JPH01270432A - Interface circuit - Google Patents

Abstract

PURPOSE:To reduce the intensity of the electric field of leaked radio waves with a small number of parts and low cost by constituting an interface circuit of an amplitude attenuator which reduces the amplitude of a digital signal and an amplitude amplifier which increases the output of said amplitude attenuator to the amplitude of the digital signal. CONSTITUTION:In input signal A is a digital signal, and switching edges of the signal are sharp and include overshoot and undershoot. This signal A has the voltage divided by resistances R1 and R2 of an amplitude attenuator 101 and is smoothed by a capacitor C1 to obtain a smooth signal B. This signal B is inputted to an amplitude amplifier 102 and is received by a coupling capacitor C2 and is amplified by an operational amplifier having the amplifying function or an HCO4 or the like which is a TTL IC of a C-MOS process, thus obtaining a signal C which can be processed in the TTL level. Since the signal B is more smooth than the signal A, the energy radiated from a cable is reduced.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an interface circuit that transfers high-speed signals. [Prior Art] In conventional interface circuits, when transferring high-speed signals, in order to reduce the electric field strength of leaked radio waves,
A product made of ferrite beads was inserted into the signal line. [Problem to be solved by the invention] However, the above-mentioned conventional technology cannot sufficiently reduce the electric field strength of leaked radio waves, and in Japan, the tolerance stipulated by the Voluntary Control Association for Interference by Information Processing Equipment (VCCI) In the United States, it is not possible to meet the allowable values stipulated by the Federal Communications Commission (FCC), so the board on which electronic components are mounted is made into a multilayer board, or the casing is made of metal to improve the shielding effect and comply with regulations. Countermeasures were taken to satisfy the permissible values. Such a method has the problem of significantly increasing costs. SUMMARY OF THE INVENTION The present invention is intended to solve these problems, and its purpose is to provide a means for sufficiently reducing the electric field strength of leaked radio waves in an interface circuit with a small number of components and at low cost.

[Means to solve the problem]

The interface circuit of the present invention is characterized by comprising an amplitude attenuator that reduces the amplitude of a digital signal and an amplitude amplifier that increases the output of the amplitude attenuator to the amplitude of the digital signal.

[For use]

According to the above configuration of the present invention, harmonic components of the signal are removed by attenuating overshoots and undershoots that occur at signal switching points using an amplitude attenuator that reduces the amplitude of the digital signal. Even if the output signal from this amplitude attenuator is interfaced via a cable etc., the electric field strength of leakage radio waves due to harmonic components will be very small.After the 6th order interface, from the amplitude attenuator The output of the amplitude amplifier TTL
Digital data processing is possible by amplifying the data to a high level. [Embodiment] FIG. 1 is a circuit diagram in an embodiment of the present invention.
01 is an amplitude attenuator that reduces the amplitude of the digital signal, and 102 is an amplitude amplifier that increases the output of the amplitude attenuator to the amplitude of the digital signal. The input signal A of the amplitude attenuator LOT is a digital signal as shown in A of FIG. 2, and the switching edge of the signal is steep and includes overshoot and undershoot. Therefore, after dividing the input signal by resistors R1 and R2, smoothing is performed by capacitor C1. As a result, the output signal of amplitude attenuator 101 becomes a smooth signal as shown in FIG. 2B. When the signal is converted as shown in B in Figure 2, the energy radiated from the cable becomes much smaller than when the signal A is interfaced from one board to the other via a cable, and the electric field strength of leaked radio waves is reduced. becomes smaller. The amplitude amplifier 102 amplifies the amplitude of the B signal in order to process the data received via the interface at the TTL level. For this purpose, after receiving the B signal with the coupling capacitor C2, the H
Amplification is performed using CO4 or the like, where R3 is a resistor that determines the amount of feedback. [Effect of the invention 1] As described above, according to the present invention, the number of components is small, such as the amplitude attenuator consisting of two resistors and one capacitor, and the amplitude attenuator consisting of two resistors, one capacitor, and an operational amplifier. This has the effect of sufficiently reducing the electric field strength of leakage radio waves at a low cost.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the operation of the present invention. FIG. 2 is a signal waveform diagram showing waveforms at each operating point in a circuit diagram showing the operation of the present invention. 101...Amplitude attenuator 102...Amplitude amplifier and above Applicant Seiko Epson Co., Ltd. Agent Patent attorney Kizobe Suzuki (and 1 other person) Figure 1 Figure 2

Claims (1)

[Claims] An interface circuit comprising an amplitude attenuator that reduces the amplitude of a digital signal and an amplitude amplifier that increases the output of the amplitude attenuator to the amplitude of the digital signal, and is characterized in that the signal amplitude is reduced and then transferred.