JPH071854B2 - Non-linear companding circuit - Google Patents

Description

The present invention relates to a non-linear companding circuit, that is, a circuit in which a compression rate or an expansion rate of an output level changes non-linearly according to an input level.

[Outline of Invention]

Input signals with different levels to multiple limit circuits that have the same amplitude limit characteristics to form multiple signals with different limit points (break points), and add them at a specified polarity and ratio to obtain a nonlinear I / O characteristics are obtained.

[Conventional technology]

This type of non-linear companding circuit has conventionally been composed of a broken line approximation circuit using a diode and a logarithmic amplification circuit. Since these circuits use the non-linear characteristics of the PN junction of the diode or transistor, the temperature characteristics are essentially poor, and the high frequency characteristics are poor due to the capacitance of the PN junction. There is also a drawback that the shape of the curve is fixed, an arbitrary function (order) cannot be selected, and minute levels and bidirectional signals cannot be handled.

The present invention aims to solve these problems.

[Means for solving problems]

The non-linear companding circuit according to the present invention includes a voltage dividing circuit 3 for dividing an input level into a plurality of parts and a plurality of limit circuits for limiting each divided output with substantially the same amplitude limit characteristic (the difference between the embodiments. Dynamic amplifiers 4a to 4c) and an adder circuit for adding the outputs of the limit circuits with a predetermined polarity and ratio.

[Action]

Arbitrary expansion or compression characteristics can be obtained by the division ratio and the addition ratio. Since it does not use a diode, it has good temperature and frequency characteristics and is suitable for a wide-band nonlinear processing circuit. It operates at a small input level and also works with bidirectional input (AC).

〔Example〕

FIG. 1 shows an embodiment of a decompression circuit of a non-linear companding circuit according to the present invention. The output of the input signal source 1 (for example, a video signal having a bandwidth of 10 MHz) is supplied to an amplifier 2 that produces a balanced output,
The amplifier outputs having opposite polarities are further divided into a plurality of (three in this example) signals whose levels have been adjusted by the voltage dividing circuit 3.
The three voltage-divided outputs are given to the differential amplifiers 4a to 4c, respectively, and are subjected to the swing limit by the limit characteristic peculiar to the differential amplifier. The differential amplifiers 4a to 4c have ± 4 KT / q (K: Boltzmann constant,
It saturates above the differential input of (T: absolute temperature, q: electron charge).

2A to 2C show the input / output characteristics of the differential amplifiers 4a to 4c. In FIG. 2A, since the input of the differential amplifier 4a is not divided by the voltage dividing circuit 3, the original limit characteristics of the differential amplifier 4a are shown. Show. In b and c, the inputs of the differential amplifiers 4b and 4c are divided by the resistors R1 to R3 of the voltage dividing circuit 3, so that the input level at which the limit occurs is higher than the characteristic of a. That is, the input voltage limit occurs a _{v c> v b> v a} .

When the outputs a to c of the differential amplifiers 4a to 4c are weighted by the resistors R4 to R6 and added by the differential amplifier 5 having the feedback resistor R7, the extension characteristic (the smaller the level is, the larger the gain) is as shown in FIG. Output is obtained. The addition ratio may be the reciprocal of the voltage division ratio. If the input is an AC signal, symmetrical bidirectional output characteristics are obtained as shown in FIG.

FIG. 4 shows an embodiment of a compression circuit, which comprises an amplifier 2, a voltage dividing circuit 3, limiting differential amplifiers 4a and 4b, adding resistors R3 to R5, and a differential amplifier 5 in the same manner as in FIG. There is. In this example, for the input signal a of the opposite polarity obtained from the amplifier 2,
The positive polarity signals b and c, which have been subjected to the swing limit by the differential amplifiers 4a and 4b, are added at a predetermined ratio, and by subtracting ab-c, the compression characteristic (small level and gain) as shown in FIG. Got a small).

