SU661737A1 - Adjustable frequency generator - Google Patents

Description

(54) CONTROLLED FREQUENCY GENERATOR

The invention relates to a pulse technique and can be used in devices of the measuring technique as a voltage-to-frequency converter.

A known voltage converter is a frequency that contains the time setting the capacitor, controlled current generators, electronic switches, a comparator, and a source of reference voltage (1. The converter is based on recharging the capacitor using control current generators whose output current is proportional to the input voltage.

The drawback of the device is the high complexity of the electrical circuit, the relatively high temperature coefficient of the output frequency given the complexity of the converter.

Of the known devices, the closest to the technical nature of this invention is a voltage-frequency converter containing a control voltage source, a controlled transistor bridge, an integrating amplifier, a reference voltage driver, resistors, a comparator, a trigger with a counting input, diodes 2 The operation of the converter is based on changes in the direction of the recharge of the capacitor by changing the position of its plates relative to the time of the driving resistor, which is carried out with

using a controlled transistor bridge.

The disadvantage of such a generator is low voltage-frequency conversion accuracy, since the voltage from the capacitor is transmitted to the input of the comparator.

through diodes, which causes a high level of additional temperature error of multiplicative nature. In addition, the device has a strong dependence of the output frequency on the input resistance of the comparator and the resistance of the transistors of the controlled bridge in the closed state, which is a source of additional non-linear conversion bumps and increases the sensitivity threshold of the converter. Resistance

closed bridge transistors

The input resistance of the comparator shunts an integrating capacitor, reducing the constant charge time of the capacitor and the level to which the voltage across the capacitor tends to charge. Since the time the driving resistor must have a lot of resistance, whose resistance of the open transistors of the controlled bridge, the resistance must be chosen from a fairly rigid and not always satisfactorily fulfilled condition:

.r,

where ROT, RST are the resistances of the open and closed transistors of the bridge control, respectively;

R to - the input resistance of the comparator;

R is the resistance time of the driving resistor. ,

The purpose of the invention is to improve the accuracy and dynamic properties of the converter.

The goal is achieved by the fact that in a voltage-frequency converter containing a source of control voltage, a controllable bridge, an integrating amplifier, a KoMoapatop form of the reference voltage, and resistors, the controllable bridge is made of a resistance-transistor, two connected resistors are connected to the source of control voltage, the connection point of these resistors is connected to the non-inverting input of the integrating amplifier, the inverting input of which is connected to the connection point of the transistor The gates of the controlled bridge and the output are to the first input of the comparator, the second input of which through a resistor is connected to the connection point of the resistors of the controlled bridge, and the outputs of the comparator are connected to the control electrodes of the bridge transistors.

The drawing shows a structural electric generator circuit of a controlled clock TOTbl.

 The generator circuit contains a controlled resistor-transistor bridge 1, which includes a resistive voltage divider with resistors 2 and 3, a chain of series-connected field-effect transistors 4 and 5, an integrator consisting of an operational amplifier 6, the time of the setting resistor 7 and a capacitor 8, and a resistor 9, a connected non-inverting input amplifier 6, a comparator 10 with a paraphase output, containing a paraphase amplifier 11 and resistors 12, 13, 14 shaper 15 of the reference voltage, made on the resistor 16 and zener diodes 17, 18 controlled type and source 19 control voltage.

The operation of the controlled frequency generator is as follows.

Let the initial state of the generator be such that at the first output of the paraphase

amplifier 11. has a positive voltage. In this case, the driver 15 of the reference voltage forms the reference voltage of positive polarity, field-effect transistor 4 is open, and transistor 5 is closed. Under these conditions, the integrator is supplied with a voltage from the input source of positive polarity, and a linearly falling voltage is generated at the output of the amplifier, the rate of change of which is proportional to the voltage of the input signal. As soon as the voltage at the integrator reaches the threshold value, the comparator amplifier I1 tilts and goes into a new state. In the new state, at the first output of the amplifier And there is a negative voltage, and at the second output - a positive one. In this case, the transistor 4 is closed, and the transistor 5 is open, and a negative voltage is now applied to the input of the integrator 6.

from the source 19 of the control voltage. At the output of the integrator, a linearly rising voltage is formed with a rate of increase proportional to the voltage of the input signal. The circuit is in a new state as long as the voltage at

the integrator output will not reach the reverse polarity threshold value. Comparing the voltage of an integrator with a voltage on a precision compensated Zener diode allows you to strictly stabilize

amplitude of triangular vibrations. The requirements for the input resistance of the comparator are low, since the formation of triangular oscillations takes place on an integrator built on an operational amplifier, and this means, to a large extent, insensitive to the load. The amplitude of the triangular oscillations is determined by the ratio of the resistances of the resistors 12, 13 of the comparator.

In this converter, the second input of the paraphase amplifier 11 is connected via a resistor 14 to the output of a resistive divider of the controlled bridge 1, which is necessary to improve its dynamic properties. In a number of cases, the signal of the control voltage source may contain short impulses of interference or have the character of a rapidly varying function in certain areas. All this causes synchronous changes at the integrator output — and may cause premature

or with a delay in triggering the comparator 10. In order to eliminate the said effect in the generator, there is a described connection of one of the inputs of the comparator, which compensates for voltage fluctuations

the non-inverting input of the integrating amplifier 6 (and hence the integrator output) by synchronizing the trigger threshold of the comparator 10.

In the present invention, it is not at all necessary that the resistance time of the driving resistor 7 be much longer than the resistance of the closed transistor of the controlled bridge 1, but it is enough that: 2R7 / R3, .T,

which allows not only a much larger range to choose the value of the resistor time of the master resistor 7 than in the prototype, but also more to satisfy the reduced condition, thereby reducing the destabilizing effect of the parasitic parameters of the controlled bridge.

In practice, such a circuit solution allows to increase the accuracy of voltage-to-frequency conversion by more than an order of magnitude.

Claims (2)

1. Journal Electronik.Nb 3, 1972, p. 83 2.Pr Nishnikov V.A. Integrating 0 dc digital voltmeters. Leningrad, “Energie, 1976, p. 138, fig. 3-21.