JPH10322131A - Envelope detecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the potential of the connection of a coupling capacitor with a diode from being made unstable, and to prevent the forward voltage of the diode from being affected by a temperature change in an envelope detector circuit, using the coupling capacitor and the diode. SOLUTION: A coupling capacitor 23, a diode 24, and a low-pass filter 25 are connected in this order, and an amplitude modulated wave signal is envelope-detected, and a modulated wave signal is extracted. An inversion input terminal 26a and a non-inversion input terminal 26b of an operating amplifier 26 are connected to both edges A and B of the diode 24, and an output terminal 26c of the operational amplifier 26 is connected via a resistance 27 for feedback with the inversion input terminal 26a. The operational amplifier 26 is constituted of an operational amplifier for a low-speed operation, or the low-pass filter 25 is connected with the both input terminals 26a and 26b sides, so that the operational amplifier 26 is operated with only the frequency band of the modulated wave signal, and the potentials of the both edges of the diode 24 is maintained to be the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an envelope detection circuit for extracting a modulated wave signal from an amplitude-modulated wave signal obtained by amplitude-modulating a carrier signal with a modulated wave signal, and more particularly to an envelope detection circuit using a diode. .

[0002]

2. Description of the Related Art Conventionally, as a circuit of this type, FIG.
As shown in the figure, a coupling capacitor 13 is provided between the input terminal pair 11a, 11b and the output terminal pair 12a, 12b.
, Diode 14, resistor 15a and capacitor 15
An envelope detection circuit (first conventional example) in which a low-pass filter 15 made of b is connected in this order is well known.

In the envelope detecting circuit of the first conventional example, the potential at the connection point A between the coupling capacitor 13 and the diode 14 does not become indefinite when the diode 14 is not conducting. A resistor 16 may be connected between the output terminal 11b and the output terminal 12b as shown in FIG. 8 (second conventional example), or a diode 17 may be connected as shown in FIG. 9 (third conventional example). Are known.

[0004]

However, in the first prior art example, as described above, the diode 14 is in a non-conductive state during the positive half cycle of the input signal, so that the connection point A is not connected. The potential becomes unstable. To be precise, the potential at the connection point A is not always constant because it depends on the capacity of the coupling capacitor 13, the frequency of the input signal, the waveform, and the like. As a result, there is a problem that it is difficult to use the absolute value of the voltage of the output signal. Also, the forward voltage Vf of the diode 14 changes due to a temperature change (for example,
It changes at a rate of -2.5 mV / ° C for silicon diodes, and -1.5 mV / ° C for Schottky barrier diodes.
Therefore, there is also a problem that the signal voltage after detection also changes with temperature, and it is difficult to use the absolute value of the output signal in an environment where the temperature changes.

In the second prior art, if the resistor 16 has a large resistance value, the problem of the indefinite potential at the connection point A is not so much reduced. Since the power of the input signal is consumed by the resistor 16, there is a new problem that the efficiency of the envelope detection circuit is reduced. Further, in the third conventional example, although the problem of the indefinite potential of the connection point A is improved, the forward voltage Vf of the diode 17 (for example, about 0.7 V for a silicon diode and about 0.7 V for a Schottky barrier diode). 0.4V), the input signal is ± V
Since the diodes 14 and 17 are in a non-conducting state when between f, the potential of the connection point A remains indefinite when in this non-conducting state. Further, even in these second and third conventional examples, the problem of temperature change of the forward voltage Vf of the diode 14 still remains.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and an object of the present invention is to provide an envelope detection circuit suitable for utilizing the absolute value of the output signal with a simple configuration. It is in.

In order to achieve the above object, the first aspect of the present invention is described.
The configuration characteristic of the coupling capacitor, the diode and the low-pass filter are connected in this order, in the envelope detection circuit for extracting the modulation wave signal from the amplitude modulation signal obtained by amplitude-modulating the carrier signal with the modulation signal, An inverting input terminal was connected to a connection point between the coupling capacitor and the diode, a non-inverting input terminal was connected to a connection point between the diode and the low-pass filter, and an output terminal and the inverting input terminal were connected via a resistor. An operational amplifier (operation amplifier) is provided, and the operational amplifier is configured as a low-speed operation operational amplifier that does not respond to the carrier signal but responds to a signal in a frequency band to which the modulated signal belongs.

According to the first structural feature, the operational amplifier does not operate on the carrier wave signal but operates only on the modulated wave signal to keep the voltage across the diode the same. Therefore, the problem of indeterminate potential at the connection point between the coupling capacitor and the diode is solved without impairing the rectifying operation of the diode, and the problem of temperature change of the forward voltage of the diode is also solved. According to the feature, an envelope detection circuit suitable for utilizing the absolute voltage value of the output signal with a simple configuration is realized.

