JPS62263705A - Linearity compensating circuit - Google Patents

Abstract

PURPOSE:To attain the accurate level display by compensating the nonlinearity of a diode applying mean value detection by a positive feedback circuit comprising an operational amplifier. CONSTITUTION:The titled circuit consists of a diode circuit 1 applying mean value detection to an AC signal, a smoothing circuit 2, an operational amplifier 3 amplifying the output signal of the smoothing circuit 2, a negative feedback circuit 4 for the operational amplifier 3 and a positive feedback circuit 5 compensating the nonlinearity of the diode circuit 1. The positive feedback circuit 5 includes the diode similar to that for detection and a value corresponding to the output signal of the operational amplifier 3 is fed back positively when the level of an input AC signal is small, and the positive feedback quantity is suppressed to a prescribed value, then the nonlinearity of the detection diode when the AC signal level is small is compensated and the resulting output signal is obtained.

Description

[Detailed Description of the Invention] [Summary] In an AC signal level meter, etc., the device detects the average value of the AC signal with a diode, amplifies it with an operational amplifier, and displays the AC signal level with a meter, etc. The nonlinearity of the diode that performs average value detection is compensated for by the positive feedback circuit of the operational amplifier.

[Industrial application field]

The present invention provides a linearity compensation circuit that compensates for the nonlinearity of the diode that performs the average value detection when various types of AC signals are average-value detected by a diode and amplified by an operational amplifier to display the level of the AC signal. It is related to.

2. Description of the Related Art In various electronic devices, it is widely used to display the level of an AC signal and adjust each part to reach a desired level. In this case, a common configuration is to detect the average value of the AC signal and display it on a meter or the like. Furthermore, the level range of AC signals to be displayed is very wide, and it is desired that even minute level AC signals can be displayed accurately.

[Conventional technology]

FIG. 5 is a block diagram of the main parts of the conventional example, in which the input terminal 30
An alternating current signal is applied to the circuit, detected by a diode circuit 31, smoothed by a smoothing circuit 32, and sent to an operational amplifier 33.
is input to one terminal of A negative feedback circuit 34 is connected between the output terminal of the operational amplifier 33 and one terminal, and the child terminal is grounded.

Therefore, the operational amplifier 33 operates as an inverting amplifier, and the output signal as a DC voltage is applied from the output terminal 35 to a level meter (not shown), etc., and the average value or effective value of the AC signal applied to the input terminal 31 is The value is displayed.

FIG. 6 shows the specific circuit of FIG. 5, where 4o is an input terminal;
41 is a diode, 42 is a capacitor, 43 is an operational amplifier, 44 is a resistor, 45 is an output terminal, and 46 to 49 are resistors. FIG. 7 is an explanatory diagram of the operation, and (a) is the input terminal 4.
0, the peak value is Vin
Then, the AC signal a is expressed as Vin-sinωt. Note that ω is 2πf, and f is the frequency of the AC signal.

The input AC signal a is detected by the diode 41, and the detected output signal S becomes a half-wave rectified output signal as shown in FIG. 7(b). The dotted line in (b) indicates the forward voltage Vd due to the diode 41. This detection output signal is smoothed by a smoothing circuit and
This results in a DC signal C shown in (C) of the figure. This DC signal C is input to one terminal of the operational amplifier 43, and since the operational amplifier 43 operates as an inverting amplifier, the output signal d becomes as shown in (d> in FIG. 7. That is, the smoothed DC signal When the signal C is 10, the output signal d of the operational amplifier 43 is inverted and amplified to -V.

The equivalent resistance that generates the forward voltage Vd of the diode 41 is RdI, and the resistors 44.46 to 49 are R44R4, respectively.
&~R49 and R44=R47+R,8, the following equation holds between the input AC signal a (Vin) and the output signal d (1).

