JPS6151662A - Signal detection circuit - Google Patents

Abstract

PURPOSE:To attain sure signal detection even if the level of an input voltage is fluctuated by comparing an input voltage with the input voltage through an anti-parallel circuit comprising rectifier elements and a capacitor. CONSTITUTION:The input voltage such as an AC signal is compared with a positive or negative voltage corresponding to a peak of the input voltage outputted when the peak potential difference is a prescribed value or over in response to the peak of the input voltage through a circuit 2 consisting of an anti- parallel circuit comprising diodes D1, D2 and a capacitor C connected thereto by a comparator 1. The positive or negative detection pulse is given as the output and even if the level of the input voltage is fluctuated and the peak level is fluctuated due to noise in the range where the peak level is within a prescribed value, the detection signal is detected surely.

Description

DETAILED DESCRIPTION OF THE INVENTION 3.1 Industrial Application Field This invention relates to a signal detection circuit used to extract a signal from an input voltage.

3.2 Prior Art and Its Disadvantages In order to read signals recorded magnetically or optically on a recording medium, conventionally, a voltage input via a read head and an amplifier circuit is applied to a slicer. Alternatively, a waveform processing circuit such as a limiter is used to manipulate the waveform by selecting the amplitude, but the level set in the conventional waveform processing circuit is always constant. Therefore, if the input voltage has a stable waveform as shown in FIG. 3(a), the predetermined level j! ,,zz can provide an output that faithfully corresponds to the input waveform as shown in the lower part of the figure. When the level falls below a predetermined level, as shown below, the output no longer corresponds to the input waveform, resulting in low signal readout accuracy.

3.-3 Purpose of the Invention In view of the above points, the present invention provides a reliable system that is independent of the fluctuations in the input voltage level due to the transport conditions of the recording medium, the recording density, the amplification factor, etc. An object of the present invention is to provide a signal detection circuit capable of detecting a signal.

The present invention is particularly effective when applied to reading signals magnetically or optically recorded as barcodes on cards, etc., but is not limited to this, and is applicable to AC signals including peaks. It can be widely used to detect signals when they are input by

3.4 Embodiments of the Invention Next, the invention will be explained based on the drawings of FIGS. 1 to 3.

FIG. 1 shows a signal detection circuit according to the present invention, which is composed of a voltage comparator 1 consisting of a differential amplifier circuit, etc., and a circuit 2 connected to the negative input terminal of the voltage comparator.

Circuit 2 includes two rectifying elements D1. It consists of a parallel circuit 2a formed by connecting Dz's in such a way that the directions of their forward currents are opposite to each other, and a capacitor C provided between the parallel circuit and the voltage comparator.

The rectifying elements Ds and D2 utilize the voltage drop characteristics of their forward currents, and use diodes. The capacitor C is used to hold the voltage at the peak when the input voltage passes each positive and negative peak until the discharge voltage of the capacitor becomes equal to the input voltage.

With this configuration, if an AC input signal is now input to the input terminal 3, the waveform of the first input ■ of the voltage comparator 1 will be the same as the AC input signal, as shown by the solid line in FIG. Since the waveform is increasing up to the point of 1 degree Celsius, the current flows in the forward direction through the rectifying element D1. Then, due to the forward characteristic of the rectifying element D1, the voltage at the second input (2) follows the voltage at the second input (2) at a voltage that is lower than the voltage at (2) by MDI. However, when the input voltage exceeds the peak, due to the action of capacitor C,
■As a result, the voltage maintains the voltage at the peak of the input voltage,
At time t2, the voltage of the first input (■) of the comparator and the voltage of the second input
The voltages of input ■ become equal. Therefore, in the region 1, the voltage of VDl is applied to the voltage comparator 1, so the output 2 of the signal detection circuit becomes positive as shown in the lower part of FIG.

In region B, the first input ■ tends to decrease, so the current flows from ■ through the rectifier D2 toward ■, VD2 is applied to comparator 1 due to the forward voltage of D2, and its output ■ becomes becomes negative.

Similarly, in regions C, D, and E, positive and negative outputs are produced corresponding to each peak of the input signal, regardless of the level of the input signal.

In the region F, the input signal has small peaks pt, I
)z, but since the peak-to-peak voltage is smaller than the forward voltage VDz of the rectifying element D2, it does not change the current direction of the rectifying element and is not reflected in the output. Even when a small peak occurs on the positive voltage side of the input signal, the same effect is performed by the rectifying element D1.

Such small peaks are generally caused by noise. Therefore, by setting the amplification factor at the front stage of this signal detection circuit so that the mixed noise is smaller than the forward voltage of each rectifying element in the parallel circuit, this signal detection circuit can be made unaffected by noise. can do.

3.5 Effects of the Invention As described above, according to the invention, a signal that changes in positive or negative is output every time a peak of the input voltage is detected, so that the signal can be reliably obtained without being affected by fluctuations in the level of the input signal. signal can be detected.

Further, if the potential difference between the front and rear peaks is below a certain level, this is ignored and no output is performed, so it is possible to provide a highly reliable signal detection circuit that is not affected by noise.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
FIG. 3 is a diagram showing the waveforms of the first input and the second input indicated by the symbols ■ and ■ in the figure, and the waveform of the output indicated by the symbol ■. FIG. 3 is a diagram illustrating the prior art. 1... Voltage comparator 2... Circuit 2a... Parallel circuit Dl, Dz... Rectifying element C... Capacitor Figure 1 Section 3 (=)

Claims (1)

[Claims] The input voltage is applied directly to a voltage comparator as its first input, and on the other hand, a capacitor is connected to a parallel circuit in which two rectifying elements are connected so that the forward current directions are opposite to each other. A signal detection circuit characterized in that the signal is supplied to the voltage comparator as its second input through a connected circuit.