JPH02188088A - Carrier signal generating circuit - Google Patents

Abstract

PURPOSE:To realize the carrier signal generating circuit which has large suppres sion characteristics and requires no expensive filter by providing an oscillator whose frequency is N times as high as a carrier frequency fC required for VTR and a 1/N frequency dividing circuit. CONSTITUTION:A VCO 1 which generates a signal almost at a 535fH frequency outputs a signal of 535fH with an input control voltage. The 1/2 frequency divid ing circuit 2 divides the frequency of the 535fH signal by two to generate a 535/2fH signal. A filter 3 which passes only a fundamental wave of 535/2fH removes higher harmonics. The 535/2fH signal consisting of only the fundamental wave is inputted to a 4-phase signal generating circuit 4. The four-phase signal is a signal which shifts in phase by 90 deg. each and inputted to input terminals 5 and 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a carrier signal generation circuit for generating a carrier necessary for frequency conversion of a color signal of a video tape recorder (VTR).

[Conventional technology]

In a home VTR, the chrominance signal is band-converted to the low frequency band of the FM-converted luminance signal, and then recorded and reproduced. The low-pass converted color signal carrier frequency is 40fH (fu
; horizontal synchronization frequency), the frequency of the carrier signal required for band conversion is fsc + 40 fH (
fsc: color subcarrier frequency in video signal).

The conventional method for generating this fsc+4OfH carrier signal fC is to divide the frequency from nx4ofH by n to generate a four-phase 40fH signal with a phase difference of 90', as described in Japanese Patent Laid-Open No. 57-123785. % Two signals with a 90° difference are input to two frequency converters through low-pass filters (LPFs), while the 90° difference is input from the fsc crystal oscillator.
A method of combining two signals with a 0° difference into the two 4OfH signals mentioned above, inputting them to the frequency converter, and synthesizing the outputs of the two frequency converters, and a method of generating the output by combining the two signals with a difference of 0 degrees, and a technical report of the Television Television Society ( VoL12.1'&17 ppl~6°T
As described in EBS '88-8), one voltage-controlled oscillator (VCO) is frequency-divided to generate one-phase 40fH component, and after frequency conversion of the fsc signal through an LPF, only the fsc+40LH component is generated. Take f8c
There is a method of generating four-phase signals with a 90° difference at a frequency of +4ofH.

[Problem that the invention seeks to solve]

These systems include a frequency conversion circuit that multiplies the fsC and 4OfH signals, and an LPF that reduces harmonics of the rectangular 40fH signal. From the outputs of the 40fH signal generation circuit and the frequency converter, unnecessary signal components of /X40fH (an integer of 1>2) and mfBC±nX40fH (an integer of m>l, n>2) are generated. A band pass filter (BPF) or the like is provided at the output of the frequency converter to reduce unnecessary components, but they cannot be completely removed.

In addition, the unnecessary signal components are removed from the power supply wiring on the integrated circuit.

Crosstalk may occur to other blocks via ground wiring, etc., resulting in signal S/N degradation.

An object of the present invention is to eliminate the drawbacks of the above-mentioned prior art and eliminate the need for expensive filters with large suppression characteristics.

Another object of the present invention is to provide a carrier signal generation circuit that improves performance.

[Means for solving problems]

The fsc of NTSC TV is 455/2.
fH (fH=15734-265) (Z), and with V '11' R of the above-mentioned method of converting to the frequency of 40 fH, the required carrier signal frequency fc is fc==fBc+401H=average fH.

fC can be generated by providing an oscillator that is N times larger than fC and a K frequency dividing circuit.

[Effect]

As a result, there is no generation of harmonic components of 40 fH, and
No frequency converter is required and fC can be generated.

Conventionally, from fsc±320 fH/8 component to fsc14
('SC+40fH)×
After generating 2, the frequency is divided by -, so that unnecessary components no longer appear. Therefore, frequency conversion can be performed without unnecessary components as a carrier signal. Furthermore, since no unnecessary signal components are generated, crosstalk to other circuit blocks formed on the semiconductor substrate does not occur, and the S/N ratio can be improved.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. l is a VCO that oscillates near # wavenumber of 535fH, and the control voltage input to 8 determines that the nearest harmonic is 535fH (approximately 8.4M), which is a simple L P F
Alternatively, BPF may be used.

Enter the signal generation circuit. The 4-phase signals are signals whose phases are shifted by 90 degrees from each other, and the 4-phase signals are selected by the head switching signal and horizontal synchronization signal input to the input terminals 5 and 6, and are output to the output terminal 7 as a carrier signal. Output. This signal is used for frequency conversion of the color signal.

〔Effect of the invention〕

According to the present invention, since a frequency converter is not necessary, 4
The filter provided in front of the phase signal generation circuit can be simplified, and since there is no circuit for generating the 40fH signal, unnecessary harmonic components are not generated, and the influence on other blocks can be eliminated.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention. 1... Voltage controlled oscillator, 2... T frequency divider circuit, 3...
...Filter, 4...4-phase signal generation circuit, 5...4
Phase control signal input terminal 1.6... 4-phase control signal input terminal 2.7... Carrier signal output terminal, 8... Oscillator control signal input terminal.

Claims (1)

[Claims] 1. In a video recording and reproducing apparatus that performs low frequency conversion of a chrominance signal into a signal whose phase shifts in synchronization with a horizontal synchronizing signal and records and reproduces the signal, the carrier frequency (f_S_C) of the chrominance signal and the horizontal K/L times (K, L
is an integer), a frequency dividing circuit that divides the output of the first oscillator by L/K, and a signal whose phase changes in synchronization with a horizontal synchronizing signal from the frequency dividing circuit output. 1. A carrier signal generation circuit comprising: a carrier signal generation circuit.