SU949663A1 - Logarithm determining device - Google Patents

Description

The invention relates to automation and computing and can be used in devices of information-measuring and computing equipment.

The known method of determining the logarithm, based on the use of the natural electrical characteristics of the elements, for example, on the use of the logarithmic dependence of the output voltage of the diode included in the feedback circuit of the operational amplifier, on the voltage on its amplifier 1.

However, this method has insufficient accuracy due to the significant effect of destabilizing factors on the characteristics of the elements.

The closest in technical essence to the present invention is a method for determining the logarithm, which consists in periodically accumulating a charge to obtain a corresponding voltage level equal to a given reference voltage level, and in a subsequent decrease of this charge C2.

The known method is characterized by insufficient accuracy due to the instability of the parameters of the element; of the discharge circuit, since 1 logarithm is determined from

5t RClnilil,

(one)

and about

where t is the conversion time,

those. discharge time of the discharge capacitor; R and C - resistance and capacitance

discharge circuit; - input voltage; Wow. - set voltage. As follows from formula (1), the relative error of the conversion time (L is equal to the sum of the relative error of resistance "LD and capacitance eLc of the discharge circuit. In addition, when measuring the conversion time t, an error is inevitably caused by a mismatch between the beginning and the end of the time interval t with pulses generator of the exemplary frequency, i.e., error due to asynchrony, SLs. Therefore, the method error of the method is equal to the sum of the relative errors of the resistance and the capacity of the discharge circuit and the error from the carried% 3 (rnostn.

thirty

and has a relatively large value.

The purpose of the invention is to improve the accuracy of determining the logarithm.

The goal is achieved by the fact that in the method of determining the log-5 rhyme, which consists in the periodic accumulation of charge to obtain the corresponding voltage level equal to the specified reference voltage level, and in the subsequent decrease of the charge tons of periodically repeated metered quantities of electricity, the charge is reduced until the corresponding level of the voltage equal to the input signal is equal and the number of dosages is calculated.

The repetition period of metered quantities of electricity is chosen longer than the accumulation time of charge — jn yes, and the number of dosages is counted from the moment the accumulation of charge begins until the corresponding voltage level is equal to the input signal.

The drawing shows an exemplary .-, functional block diagram of the device illustrating the inventive method. The logarithm is determined with. a functional circuit consisting of condenser 1, keys 2 and 3, metering capacitor 4, key 5 and comparator 6.

Capacitor 1 is charged to a predetermined voltage level UQ (this corresponds to the accumulation of charge until a corresponding voltage level of 35 is obtained equal to the reference voltage), a short to short enough for battery charging time kLuch 2. Then discharged metered quantities of electricity those. 40 accumulated charge reduces the periodically repeated imis with metered amounts of electricity.

The metered amounts of electricity are formed by periodically connecting to the capacitor 1 by means of the key 3 of the metering capacitor 4. The pulse repetition rate is set to the key of the key 3, and from the speed point of view, the repetition period of these pulses is longer than that required for charging. Capacitor 1 (i.e., the dosage repetition period is longer than the accumulation time of the charge). In the pauses between the pulses of a given 5 frequency, when the switch 3 is open, they close the switch 5 and the discharge metering capacitor 4. Comparator 6 compares the voltage levels on the capacitor 1 and a voltage proportional to 60 to the input signal. When these levels are compared, again produce a charge of capacitor 1 to a predetermined voltage level K and then repeat the process described above.65

The logarithm is determined by the number P of pulses of a given frequency (switching key 3), calculated for a time equal to the repetition period of the charge-discharge process of capacitor 1 (this time is determined by comparator 6)

(2)

where f С + С.

С - capacitor capacity 1 С - capacity of the metering capacitor 4.

The existence of a logarithmic relationship between the number of pulses n and the input signal Ug can be explained as follows. With each closure of the key 3, i.e. when ictuls of a given frequency arrive, the metering capacitor 4 takes away part of the charge of capacitor 1. As a result, the voltage on the capacitor 1 decreases in discrete levels, steps.

Uli - f Uo and f- (f - 1) Uo,

where and is the voltage across the capacitor 1 and its increment after an i-ro pulse of a given frequency. The methodical error of the proposed method can be determined as follows. From formula (2) it follows that the relative error in determining the number of pulses n is equal to the relative error in the logarithm of logf

CL 4.

The absolute error of the logarithm, as is known, is equal to the relative error of the number under the sign of the logarithm,

.

Considering that the capacity of the metering condenser 4 is much less than the capacity of the capacitor 1

C4 "C

-t

we get

G,

and therefore

one

Claims (2)

 The proposed method for determining the logarithm of the operation of the comparator 6 occurs synchronously with a given frequency, and therefore, when counting the number of pulses n in a time determined by the comparator 6, the error due to non-synchronism does not occur. Thus, the methodological error of the proposed method is cL „+ o ns“ “and much less than the methodical error of the known method. The use of the proposed method of logarithm determination provides, in comparison with the known ones, greater accuracy, a decrease in the effect of destabilizing factors on accuracy, as a result, a greater range of operating temperatures, an increase in the reliability of operation, and the exclusion of individual settings of devices that implement the method. which is especially important under the conditions of their mass production, since the time and cost of production are reduced. Claim 1. The method of determining the logarithm, which consists in the periodic accumulation of charge to obtain the corresponding eiviy voltage level equal to the specified reference voltage level, and in the subsequent decrease of this charge, is also different in that the charge reduction is made by periodically repeating dosage quantities of electrical energy, the charge is reduced until the corresponding level is equal to the voltage applied to the input signal, and the number of dosages is calculated. 2. Method POP1, characterized in that the repetition period. The metered quantities of electricity are chosen to be larger than the accumulation time of the charge, and the number of dosages is counted from the beginning of the accumulation of charge to the moment of equality of the voltage level corresponding to it. The input signal. Sources of information taken into account in the examination 1. Reference nonlinear circuits. Ed. D. Sheingold, M., Mir, 1977, p. 181-182. . 2. Authors certificate USSR 669484, cl. H 03 K 13/02, 1979 (prototype). BUT V / v -about about / w