JPS5827368Y2 - signal processing device - Google Patents

Description

[Detailed description of the invention] This invention relates to a signal processing device for a magnetic recording and reproducing device.The purpose of this invention is to eliminate sag without deteriorating the response characteristics of an automatic gain control circuit (AGC circuit) through a simple circuit configuration. It is an object of the present invention to provide a signal processing device that can eliminate this.

Conventional magnetic recording/playback devices connect various signals with different input levels, such as camera signals, television signals, and video tape recorder output signals, as input video signals, or connect electromagnetic conversion signals such as video tapes and video heads. An AGC circuit is used to compensate for signal level instability caused by variations in characteristics.

However, in the AGC circuit of a relatively simple device intended for home use, a sag of about 2 to 4% usually occurs.

This sag occurs when the low frequency characteristics of the video signal transmission system deteriorate, and for example, if the frequency characteristics are as shown in FIG. 4a, the sag increases.

When this sag increases, the period separation circuit is likely to malfunction, and if the synchronous signal separated from the sync signal is used to clamp the video signal, the clamp circuit malfunctions, causing a flicker phenomenon that makes the screen difficult to see.

Furthermore, in a device that uses this synchronization signal to operate a time-base fluctuation correction circuit that removes time-base fluctuations in color signals reproduced from a magnetic recording/playback device, the position of the synchronization signal is equivalently shifted due to the influence of sag. However, there was a drawback that the hue unevenness of the color signal, especially at the beginning of the field, was observed.

Furthermore, due to incomplete operation of the burst gate pulse, not only the burst signal but also noise and non-burst color signals are extracted and rejected, causing the APC circuit to malfunction and causing hue unevenness.

This invention is designed to remove sag in the AGC circuit without deteriorating the response characteristics of the AGC circuit, and its configuration will be explained below with reference to the drawings shown as examples.

The gist of this invention is that it is equipped with an AGC circuit and can also be used in magnetic recording and reproducing devices that record and reproduce television signals.
The point is that at least a resistor and a capacitor are combined to form a terminal network in which the low frequency characteristic level increases compared to the high frequency characteristic level, and the terminal network is connected to the AGC circuit to eliminate sag. It is in.

FIG. 1 shows a conventional general AGC circuit, in which 1 is a video signal input terminal, Tr3 is a transistor constituting a first emitter follower, and R1, 5R2, and R3 are transistors constituting the first emitter follower.
Bias resistors, C1 and C2, forming the emitter follower of
, C3, C4 are coupling capacitors, T1. T
r3 is a transistor having amplifier 2, and R7-R14 are transistors having the amplifier Tr.
2; Bias resistor that constitutes Tr3; Tr4 is a transistor that constitutes the second emitter follower; R15 is an emitter resistor that constitutes the second emitter follower; D1;
, D2 is a diode, Tr5 is a field effect transistor (EET), R4-R6 is a bias resistor that biases the source of FET (Tr5), C is FET (Tr5)
Capacitor C6, R1 stabilizes the source potential of
6 is an integration time constant, 2 is a DC voltage, and 3 is an output terminal of the AGC circuit.

The video signal applied to input terminal 1 is sent to amplifier Tr3. T
The coupling capacitor C4 is amplified and impedance-converted by the diode D1.r3. It is rectified by D2 and converted to a DC voltage to control the gate of the FET (Tr5.).

That is, the level of the output terminal 3 of the AGC circuit is kept constant by changing the impedance between the drain and source of the FET (Tr5) by changing the DC voltage applied to the gate of the FET (Tr5).

In the above AGC circuit, the elements that cause sag include the coupling capacitors C1 to C4 or the integration time constants C and R16.Sag can be reduced by increasing the capacitance of the coupling capacitor, but the AGC circuit Response characteristics deteriorate.

Therefore, in order to remove the sag without deteriorating the AGC response characteristics, an equivalent circuit as shown in FIG. 2 was constructed.

