JPS5936491A - Frequency difference detecting circuit - Google Patents

Abstract

PURPOSE:To detect the frequency difference of an intermittent wave with high accuracy, by generating a sawtooth wave in response to the phase difference between a reference signal and an input signal, comparing the sawtooth wave with a different threshold value for generating plural pulse signals, and generating a discriminating signal thereby. CONSTITUTION:An oscillating output signal from an oscillator 3A is applied to a reset terminal R of a flip-flop circuit 11 and a reference output signal from an oscillator 12 is applied to a set terminal S. An output of the flip-flop circuit 11 is inputted to a low pass filer 16 via a subtractor 13 and a switch circuit 14 to obtain the sawtooth wave signal, which is supplied to Schmitt circuits 17, 18 having two different threshold values, and after a prescribed pulse signal is formed, the signal is supplied to a flip-flop circuit 19 as a discriminating signal generating means. After the output is converted into a DC voltage at a diode 20 and a capacitor 22, the result is applied to the oscillator 3A as a control voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a frequency difference detection circuit, particularly to a SECAM type V
The present invention relates to a frequency difference detection circuit suitable for use in detecting a frequency difference of an intermittent wave such as a carrier signal used in frequency low-frequency conversion of a carrier color signal in TIt.

BACKGROUND TECHNOLOGY AND PROBLEMS Generally, in a SECAM system color television signal, the carrier color signal (chroma signal) is 4.40625MH
A signal in which the z subcarrier is frequency modulated by the red color difference signal (It-Y) and a signal in which the 4.25 MHz subcarrier is frequency modulated by the bamboo color difference signal (B-Y) are alternately transmitted every horizontal interval. The trapezoidal waves are arranged in nine horizontal sections after the vertical synchronization signal in each vertical retrace section. A color discrimination signal (Hr D ) that is frequency-modulated to a different frequency in each section is inserted.

In a VTR that performs low frequency conversion on the frequency of the carrier color signal of the color video signal and then records the signal by superimposing it on, for example, an FM modulated luminance signal, the frequency of the carrier color signal is transferred to the recording system. A frequency conversion circuit is provided for low frequency conversion, and this frequency conversion circuit is supplied with a carrier signal for frequency conversion in addition to the chroma signal. FIG. 1 schematically shows the structure of the frequency low-frequency conversion part of the carrier color signal in an Sl':CAM system VTR. Therefore, in the HID frequency conversion circuit (2), between the red color difference signal (R-Y) and the blue color difference signal (B-Y) in the carrier color signal, the 4.25 MHz blue color difference signal (B-Y ) is detected and C1 is 4.40625MH here.
z and supplied to the voltage controlled oscillator (3) as a drive signal. The oscillation output signal from the oscillator (3) is supplied to the frequency conversion circuit (4), which converts the low frequency conversion signal (3:1. ■, mixed with 353.■(), approximately 5.0
A second frequency conversion circuit (
6). In this frequency conversion circuit (6), it is mixed with the carrier color signal supplied from the chroma processing circuit (1) through the chroma delay circuit (power), and is mixed with the carrier color signal supplied from the chroma processing circuit (1) through the output terminal (8
) is extracted as a carrier color 351 353 signal (8'H-s'n) that has been low-pass converted.

By the way, in FIG. 1, the oscillator (3) is L in this case.
A C oscillator is used, and its frequency is adjusted by adjusting the coil of a tank circuit consisting of a fixed capacitor and a variable coil.Therefore, adjusting the frequency to 1M is troublesome and time-consuming. Ta.

OBJECTS OF THE INVENTION In view of the above, it is an object of the present invention to provide a frequency difference detection circuit that can accurately detect even when the frequency signal to be detected is an intermittent wave, and can eliminate adjustment.

Summary of the Invention The present invention includes a sawtooth wave generating means that generates a sawtooth wave according to a phase difference between a reference signal and an input signal, and a sawtooth wave generating means that has different threshold values and generates a plurality of pulse signals according to the sawtooth wave. and a discrimination signal generation means that generates a discrimination signal corresponding to the frequency difference between the reference signal and the input signal using a plurality of pulse signals.
Even in the case of an intermittent wave such as a gear rear signal for carrier color signal low-frequency conversion in the SECAM system, the frequency difference can be detected with high precision (and the frequency adjustment of the voltage controlled oscillator used during frequency conversion) is possible. can be made unadjusted.

Embodiments Hereinafter, embodiments of the present invention will be explained in detail with reference to FIGS. 2 to 5, taking as an example the case where the embodiments of the present invention are applied to the low-frequency conversion circuit section of the carrier color signal in an SE(,:AM system) VTR as described above. do.

