JPS5992691A - Monlinear emphasizing circuit - Google Patents

Abstract

PURPOSE:To make the amount of emphasis of a nonlinear emphasizing circuit symmetrical for a center frequency by adding a capacitor in parallel to one couple of diodes which are connected reversely in parallel to constitute a limiter circuit. CONSTITUTION:A macro signal from an input terminal IN is amplified by a transistor (TR)Q3 and supplied to a circuit T which traps the center frequency and the limiter circuit LM. The limiter circuit LM is provided additionally with the capacitor C4 in parallel to one couple of the diodes which are connected reversely in parallel. Consequently, the operation of the limiter as less deterioration as the frequency is higher. The limiter level is controlled by TRs Q4 and Q5 according to the input level and an output having symmetry for the center frequency is obtained as the output of a TRQ6 constituting a buffer amplifier.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a non-linear 177177 circuit applied to a chroma emphasis circuit of a VTR device capable of dense recording.

(b) Conventional technology VTR devices tend to record more and more densely with the aim of miniaturization, and in the recently announced 8mm video, the track pitch of the video track in long play mode is 10mm. 5μm (19.5μm for β■)
It has become extremely small. Also, the video tracks are recorded in an overlapping manner and are not aligned. These facts work against obtaining a sufficient S/N ratio of chroma signals. Therefore, in order to improve the S/N ratio of the chroma signal, a recording/reproducing method has been proposed in which a non-linear emphasis is applied to the chroma signal during recording, and a de-en 71 system corresponding to this emphasis is applied during reproduction.

Here, focusing on the emphasis characteristic, it is necessary to apply an emphasis amount symmetrically to each of the upper and lower sidebands of the AM-modulated chroma signal. However, when a chroma signal is applied to the currently proposed emphasis circuit shown in FIG. 1, the amount of emphasis becomes asymmetrical as shown in FIG. In Figure 2, the horizontal axis shows the frequency (center frequency fO
:6.58MHz; Subay frequency: 1MHz)
, the vertical axis shows the output level, and the parameters are the input signal level (A%B, C are the input OdB, -10
dB, -20 dB) (the same applies to the frequency characteristic diagrams below). As shown in the figure, the amount of emphasis at each input level is asymmetric with respect to the center frequency. This is because in the Chromaen 71 system circuit shown in Figure 1, the collector of the first stage transistor (Q3) is connected to the transistor (Q4) of the trap circuit (T) and limiter circuit (LM'), and these It is recognized that this is because the gain in the high frequency range is reduced compared to the low frequency range due to the capacitance. In general, it is difficult to eliminate this asymmetry because the trap frequency of the trap circuit is determined. Furthermore, this tendency is remarkable when the trap circuit is constructed from components made into small chips.

By the way, if you try to correct this asymmetry only by correcting the frequency characteristics of the preamplifier used to amplify the head output during playback, you will find that at a certain input level (for example -20d
It can be adjusted to obtain symmetry with respect to B), but as a result of this adjustment, the amplitude correction at high frequencies works similarly for all input level signals, so the On the contrary, a problem arises for a QdB input, -13 dB input, whose characteristics were not so strongly asymmetric.

(c) Object of the Invention The objective of the invention is to make the amount of emphasis of the am/linear emphasis circuit symmetrical with respect to the center frequency (carrier frequency).

B) Structure of the Invention The present invention provides a frequency characteristic to the limiter level of a limiter circuit that provides emphasis on a chroma signal, and more specifically, the reduction in gain in the high frequency range mainly caused by a trap circuit can be suppressed to the maximum effect of the limiter of the limiter circuit. The feature is that compensation is performed by lowering the base as the higher the frequency range goes (this corresponds to increasing the gain on the high frequency side in terms of emphasis characteristics). Specifically, this compensation can be realized by attaching a capacitor of an appropriate value across a pair of diodes connected in antiparallel to each other that constitute the limiter circuit.

(E) Embodiment FIG. 4 mainly shows the chroma signal transmission system of a VTR device equipped with the circuit of the present invention, FIG. 5 is a circuit configuration diagram of the non-linear emphasis circuit of the present invention, and FIG. It is a frequency characteristic diagram of the output of the same circuit. Further, FIG. 7 is a circuit diagram of the preamplifier, and FIG. 8 is a frequency characteristic diagram of the output of the circuit.

In FIG. 4, (1) is a recording system, and 1) is a reproduction system.

The recording system (I) includes an input terminal (1), a preamplifier (2), a non-linear 177177 circuit (3), a low-frequency conversion circuit (4), a recording amplifier (5), and a recording/playback switch (6).
) and a magnetic head (7), while the reproduction system (I) includes a preamplifier (8) that receives the output from the switch (6), a high frequency conversion circuit (9), and a non-linear amplifier 1-sis circuit (1).
0) and an output terminal Ql1. Recording system (1)
As is well known, the recording system and the reproduction system 1) are complementary, so the recording system will be described below.

A color subcarrier signal of a standard color television signal is input to the input terminal (1). NT8C! The system is nominally one in which a 58 MHz subcarrier is modulated in two orthogonal phases (
This is hereinafter referred to as a chroma signal). Preamp (2)
) is to amplify this chroma signal, and as shown in Figure 8, it has high-frequency emphasis characteristics shown in characteristics A, B, and 0 for each input of QdB, -10 dB, and -23 dB, respectively. This preamplifier (21) adjusts the level so that the output of the non-linear emphasis circuit described later becomes QdB for each input at the center frequency (3.5Bmnz), and generally it is not necessary to have high-frequency emphasis characteristics. However, in this embodiment, a non-linear 177 is used to simplify the adjustment work.
The high frequency enhancement in the 177 circuit (3) is shared.