The equivalent resistance Rd of the diode 41 is approximately constant above the value of the current flowing through the diode 41, but becomes a large value when the current is small. Therefore, the input voltage Vin applied to the input terminal 40 and the output voltage 1 appearing at the output terminal 45 have the relationship shown by the solid line curve in FIG.

That is, the diode 41
An error corresponding to the forward voltage Vd (average value) occurs.

This error is not constant τ, but the equivalent resistance R of the diode 41
d.

In order to compensate for the nonlinearity caused by the diode 41 as shown in FIG. 8, a configuration shown in FIG. 9, for example, is known. In the figure, 50 is an input terminal, 51 is a diode,
52 is a capacitor, 53 is an operational amplifier, 54 is a negative feedback circuit, 55 is an output terminal, 56 to 59, 60 to 63 are resistors,
64.65 is a diode.

The nonlinearity caused by the diode 41 that detects the input AC signal is compensated for by the combination circuit configuration of the diodes 64, 65 and the resistors 60 to 63 in the negative feedback circuit 54. In other words, when the input AC signal level is low, the detection diode 5 is
This is intended to compensate for the nonlinearity of 1.

[Problem that the invention seeks to solve]

In the conventional examples shown in FIGS. 5 and 6, since the nonlinearity of the diode 41 for detecting the AC signal is not compensated for, the output voltage differs from the input voltage as shown in FIG. This results in the appearance of linearity, which has the disadvantage that it is not possible to accurately display the AC signal level.

In the conventional example shown in FIG. 9, if the combination of diodes 64, 65 and resistors 60 to 63 provided in the negative feedback circuit 54 is simple, the nonlinearity of the detection diode 51 can be sufficiently compensated for. In reality, a more complicated configuration than that shown is required. Therefore, the disadvantage is that the circuit configuration becomes complicated and expensive.

An object of the present invention is to compensate for the nonlinearity of a detection diode with a simple configuration.

[Means for solving problems]

The linearity compensation circuit of the present invention performs compensation using a positive feedback circuit of an operational amplifier, and will be explained with reference to FIG. A diode circuit 1 and a smoothing circuit 2 for detecting the average value of an AC signal, an operational amplifier 3 for amplifying the output signal of the smoothing circuit 2, a negative feedback circuit 4 of the operational amplifier 3, and a non-linear circuit of the diode circuit 1. It is equipped with a positive feedback circuit 5 that compensates for the negative effects.

[Effect]

The positive feedback circuit 5 includes a diode similar to a detection diode, so that when the level of the input AC signal is low, a value corresponding to the output signal of the operational amplifier 3 is positively fed back, and when the level of the AC signal is high, the value corresponding to the output signal of the operational amplifier 3 is fed back. Since the amount of positive feedback is suppressed to a predetermined value, it is possible to obtain an output signal that compensates for the nonlinearity of the diode for the wave when the level of the AC signal is small.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a circuit diagram of an embodiment of the present invention, in which 10 is an input terminal, 11 is a diode, 12 is a smoothing circuit, 13 is an operational amplifier, 14 is a resistor forming a negative feedback circuit, 15 is a positive feedback circuit, 16 to 18, 20 to 22 are resistors, 19 is a capacitor, and 23 is a diode.

The positive feedback circuit 15 includes resistors 20 to 22 and a diode 23, and is connected between the output terminal and the child terminal of the operational amplifier 13. Therefore, the output signal of the operational amplifier 13 is fed back positively to the child terminal of the operational amplifier 13 via the resistors 22 and 21, and negatively fed back to one terminal via the resistor 14. The positive feedback circuit 15 is provided with a diode 23, and the values of the resistors 20 to 22 are selected so that the same current as the current flowing through the detection diode 11 flows. Therefore, the forward voltage V of the detection diode 11
The forward voltage of the diode 23 has the same value as d, and this voltage is positively fed back to the operational amplifier 13 to compensate for the nonlinearity of the detection diode 11.

