JPH04222905A - Bias oscillation circuit - Google Patents

Abstract

PURPOSE:To enable a prevention of phase distortion in a low range chrominance signal (e) by phase-synchronizing a reference signal (b) which is used at the time of conversion from a video color signal to the low range chrominance signal, to the low range color signal and also to an AC bias signal. CONSTITUTION:The subject bias oscillation circuit 12 is furnished with a color process circuit 13 whereby the video color signal (d) is converted to the low range chrominance signal (e) phase-synchronized to the reference signal (b), and also this circuit outputs the AC bias signal (m). The AC bias signal (m) of this bias oscillation circuit 12 is the one phase-synchronized to the aforementioned reference signal (b).

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a bias oscillation circuit that performs alternating current bias recording, and more specifically to a bias oscillation circuit that synchronizes the phase of an audio signal with the phase of a low-frequency color signal used when recording video. It relates to oscillation circuits.

0002

[Prior Art] A VTR (Video Tape Recorder) is capable of recording and reproducing audio and video signals.
) has a bias oscillation circuit for recording audio signals, and the conventional bias oscillation circuit is configured to generate an AC signal having a frequency fAC of 70.0 KHz output from an LC oscillator 51, as shown in FIG. After the bias signal f is amplified by the amplifier 52 to produce the bias oscillation output g, the fixed head 5
3 to record on a magnetic tape (not shown).

On the other hand, video signals are recorded by converting the color signal into a low frequency color signal lower than the normal frequency for the purpose of narrowing the band of the recording signal and reducing the time axis fluctuations that the color signal receives. This low-range color signal is formed by a color processing circuit. That is, as shown in FIG. 3, this color process circuit includes a horizontal synchronization separation circuit 59, a multiplier circuit 55, a crystal oscillator 56, a first frequency converter 57, and a second frequency converter 58. The frequency converter 57 converts the reference signal b and the low-range color carrier wave a.
A second frequency converter 58 generates a low frequency color signal e from the video color signal d using a composite signal c phase-synchronized with the reference signal b.

Thereby, the audio signal and the video signal are generated by the AC bias signal f of the bias oscillation circuit 54 shown in FIG.
Since the signal is recorded in phase synchronization with the reference signal b of the color process circuit 60 in FIG. 3, stable recording and reproduction is possible.

[0005]

However, the conventional bias oscillation circuit 54 described above has a problem in that it tends to cause phase distortion in the low-range color signal e. That is, since the LC oscillator 51 of the bias oscillator circuit 54 is independent from the crystal oscillator 56 of the color process circuit 60, the AC bias signal f output from the LC oscillator 51 is equal to the low gamut color output from the crystal oscillator 56. Oscillation occurs independently of signal e, and both signals f and e are often out of phase. At this time, the bias oscillation output g recorded via the fixed head 53 is at the carrier frequency (fs=
It has a 9th harmonic (9×fAC=630 KHz) which has a frequency substantially equivalent to 629.4 KHz). Therefore, if the bias oscillation output g is recorded with its phase shifted from that of the low-range color signal e, phase distortion will occur in the low-range color signal e.

Accordingly, an object of the present invention is to provide a bias oscillation circuit that can synchronize the phase of the AC bias signal f with the phase of the low-range color signal e.

[0007]

[Means for Solving the Problems] In order to solve the above problems, the bias oscillation circuit of the present invention is equipped with a color processing circuit that converts a video color signal into a low-frequency color signal phase-synchronized with a reference signal. This is a bias oscillation circuit that outputs an AC bias signal used for recording audio signals, etc., and is characterized in that the AC bias signal is phase-synchronized with the reference signal.

[0008]

[Operation] According to the above configuration, the reference signal of the color processing circuit used when converting the video color signal to the low-range color signal is in phase synchronization with the low-range color signal, and is in phase with the AC bias signal. It's in sync. Therefore, in the bias oscillation circuit, the phase of the AC bias signal is synchronized with the phase of the low range color signal, so that it is possible to prevent phase distortion of the low range color signal due to the AC bias signal.

[0009]

[Embodiment] An embodiment of the present invention will be described below with reference to FIG.

The bias oscillation circuit according to this embodiment is shown in FIG.
As shown in the figure, the crystal oscillator 2 of the color process circuit 13
1, and this frequency dividing circuit 1 has a frequency fc of 3.58 MHz from a crystal oscillator 2.
The reference signal b is inputted. This frequency dividing circuit 1 is connected to a comparator circuit 3, and outputs to the comparator circuit 3 a bias reference signal j obtained by frequency-dividing the reference signal b.

[0011] The comparator circuit 3 also has V
A CO circuit 5 is connected, and an AC bias signal m is input from the VCO circuit 5. and,
This comparator circuit 3 detects a phase difference between a bias reference signal j and an AC bias signal m, and outputs a DC signal k corresponding to the phase difference. Further, the comparator circuit 3 is connected to the above-mentioned VCO circuit 5 via an LPF circuit 4 that removes high frequency components, and this VCO
The circuit 5 receives a DC signal l input via the LPF circuit 4.
It outputs an AC bias signal m having an oscillation frequency corresponding to the oscillation frequency.

The above VCO circuit 5 is connected to a comparator circuit 3, and is also connected to a fixed head 7 via an amplifier circuit 6 that amplifies the input signal to a predetermined voltage level.
The fixed head 7 records the bias oscillation output g input from the amplifier circuit 6 on a magnetic tape (not shown).

