JPH01125190A - Voltage control oscillator for secam encoder - Google Patents

Abstract

PURPOSE:To omprove detecting accuracy and to stabilize an operation by providing a gate switch and sampling a detected voltage within a time in a gate. CONSTITUTION:A voltage control oscillating circuit (VCO)1, a reference frequency signal oscillator 2, an FM detector 3, a gate switch SW1 to the FM detector 3 of a VCO output and a reference frequency output, a charge switch SW2 to the sample hold capacitor of an FM detected output, an error amplifier 4, a capacitor C1 for sample holding the FM detecting voltage of a reference frequency signal, a capacitor SW2 for sample holding the FM detected voltage of a VCO output frequency and a detected voltage sample hold circuit 6 are provided. In this case, the detected voltage is sampled within the time in the gate. Thereby, an erroneous voltage is not sample held at the time of changing over the switch but a stable and correct detected output is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of a voltage controlled oscillator in a SECAM type composite video signal generator.

[Conventional technology]

Conventionally, there was a device of this type as shown in Figure 40.
In the figure, 1 is a voltage controlled oscillator circuit (hereinafter referred to as VCO), 2 is a reference frequency signal oscillator, 3 is an FM detector, and 4 is a reference frequency signal oscillator.
5 is an error amplifier, 5 is a low-pass filter (hereinafter referred to as LPF), s- is an interlocking switch, and 'l+cffi is a sample-hold capacitor.

Next, the operation will be explained using FIGS. 4 and 5.

(1) First, the case where the circuit shown in FIG. 4 operates according to the timing shown in FIG. 5(a) will be explained.

(a) Subcarrier blanking (hereinafter referred to as 5CBLK)
At first, the switch S- is set to the B side, the reference frequency is FM-detected, and this is used as the reference voltage to charge the sample-hold capacitor C.

佽) At the timing of the 5CBLK pulse after the next IH (horizontal period), switch S- is set to the A side, FM detects the oscillation frequency of vCO, and charges the sample-hold capacitor at with this voltage.

(C) (a), (The voltage obtained by the operation of bl is input to the error amplifier, the VCO error voltage with respect to the reference frequency is detected, and this VCO error voltage is fed back to the VCOL via the LPF5.

(2) Next, the case where the circuit shown in FIG. 4 operates according to the timing shown in FIG. 5 will be explained.

(a) From the start of composite blanking (hereinafter referred to as CBLK) to the start of the synchronization signal, the VCO is reset to create an initial state.

(b) Next, while the switch S- is on the B side, the reference signal is subjected to FM detection, and this is used as the reference voltage for generating the reference frequency to the sample-hold capacitor C.

to charge.

(C) After the VCO reset pulse (P, ) is turned off, the VCO
1 starts oscillating from the initial state. switch S- to A
During the period when the VCO is on the side, the oscillation frequency of this VCO is subjected to FM detection, and this voltage is charged to the sample and hold capacitor C.

(d) After applying the voltage obtained in the operations of (b) and (C) to the LPF 5 via the error amplifier 4, feedback is applied to vCO, and the control loop is activated so that the oscillation frequency matches the reference frequency.

(e) Within CB LK, the VCO is caused to oscillate at the reference frequency every H, and during the remaining video period of IH, the VCO is caused to perform FM modulation operation using the color difference control input voltage.

[Problem that the invention seeks to solve]

The conventional voltage-controlled oscillator for SECUM encoders is configured as described above, and in the operation shown in Figure 5(a), the switch that inputs the signal to the FM detector and the switch that samples and holds the detected voltage are the same. Since the switching occurs at different timings, there is a possibility that accurate detection voltage cannot be sampled and held at the switching timing, especially at the moment the switch is turned off.

In addition, in the operation shown in Figure 5), since FM detection is performed for each H of both the VCO output and the reference 282f frequency, the system itself appears to be stable, but this method also suffers from the same drawbacks as described above. In particular, since the timings for switching the switch 3 to the A side and the B side are close to each other, the influence of malfunctions when the timings deviate is large.

The present invention was made to solve the problems of the conventional ones as described above, and an object of the present invention is to obtain a voltage controlled oscillator for a SECUM encoder with stable operation.

[Means for solving problems]

The voltage controlled oscillator for SECOM encoder according to the present invention includes:
A gate switch is provided to switch the input of the FM detector between the vCO output and the reference frequency, and the detection voltage is sampled within the time period inside the gate.

[Effect]

In the present invention, since the device is configured as described above, it is possible to avoid sampling and holding an incorrect voltage when changing the switch, and a stable and accurate detection output can be obtained.

〔Example〕

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

FIG. 1 shows a voltage controlled oscillator for a SECUM encoder according to an embodiment of the present invention, and in the figure, 1 is a VCO;
Consists of an emitter-coupled multi-by-break oscillator.