FIG. 2 shows the circuit configuration of this embodiment. In this figure, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

In this embodiment, a voltage controlled oscillator (3A) using a fixed coil and a variable capacitance element is used in the tank circuit. Then, the output signal from the frequency conversion circuit (2) is supplied to the injection terminal Tl of this oscillator (3A), and the control terminal 1
A voltage control signal, which will be described later, is supplied to (2).

Now, in this embodiment, a direct RS flip-flop circuit α1] is provided on the output side of the oscillator (3A), and the reset terminal l of this flip-flop circuit 0υ is connected to the oscillator (3A).
An oscillation output signal Sv as shown in FIG. 3B is supplied from the oscillator (171) to the set terminal S, and a reference output signal St as shown in FIG. As can be seen from Fig. 3A, the oscillator output signal Sy of the oscillator (12+ As for this f!fIVT
In the case of R, there is a built-in crystal oscillator that generates a frequency of 282 fH for convenience during playback, so this is used.

The output signal of the group is supplied to a flip-flop circuit (for example, a subtracter 03 consisting of a differential amplifier), and this subtracter θ3
) is supplied to the switch circuit (14), and the gate pulse PG as shown in FIG. 3C is supplied from the gate pulse input terminal (15). Only the section T excluding the no-signal part and the injector 3 part (the raised part at the leading edge in the figure) is extracted and supplied to the low-pass filter (L6). Therefore, a sawtooth wave (Fj number S-r) corresponding to the phase difference between the oscillation output signal SV and the reference output signal SR is obtained on the output side of the low-pass filter α0.

That is, as shown in the third diagram, when the oscillation frequency f■ of the excavation output signal sy is smaller than the reference frequency fg of the reference output signal SR, a sawtooth 6P A-shaped wave (No. H STI) with a negative slope is generated.
is obtained, and on the other hand, when the oscillation frequency f is larger than the reference frequency fat, a sawtooth wave with a positive slope (No. II ST2 is obtained), and when both are approximately equal, a sawtooth wave with no or approximately straight line is obtained. Signal ST3 is obtained.In addition, this die reflex) RS
A method of obtaining a sawtooth wave using a non-rip 70 tube circuit, etc. is described in Japanese Patent Application No. 55-9261 filed earlier by the present applicant.
Details are given in No. 7.

The sawtooth wave signal S1- thus obtained at the output side of the low-pass filter Q6) is applied to a voltage comparator circuit having two different threshold values as a pulse generating means, for example, hysteresis%.
After forming a predetermined pulse signal by comparing it with these threshold values, a flip-flop circuit, e.g., T
For example, the output signal SA of the Schmitt circuit (17) is supplied to the direct reset terminal R of the flip-flop circuit H, and the output signal sB of the Schmitt circuit 0 group is supplied to the flip-flop circuit θg. The flip-flop circuit 01 may be of any other type, such as a D type or a JK type, as long as it can achieve the same function as the flip-flop circuit 01.

Next, the circuit operation of this Schmitt circuit (171, (IQ) and flip-flop circuit α 俤 will be explained in detail with reference to the signal waveforms of FIGS. 4 and 5. The threshold is VTHA, the lower threshold is VT
LA, and the higher threshold of the Schmitt circuit (+8) is V
THB, and the lower threshold value is VTLB. Now, the oscillator (
The oscillation frequency fv of 3A) is the reference frequency f of oscillator 02)
When it is smaller than R, a sawtooth wave signal ST1 with a negative slope as shown in FIG. 4B is generated at the output side of the low-pass filter (16) every period of the gate pulse Pc (FIG. 4A). This signal ST is extracted from the Schmitt circuit θη and θ~
is supplied to In Schmitt circuits (+7) and (18), the input gradually increases from a low level to a constant voltage (threshold V
TH), the output inverts at that moment, and conversely, the input gradually decreases from a high level until it reaches a certain voltage (threshold V
TL), at that moment the output is inverted again and returns to its original state. The difference between both voltages is hysteresis. Therefore, output signals SA and sB as shown in FIG. 4C and D are output to the output sides of the Schmitt circuits 07) and 0, respectively. The signal SA is supplied to the terminal I'L of the flip-flop circuit 011), and the signal sB is supplied to the terminal T of the Norinob flop circuit θl. The output level of the output terminal Y of the flip-flop circuit 09 is the same as that of the terminal I1. When the level of this terminal is high level, it is always low level, and when the level of this terminal becomes low level, it becomes high level in synchronization with the rise of the signal sB supplied from the Schmitt circuit (l (to) to terminal T) Therefore, when the oscillation frequency rV of the oscillator (3A) is smaller than the reference frequency fR of the oscillator 0, the output signal SY at the output terminal Y of the Norinob flop circuit 01 is as shown in FIG. As shown in , only a whisker appears.On the other hand, when the oscillation frequency fV of the oscillator (3A) is larger than the oscillator α force no I (applied wave number fR), the 51st gJB is applied to the output side of the low-pass filter Oo. A sawtooth wave signal ST2 with a positive slope as shown in FIG. 3, so the outputs of the Schmitt circuits 0 and 1 are compared with their thresholds.
Output signals SA and sB as shown in FIG. 5C and D, respectively, are obtained at 111 and supplied to the flip-flop circuit. Therefore, in this case, an output signal SY with a wide pulse width as shown in FIG. 5E is derived at the output terminal Y of the flip 70 tube circuit α9).