A second structural feature of the present invention is that the operational amplifier for the low-speed operation is used instead of the operational amplifier in the first characteristic, and the inverting input terminal and the non-inverting input terminal of the operational amplifier are connected to the operational amplifier. A filter for passing a signal in a frequency band to which the modulated wave signal belongs without passing the carrier wave signal is interposed between each of the two connection points.

According to this second structural feature, since the filter blocks the input of the carrier signal to the operational amplifier and allows the input of the modulated signal, the operational amplifier is connected to both ends of the diode only for the modulated signal. Operate so as to keep the same potential. Therefore, also with the second feature, an envelope detection circuit suitable for utilizing the absolute value of the output signal with a simple configuration as in the case of the first configuration feature is realized. Further, in this case, by changing the frequency characteristic of the filter, the filter can be applied to a carrier signal and a modulated signal having an arbitrary frequency.

[0011]

Embodiment

a. First Embodiment First, a first embodiment of an envelope detection circuit according to the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of the envelope detection circuit according to the first embodiment. .

The envelope detection circuit has a pair of input terminals 21a and 21 for inputting an amplitude-modulated wave signal obtained by amplitude-modulating a high-frequency carrier signal with a low-frequency modulated wave signal.
b, and a pair of output terminals 22a and 22b for outputting a modulated wave signal extracted from the amplitude modulated wave signal.

A coupling capacitor 23 between the input terminal 21a and the output terminal 22a for blocking the passage of the DC signal component and passing only the AC signal component, and blocking the passage of the positive signal component for the negative connection. And a rectifying diode 24 that allows only the signal component of the rectifier to pass therethrough.
The input terminal 21b and the output terminal 22b are connected by a conducting wire. Between the diode 24 and the output terminal 22a, a resistor 25a and a capacitor 25b each having one end connected to the output terminal 22a and the other end connected to the output terminal 22b are provided in parallel. The resistor 25a and the capacitor 25b constitute a low-pass filter 25. The filter 25 removes the carrier signal and guides only the modulated signal to the output terminals 22a and 22b.

The envelope detection circuit comprises an operational amplifier 26 composed of a low-speed operation operational amplifier (operational amplifier; operational amplifier) that does not respond to a carrier signal but responds to a signal below a frequency band to which a modulated signal belongs.
It has. The inverting input terminal 26a of the operational amplifier 26 is connected to a connection point A between the coupling capacitor 23 and the diode 24.
And the non-inverting input terminal 26b of the operational amplifier 26
Is connected to a connection point B between the diode 24 and the low-pass filter 25, and a feedback resistor 27 is connected between the output terminal 26c and the inverting input terminal 26a of the operational amplifier 26.

In the envelope detection circuit according to the first embodiment configured as described above, when an amplitude-modulated wave signal (see FIG. 2A) is input to the input terminals 21a and 21b, the coupling capacitor 23 is turned on. The DC signal component included in the amplitude modulated wave signal is removed, and the diode 24 performs half-wave rectification on the amplitude modulated wave signal from which the DC signal component has been removed to obtain a negative AC signal (see FIG. 2B). Output, low-pass filter 2
5 removes the carrier signal from the half-wave rectified AC signal, extracts only the modulated wave signal (see FIG. 2C), and outputs it to the output terminals 22a and 22b. Thereby, envelope detection of the amplitude modulated wave signal is performed.

On the other hand, during the envelope detection operation, the operational amplifier 26 operates only at the connection point A between the coupling capacitor 23 and the diode 24 and at the diode 24
And the node B of the low-pass filter 25 is maintained at the same potential. That is, when the potential of the connection point A becomes higher than the potential of the connection point B, the potential of the inverting input terminal 26a becomes higher than the potential of the non-inverting input terminal 26b. Therefore, the operational amplifier 26 reduces the potential of the output terminal 26c. It acts to lower the potential of the connection point A via the resistor 27. Conversely, when the potential of the connection point A becomes lower than the potential of the connection point B, the potential of the inverting input terminal 26a becomes non-inverting input terminal 2
6b, the operational amplifier 26 acts to increase the potential of the output terminal 26c and increase the potential of the connection point A via the resistor 27.

In this case, the operational amplifier 26 is constituted by an operational amplifier for low-speed operation, and does not respond to the carrier wave signal but responds to a signal below the frequency band to which the modulated wave signal belongs. The operation of matching the potentials is effective only for the modulated wave signal. Since the above operation is not effective for the carrier signal, the half-wave rectification operation by the diode 24 works effectively.

