JP2573202B2 - Noise removal circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a digital circuit noise elimination circuit.

[Conventional technology]

In recent years, the number of products including both a communication analog circuit and a digital circuit, such as a liquid crystal TV, a pager, and a digital video, has increased.

In making such a product, it is necessary to completely eliminate noise at the connection point from the analog circuit to the digital circuit. RC time constant circuits are often used as conventional noise removal circuits, and simply integrate a signal before sending it to a digital circuit.

[Problems to be solved by the invention]

For example, when a sync signal is separated from a composite video signal and input to a digital circuit, the conventional noise elimination circuit cannot completely remove the noise, but also averages and overlaps the whisker noise and the sync signal. However, the periodic stability of the signal edge has been disturbed.

FIG. 3 is a circuit diagram showing an example of a conventional noise elimination circuit. The synchronization signal A is composed of a resistor 1 and a capacitor 2.
When the signal is input to the RC time constant circuit, the signal is integrated and becomes a signal B. Further, the waveform is shaped by an amplifier constituted by the inverters 3 and 4, and the signal is output as a signal C.

FIG. 4 shows each signal A,
It is a time chart figure which shows the form of B and C.

The input signal A includes a synchronizing signal having a period T and a whisker-like noise n. When this signal is passed through the RC time constant circuit and the inverters 3 and 4, the signal becomes like a signal C. The whisker-like noise n continuously coming in is not removed.

Further, the portions indicated by the broken lines of the signals B and C show the case where there is no whisker noise n. It can be seen that the period of the rising edge is deviated by ΔT due to the whisker noise n.

Such a synchronizing signal causes fine horizontal vibration noise or the like on the TV screen. The present invention seeks to solve such a problem.

[Means for solving the problem]

The noise elimination circuit of the present invention is different from a conventional noise elimination circuit comprising an RC time constant circuit and an amplifier by an exclusive-OR gate (hereinafter referred to as an EX-OR gate) and the EX-OR gate. A controlled transmission gate (hereinafter referred to as TG),
A signal for integration, which is an output of the RC time constant circuit, and an output terminal of an amplifier, which outputs an output signal having the same phase as an input signal input to the noise elimination circuit, are connected via TG. The TG is turned on when the output signal of the amplifier that outputs an output signal having a phase opposite to that of the input signal and the input signal logically match, and the TG is turned off when the signal does not match. The influence of the whisker-like noise is removed by forcibly pulling the signal of the integration by the constant circuit to the logic level of the output signal of the amplifier that outputs the output signal in phase with the input signal.

〔Example〕

FIG. 1 is a circuit diagram showing one embodiment of the present invention. The configuration is such that an EX-OR gate 5 and a TG 6 are added to the circuit composed of the RC time constant circuit and the two-stage inverting amplifier of FIG. Input signal A
A signal D 'which outputs a logic "L" is detected when a match is detected with the signal C' of the output of the first inverting amplifier 3 which is an amplifier which outputs an output signal having a phase opposite to that of the first inverting amplifier 3. I do.

The output terminal of the EX-OR gate 5 is connected to the control terminal of TG6.
G6 is controlled.

Further, when the signal D at the output of the EX-OR gate 5 is logic "L", the signal B of the integration by the RC time constant circuit constituted by the resistor 1 and the capacitor 2 is converted to the signal C of the output having the same phase as the input signal A.
Is forcibly pulled into the logic level of the signal C at the output of the second inverting amplifier 4, which is an amplifier that outputs
Resistance 1 and capacitance 2 which are output terminals of RC time constant circuit
Is connected to the input terminal of the first inverting amplifier 3 and connected to the output terminal of the second inverting amplifier 4 via TG6.

At this time, the ON resistance of the second inverting amplifier 4 and the TG 6 is designed to be lower than the resistance 1 constituting the RC time constant circuit.

FIG. 2 is a time chart of the noise elimination circuit of the present invention. The input signal A is the same as that shown in FIG. 4, but the integration signal B is the output of the EX-OR gate 5 when the logic of the input signal A matches the signal C 'of the output of the first inverting amplifier 3. The signal D becomes logic "L", and TG6 is made conductive, and R
The signal B of the integration by the C time constant circuit is forcibly pulled into the logic level of the output signal of the second inverting amplifier.

Since the integration signal B of the RC time constant circuit is forcibly pulled to the logic level of the signal output from the second inverting amplifier, the integration signal B output from the RC time constant circuit is output from the first inverting amplifier. It does not have a signal waveform that inverts the output.

Thus, the signal C at the output of the second inverting amplifier 4 is
Has completely eliminated the effects of beard-like noise.

〔The invention's effect〕

In the noise elimination circuit of the present invention, the RC time constant is set to 0.5 to
If the time is adjusted to 3 microseconds, noise can be removed from the output of the video signal sync separation circuit, and an accurate horizontal sync signal can be extracted. Therefore, an improvement in image quality can be expected in an area where the electrolytic strength is weak.

Furthermore, by adjusting the time to 6 to 25 microseconds, it is possible to extract only the vertical synchronization signal from the horizontal synchronization signal, and also to extract digital data from the AM or FM demodulated signal in a pager or other data communication device. It has a wide range of applications, such as the ability to demonstrate its power, and greatly contributes to the industry.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of the noise elimination circuit of the present invention, FIG. 2 is a time chart showing the operation of the noise elimination circuit of the present invention,
FIG. 3 is a circuit diagram of a conventional noise elimination circuit, and FIG. 4 is a time chart showing the operation of the conventional noise elimination circuit. 1 ... resistance, 2 ... capacitance, 3 ... first inverting amplifier, 4
... Second inverting amplifier, 5... EX-OR gate (exclusive or gate), 6... TG (transmission gate).

Claims (1)

(57) [Claims] A noise comprising an RC time constant circuit for integrating an input signal input to a noise removing circuit, and at least two stages of amplifiers for amplifying and binarizing an integrated signal from the RC time constant circuit and sending out an output signal. In the elimination circuit, an exclusive OR gate and a transmission gate controlled by an output signal of the exclusive OR gate are provided, and integration of the RC time constant circuit is performed via the transmission gate. A signal is connected to an output terminal of the amplifier that outputs an output signal having the same phase as the input signal, and further, when the output signal of the amplifier that is out of phase with the input signal is logically coincident with the input signal, the transmission signal is output. A noise elimination circuit having a configuration in which a gate is turned on and a non-conduction state is set when a mismatch occurs.