JPH0427262Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention relates to a video signal correction circuit that improves a reproduced video signal waveform.

(b) Prior art Video tape recorders record video signals in FM modulation. It is known that this FM modulation recording/reproduction causes deterioration in high frequencies during magnetic recording/reproduction, and as a result, the waveform of the demodulated reproduced video signal becomes dull. Therefore, in order to emphasize the high frequency range of the recorded video signal before FM modulation, an emphasis circuit is usually provided before the FM modulation circuit. Since this emphasis circuit emphasizes high frequencies, overshoot and undershoot occur in the recorded video signal. However, the overshoot of the reproduced video signal demodulated during reproduction causes the waveform to become dull due to high frequency deterioration of the reproduced FM video signal.

In order to correct this frequency characteristic deterioration, it is usually regenerated.
A method is used to emphasize the high frequencies of the FM video signal. Although this method improves the overshoot waveform to some extent, it is known that it causes deterioration of SN.

(c) Purpose of the invention Therefore, the present invention proposes a new video signal correction circuit that improves the distortion of the reproduced video signal waveform without causing SN deterioration.

(d) Structure of the invention The present invention is characterized in that the delay time in the low and high frequencies of the reproduced FM video signal is reduced compared to the delay time in the middle range.

(E) Embodiment The present invention will be described below with reference to an illustrative embodiment. FIG. 1 shows a circuit block diagram of this embodiment. As is clear from this figure, the playback amplifier 1 that inputs the video head output inputs the amplified output to the high-pass filter 2 to separate only the playback FM video signal (luminance signal), and phase-shifts the playback FM video signal. It is input to circuit 3.

In this phase shift circuit, as shown in Fig. 2, the reproduced FM video signal ^e1 is input to the base of a transistor Q whose collector resistance RC and emitter resistance RE are 560Ω. Coil L, 27pF capacitor C, and 1KΩ resistor R
The transfer output ^e2 is derived from the connection point between the capacitor C and the resistor R.

Therefore, the input/output ratio of the phase shift circuit is e ₂ /e ₁ = −(1−ω ² ×39×10 ⁻⁶ ×27×10 ⁻¹² )/(1
−ω ² ×39×10 ^-6 ×27×10 ^-12 ) +jω×27×10 ^-12 ×10 ³ /+jω×27×10 ^-12 ×10 ³ , and the delay time τ(ω) is τ(ω)= 1/ω・arg(e ₂ /e ₁ ). FIG. 3 illustrates this delay characteristic. As is clear from this figure, the delay time tends to increase as the frequency increases, reaches its maximum within the original FM carrier frequency deviation range (3.6MHz to 4.8MHz), and then decreases as the frequency increases. become a trend.
Therefore, this phase shift circuit makes the delay times in the low and high frequencies shorter than the delay times in the middle range. Therefore, the reproduced video signal waveform obtained by inputting the phase-shifted output to the FM demodulation circuit 4 would be a rounded waveform as shown by the broken line in FIG. 4 without the phase-shifting circuit. Because of this, the rise and fall become steeper as shown by the solid line, and the rise and fall characteristics are improved. Therefore, the rise and fall characteristics of the output derived through the de-emphasis circuit 5 are also improved.

(f) Effects of the invention Therefore, according to the invention, the reproduced video signal waveform can be improved without impairing the SN by simply arranging a phase shift circuit, and the effect is great.

[Brief explanation of the drawing]

Each of the figures shows an embodiment of the present invention, with Fig. 1 showing a circuit block diagram, Fig. 2 showing a main part circuit diagram, Fig. 3 showing a diagram explaining delay characteristics, and Fig. 4 showing a diagram explaining waveforms. . 3... Phase shift circuit, 4... FM demodulation circuit.

Claims (1)

[Scope of claim for utility model registration] A reproduction amplification circuit that amplifies a reproduction FM video signal,
A high-pass filter that separates the amplified reproduced FM video signal, and an FM demodulator that demodulates the separated signal.
In a reproduced video signal processing circuit that includes a demodulation circuit and a circuit that de-emphasizes the demodulated signal, the delay time is maximum within the FM carrier frequency shift region in the preceding stage of the FM demodulation circuit, and the delay time is maximum within the FM carrier frequency shift region. A video signal correction circuit comprising a phase shift circuit having a delay characteristic in which delay time is set to be small in lower and higher frequencies.