JPH0456410A - Radiation noise reduction circuit - Google Patents

Abstract

PURPOSE:To eliminate an spurious harmonic component while minimizing the signal delay by providing a means inserting a varactor diode between a signal line and a power supply, or between a signal line and ground, or between the signal line and the power supply and also between the signal line and ground to the circuit. CONSTITUTION:When the output of an OSC is at a high level, the potential difference between the output of the OSC and a power supply Vcc is almost zero, a static capacitance of a diode 2 is maximum. When the output of the OSC is at a low level, the potential difference between the output of the OSC and ground is almost zero, a static capacitance off a diode 3 is maximum. When the output of the OSC is almost at a threshold voltage, a voltage of about Vcc/2 is applied to the diodes 2, 3 respectively. When the diodes whose static capacitance does not give any effect on a signal waveform from the OSC in this voltage state are selected, a spurious harmonic component is eliminated while minimizing the signal delay.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a radiation noise reduction circuit, and particularly to a radiation noise reduction circuit for harmonics generated during switching of a logic circuit.

[Conventional technology]

Conventional radiated noise reduction circuits reduce radiated noise to the outside of the device by inserting an EMI filter that combines an inductance and a capacitor into a signal line and removing harmonic components of a rectangular wave.

[Problem to be solved by the invention]

In the conventional radiation noise reduction circuit described above, the components of the EMI filter are fixed constants, so the overall output waveform is significantly blunted with respect to the input waveform, and this appears as a signal delay, reducing the circuit's operating margin. However, in the worst case, normal operation may no longer be possible.

[Means to solve the problem]

The radiation noise reduction circuit of the present invention includes means for inserting a variable capacitance diode between a signal line and a power supply, between the signal line and the ground, or between the signal line and the power supply, and between the signal line and the ground.

〔Example〕

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

The radiation noise reduction circuit shown in FIG. 1 outputs a rectangular wave using 03C1 as a clock.

A variable capacitance diode 2 is inserted between 08C1 and the power supply Vcc with its cathode connected to the power supply Vcc.

Further, a variable capacitance diode 3 is inserted between the output of 03C1 and the ground with its anode connected to the ground.

Next, the operation will be explained.

When the output of O3C is at a high level, the potential difference with the power supply Vcc is almost 0, so the capacitance of the variable capacitance diode 2 is maximum, which acts on the high level of the output of O5C1.

Conversely, when the output of 0SCI is at a low level, the potential difference with the ground is approximately O, so the capacitance of the variable capacitance diode 3 is at its maximum, which acts on the low level of the output of 03CI.

Near the threshold voltage, a voltage of about Vcc/2 is applied to each of the variable capacitance diodes 2 and 3, but the static capacitance I at this time is such that the influence of 03CI on the signal waveform can be ignored. By selecting a variable capacitance diode with a value that minimizes signal delay,
Remove unnecessary harmonic components. This situation is shown in FIG.

〔Effect of the invention〕

The radiation noise reduction circuit of the present invention has the advantage of being able to remove unnecessary harmonic components while minimizing signal delay.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
FIG. 3 is a waveform diagram for explaining the operation of the radiation noise reduction circuit shown in the figure. 1...08C12~3...-Variable capacitance diode. Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] A radiation noise reduction circuit comprising means for inserting a variable capacitance diode between a signal line and a power supply, between the signal line and the ground, or between the signal line and the power supply, and between the signal line and the ground.