JPS5831545B2 - Jido Hoshiyou Souchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention eliminates fluctuations in output voltage due to input offset voltage, which is a problem in precision measurement amplifiers, and dark current when a photomultiplier tube, etc. is connected to the input side. An object of the present invention is to provide an automatic compensation device that can compensate for a reference voltage and can compensate for the reference voltage in a short time even if unexpected noise occurs during compensation.

Conventionally, as an automatic zero point compensation circuit for an amplifier, a circuit including digital processing as shown in FIG. 1 has been known.

That is, as shown in FIG. 1, the comparator 2 determines whether the output voltage of the amplifier 1 is positive or negative, and the reversible counting circuit 4 receives an addition or subtraction instruction from the output signal of the comparator 2 and counts the pulses from the oscillator 3. do.

The digital output of the reversible counting circuit 4 is converted into an analog quantity by a digital-to-analog (D/A) converter 5,
It is fed back to the input side of the amplifier 1 as a compensation voltage.

In this way, since the reversible counting circuit 4 performs addition or subtraction until the absolute value of the output voltage of the amplifier 1 becomes zero, zero point compensation can be performed automatically.

Furthermore, by applying the holding signal 6 to the digital signal holding terminal of the reversible counting circuit at the start of the measurement, the compensation voltage is held during the measurement.

However, the amplifier 1 generally includes a delay element, and stable compensation cannot be achieved unless the oscillation frequency of the oscillator 3 is considerably lowered.

Furthermore, the lower the oscillation frequency is, the smaller the fluctuation in the compensated voltage that is fed back, and the less error there is when it is held at the start of measurement.

On the other hand, if the oscillation frequency is set too low, the response will be slow, and if unexpected noise occurs, it will take a long time for the output voltage of the amplifier to reach zero, making it unsuitable for automatic measurement equipment that performs continuous measurements. There were drawbacks.

The present invention switches the frequency of the oscillator in two stages depending on the output voltage level of the amplifier in order to compensate for the above-mentioned conventional drawbacks.

FIG. 2 is a block diagram of one embodiment of the present invention.

In FIG. 2, the voltage level of the output voltage of the amplifier 7 is determined by a comparator 8.

The comparator 8 has a configuration as shown in FIG.

When the output voltage of the amplifier I is applied to the terminal 20, the operational amplifier 12, the resistor 17, and the inverter 19 function as a comparator for comparing with the reference voltage Vo, and a signal as shown in FIG. 4a is obtained at the terminal 21.

Operational amplifiers 13, 14, resistor 18, variable resistor 15.16
operates as a window comparator and determines whether the voltage at terminal 20 exists between the voltages V and V+ given by variable resistors 15 and 16, and a signal as shown in FIG. 4 is obtained at terminal 22. It will be done.

Returning to FIG. 2, one embodiment of the present invention will be explained.

The reversible counting circuit 10 receives the signal 2 sent from the comparator 8.
Pulses from the oscillator 9 are counted while adding if 1 is "L" and subtracting if 1 is "H".

The oscillator 9 also receives a signal 2 sent from the comparator 8.
2, the frequency is switched in two stages, and when the signal 22 is "L'', a high frequency pulse is generated, and when the signal 22 is "H", a low frequency pulse is generated.

The digital output of the reversible counting circuit 10 is sent to the D/A converter 11.
is converted into an analog quantity by the amplifier 7 as a compensation voltage.
is fed back to the input side.

At the start of measurement, the holding signal 23 is sent to the reversible counting circuit 10.
By applying the digital signal to the digital signal holding terminal, the counting activity is stopped and the compensation voltage can be held and measurements can be made.

Here, the above V- and ■+ are the reference voltage V.

(However, V < V.

V+) and the output voltage of amplifier 7 is larger than ■−.
In a range smaller than +, the frequency of the oscillator 9 is low and the response is slow, so the fluctuation in the feedback output is small and the error when the holding signal 23 is applied is also small.

On the other hand, due to unexpected noise, the output voltage of the amplifier 7 becomes smaller than V- or larger than V+, and becomes the reference voltage V.

If the voltage deviates significantly from the reference voltage V, the frequency of the oscillator 9 becomes higher and the response becomes faster, so that the reference voltage V is restored in a short time.

You can return to the vicinity. According to the present invention, since compensation can be performed at an extremely low frequency in the compensation state, fluctuations in the feedback output are small and tx measurement errors are also reduced.

Also, even if unexpected noise occurs, the reference voltage ■.

If the frequency goes out of the range set by V- and ①+, the response may be fast even if the frequency is high, or the reference voltage V may drop quickly.

Since it is returned to the vicinity, it is suitable for continuous measurements such as automatic measuring equipment.

Note that the present invention uses a reference voltage V.

If it is set to zero V, it becomes an automatic zero point compensation circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional automatic zero point compensation circuit, FIG. 2 is a block diagram of an automatic compensation device according to an embodiment of the present invention, FIG. 3 is an electric circuit diagram of a comparator used in the present invention, and FIG. 4 is a block diagram of a conventional automatic zero point compensation circuit. a and b are output signal waveform diagrams of the same comparator. 7...Amplifier, 8...Comparator,
9... Oscillator, 10... Reversible counting circuit, 11... Digital analog converter.

Claims (1)

[Claims] 1 Compare the output voltage of the amplifier with a preset reference voltage to output a first signal, and determine whether the output voltage is within a preset voltage range that includes the reference voltage. an oscillator whose frequency changes in two steps according to the second signal; and an oscillator that adds or subtracts output pulses from the oscillator under the control of the first signal, and adds or subtracts the output pulses from the oscillator under the control of the first signal. or a reversible counting circuit having a digital signal holding terminal for controlling whether or not to perform subtraction, and a digital-to-analog converter that converts the digital output of the reversible counting circuit into an analog quantity and feeds it back to the input side of the amplifier as a compensation voltage. Automatic compensation device equipped with