In other words, in Fig. 2, a T-shaped equibivalent circuit is constructed from resistors R, R and capacitor C1, and if this equivalent circuit and the AGC circuit described above are connected as shown in Fig. 2, Fig. As shown in the figure, when the frequency is low, the impedance of capacitor C1 is large, so the output level is high; when the frequency is high, the impedance is small, the output level is small, the low frequency characteristics are improved, and sag can be removed. can.

Figure 3 shows an embodiment of the present invention in which an equivalent circuit is incorporated into an actual magnetic recording/playback device, where 1 is an input terminal into which a video signal is input, and L is a tiller line indicating the brightness of the video signal. The time timing of the luminance signal and the color signal is adjusted when the signal and the color signal are processed separately in a form suitable for recording.

R1 is a termination resistor for the video signal, and R2 is an input matching resistor inserted between the video signal input terminal 1 and the low-frequency P amplifier T.

Generally, when a button is used in an apparatus for recording and reproducing television signals, the signals are FM modulated and then recorded on a magnetic medium.

Therefore, this low frequency filter T is used for the purpose of removing unnecessary high frequency components and color signals contained in the television signal (bandwidth: 3 MHz) in order to prevent overmodulation in the path 1 before FM modulation. It is used.

R3 is a matching resistor that connects the low-frequency P booster T and the delay line L, R2+R3 corresponds to the resistor R1 in Figure 2, and the resistor R4 and capacitor C0 in Figure 3 are the second resistor, respectively.
It corresponds to the resistor R2 and capacitor C1 in the figure, and also serves as the termination resistor R6 of the low-frequency amplifier T and the sag compensation resistor.

A series circuit of termination resistor R4 and capacitor C is connected in series between the input terminal of coupling capacitor C2 and ground.

If this coupling capacitor C2 and the AGC circuit are connected as shown in FIG. 3, a frequency characteristic as shown in FIG. 4C can be obtained.

In the case of the configuration shown in FIG. 3, the termination resistor R4 of the low frequency amplifier T and the sag compensation resistor (resistance R2 in FIG. 2) can be used in common, resulting in extremely low cost, and by adding the capacitor C1, The sag can be easily corrected, and since the DC component is cut, the DC potential of the terminal 1 can be set to any value, making the design very easy.

And AGC sag can be easily corrected.

As described above, the present invention is a low-frequency amplifier used to prevent overmodulation, etc. before FM modulating a luminance signal in a magnetic recording/playback device for recording and playing back television signals. A circuit for preventing sag is formed by combining a matching resistor of an electric circuit with a low-frequency r pumping function, such as a delay line for adjusting time timing, and a termination resistor of the electric circuit. Therefore, with the simple configuration of adding the capacitor C1, sag can be removed without deteriorating the AGC response characteristics, thereby preventing malfunction of the synchronous separation circuit, incomplete operation of the burst gate pulse, and There is no risk of phenomena such as flicker occurring.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of an AGC circuit used in the signal processing device according to the invention, Fig. 2 is a circuit diagram showing an example of an equivalent circuit used in the invention, and Fig. 3 is a circuit diagram showing an example of the AGC circuit used in the signal processing device according to the invention. FIG. 4 is a frequency characteristic diagram, in which a is a conventional example, and b and c are examples using the device of the present invention. 1... Video signal input terminal, R2... Input matching resistor, T... Low frequency P plate cover, R4... Termination resistor, C1... Capacitor, C2... Coupling capacitor.

Claims (1)

[Scope of utility model registration request] Connect the video signal input terminal to the input matching resistor.
Connect to the input terminal of an electric circuit having a low-frequency p-wave function and a delay function, and connect the output terminal of the electric circuit to the input terminal of an automatic gain control circuit via a coupling capacitor.
A signal processing device characterized in that a termination resistor and a capacitor are connected in series between the input end of this coupling capacitor and ground.