As a result, according to the first embodiment, the potential of the connection point A between the coupling capacitor 23 and the diode 24 is lower than that of the diode 24 and the low-pass signal with respect to a frequency signal that is lower than the frequency range of the modulated wave signal including DC. Filter 2
5 is maintained at the same potential as the connection point B, the connection point A does not become unstable, and the problem of the temperature change of the forward voltage of the diode 24 is solved. An envelope detection circuit suitable for using the absolute value is realized. Further, according to the first embodiment, the operational amplifier for low-speed operation is used, and since the operational amplifier for low-speed operation is inexpensive, the cost of the entire circuit can be reduced. Further, since the diode 24 and the operational amplifier 26 can be monolithically formed on a semiconductor wafer by the same process, the size of the circuit can be reduced.

Next, a specific example in which the envelope detection circuit according to the first embodiment is applied to a clock signal generation circuit that generates a clock signal from a correlation peak waveform signal (see FIG. 4) and generates the clock signal will be described. Note that the correlation peak waveform signal is, for example, S
This is provided from the AW matched filter.

As shown in FIG. 3, the clock signal generating circuit includes a low-pass filter 25 and output terminals 22a and 22a.
b has a comparator 31 connected between them. The negative input terminal of the comparator 31 is a diode 24 and a low-pass filter 25.
, And a positive input terminal of the comparator 31 is connected to an output terminal of a comparison voltage generator 33 connected to a reference voltage source 32. The comparison voltage generator 33 generates a predetermined negative comparison voltage. A connection point between the reference voltage source 32 and the comparison voltage generator 33 is connected to one end of the resistor 25a and one end of the capacitor 25b, and is connected to the input terminal 21b via the capacitor. Capacitor 3
4 indicates that the influence of the reference voltage source 32 is not affected by the input terminals 21a and 21b.
This is to prevent it from appearing in

In the application example configured as described above,
A correlation peak waveform signal having an amplitude proportional to the input signal from the SAW matched filter is supplied to input terminals 21a and 21a.
When input to 21b, the coupling capacitor 23, the diode 24, and the low-pass filter 25 supply a detection signal representing the negative envelope of the input correlation peak waveform signal to the comparator 31. The comparator 31 outputs a high-level signal when the detection signal is lower than the comparison voltage generated from the comparison voltage generator 33, and outputs a low-level signal when the detection signal is higher than the reference voltage. I do. As a result, the comparator 31 outputs a pulse train signal corresponding to the correlation peak waveform signal, that is, a clock signal.

As described above, as a result of applying the envelope detection circuit according to the present invention to the clock signal generation circuit, the potential of the connection point A is lower than the frequency range of the modulated wave signal including DC by the operation of the operational amplifier 26 as described above. Is kept the same as the potential of the connection point B for the frequency signal of Therefore, connection point A
And the problem of temperature change of the forward voltage of the diode 24 is solved, so that it is possible to accurately generate a clock signal corresponding to the absolute value of the output signal of the envelope detection circuit. it can.

B. Second Embodiment Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a block diagram showing an envelope detection circuit according to the second embodiment.

This envelope detection circuit can use various operational amplifiers 26 instead of the operational amplifier for low-speed operation as in the first embodiment, and can be connected to the inverting input terminal 26a and the non-inverting input terminal 26b of the operational amplifier 26. A, B
Is the same as that of the first embodiment except that low-pass filters 28a and 28b are respectively connected between the first and second embodiments. The low-pass filters 28a and 28b block signals having frequencies higher than the frequency band to which the modulated signal belongs, and pass signals having the same frequency band or less.

In the second embodiment thus constructed, when an amplitude-modulated wave signal is input to the input terminals 21a and 21b, the coupling capacitor 23, the diode 24 and the low-pass filter 25 convert the amplitude-modulated wave signal into an envelope. Detect and output. The low-pass filters 28a and 28b are
By removing the carrier signal component included in the amplitude modulated wave signal,
Inverted input terminal 2 of operational amplifier 26 only for modulated wave signal component
6a and the non-inverting input terminal 26b, respectively, so that the operational amplifier 26 matches the potentials of the two connection points A and B only for the modulated wave signal, as in the first embodiment. Also in this case, since the above operation is not effective for the carrier signal, the half-wave rectification operation by the diode 24 works effectively.

As a result, also in the second embodiment,
Since the potential of the connection point A is prevented from becoming unstable and the problem of the temperature change of the forward voltage of the diode 24 is solved, it is suitable for using the voltage absolute value of the output signal with a simple configuration. An envelope detection circuit is realized. Also,
According to the second embodiment, if the cut-off frequency of the low-pass filter 25 is changed, the cut-off frequency is effective for a modulated wave signal and a carrier wave signal having an arbitrary frequency. Further, also in the second embodiment, since the diode 24 and the operational amplifier 26 can be monolithically formed on a semiconductor wafer by the same process, the circuit can be downsized.

