disks, which are inexpensive and have a relatively large storage capacity, to electronically capture still images of subjects. Electronic still camera systems have been developed that record on a magnetic disk and reproduce one image using a separately provided television system, printer, or the like. Furthermore, a video magnetic recording system has also been realized in which a still image recorded on a visible recording medium such as ordinary film or photographic paper is photographed and recorded on a magnetic disk.

Recording of a video signal on such a magnetic disk is performed by FM modulating the video signal over a wide frequency range of about 10 MHz and using a relatively high frequency. Relatively low frequency range (e.g. 200KH
z) can be opened for recording data other than video signals, and this type of inter-industry format standard uses such low frequencies to transfer various data onto magnetic disks by frequency multiplexing. It is permitted to record.

A series of DPSK systems have been used as a modified 8-week system for recording this type of data. This modulation method will be described in detail later, but modulation and demodulation circuits based on this modulation method, particularly circuits using an analog PLL as a demodulation circuit, are known (for example, Utility Model Application No. 59-184918
). Since this demodulation circuit is of an analog type, it is difficult to determine and adjust circuit constants, and the circuit configuration is also relatively complicated.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and provide a PSK iU four-tone circuit with a simple circuit configuration.

The DPSK demodulation circuit according to the present invention is characterized by comprising a carrier signal generation circuit for DPSK demodulation, and an exclusive OR circuit which receives as input a signal modulated by data and the carrier signal.

The carrier signal generation circuit converts the output pulse signal of the two-edge extraction circuit into a rectangular wave signal with the same period and duty of l/2. It consists of a conversion circuit that converts the signal, and a frequency divider circuit that doubles the period of the output signal of the conversion circuit.

According to this invention, since the demodulation circuit is digitalized, the configuration of one circuit can be relatively simplified, and there is almost no need for adjustment thereof. Also.

Since there is no need to use analog components, problems such as consideration of temperature characteristics and compensation thereof are greatly reduced. Furthermore, it will be easier to use ICs, which will lead to cost reductions, and digitalization will also simplify the interface with computers, especially microprocessors.

Furthermore, according to the present invention, since the carrier signal generation circuit generates the carrier signal using the modulated signal, that is, the signal to be demodulated, the rising or falling edge is synchronized with it regardless of the phase shift caused by the data. It becomes possible to obtain a carrier signal with a sharp rise and fall, and there is no need to provide a separate carrier signal oscillation circuit.

'□ Description of Embodiment In this embodiment, the present invention is applied to a circuit for demodulating a data read signal obtained by separating a video signal from a magnetic disk read signal in the above-mentioned magnetic recording/reproducing apparatus.

FIG. 1 is recorded on a magnetic disk. Alternatively, it shows the frequency spectrum of an FM modulated color video signal reproduced from a magnetic disk. Chrominance (color difference) and luminance (brightness) signals are distributed over a wide frequency range on the order of 10MHz. According to the format standard, the frequency f of the carrier signal of the data multiplex recording signal that is weighted and recorded on such a video signal by the frequency multiplexing method is 204.54 KHz (-13f
, f: horizontal scanning frequency).

The data format of data in data multiplex recording is also defined, which is initial bit,
(1 bit), field/frame data (2 bits), track address data (7 bits), year/month/day data (19 bits), and user use data (27 bits).

In a device capable of recording frame images, it is essential to record field/frame data to distinguish whether the recorded video signal is a frame image or a field image. User usage data is data that is needed by the user of the device for control of the device or for other purposes.

, 1-The DPSK method as the modulation method described above is as follows.

In the series of data to be recorded such as the above initial bits, field/frame data, track address data, etc., as shown in Figure 2, if a change appears in the bits of this recording data (for example, from 1 to O). , or from 0 to 1), the corresponding bit of the difference data is set to 1, and if there is no change in the bit of the recording data, the corresponding bit of the difference data is set to 0.
Create differential data.

With such differential data, the carrier (frequency f
-t3fl, ) as shown in FIG.
and π). That is, when the difference data bit is 0, the phase of the carrier is set to π, and when the difference data bit is 1, the phase of the carrier is set to π.

The bit rate of differential data is basically 4H interval (H
: period between horizontal synchronizing pulses) is 1 bit. That is, the phase of the carrier is changed in accordance with the difference data for each 4H interval (including cases in which the phases are the same if the difference data are the same).

However, according to the format standard, the bit rate for user data may be set to 1 bit per 2H interval.

FIG. 3 shows a case where the difference data is 011..., and HD is a signal synchronized with the horizontal synchronization signal. Also, regarding the carrier waveform.

Only the portions where the phase shifts are illustrated with the frequencies enlarged, and illustration of other portions is omitted.

FIG. 4 shows the basic configuration of a DPSK modulation circuit. Further, FIG. 5 shows waveforms of various input signals and two output signals in the circuit of FIG. 4.

Since the differential data signal represents a change in the data to be recorded as described above, it can be easily obtained from the signal of the data to be recorded using a known simple logic circuit. This differential data signal is an exclusive OR (Ex-
is applied to one input terminal of the OR) circuit 11. Ex-
The other input terminal of OR circuit II has the frequency f described in 1-
carrier signal is given. The carrier signal could be obtained from the generation circuit.

As a result of the Ex-OR logic of the differential data signal and the carrier signal, the phase of the carrier signal is shifted by π when the bits of the differential data are inverted. This Ex-
The OR output is a band pass filter (BPF) 1 that passes only signals with frequencies near the frequency f of the carrier signal.
The filter 2 converts the signal into a recording signal that changes smoothly.