The inverted output signal Sy (inverted signal of the output signal sy) of the flip-flop circuit θ0 derived in this way is applied to the cathode/anode of the diode (20) and the resistor (2).
), the capacitor (27J) is supplied as a control signal to the control terminal ``l''2 of the oscillator (3A). That is, the oscillation frequency fv of the oscillator (3A) is supplied to the oscillator (I2
), the output signal sy of the flip-flop circuit 01 is substantially at a low level, so its inverted output signal SY is at a high level, and therefore the diode fault 2()) is in a non-conducting state, so at this time, a voltage corresponding to the charge charged in the capacitor (22) is directly supplied to the control terminal T2 of the oscillator (3A) from the power supply voltage +Vcc via the resistor 01). The oscillation frequency fy of the oscillator (3A) is set to a predetermined center frequency (equal to the reference frequency fR).On the other hand, the oscillation frequency ry of the oscillator (3A) is set to the oscillator θ2).
When the reference frequency fR from
[]) becomes conductive, the charge on the capacitor (2) is discharged through this diode α)) for the duration of the signal sy, and its terminal voltage drops, and this voltage is used as a control signal to control the oscillator (3A). The oscillation frequency fv of the oscillator (3A) is controlled to a predetermined oscillation frequency (reference frequency fR) according to the error amount.In other words, if the slope of the sawtooth wave signal ST is positive In this case, a negative pulse signal is generated, which is converted into a DC voltage by the resistor 01) and the capacitor (2) and then supplied to the oscillator (3A) as a control voltage.Then, the control voltage supplied to this oscillator (3A) The magnitude of the voltage corresponds to the positive or negative of the difference (fv-fR) between the oscillation frequency and the reference frequency. Therefore, by supplying such a control voltage to the control terminal T2 of the oscillator (3A), the oscillator (3A) This means that the oscillation frequency of can be controlled 1111 to a predetermined center frequency.

APPLICATION EXAMPLE In the above-mentioned embodiment, this invention is applied to the SECAM system V
Although the case where the frequency difference between the carrier signal and the reference signal for carrier chrominance signal low-band conversion in TIt is detected is explained as an example, the case is not limited to this. Similarly applicable.

Effects of the Invention As described above, according to the present invention, a sawtooth wave is generated according to the phase difference between a reference signal and an input signal, and a plurality of pulse signals are generated by comparing this sawtooth wave with different threshold values. Since a discrimination signal corresponding to the frequency difference between the reference signal and the input signal is generated using these multiple pulse signals, the SAC
Even when detecting the frequency difference of an intermittent wave such as a carrier signal for low frequency conversion in an AM system, it can be detected with high accuracy.For example, this detection circuit can be used as an oscillator for low frequency conversion of a carrier color signal in a SECAM system VTR. When used in the control loop of the present invention, the oscillator does not have to be adjusted to the frequency W8 as in the conventional case, and the adjustment process can be omitted.

[Brief explanation of drawings]

FIG. 1 is a block diagram schematically showing a low-pass conversion circuit for a carrier color signal in a SECAM system VTR, and FIG. 2 shows a low-pass conversion circuit for a carrier color signal in v'rrt of the SECAM system. FIGS. 3 to 5 are signal waveform diagrams for explaining the operation of FIG. 2. FIGS. (3A) is a positive pressure control oscillator, αυ is a die reflex) RSS
Flip Flora circuit, α is the reference oscillator, (13 is the subtractor, 04) is the switch circuit, α6) is the low-pass filter, (1
7) , ae is a Schmitt circuit, 01p is a T-type flip-flop circuit, C(me is a da/f ode, Qυ is a resistor,
(The second success is the capacitor. -5(

Claims (1)

[Claims] a sawtooth wave generating means for generating a sawtooth wave according to a phase difference between a reference signal and an input signal; a pulse generating means having different threshold values and generating a plurality of pulse signals according to the sawtooth wave; and discrimination signal generating means for generating a discrimination signal corresponding to the frequency difference between the reference signal and the input signal from the plurality of noise signals.