JPS63257335A - Level detection circuit - Google Patents

Abstract

PURPOSE:To shorten the level detection time by connecting an overshoot generating circuit with the pre-stage of a low pass filter so as to shorten the time till the detection output reaches a threshold voltage. CONSTITUTION:The overshoot generating circuit is connected in series with an input signal and a detection circuit 2, a low pass filter 3 and a comparator 4 are connected succeedingly. The comparator 4 compares a detection output S0 from the low pass filter 3 with a reference threshold voltage Vth to detect the level. Thus, even when the input signal level is small and the detected output S0 exceeds the threshold voltage Vth slightly, since the input signal waveform overshoots, the leading is made quick. Thus, the arrival time t0 of the detection output till the threshold voltage is shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a level detection circuit, and more particularly to a level detection circuit that aims to shorten the detection time of a detection output level.

[Conventional technology]

-a, various electronic and electrical devices are provided with a level detection circuit for comparing the input signal with a reference signal and detecting the level of the human input signal. Conventionally, this type of level detection circuit is
It is configured as shown in functional blocks in FIG.

That is, in FIG. 4, the human input signal is detected by the detection circuit 12, the next-stage low-pass filter 13 extracts only the detected output, and the final-stage comparator 14 compares it with a specified threshold voltage VLh to determine the input signal. Level detection is performed to determine whether the signal level is equal to or higher than a reference level.

In this circuit, the rise characteristic of the detection output when the human input signal SIN is input is determined by the time constant of the low-pass filter 13. That is, when an input signal whose level is large and the detected output Sl is sufficiently larger than the threshold voltage VLh is input, the rise characteristic of the detected output is as shown in FIG. 5(a), whereas when the level is small, the detected output When an input signal in which S2 is slightly larger than the threshold voltage VLh is input, the rise characteristic of the detected output is as shown in FIG. 5(b).

[Problem that the invention seeks to solve]

In the conventional level detection circuit described above, as shown in FIG. 5(b), when the detection output S2 is slightly larger than the threshold voltage of the comparator 14, the detection output reaches the threshold voltage. Rise time t until reaching
2 becomes larger than the rise time t shown in FIG. 5(a), which causes a problem that the level detection time at the time of signal input becomes longer.

SUMMARY OF THE INVENTION An object of the present invention is to provide a level detection circuit that can shorten the time required for a detection output to reach a threshold voltage, thereby shortening the level detection time.

[Means for solving problems]

The level detection circuit of the present invention includes a detection circuit that detects an input signal, a low-pass filter that passes only the detection output from the detection circuit, and a comparator that compares the low-pass filter output with a reference value to detect the level. In the level detection circuit provided, an overshoot generation circuit is connected at least before the low-pass filter, and even if the detection output is slightly larger than the reference value, the overshoot characteristic makes the rise steep, and the reference value is reached in a short time. It is configured to do so.

〔Example〕

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

FIG. 1 is a functional block diagram of an embodiment of the present invention.

In FIG. 1, in this embodiment, an overshoot generating circuit 1 is connected in series with respect to an input signal, followed by a detecting circuit 2. A low pass filter 3 and a comparator 4 are connected. In this comparator 4, the detection output S0 from the low-pass filter 3 and the reference threshold voltage V
Level detection is performed by comparing with Lh.

When the human input signal SIN is input, the overshoot generation circuit 1 generates a second
An overshoot characteristic S7 as shown in the figure can be obtained, and this is output to the detection circuit 2 at the next stage.

Therefore, according to this configuration, even if the input signal level is small as shown in FIG. 3 and its detected output S0 is slightly higher than the threshold voltage, the input signal waveform will not overshoot as shown in FIG. As a result, the rise becomes steeper, and the time L0 for the detection output to reach the threshold voltage is shortened.
4, that is, compared to the conventional level detection time t shown in FIG. 5(b), the level detection time t in FIG. 1. >1. This makes it possible to shorten and speed up the level detection time.

Here, the overshoot generation circuit 1 is connected after the detection circuit 2 in the same manner as in FIG. 2.

It is clear that an overshoot waveform of the detected output is obtained, and the level detection time can be shortened in the same way as described above.

〔Effect of the invention〕

As described above, the present invention connects an overshoot generation circuit to a level detection circuit that includes a detection circuit, a low-pass filter, and a comparator, and uses overshoot characteristics to make the rise steep and reach a reference value in a short time. Therefore, even if the detection output is slightly larger than the reference value, the time it takes for the detection output to reach the reference value can be shortened, and the level detection time at the time of signal input can be shortened.

[Brief explanation of the drawing]

Figure 1 is a functional block diagram of the level detection circuit of the present invention, Figure 2 is an overshoot waveform diagram of the detection output when a signal is input, and Figure 3 is the time taken for the detection output to reach the threshold voltage in the present invention. Figure 4 is a functional block diagram of a conventional level detection circuit, and Figure 5 (a) shows the time required for the detection output to reach the threshold voltage in the conventional circuit when the detection output is sufficiently larger than the threshold voltage. FIG. 5(b) is a diagram showing the time required for the detection output to reach the threshold voltage in the case where the detection output in the conventional circuit is slightly larger than the threshold voltage. ■... Overshoot generation circuit, 2... Detection circuit,
3...Low pass filter, 4...Comparator, 1
2...Detection circuit, 13...Low pass filter, 14
...Comparator, S,,S,,S,...Detection output, SIN...Input signal, SE...Envelope characteristic, tO+UI+t2...Arrival time. Figure 3

Claims (2)

[Claims] (1) In a level detection circuit that includes a detection circuit that detects an input signal, a low-pass filter that passes only the detection output from the detection circuit, and a comparator that detects the level by comparing the low-pass filter output with a reference value. . A level detection circuit, characterized in that an overshoot generation circuit is connected at least before the low-pass filter. (2) The level detection circuit according to claim 1, wherein the overshoot generation circuit is connected before the detection circuit.