2 is a reference frequency signal oscillator, which has a reference frequency (282h
=4.40625MHz) is input from the outside. 3 is an FM detector, and only one is provided. st+t is a gate switch (detector input gate circuit) for supplying the vCO output or 2B2rw reference frequency output to the FM detector 3; SW2 is a charging switch for supplying the FM detection output to the sample-hold capacitor. 4 is error amplifier, CI
is a capacitor for sampling and holding the FM detection voltage of the reference frequency signal, C8 is a capacitor for sampling and holding the FM detection voltage of the CO output frequency, 6 is a detection voltage sample and hold circuit, and the switch S
W2, a sample hold capacitor 'l+c2, and an error amplifier 4.

Next, the operation will be explained.

■ VCO output gate pulse and 282f from two pulses: CBLK pulse and line switch (LSW) pulse
, 4 reference frequency gate pulses and switch SWI
Switch operation with .

■ Create a vCO reset signal from the CBLK pulse and composite synchronization (C5ync) pulse, and reset vCo every H.

■ Create sampling pulses (S, P,) for a specified time from the end of the C5 sync pulse, create VCO frequency detection outputs s, p, and 282fN reference frequency detection outputs s, p from the LS-pulse, and use switch SW2. Operate the switching operation.

(2) When the switch SW2 is switched to the B side while the switch SWI is switched to the B side, an external reference frequency is FM detected and sampled and held in the capacitor c1 as a reference voltage for generating the reference frequency.

(2) When the switch SW2 is switched to the A side while the switch SWI is switched to the A side, the oscillation frequency of the VCO is FM detected, and this voltage is sampled and held in the capacitor c as the oscillation frequency detection voltage of the VCO.

■ Capacitor c++C! The voltage sampled and held is input to the error amplifier 4, and the output error voltage is input to the LPF.
5, feedback is applied to vCO to create a control loop so that vCo oscillates at the reference frequency within CBLK every interval H.

(2) During periods other than CBIJ, this VCO performs FM modulation operation using the color difference input control voltage.

In this way, in this embodiment, sampling of the detection output voltage is performed within the gate switch, so the erroneous voltage sample and hold that occurs when switching the switch, which occurs in the conventional example, is eliminated, and stable and accurate detection output can be sampled and held. It is. Furthermore, the gate pulses for s and p at intervals of H can be created using LS-pulses and CBLK pulses,
This is a very simple and new attempt to generate H gate pulses.

In addition, although the application was not specifically explained in the above embodiment, it can be applied to all systems in which it is necessary to adjust the oscillation frequency of the vCO to the reference frequency for a certain period of time.

〔Effect of the invention〕

As described above, according to the voltage controlled oscillator for a SECUM encoder according to the present invention, a gate switch is provided at the input of the VCO output and the reference frequency to the FM detector, and sampling of the detected voltage is performed within the time inside the gate. Since the configuration is configured to perform this, it is possible to realize a vCO system for a SECUM encoder with high error voltage detection accuracy (and high stability) with reference frequency oscillation.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a voltage controlled oscillator for a SECUM encoder according to an embodiment of the present invention, FIG. 2 is a time chart showing the operation timing of the voltage controlled oscillator ρ for a SECUM encoder in FIG. 1, and FIG. Figure 1 is a timing chart showing the relationship between the VCOIJ settling, the VCO sampling pulse, and the reference oscillation frequency sampling pulse of the voltage controlled oscillator for the SECUM encoder. Figure 4 is a circuit diagram of the conventional voltage controlled oscillator for the SECUM encoder. , FIG. 5 is a timing chart showing the operation timing of a conventional voltage controlled oscillator for a SECUM encoder. In the figure, 1 is a VCO (voltage controlled oscillation circuit), 2 is a reference frequency oscillation circuit, 3 is an FM detector, 4 is an error amplifier, 5 is a low-pass filter, SWI switch (detector input gate circuit), SW2 is a switch, CI+C! 6 is a sample and hold capacitor, and 6 is a detection voltage sample and hold circuit.

Claims (1)

[Claims] (1) A voltage-controlled oscillator used in a SECUM encoder that generates a SECAM-type composite video signal, which includes one voltage-controlled oscillator circuit that performs FM modulation according to the color difference control input voltage, and the start of composite blanking. a reset circuit that resets the voltage controlled oscillator circuit from 100 to a start period of the composite synchronization signal; a detector input gate circuit that alternately inputs the oscillation signal or reference frequency signal of the voltage controlled oscillator circuit to the FM detector; The detected voltage of the oscillation frequency of the controlled oscillation circuit is R-Y
a detection voltage sample and hold circuit that samples and holds the detected voltage of the frequency of the reference frequency signal within the gate time of composite blanking of the period B-Y; A voltage controlled oscillator for a SECUM encoder, characterized in that feedback is applied to the voltage controlled oscillator circuit during blanking so that its oscillation frequency matches the reference frequency.