Next, an example is shown in which the envelope detection circuit according to the second embodiment is applied to a circuit for measuring the level of an amplitude-modulated wave signal. In this case, a DC voltmeter 35 is connected between both output terminals of the low-pass filter 25 as shown in FIG. According to this, the coupling capacitor 2
3, the instantaneous level of the modulated wave signal from the diode 24 and the low-pass filter 25 is measured by the DC voltmeter 35. As a result, also in this application example, the potential of the connection point A does not become unstable and the diode 24
Therefore, the problem of the temperature change of the forward voltage can be solved, so that the level of the modulated wave signal can be accurately measured.

C. Modified Example In the first and second embodiments, a negative modulated wave signal is extracted from the amplitude modulated wave signal. However, a positive modulated wave signal may be extracted. In this case, FIG.
The diodes 24 of 3, 5, and 6 may be connected in the opposite direction, that is, the anode of the diode 24 may be connected to the input terminal 21a, and the cathode may be connected to the output terminal 22a. However, in FIG. 3, the positive input terminal of the comparator 31 is connected to the output of the low-pass filter 25, and the comparison voltage generator 33 is connected to the negative input terminal of the comparator 31 to output a positive signal from the generator 31. It is necessary to generate a comparison voltage.

Further, in the first embodiment, the operational amplifier 26 is constituted by a low-speed operation operational amplifier which responds to a signal lower than the frequency band to which the modulated wave signal belongs. May be constituted by a low-speed operation operational amplifier that responds to the above-mentioned signal. Further, the low-pass filter 28 according to the second embodiment
a and 28b may be configured by band-pass filters that pass only signals in the frequency band to which the modulated wave signal belongs.

Further, contrary to the first and second embodiments, the envelope detection circuit according to the first embodiment may be applied to a level measuring circuit for an amplitude-modulated wave signal. The envelope detection circuit according to the embodiment may be applied to a clock signal generation circuit.

[Brief description of the drawings]

FIG. 1 is a block diagram of an envelope detection circuit according to a first embodiment of the present invention.

FIGS. 2A to 2C are signal waveform diagrams of each section of the envelope detection circuit for explaining the operation of the envelope detection circuit;

FIG. 3 is a block diagram of a clock signal generation circuit to which the envelope detection circuit according to the first embodiment is applied.

FIG. 4 is a waveform diagram of the correlation peak waveform signal of FIG.

FIG. 5 is a block diagram of an envelope detection circuit according to a second embodiment of the present invention.

FIG. 6 is a block diagram of an amplitude modulation wave signal level measurement circuit to which the envelope detection circuit according to the second embodiment is applied.

FIG. 7 is a block diagram of an envelope detection circuit showing a first conventional example.

FIG. 8 is a block diagram of an envelope detection circuit showing a second conventional example.

FIG. 9 is a block diagram of an envelope detection circuit showing a third conventional example.

[Explanation of symbols]

23: coupling capacitor, 24: diode, 25
... low-pass filter, 26 ... operational amplifier, 27 ... resistor,
28a, 28b ... low-pass filters.

Claims (2)

[Claims] 1. An envelope detection circuit for connecting a coupling capacitor, a diode, and a low-pass filter in this order and extracting a modulated wave signal from an amplitude-modulated wave signal obtained by amplitude-modulating a carrier signal with a modulated wave signal. An operational amplifier having a terminal connected to a connection point between the coupling capacitor and the diode, a non-inverting input terminal connected to a connection point between the diode and the low-pass filter, and an output terminal connected to the inverting input terminal via a resistor. An envelope detection circuit, wherein the operational amplifier is provided with a low-speed operation operational amplifier that does not respond to the carrier signal but responds to a signal in a frequency band to which the modulated signal belongs. 2. An envelope detection circuit for connecting a coupling capacitor, a diode, and a low-pass filter in this order, and extracting a modulated wave signal from an amplitude-modulated wave signal obtained by amplitude-modulating a carrier signal with a modulated wave signal. An operational amplifier having a terminal connected to a connection point between the coupling capacitor and the diode, a non-inverting input terminal connected to a connection point between the diode and the low-pass filter, and an output terminal connected to the inverting input terminal via a resistor. A filter that interposes a signal of a frequency band to which the modulated signal belongs without passing the carrier signal between each of the inverting input terminal and the non-inverting input terminal of the operational amplifier and the two connection points. An envelope detection circuit characterized in that: