JP2514977B2 - VCO device for secum encoder - Google Patents

Description

The present invention relates to a VCO in a secum-type composite video signal generator.

[Conventional technology]

Conventionally, this type of device has been shown in FIG. In the figure, 1 is a voltage controlled oscillator (hereinafter referred to as VOO), 2 is a current source capable of controlling current, 3 is a reference generator that generates a reference frequency signal of 282fH, 4 is an FM detector, and 5 is a differential amplifier. , C1 and C2 are capacitors for sample hold (S / H), C3 is a low pass filter, and SW is a switch.

Next, the operation timing of this conventional VCO system
Description will be given with reference to FIG.

(1) Part 1 (a) Within the SC BLK pulse, first set the switch SW to the B side, perform FM detection of the reference frequency, and use this as the reference voltage to charge the S / H capacitor C1.

(B) The switch SW is set to the A side at the timing of the next pulse in SCBLK of 1H, the oscillation frequency of the VCO is FM detected, and this voltage is charged to the S / H capacitor C2.

(C) The voltage obtained in (a) and (b) is input to the error detection amplifier 5, and the VCO error voltage with respect to the reference is fed back to VCO1 through a low pass filter composed of a capacitor C3.

(2) Part 2 (a) Further, the pulse of FIG. 4 (b) is made by two pulses of C.BLK pulse and SCBLK pulse.

(B) When the switch SW is set to the B side, the reference frequency is FM detected and the S / H capacitor C1 is charged with this as the reference voltage.

(C) When the switch SW is on the A side, VCO1 frequency detection is performed and the capacitor C2 is charged.

(D) The voltage of capacitors C1 and C2 is set to the error detection amplifier 5
The error voltage is input to and is passed through a low-pass filter consisting of capacitor C3, and feedback is applied to VCO.

[Problems to be solved by the invention]

The conventional VCO device for the secum encoder is configured as described above, and at the drive timing shown in Fig. 4 (a), the S / H of the detection voltage is performed every two horizontal periods for both the VCO and the reference frequency detection. Error voltage detection capability and accuracy are low. In addition, since the detection is performed in the interval horizontal period, the accuracy and stability of the reference voltage itself is not good.

Further, in the drive timing of FIG. 4 (b), since the reference signal is always detected during the period other than the VCO detection, the accuracy and stability as the reference voltage are excellent, but it is always (close to) FM.
A beat may occur because the detector is performing a detection operation. This is because, in the secum system, two sub-carriers, 282fH (= 4.40625MHz) and 272CfH (= 4.25MHz), are repeatedly used for every H, so the difference between the two must be noted at 10fH.

The present invention has been made in view of the above problems of the conventional one, and an object thereof is to obtain a VCO device for a secum encoder which can perform stable reference oscillation.

[Means for solving problems]

The VCO device for the secum encoder according to the present invention is provided with the VCO detection period and the reference signal detection period independently within the C.BLK pulse, and the first short-time VCO of 1H for stable operation of the VCO.
A set time is provided, and the above-mentioned operation is performed every H every time within a C.BLK pulse.

[Action]

In the present invention, as described above, at various timings.
Since the VCO is reset and fed back, the error voltage detection capability and accuracy are high, and stable reference oscillation can be performed.

〔Example〕

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

FIG. 1 shows a secum encoder according to an embodiment of the present invention.
A VCO device is shown, and in the figure, the same reference numerals as those in FIG. 3 indicate the same parts. 1 is an emitter-coupled voltage controlled oscillator (hereinafter referred to as VCO), 2 is a controllable current source, 3 is a reference signal oscillator, 4 is an FM detector, 5 is a differential amplifier (error detector), and SW is interlocked. The switch realizes the VCO reset circuit in the no connection position. Also C1, C2
Are sample and hold capacitors, for reference and VCO respectively
C3 is a low pass filter capacitor.

 Next, the operation will be described with reference to FIG.

(1) Create VCO reset pulse and SW pulse from C.BLK pulse, SCBLK pulse, and C.Sync pulse.

(2) When the reset pulse turns ON, VCO1 completely stops oscillation and enters the initial reset state.

(3) While the switch SW is on the B side, the reference signal is FM-detected and the capacitor C1 is charged with this as a reference voltage for generating the reference frequency.

(4) After the reset pulse is turned off, VCO1 starts oscillating from the initial state.

(5) While the switch SW is on the A side, set the VCO oscillation frequency to F
M detection is performed and this voltage is charged to the capacitor C2 as a detection voltage of the VCO oscillation frequency.

(6) The error voltage output of the voltage charged in the capacitors C1 and C2 is held in the capacitor C3.

(7) This error voltage feeds back to VCO1 and activates the control loop so that the oscillation frequency matches the reference frequency.

(8) Perform the above operation for each H within the C.BLK pulse and perform VCO
Is oscillated as a reference and FM modulation is operated by the color difference control input during the video period.

Since the present embodiment is configured as described above, (1) Since the VCO and the reference signal are detected every H,
The error voltage detection capability is high, and the reference voltage accuracy is stable.

(2) With the exception of SCBLK, the reference signal is not input and the FM detector also stops operating, so there are no problems such as beats.

〔The invention's effect〕

As described above, according to the present invention, the VCO reset circuit operates from the start of composite blanking to the start time of the composite sync signal, and the VCO oscillation frequency detection is performed from the start time of the sync signal to the end of subcarrier blanking. Operates up to time, the frequency detection of the reference frequency signal operates from the subcarrier blanking end time to the composite blanking end time, and feeds back so that the VCO oscillation frequency matches the reference frequency within the composite blanking. Since it is configured so that the detection error voltage is detected accurately, the stability of the reference voltage is good, and there is an effect that it is possible to realize a secum encoder VCO without problems such as beats.

[Brief description of drawings]

FIG. 1 shows a VC for a secum encoder according to an embodiment of the present invention.
FIG. 2 is a circuit diagram of the O device, FIG. 2 is a diagram showing operation timing of FIG. 1, FIG. 3 is a circuit diagram of a conventional VCO system for a secum encoder, and FIG. 4 is a diagram showing third operation timing. . In the figure, 1 is a VCO, 2 is a current source, 3 is a reference frequency oscillator, 4 is an FM detector, 5 is a differential amplifier, SW is an interlocking switch (VCO reset circuit), C1 and C2 are S / H capacitors, and C3. Is a low-pass filter.

Claims (2)

(57) [Claims] 1. A VCO device used for a secum encoder, comprising: one VCO, a reference frequency oscillator, an FM detector for detecting the output of the VCO or the reference frequency oscillator, and the VCO detection output. And two capacitors for sampling and holding the reference frequency detection output respectively, and switching the VCO output or the output of the reference frequency oscillator and inputting it to the FM detector, and the output of the FM detector on the corresponding side. An interlocking switch that distributes to two capacitors, an error detector that compares the holding voltage of the two capacitors and feeds back the error voltage of both capacitors to the VCO, and a VCO reset circuit for resetting the VCO are provided. The VCO reset circuit operates from the start of composite blanking to the start time of the composite sync signal, and the VCO oscillation frequency The wave operates from the start time of the sync signal to the end time of the subcarrier blanking, and feedback is applied so that the VCO oscillation frequency matches the reference frequency within the composite blanking. VCO equipment. 2. The interlocking switch comprises two switches each having one throw and three poles, and the VCO reset circuit is realized in a non-connection position of the two switches. VCO device for Secum encoder.