JPS5963893A - Modulating circuit - Google Patents

Abstract

PURPOSE:To remove the phase shift of a carrier by constituting titled circuit of a carrier oscillator and an AM modulator and feeding back from the output side to the input side of the AM modulator through an AC feedback means. CONSTITUTION:The phase difference of carriers between a carrier signal from the carrier oscillator 1 and the modulated output from the AM modulator is small when the current of the AM modulator 2 is high, and large when the current of the AM modulator 2 is low. If AC feedback is applied from the output side to the input side of the AM modulator through a feedback capacitor 15, the output of the carrier oscillator 1 and the feedback signal are synthesized basing a vector as an input, so that an input phase is automatically compensated and an output phase can be also compensated.

Description

Detailed Description of the Invention (a) Technical Field The present invention relates to a modulation circuit in a magnetic recording/reproducing device, etc., and particularly relates to a modulation circuit that can minimize the phase shift of a chroma signal when recording and reproducing a color video signal. .

(b) Background Art Magnetic Recording Repainting N: In video playback equipment for (VTR), video discs, television games, etc., it is necessary to convert the video signal to the receiving band of the television receiver.

Therefore, as shown in Figure 1, the output signal (V
C) and the video signal (Vi) to the AM modulator (λ),
A configuration in which a converted output (V, ) is obtained from the AM modulator (2) is often used.

However, the conversion output (Vo) linearity (linearity DG
) and the phase shift (DP) of the chroma signal when luminance modulation is applied. If these deteriorate with respect to the original signal, not only the luminance signal but also the original color cannot be reproduced.

Therefore, making the DG and DP small is an important point in the modulation circuit.

In general, a converter has a configuration as shown in Figure 2, where the input terminals (5) (6) of the first differential pair transistors (3) (4)
) with a carrier wave signal source (7) connected to the second differential pair transistor (9) connected to the common emitter and the power supply terminal (8).
Modulation input terminal allα connected to each base of 1QO)
A modulated input signal is applied to the output terminal OJ, and a converted output is obtained from the output terminal OJ. In the figure, Q4 indicates a constant current source.

In this case, the modulation input signal converts a video signal into a current, and modulates the switching operation of the transistors (3) and (4).

Here, the carrier wave of the converted output is the transistor (3) (
As the emitter resistance (re) of 4) fluctuates with respect to the modulation signal, phase modulation is applied to the luminance signal level, and as a result, the phase shift (DP) increases.

Since the phase of the chroma signal (CI()) changes with respect to the luminance level of the video signal (luminance and chroma signals), this pattern can be seen from state P to state Q with the step-like waveform video signal shown in Figure 4.
Like R and S (when expressed as a vector, phase fluctuations appear.

(c) Purpose of the present invention The purpose of the present invention is to compensate for the phase shift that has occurred in conventional modulation circuits.

B) Embodiment of the present invention FIG. 3 is an example of the modulation circuit of the present invention, FIG. 4 is an explanatory waveform diagram of the same circuit, and FIGS. A vector diagram in the corresponding case, and FIG. 5(c) shows a vector composite diagram when phase correction is performed in the case of implementing the present invention.

Next, to explain the present invention in detail, the fourth
Apply a step wave video signal as shown in the figure.

At this time, each of the chroma signals (a), (b), (c), and (d) fluctuates as follows (in the conventional example, a phase shift of the chroma signal occurs with respect to the luminance level).

In addition, the carrier wave signal from the carrier wave oscillator (1) and the AM modulator (
Looking at the carrier wave phase difference with the conversion output from 21, in the area marked ■ in Fig. 4, the input/output phase difference is small (Fig. 5 (a)) because the AM modulator (gradient current is large); AM in the area of
The current of the modulator (2) is small, and the input/output phase difference is large (Figure 5 (b)). Like,
The vector diagram shown in FIG. 5 is obtained.

Therefore, the feedback capacitor α9 is connected from the output side of the AM modulator ■.
When AC feedback is applied on the input side by
i', so that the input phase is automatically corrected and therefore the output phase can be corrected.