On the other hand, the crystal oscillator 2 connected to the bias oscillation circuit 12 is also connected to the first frequency converter 8, and outputs the reference signal b to the first frequency converter 8. ing. This first frequency converter 8 includes:
A horizontal synchronization separation circuit 11 is also connected via the multiplier circuit 10, and a video luminance signal h is input to the horizontal synchronization separation circuit 11. The horizontal synchronization separation circuit 11 separates the horizontal synchronization signal i (fH = 15.7 KHz) from the input video luminance signal h, and the multiplier circuit 10 multiplies the horizontal synchronization signal i by 40 times. A low gamut color carrier wave a having a carrier frequency fs of 629.4 KHz is output to the first frequency converter 8.

The first frequency converter 8 to which the above-mentioned low-range color carrier wave a and reference signal b are input is connected to a second frequency converter 9.
The second frequency converter 9 is connected to the second frequency converter 9, which combines the low-range color carrier wave a and the reference signal b, and outputs the carrier frequency fc+fs.
is a composite signal c whose phase is synchronized with the reference signal b at 4.2MHz.
It is designed to output . The second frequency converter 9 also receives a video color signal d having a carrier frequency fc of 3.58 MHz, and the second frequency converter 9 converts the video color signal d and the composite signal c. As a result, a low frequency color signal e having a carrier frequency fc of 629.4 KHz and phase-synchronized with the composite signal c is output.

In the above configuration, the bias oscillation circuit 1
The second operation will be explained below.

When the crystal oscillator 2 of the color process circuit 13 starts operating, a reference signal b having a frequency fc of 3.58 MHz is output.
is input to the first frequency converter 8 and the frequency divider circuit 1 of the bias oscillation circuit 12. At this time, the first frequency converter 8 includes the reference signal b as well as the multiplier circuit 10.
A low gamut color carrier wave a having a carrier frequency fs of 629.4 KHz is input from , and this low gamut color carrier wave a and a reference signal b are synthesized by the first frequency converter 8 to generate a signal of 4.2M.
It has a carrier frequency fc+fs of Hz and is output as a composite signal c phase-synchronized with the reference signal b.

The above composite signal c is input to the second frequency converter 9, and the video color signal having a carrier frequency fc of 3.58 MHz is input to the second frequency converter 9. d is phase-locked to the above composite signal c,
It is converted into a low-pass color signal e having a carrier frequency fc of 629.4 KHz.

On the other hand, the frequency dividing circuit 1 of the bias oscillation circuit 12
The reference signal b input to
It will be output as a bias reference signal j having a frequency fAC of 0.0 KHz, and this bias reference signal j will be input to the comparator circuit 3. At this time, the comparator circuit 3 is also input with an AC bias signal m output from the VCO circuit 5, and the comparator circuit 3 receives a DC signal k proportional to the phase difference between the bias reference signal j and the AC bias signal m. will be output.

After high frequency components are removed from the above DC signal k in the LPF circuit 4, the DC signal k is sent to the VCO circuit 5 as a DC signal l.
By feeding back to the comparator circuit 3, the VCO circuit 5 outputs an AC bias signal m whose phase is synchronized with the bias reference signal j. Thereafter, the above AC bias signal m is amplified to a predetermined voltage level by the amplifier circuit 6 to produce a bias oscillation output g, which is recorded on a magnetic tape (not shown) via the fixed head 7.

As described above, in the bias oscillation circuit 12 of this embodiment, the AC bias signal m is amplified in phase synchronization with the bias reference signal j, which is based on the reference signal b, which is phase synchronized with the low frequency color signal e. The bias oscillation output g is recorded. Therefore, the bias oscillation circuit 12 is capable of synchronizing the phase of the AC bias signal m with the phase of the low-range color signal e, thereby preventing the occurrence of phase distortion of the low-range color signal e due to the bias oscillation output g. is now possible.

[0021]

As described above, the bias oscillation circuit of the present invention is equipped with a color processing circuit that converts a video color signal into a low-frequency color signal that is phase-synchronized with a reference signal, and is equipped with a bias oscillation circuit that outputs an AC bias signal. The circuit is configured such that the AC bias signal is phase-locked to the reference signal.

[0022] As a result, since the reference signal used when converting the video color signal to the low-range color signal is phase-synchronized with the low-range color signal and also with the AC bias signal, the AC bias signal is synchronized with the AC bias signal. The phases of the signal and the low-range color signal are synchronized, and as a result, it is possible to prevent phase distortion of the low-range color signal.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a bias oscillation circuit and a color process circuit.

FIG. 2 is a circuit diagram of a bias oscillation circuit.

FIG. 3 is a circuit diagram of a color process circuit.

[Explanation of symbols]

1 Frequency divider circuit 2 Crystal oscillator 3 Comparator circuit 4 LPF circuit 5 VCO circuit 6 Amplifier circuit 7 Fixed head 8 First frequency converter 9 Second frequency converter 10 Multiplier circuit 11 Horizontal sync separation circuit 12 Bias oscillation circuit 13 Color process circuit

Claims (1)

[Claims] 1. A color processing circuit for converting a video color signal into a low-frequency color signal phase-synchronized with a reference signal;
1. A bias oscillation circuit that outputs an AC bias signal, wherein the AC bias signal is phase-synchronized with the reference signal.