This data recording signal is combined with a video signal, that is, a chrominance signal and a luminance signal.

Magnetic recording is performed on a predetermined track on a magnetic disk by a magnetic head.

Regeneration of the data signal is similarly achieved by demodulating the data read signal using an Ex-OR circuit. That is, by passing the signal read from the magnetic disk by the magnetic head through a bandpass filter whose center pass frequency is the frequency f of the carrier signal, the video signal is separated from the read signal, and a data modulated carrier signal is obtained. . This modulated carrier signal is waveform-shaped and then sent to the Ex-OR circuit together with the carrier signal. Ex
It can be easily understood from FIG. 5 that a signal representing differential data is obtained from the -OR circuit. Conversion from differential data to data can also be performed using a simple logic circuit.

Now, the most important thing in demodulation using such an Ex-OR circuit is to generate a carrier signal for demodulation that accurately synchronizes with a carrier signal modulated by data. As mentioned above, the modulated carrier signal has a phase of 0 or π depending on the data, so the carrier signal for demodulation is not synchronized with the modulated carrier signal in a strict sense, but for demodulation The timing of the rise of the carrier signal must match the rise (in the case of phase 0) or fall (in the case of phase π) of the modulated carrier signal.

The present invention is primarily directed to how to generate a carrier signal for demodulation having a rising edge that coincides with the rising edge or falling edge of a modulated carrier signal.

FIG. 6 shows a demodulation circuit which is an embodiment of the present invention. FIG. 7 shows the waveform of the output signal of this circuit.

The read signal from the magnetic disk has a carrier signal frequency f
A band pass filter with a center pass frequency of if is manually applied, and the high frequency FM modulation 1 image signal component is removed, a carrier signal modulated by data is extracted, and this data signal is waveform-shaped and becomes a rectangular wave. This becomes signal A. Since this signal A is phase shift keyed using differential data, when the differential data (refer to the demodulated differential data signal F) is 0, its phase is 0. If the data is 1, the phase is π.

This modulated carrier signal A is sent to one input terminal of an Ex-OR circuit 7 for demodulation on the one hand, and is sent to one input terminal of another Ex-OR circuit 3 on the other hand and to a delay circuit. 4. Manpower. The delay circuit 4 slightly delays the human input signal, and its output B is sent to the other input terminal of the Ex-OR circuit 3.

In the Ex-OR circuit 3, an Ex-OR operation is performed on the modulated carrier signal A and the signal B that is slightly delayed, so that the signal A rises.

Both falling edges are extracted and the carrier signal f
A pulse signal C having a frequency of 28fh, which is twice that of , is obtained. The pulse signal C could also be obtained by using a two-way differential circuit instead of the combination of the Ex-OR circuit 3 and the delay circuit 4.

This pulse signal C is then P L L (Phase L
(ockedloop) circuit 5, and the frequency of this PLL 5 is locked to 26th. A PLL is generally composed of nine phase comparators, a low-pass filter, and a voltage-controlled oscillation circuit, but the voltage-controlled oscillation circuit of a PLL whose frequency is fixed at 26fh has one frequency of 26fb and a duty of 1/2. A square wave signal is obtained.

This rectangular wave signal is input to a 1/2 frequency divider circuit 6 which halves the frequency, and is converted there into a carrier signal E having a frequency of 13fh. This carrier signal E is input to the other input terminal of the Ex-OR circuit 7.

The Ex-OR circuit 7 uses this carrier signal E to convert the signal A.
demodulation is performed.

The output signal F of the Ex-OR circuit 7 represents differential data. If necessary, this signal F may be input to a low-pass filter to remove noise components such as so-called "whiskers", and then waveform shaped by discrimination at an appropriate threshold level in a comparator circuit.

As described above, even though the modulated carrier signal A is phase-shifted according to the differential data, the carrier signal of the same frequency with which the rising or falling edge of the modulated carrier signal A is synchronized. Since E is obtained, accurate demodulation can always be performed in the Ex-OR circuit 7.

[Brief explanation of drawings]

FIG. 1 is a diagram showing frequency spectra of video signals and data recording signals recorded on a magnetic disk. FIG. 2 is a diagram showing how data to be recorded is converted into differential data. FIG. 3 is a waveform diagram showing how carrier phase shift keying is performed using the DPSK method. FIG. 4 is a circuit diagram showing the principle of a modulation circuit based on the DPSK system, and FIG. 5 is a waveform diagram showing its operation. FIG. 6 is a circuit diagram showing a detailed embodiment of the present invention,
FIG. 7 is a waveform diagram showing the operation. 3...Ex-OR circuit. 4...Delay circuit. 5...PLL circuit. 6...l/2 frequency divider circuit. 7... Ex-OR circuit for demodulation. 2 Patent Applicant: Fuji Photo Film Co., Ltd. Agent
Patent attorney Asami Kato (1 other person)

Claims (1)

[Claims] A carrier signal generation circuit for DPSK demodulation, and an exclusive OR circuit that inputs a signal modulated by data and the carrier signal, wherein the carrier signal generation circuit is modulated. a double-edge extraction circuit that extracts both rising and falling edges of a signal; a conversion circuit that converts the output pulse signal of the double-edge extraction circuit into a rectangular wave signal with the same period and a duty of 1/2; A DPSK demodulation circuit consisting of a frequency divider circuit that doubles the period of the output signal.