SU877570A2 - Logarithmic converter - Google Patents

Description

54) LOGARIFMIC TRANSFORMER

This invention relates to transducers of electrical signals according to a logarithmic law and can be used in analog computing machines. On the main auth .. sv. 752372 is known a logarithmic converter containing a logarithmic element, a switch, the first input of which is connected to the input of a logarithmic converter, and the second input is connected to a constant-voltage source, the first-output generator of a commutator pulse is connected to the control input of the switch; a series-connected band-pass filter and a synchronous detector, the output of which is the output of a logarithmic converter, is connected to the control input of the synchronous detector a second output switching pulses, a high-frequency oscillator, a modulator, an adder, a band-pass amplifier connected in series, a detector, an automatic gain control unit, the switch output is connected to the auxiliary modulator input and the second input of the adder, the code of which is connected to the input of the logarithm, you - the stroke of the logarithmic element is connected to the input of the band amplifier and to the signal input of the automatic gain control unit, the output of which is connected to about the input bandpass filter. .. The known device is characterized by insufficient accuracy and stability of the amplitude characteristic, which is due to the dependence of the shape of the initial part of this amplitude of the characteristic (in the low voltage region) on the changes in the ambient temperature and the shift of the operating point (drift) of the operational amplifier included in the logarithmic element . The purpose of the invention is to improve the accuracy of work and expand the range of voltage being converted. The goal of this goal is achieved by the fact that a synchronous detector of bangers, the signal input of which is connected to the output of a bandpass amplifier, is inserted into the logarithmic converter, the output of a generator of switching pulses is connected to a control, the input of a synchronous envelope detector, the output of which is connected to

control input of the logarithm element.

The drawing shows a functional diagram of a logarithmic converter.

The converter contains a logarithmic element 1, a switch 2, a input 3 of a logarithmic converter, a constant voltage source 4, a generator of 5 switching pulses, a band-pass filter 6, a synchronous detector 7, a output 8 of a logarithmic converter, a high-frequency generator 9, a modulator 10, cy mat 11, a bandpass amplifier 12, a detector 13, an automatic gain control unit 14, a synchronous envelope detector 15.

The Converter operates as follows.

The switch 2 under the action of the generator of switching pulses 5 alternately switches the input voltage applied to the input 3 and the auxiliary voltage from the source 4 of the constant voltage.

In modulator 10, modulation of the amplitude of the sinusoidal is produced: the voltage produced by the high frequency generator 9 is directly proportional to the voltage coming from the output of switch 2. The adder

11 sums the alternating voltage from the output of the modulator 10 and the output voltage of the switch 2. The band amplifier 12 supplies the alternating voltage from the output of the logarithm element 1. The amplitude of this alternating voltage retains a constant value if the input voltage is in the logarithmic part of the characteristic of the logarithm element 1. If the input voltage falls into the region where there are deviations from the logarithmic dependence, then the voltage amplitude at the output of the band amplifier

12 decreases or increases (depending on the nature of the distortions of the quasilogarithmic characteristic) compared with the magnitude of the amplitude corresponding to the voltage of the constant voltage source 4. The difference of the amplitudes of the voltages at the output of the band amplifier 12, corresponding to the input and auxiliary voltage,. provided with a synchronous envelope detector 15. The output voltage of the synchronous detector 15 of the envelope is used as the displacement of the logarithm element 1. The indicated offset produces a current shape correction of the characteristic of the logarithmic converter.

A signal directly proportional to the amplitude of the voltage at the output of the bandpass amplifier 12 is provided by the detector 13. The path containing the bandpass amplifier 12 and the detector 13 may be narrowband, since changes in the temperature of the converter elements are a slow process. To narrow this band, a synchronous detector can be used as the detector 13. The control voltage is supplied from the output of the high-frequency generator 9. When the band is narrowed at the output of the synchronous detector, the effect of circuit noise on the output effect of the converter is reduced.

The automatic gain control unit 14 changes the amplitude of the low frequency component of the voltage at the output of the logarithmic element 1 in inverse proportion to the magnitude of the control voltage from the output of the detector 13.

The band-pass filter b transmits the harmonic of the signal with the frequency of the voltage of the generator of switching pulses 5. The amplitude of this harmonic does not depend on the parameters of the logarithmic diode of the logarithm element 1.

The advantage of the logarithmic converter is to increase the accuracy and stability of the conversion at the initial part of the amplitude characteristic, as well as the possibility of expanding the dynamic range of the input logarithmic stresses both in the direction of their reduction and increase, due to the dynamic principle of the correction of the characteristics of the logarithm element 1 in the process input voltage changes. The possibilities of expanding the dynamic range exceed one to two orders of magnitude compared with the known transducer.

Claims (1)

1. USSR author's certificate No. 752372, cl. G About -C 7/24, 1978.