(e) Effects According to the modulation circuit of the present invention, by optimizing the amount of feedback, it is possible to substantially eliminate the phase shift of the carrier wave of the converted output, and a high-performance modulation circuit can be constructed.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional modulation circuit, Fig. 2 is a circuit diagram of an AM modulator for implementing the present invention, Fig. 3 is a block diagram of a modulation circuit of the present invention, and Fig. 4 explains the present invention. FIGS. 5(a), 5(b), and 5(c) show vector diagrams for explaining the present invention. Explanation of main drawing numbers (1)...Carrier wave oscillator (of...AM modulator)
(8)...Power terminal 04)...Input terminal
(15) ...Return condenser star chart Figure 2 Figure 4 (a) (b) (lX) Procedural amendment (self-motivated) March 1980, Mr. Commissioner of the Patent Office 1, Indication of the incident 1988 Patent Application No. 174970 2 Name of the invention Modulation circuit 6 Patent applicant Address 2-18 Hondori, Keihan, Moriguchi City Name (188) Sanyo Electric Co., Ltd. 4 Agent address Keihan, Moriguchi City Hondori 2-18-5, Subject of amendment ◎ Detailed explanation of the invention in the specification, brief explanation column of drawings and drawing 6, contents of amendment (1) Part 3 of the specification @ lines 3 to 5 `` written in the second line of the page
Here...it can be corrected. '' has been corrected as follows. Note [Here, when a carrier wave signal is applied to each pace of transistors +3++41, the emitter resistance re of transistor (9) is equal to that of said transistor! 31+4) emitter potential Vei−emitter current, that is, the transistor (9
) depends on rQ=ve/Iθ from the output current e. The configuration shown in Fig. 1 has a characteristic that the smaller the current flow θ, the greater the output, that is, the time delay of the carrier wave appearing at the terminal 1. Therefore, when looking at one point of the carrier wave, the smaller the current flow e, the greater the time delay of the carrier wave appearing at the terminal 1. , the phase difference between the chroma signal and the carrier wave becomes large. On the other hand, when the modulation current is large, re becomes small, the phase delay of the carrier wave becomes small, and the shift in the input/output phase difference of the carrier wave becomes small. To explain this pattern using Fig. 5, for the input carrier wave vector (1), the ideal output vector (in a circuit whose phase is inverted with respect to the input, that is, when the phase is different by 180°) is shown in Fig. 5 (A). As shown in <vi and Vo are vectors in opposite directions. However, if the above-mentioned phase shift occurs, Fig. 5 (b)
As shown in the figure, the phase delay of the carrier causes a phase delay of the chroma signal. (c) Purpose of the Invention The purpose of the present invention is to compensate for the phase shift that has occurred in conventional modulation circuits. B) Embodiment FIG. 3 shows an example of the modulation circuit of the present invention, an explanatory waveform diagram of the fourth equivalent circuit, and FIG. 5 (c) shows a vector composition diagram when phase correction is performed by the same circuit. . Next, to explain the operation of the same circuit of the present invention, when the step wave video signal shown in FIG. 4 is applied to the input terminal 04), the chroma signals (=) (b) (c) @) are
As shown in ■■■, the phase of the chroma signal tends to shift due to the difference in brightness level. Also, looking at the carrier phase difference between the carrier wave signal from the carrier wave oscillator (1) and the conversion output from the AM modulator (!), in the area marked ■ in Fig. 4, the AM modulator (!)
The current of 2) is large, so the phase difference between input and output is extremely small and is equal to the vector diagram shown in FIG. 5(a). However, ■
As the modulation current gradually decreases from to ■, a time delay occurs from when the carrier signal is input to the AM modulator until it appears at the output terminal (1 so), and as a result, the phase part of the chroma signal is Therefore, when an AC feedback is applied from the output side of the AM modulator (2) to the input side using the feedback capacitor (16), the input signal is the output of the grain transmitter fl+ and the feedback signal α, ) as a vector. The input signal v1 in FIG. 5(c) becomes vl as a synthetic input, and the synthetic input proceeds vectorially with respect to the original human power signal, so the output signal is automatically corrected. Konarori (11) “Figure 1 is...
...is shown. "Figure 1 is a block diagram of a conventional modification circuit, Figure 2 is a main circuit diagram for explaining the present invention, and Figure 3 is a block diagram of a conventional modification circuit.
The figure is a block diagram showing a modulation circuit of the present invention, No. 4M is a waveform diagram for explaining the present invention in detail, and Fig. 5 0) to (C) are vector diagrams for explaining the present invention in detail. ”. (Ill) Figures 2 and 3 of the attached drawings are amended as shown in the attached sheet. Figure 2 above

Claims (1)

[Claims] (1) Consisting of a carrier wave oscillator and an AM modulator, the A
In a modulation circuit in which the output of the carrier wave oscillator and the video signal are applied to the M modulator, feedback is applied from the output side of the AM modulator to the input side via an AC feedback means, so that the carrier wave in the converted output of the AM modulator is The variable luer a circuit is characterized by eliminating the phase shift of the circuit.