JPH0510403Y2 - - Google Patents

Description

[Detailed explanation of the idea] (Industrial application field) The present invention relates to an envelope detector.

(Conventional example) An envelope detector has conventionally been used as a detector for detecting the presence or absence of a signal and its level. However, in conventional envelope detectors, when the carrier wave frequency and the modulation frequency are close to each other, the time constant of the smoothing circuit is increased in order to reduce the residual portion of the carrier wave.

(Problems to be Solved by the Invention) However, if the time constant of the smoothing circuit is too large, the charge cannot be discharged even if the level of the signal to be detected suddenly becomes small, resulting in poor responsiveness.

(Means for Solving the Problem) For this reason, the present invention is a circuit that reduces the discharge time constant of the detector from the middle of discharge when a signal to be detected is input.

(Function) Therefore, a detection output with less carrier wave residual components compared to the signal level to be detected can be obtained, and since high-speed discharge occurs midway after the start of discharge, a detection signal with quick response can be obtained.

(Example) FIG. 1 shows an example of the present invention. The input signal to be detected is applied from an input terminal 7 to a detector 1 with a relatively short time constant, and its detection output is sent to an amplifier 8.
A detector 1 with a relatively long discharge time constant consists of a diode 5 and a capacitor 6 whose one end is grounded.
0 and is added to amplifier 3.
The output terminal of the amplifier 3 is connected to a diode 4 connected in a direction to discharge the charge of the capacitor 6. The output of capacitor 6 is led out to output terminal 9 via amplifier 2.

The operation of the above configuration will be explained using FIG. 2. FIGS. 2a, b, c, and d show waveforms at portions a, b, c, and d in FIG. 1, respectively. Now, when a tone burst audio signal like waveform a is applied to the input terminal 7, it is detected by the short time constant detector 1,
As shown in waveform b, it becomes an envelope in which the carrier wave component remains in the audio signal frequency component, and is further processed by amplifier 3.
It is amplified by 6dB and becomes a waveform like c. Here, when the diode 4 is open, the output of the capacitor 6, which has a relatively large capacity, has a large discharge time constant, so there is no carrier wave component, but the input signal is This results in a waveform with poor responsiveness that does not result in output even if the output is interrupted. If the diode 4 is connected as shown in the figure, in a range where the output of the capacitor 6 is higher in level than the output waveform c of the amplifier 3, the diode 4 becomes conductive and discharges the charge in the capacitor 6. Therefore, as shown in waveforms c and d,
The section between the intersections 20 and 21 of the waveform c and the dotted line,
In the section between the intersections 22 and 23, the diode 4 becomes conductive and the discharge time constant becomes small, and the waveform d has a good response almost similar to the waveform c in this section.

FIG. 3 shows another embodiment of the present invention, 1
1 is a detector with a large time constant, 12 is a detector with a small time constant, and 13 is an amplifier with an amplification degree of 6 dB. Therefore, the output waveform c of the wave detector 12 is similar to the waveform c in FIG. Therefore, the output waveform d of the capacitor 6 is similar to the waveform d in FIG. 2, and in the portion where the waveform c has a high level, a detection output with a large time constant is obtained, and in the discharge portion where the waveform c has a low level, the diode 4 is conductive. As a result, a high-speed discharge waveform with good responsiveness that almost matches waveform c can be obtained. This waveform d is amplified and output to the output terminal 9.

In the embodiment of FIG. 1, the detector 1 is a half-wave rectifier circuit, but if this is changed to a full-wave rectifier circuit, the time constant of the subsequent smoothing circuit can be made smaller, improving response.

(Effects) As described above, according to the present invention, the discharge time constant of the envelope detection output signal changes to a high-speed discharge time constant during the discharge, so that residual carrier wave components can be reduced and a detection output with good responsiveness can be obtained.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure is a waveform diagram of each part, and FIG. 3 is a circuit diagram showing another embodiment of the present invention. 1, 10, 11, 12...detector.

Claims (1)

[Scope of utility model registration request] A detection amplification output circuit that obtains a large-level detection output with a small time constant, a detection circuit that obtains a small-level detection output with a larger time constant than the detection amplification output circuit, and a smoothing capacitor of the detection circuit that outputs the detection signal. An envelope detector comprising a diode connected between the outputs of the amplification output circuit in a direction to discharge the charge of the smoothing capacitor, obtaining a detection output from the smoothing capacitor and discharging at high speed during the discharge.