JPS62188404A - Detection circuit - Google Patents

Abstract

PURPOSE:To improve the degree of approximation by approximating the nonlinearity of a detection output level of a diode to a linear characteristic as a combined characteristic by means of the combination of a logarithmic converting circuit using an operational amplifier and an inverse amplifier circuit. CONSTITUTION:In constituting the titled circuit by connecting a DC amplifier circuit having a nonlinear input/output characteristic to the post-stage of a detection circuit, an element whose internal resistance changes nonlinearly depending on the applied voltage is used as a feedback resistor for an operational amplifier. The gain A of the logarithmic conversion circuit is a gain expression (A=1+Rf/RS), where Rf is the parallel combined resistance of a variable resistor, the TR S and the diode D2. RS is the resistance of an input variable resistor VR1. Since a diode D2 for reversing prevention is used while being reverse-biased, its impedance is high and the parallel impedance is negligible. On the other hand, if the internal resistance RD of a transistor (TR) S is RD, Rf=RD//VR2 is obtained, then the gain A has a nonlinear gain. Thus, the input/output is approximated to a linear characteristic by combining the input/output nonlinearities when the VR1, VR2 are changed variously.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a DC detection circuit and an envelope detection circuit,
In particular, it concerns the expansion of the dynamic range of the DC detection circuit and the sensitivity of the envelope detection circuit.The only difference between the two circuits is the time constant, so unless otherwise specified, the detection circuit also includes the envelope detection circuit. .

[Conventional technology]

There is a DC detection circuit that uses a detection diode to detect the signal using its rectification characteristics, smoothes it and extracts it as DC, and an envelope detection circuit that demodulates the modulated signal using a certain time constant.

[Problem to be solved by the invention] Conventionally, DC detection circuits have been constructed with a circuit that combines an operational amplifier and a diode as a method of improving the linearity of the detection circuit at low frequencies, and when the diode input level is low, a feedback resistor is used. Detection was performed using a so-called ideal diode circuit in which a non-linear resistance element, such as a diode, was inserted into the feedback circuit so that the feedback resistance would be low when the diode input level was high. Due to the frequency-gain characteristics, it could not be used directly at high frequencies, so it was first converted to a lower frequency using a frequency conversion circuit, and then detected using this ideal diode detection circuit.
The disadvantage was that the circuit became very complex. Furthermore, the envelope detection circuit has a narrow Guinamino range, and if it is to be used in a wide Guinamin range, it is necessary to add a complicated compensation circuit such as a distortion canceling circuit as an auxiliary circuit. This invention was made in view of the above circumstances, and its purpose is to combine the input/output characteristics of a DC amplifier circuit after high-frequency detection with an amplifier circuit having non-linear characteristics, and to obtain the overall input/output characteristics of the DC amplifier circuit. It is a circuit that approximates a straight line, and even in the case of non-linear diodes with different detection characteristics, it is a circuit that compensates by combining with a variable resistor to further improve the approximation.

[Means for solving problems]

In order to solve the above problems, this invention uses a configuration circuit in which a DC amplifier circuit with non-linear input/output characteristics is connected to the downstream stage of the detection circuit, so that the internal resistance changes non-linearly depending on the voltage. By using the change in the internal collector resistance of an element, such as a transistor, which depends on its output voltage, it is used as the feedback resistance of an operational amplifier to change the gain non-linearly. Have it. This provides a non-linear compensation type DC detection amplifier circuit which approximates the input/output characteristics to a straight line, and further obtains a higher approximation by adding an external resistor and varying this resistance. It is.

[For production]

First, to explain the operational amplifier DC amplification circuit, in the circuit shown in Fig. 1, a transistor S, a diode D2
, the parallel combined resistance of the variable resistors is R7, and the input variable resistor 2 is R5, then the gain A of the logarithmic conversion circuit becomes the gain calculation formula of a normal operational amplifier.

Here, D2 is a diode for preventing backflow, and since it is used as a reverse bias, it has a high impedance and can be ignored. On the other hand, if we consider the internal resistance of the transistor S, it is I in IO. =I simple BE・・・・・・・・・・・・−・
...(2). Here α='! /hT vBE...Base-emitter voltage IEf9...
...Emitter saturation current I, ...Emitter current Io, ...Collector current shift f = RD/Vn2, so the gain A has a non-linear gain.

FIG. 2 shows actual measurements of the nonlinear characteristics of input and output when VFLl and 2 were variously changed in a circuit that is a combination of the logarithmic conversion circuit and the inverting amplifier circuit shown in FIG. FIG. 3 shows actual measurements of the input/output characteristics of the DC detection circuit shown in FIG. 1, and this curve changes depending on the type of diode.

Therefore, by combining the characteristics shown in FIG. 3 and the characteristics shown in FIG. 2, the input/output characteristics can be approximated to a straight line.

〔Example〕

An embodiment of the linear approximation DC detection circuit according to the present invention will be described below with reference to FIG. In the linear DC detection circuit of the illustrated embodiment, CI is a DC blocking capacitor, Ll is a choke coil for causing current to flow through the diode, Dl is a detection diode, and R is a detection diode.

C2 is a smoothing resistor and capacitor. In the case of an envelope detection circuit, envelope detection can be performed using an appropriate time constant depending on the frequency. 1 and 2 are input variable resistors and feedback variable resistors, and the gain is varied by the nonlinear resistance of the transistor S. R3 is the output resistance, ■3, ■4
are variable resistors for adjusting the offset voltage of the operational amplifiers IC, IC2. The IC creates non-linear input/output characteristics, that is, logarithmic characteristics, and various non-linear input/output characteristics are created by (1) and (2). IC2 is an inverting amplifier circuit, and R4
The input resistor VR5 is a variable gain resistor for IC, and IC2.
The combination forms a normal rotation amplifier circuit. C3, C
4, C5, and C6 are power supply bypass capacitors.

〔Effect of the invention〕

As explained above, when using a DC detection circuit over a wide dynamic range, the detection output has nonlinear characteristics due to the detection characteristics of the diode, that is, the diode's differential resistance. Since it appears as a change, it cannot be used to compare input levels, and there is also the drawback that DC amplifiers tend to saturate at large levels. The DC detection amplifier circuit of the present invention can obtain an output level that approximates a linear line at the input level.

[Brief explanation of drawings]

Figure 1 shows one embodiment of the detection circuit of the present invention, and Figure 2 shows the first embodiment of the detection circuit of the present invention.
■1 of the logarithmic conversion circuit and inverting amplifier circuit in the figure, a graph showing the input/output nonlinearity when vFL2 is varied variously,
FIG. 3 is an actual measurement diagram of the input/output characteristics of the DC detection circuit shown in FIG. In the figure, IC is an operational amplifier of a logarithmic conversion circuit, IC2 is an operational amplifier of an inverting amplifier circuit, Dl is a detection diode, and S is a transistor. Figure 3 DC detection circuit input/output voltage characteristics Figure 2 Logarithmic converter input/output characteristics

Claims (1)

[Claims] (1) The output level of the detection circuit is amplified using a DC amplifier circuit, and the non-linearity of the detection output level of the diode is calculated by using an operational amplifier to calculate the nonlinearity of the diode detection output level by operating in a wide dynamic range from the very small input level to the large amplitude level. A detection circuit characterized by a combination of a conversion circuit and an inverting amplifier circuit, which approximates the nonlinearity of a diode to a straight line as a composite characteristic.