The equivalent resistance corresponding to the forward voltage Vd of the detection diode 11 is RdI, the equivalent resistance corresponding to the forward voltage VaZ of the diode 23 is Rd2, and the resistances 14.16 to 18.2
The resistance value of 0 to 22 is R34゜RI6 to R1al Rh
o~R2! Toshi, RI? + RIs = Rra
, R2□<< Rz H= R2゜, R, h<<R,
, the circuit configuration of FIG. 2 regarding the feedback circuit is represented by the circuit configuration shown in FIG. 3. At this time,
The input voltage of the positive feedback circuit is V. , its input voltage■.

If the output voltage when is manually applied to the child terminal of the operational amplifier 13 via the positive feedback circuit is 2, then the following equation is obtained. That is, as shown in FIG. 4 (A), when the input voltage ■o is increased in one direction from O, the output voltage ■2 initially increases according to the input voltage ■o, but gradually shows saturation characteristics. , the input/output characteristics exhibit nonlinearity.

The configuration of the embodiment of the present invention shown in FIG. 2 corresponds to a combination of the above-described configuration shown in FIG. 3 and the configuration shown in FIG. 6. Therefore, the output voltage Vo when the input AC signal Vin is applied to the input terminal 10 in FIG.
The output voltage ■ in the figure and the output voltage V in Figure 3
It becomes the sum of 2.

π　R+a+Rd.

When this equation (3) is transformed, it becomes. Here, if R+b=Rz□, Rd,=Rd2, it becomes π, and the operational amplifier 13
The output voltage ■o has a linear characteristic as shown in FIG. 4(B). That is, the nonlinearity in the conventional example shown in FIG. 8 can be compensated for by the positive feedback circuit 15.

〔Effect of the invention〕

As explained above, in the present invention, the average value detection output signal of the input AC signal by the diode circuit 1 and the smoothing circuit 2 is amplified and outputted by the operational amplifier 3, and the negative feedback circuit 4 and the positive feedback circuit 5 and a positive feedback circuit 5 to compensate for nonlinearity caused by the diode circuit 1. This positive feedback circuit 5 can be constructed from one diode 23 and a small number of resistors 20 to 22, and has a simple construction, which has the advantage of being an inexpensive construction. and,
Since the linearity is compensated even for minute input AC signal levels, accurate level display can be performed.

[Brief explanation of drawings]

FIG. 1 is a principle block diagram of the present invention, FIG. 2 is a circuit diagram of an embodiment of the present invention, and FIG. 3 is an explanatory diagram of the operation of an embodiment of the present invention.
4(A) and 4(B) are characteristic curve diagrams of the embodiment of the present invention, FIG. 5 is a block diagram of main parts of the conventional example, FIG. 6 is a circuit diagram of the conventional example, and FIG. 7 is a diagram of the conventional example. FIG. 8 is an explanatory diagram of non-linear characteristics caused by a diode, and FIG. 9 is a circuit diagram of a conventional example provided with a compensation circuit. 1 is a diode, a negative circuit, 2 is a smoothing circuit, 3 is an operational amplifier, 4 is a negative feedback circuit, 5 is a positive feedback circuit, 10 is an input terminal,
11 is a diode, 12 is a smoothing circuit, 13 is an operational amplifier, 14 is a resistor of the negative feedback circuit, 15 is a positive feedback circuit, 16-
18. 20 to 22 are resistors, 19 is a capacitor, 23 is a diode, and 24 is an output terminal.

Claims (1)

[Claims] A diode circuit (1) and a smoothing circuit (2) for detecting the average value of an alternating current signal, and an operational amplifier (3) for amplifying the output signal of the smoothing circuit (2).
), a negative feedback circuit (4) of the operational amplifier (3), and the operational amplifier (1) that compensates for nonlinearity of the diode circuit (1).
A linearity compensation circuit characterized by comprising the positive feedback circuit (5) of 3).