FIG. 6 shows a concrete example of the expansion circuit. When the broken line approximation characteristics shown in the input / output characteristic graph of FIG. 7 are obtained, the voltages at the respective break points A, B and C are 40 mV (1), 160 mV (4) and 320 mV.
(8). That is, the differential amplifier 4a saturates at 40 mV input, the differential amplifier 4b at 160 mV, and the differential amplifier 4c at 320 mV.
The partial pressure ratio is determined so that each of them is saturated. If the resistance R3 of the voltage dividing circuit 3 is set to 30Ω, Output a to c of each differential amplifier 4a, 4b, 4c is 0.125 (1/8),
If the ratios of 0.125 (1/4) and 1.0 (1) are added, the elongation characteristics shown by the bold line in FIG. 7 can be obtained. That is, the output c of the differential amplifier 4c having the lowest sensitivity is used as a reference (linear characteristic), and the other outputs b and a are multiplied and added.

The addition ratio is set by the resistance ladder circuit 6 of R-2R as shown in FIG. When the differential amplifiers 4a to 4c are saturated, substantially equal currents flow from the ladder circuit 6 toward the outputs of the differential amplifiers 4a to 4c. First input is 40
The differential amplifier 4a saturates at mV and the current of this amplifier 4a is 1/8.
The voltage signal appears at the output D of the ladder circuit 6 at a ratio of. Similarly, when the differential amplifier 4b is saturated with 160 mV input, the voltage of 1/4 ratio is added to the output point D, and when the differential amplifier 4c is saturated with 320 mV input, the voltage of 1 ratio is added to the output point D. To be done.

The output of the ladder circuit is taken out via the emitter follower amplifier 7.

FIG. 8 shows a concrete example of the compression circuit, which has the reverse characteristics of the decompression circuit of FIG. The voltage dividing circuit 3 corresponds to the resistor R3 in FIG.
Is a pair of differential amplifiers 4c and 4d in which the same point is input and the outputs are commonly connected. The ladder circuit 6 is provided with the outputs of the differential amplifiers 4c and 4d and the negative phase outputs of the differential amplifiers 4a and 4b.
To add (resultingly subtract).

In order to obtain the reverse characteristics of FIG.
Set the voltage division ratio so that a break occurs at each input voltage of V, 120 mV, and 40 mV. Calculating the voltage dividing resistors R1, R2, and R3, R1 =
62Ω, R2 = 120Ω, R3 = 62Ω.

When viewed from the output D of the ladder circuit 6, the weight of the output of the differential amplifier 4a is 1/4 and the weight of the output b of the differential amplifier 4b is 1/2. Since the ratio of the outputs of the two differential amplifiers 4c and 4d is 2 due to the current addition, The signals c, -b, and -a are added at the ratio of.

[Effects of the Invention] As described above, the present invention provides input signals having different levels to limit circuits having the same characteristics, obtains a plurality of signals having different limit points with respect to the inputs, and adds the signals at predetermined polarities and ratios. Since a non-linear output is obtained by changing the voltage division ratio and the addition ratio, an arbitrary expansion or compression curve can be obtained. Further, since the broken line approximation can be performed without using a diode, the temperature characteristic and the frequency characteristic are extremely good, and a wide band minute signal can be processed. Further, bidirectional (input polarity is positive / negative) symmetric characteristics can be easily obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an expansion circuit showing an embodiment of the present invention, FIG. 2 is a limit characteristic diagram showing a relationship between an input level of a differential amplifier and a limit point, FIG. 3 is an extension characteristic diagram and FIG. Is a circuit diagram of the compression circuit, FIG. 5 is a compression characteristic diagram, FIG. 6 is a circuit diagram showing a concrete example of the decompression circuit, FIG. 7 is a decompression characteristic diagram for setting a break point, and FIG. It is a graph which shows a specific example. In the reference numerals used in the drawings, 1 ... Signal source 2 ... Amplifier 3 ... Voltage dividing circuit 4a to 4c ... Differential amplifier 6 ... Ladder circuit

Claims (1)

[Claims] 1. A voltage divider circuit for dividing an input level into a plurality of voltages,
A non-linear companding circuit comprising: a plurality of limit circuits that limit each divided output with substantially the same amplitude limit characteristic; and an adder circuit that adds the outputs of each limit circuit with a predetermined polarity and ratio.