SU759988A1 - Capacitance-to-time interval meter - Google Patents

Description

The invention relates to the field of "electrical engineering and can ... be used in measuring instruments and systems.

A known instrument for measuring the capacitance of semiconductors of devices, which contains a bias voltage source, a resistor connected in series with the device under test, a switch, a capacitor, an operational amplifier, a high-pass filter, analog memory devices, an integrator, a shaper of time intervals and a counter [1].

The disadvantage of the device is that it does not allow measuring the capacitance of the pn junction, which is directly, but located in the oscillatory circuit. In addition, the device is complex and its output signal is inconvenient for conversion to digital form.

The closest technical solution to the invention is a capacitor-to-time converter, which contains a first integrator, ^Λ connected to a comparator, and a second integrator connected to a second comparator, averaging filters, switches, a voltage reference, connected to the input first integrator / generator and clock impulsoz connected with keys designed to discharge the capacitor, the output of the first comparator connected to ^one input of a temporary key pulsed voltage divider whose output communication coupled to the input of the second integrator, and the reference source .napryazheniya connected to the signal input of a key pulse divider and comparator inputs of the first and second comparators. During the master circuits of the first and second thTelectors, the exemplary and measured capacitances E2 are connected accordingly.

This transducer does not provide measurements of the controlled capacitance of a device, since the latter is measured at a certain frequency of a sinusoidal voltage at a given constant bias.

In addition, the converter does not allow measuring the capacitance of the capacitor,. located in the circuit, for example in an oscillatory circuit, which is necessary when measuring the quality factor of varicaps by the resonance method. That is, the 'device has limited functionality.

759988 4

The purpose of the invention is the expansion of the functional capabilities of the device.

The goal is achieved by the fact that in the capacitance transducer in the time interval containing the bias voltage source, an oscillating circuit, a sinusoidal voltage generator, a series-connected selective amplifier, a detector, an extremum detection unit and a trigger, an electric sensor and an electric motor are introduced, while the second input of the trigger . the hera is connected to an electric sensor, which is kinematically connected with the motor shaft and a variable capacitor of the oscillatory circuit, and the terminals for connecting the measured capacitance are connected in parallel with the variable capacitance of the oscillatory circuit.

The drawing shows a functional diagram of the proposed Converter,

The converter consists of gauges. body circuit 1, sinusoidal voltage generator 2, selective amplifier 3, detector 4, extremum determination unit 5, 'trigger 6, electric sensor 7, “-g · - ·· electric motor 8, bias voltage source 9, resistor 10 / input 11/12 and output 13 terminals. Resistor 10 is used to decouple .7 circuits of constant and alternating voltage.

The measured capacitance 'turns on' · parallel to the variable · capacitance of the oscillating circuit, which is kinematically connected with the motor shaft and has a linear. 'Dependence of the capacitance on the angle of rotation. When the motor rotates, the capacitor changes the value of its capacitance from the maximum value to zero.

The electric sensor 7 generates a voltage pulse in moment when the value of the capacitor has

..... maximum value. The electric motor has a stable rotation speed,

At the time when the variable capacitor has the maximum capacitance, circuit 1 is tuned to resonance (the measured capacitance is absent).

In the initial state, the motor 8 is turned on, the generator 2 generates a sinusoidal voltage, which is applied to the oscillatory circuit 1. The measured capacitance is not connected to terminals 11, 12. Variable loop capacity Can be in any position. At the exit

...... the oscillatory circuit may be 'some voltage' '' frequencies 'ВёВё'15Ж' ”” of torus 2. At the output of the bias source 9 there is a voltage which, when measuring the capacitance of the capacitor, does not affect the operation of the converter10 body capacity. The output signal of the circuit is amplified by amplifier 3 and detected by detector 4. At the outputs of block 5 for determining the extremum of sensor 7, there is no signal.

When measuring the capacitance of pn junctions (for example, varicap), the latter is connected to the hallmarks 11, 12, and the bias voltage source 9 sets the required constant current mode, which determines the point of the capacitance characteristic of the pn junction; the ode in which the capacitance is measured .

Given that in the initial state the variable capacitance of the oscillatory circuit can be in any state, to synchronize the operation of the capacitance converter, the sensor 7 is designed so that a voltage pulse appears at its output only when the variable capacitance of the circuit passes through its maximum value from the second time. When measuring the capacitance, it is necessary to connect the latter to the input terminals 11, 12, then turn on the motor, and the variable capacitor of the oscillatory circuit periodically changes its capacitance from the maximum value to zero, passing during this period of time the resonance moment in circuit 1 at the frequency of generator 2.

Yield voltage circuit 1 is supplied ^- to the input of the selective amplifier 3. The amplified alternating voltage is input to the detector 4, which is rectified. At the time of resonance, in circuit 1, the voltage supplied to the input of amplifier 3 will have a maximum value / Detector 4 will isolate the envelope of the alternating voltage supplied to its input. Block 5 for determining the extremum at the time of resonance in circuit 1 generates a voltage pulse that is input trigger 6,

On the other input of trigger 6, pulses from the output of sensor 7 will be received. The time interval between the pulse / coming from sensor 7 and the pulse coming from the output of block 5 will be proportional to the measured capacitance. Trigger 6 is set to the logic by the first pulse (from the sensor) unit) and take the second. The pulse width at the trigger output will be proportional to the measured capacitance. The waveform at the output of the device is very convenient for converting to voltage or a digital code. With careful implementation of the circuit, it can provide high accuracy in measuring the capacitance of capacitors, varicaps, etc.

Claims (1)

Claim A capacitance converter in a time interval containing a bias voltage source, characterized in that, in order to expand the functionality, an oscillating circuit, a sinusoidal voltage generator, series-connected selective amplifier, detector, extremum detection unit and trigger, an electric sensor and an electric motor, while the second trigger input is connected to an electric sensor, which is kinematically connected to the electric motor shaft and an alternating oscillator capacitor circuit and terminals for connecting the measured capacitance included parallel'no variable oscillation circuit capacitance.