Figure 7 is a circuit wiring diagram of this preamplifier circuit (2).The transistors (Ql) (Q2) are 28C930.
So, the resistors R1 to R7 are 4.7K, 1.5K, and 6K, respectively.
．． 8, 500, 560. 4.7 and 11.2 Ωte, capacitor C1 is 103μF, coil Ll is 47μH,
Ru. The non-linear 177177 circuit (3) receives the output of the preamplifier circuit (2) and provides the output shown in FIG. As shown in characteristics A, B, and C for each of the above-mentioned inputs, the device operates so as to provide outputs that are symmetrical with respect to the center frequency (3.58 MH2).

Figure 5 shows this non-linear emphasis circuit (31(2)
It is a circuit wiring diagram. The basic configuration of this circuit is the same as that shown in Figure 1, and in this example, a capacitor (04) (capacitance value 2PF) is attached in parallel to a set of diodes connected in anti-parallel that make up the limiter circuit. It is characterized by what it does. In Figure 5, (Q3) is a transistor that amplifies the chroma signal from the input terminal (IN), (T) is a trap circuit that traps the center frequency together with stray capacitance, and (LM) is a set of antiparallel Diode (DI) (D2) connected to choke coil (L4)
), and a limiter circuit including a frequency characteristic correction capacitor (C4), (Q4) and (Q5) are transistors that control the limiter level according to the input signal level, and (Q6) is a transistor forming a buffer 1 amplifier. Here, a limiter circuit (Lm) including a dividing resistor (R12), a capacitor (C2), a trap circuit (T), and transistors (Q4) (Q5) connected to the collector of the transistor (Q3) is input. The load is dynamically varied with respect to the signal, and as a result, it acts on the transistor (Q6) to derive a non-linear emphasis signal having the frequency characteristics shown in FIG. Each transistor (Q
3) - (Q6) are 280930, diode (DI) (
D2) is 181925, bias resistor (R8) ~
(R16) is 4.7K, 6.1,3[]0.680.2
20.27.3゜01100 and 300Ω, coils (L2) to (L4) are 270μ and 110μ, respectively.
, 270μH, and a capacitor (02) (03
) is 103μ, 13PF.

This non-linear amplifier system circuit (31 is a limiter circuit (
(LM) contains a capacitor (C4), which reduces the effectiveness of the limiter at high frequencies. Follow,
The characteristic of this circuit (3) is that it does not increase the gain on the high frequency side, but compensates for the drop in the high frequency range as shown in Figure 2 in the circuit of Figure 1, and as shown in Figure 6, each input A against
It exhibits symmetrical output with respect to the center frequencies shown in %B and C.

The low-frequency conversion circuit (4) and subsequent circuit configuration are those of a general VTR.
Since this is well known to the device, the explanation will be omitted. In this embodiment, non-linear emphasis is applied to the chroma signal before low-frequency conversion, but it is also possible to apply a similar non-linear emphasis to the chroma signal after low-frequency conversion. stomach.

(f) Effects of the Invention In the present invention, a capacitor is attached in parallel to a set of diodes connected in antiparallel that constitute a limiter circuit.
This is useful because it can extremely easily eliminate asymmetry in general nonlinear 177171 circuits that do not have this.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a conventional non-linear engine 7 assist circuit, FIG. 2 is a frequency characteristic diagram of the same circuit, and FIG. 6 is a frequency characteristic diagram of an improved example. FIG. 4 shows a V equipped with the circuit of the present invention.
A block diagram of the TR device, FIG. 5 0 is a circuit configuration diagram of the non-linear 177171 circuit of the present invention,
FIG. 6 is a frequency characteristic diagram of the output of the same circuit. FIG. 7 is a circuit diagram of the preamplifier, and FIG. 8 is a frequency characteristic diagram of the output of the circuit. Explanation of main drawing numbers (LM)...Limiter circuit, (T)...
Trap L14)... Capacitor. School-515- Figure 6 Nuhen frequency wave board 1.0MHJ! Figure 7 Figure 8 7 Men M51! IK 1MHz '↑Procedure
Amendment (spontaneous) January 2, 1980 1, -pT+ Indication 1988 Patent Application No. 2 os 2 q $ 2, Name of Invention Patent Applicant Address Keihan Hondori, Moriguchi City 2-18 Name (188) Sanyo Electric Co., Ltd. Representative Kaoru Iue 4, Agent address 2-18 Keihan Hondori, Moriguchi City Contact information: Telephone (Tokyo) 835-111 Tokyo Patent Center Resident Kamata 5, Amendment Target (1) Column 6 of "Detailed Description of the Invention" of the specification, contents of amendment (1) Lines 16 to 17 of page 3 of the specification are amended as follows. ``By the way, this asymmetry is determined by the frequency of the preamplifier.''
dB". (3) Lines 12 to 14 of page 8 are corrected as follows. [) and (Le 4) are both 270μH, furthermore, the capacitor (C2) is 0.01μ', and (Ls) (C5) is a trap circuit that resonates with the subcarrier frequency (3.58MHz). . "that's all

Claims (1)

[Claims] (1) An input terminal to which an input signal is applied, an input signal from this input terminal to a limiter circuit that changes the limiter level according to the input signal level, and a trap circuit that traps the center frequency of the input signal. In a non-linear 177177 circuit comprising a circuit for forming a non-linear emphasis signal and an output terminal for deriving this non-linear emphasis signal, the limiter circuit is connected in parallel to a set of diodes connected in anti-parallel to each other. A non-linear emphasis circuit characterized by the addition of a capacitor.