JPH0996651A - Amplification circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect output signal of a sensor with high resolution by comparing the output signal of the sensor with a reference signal by a comparator and by switching the reference signal in accordance with output of the comparator by a reference signal selector. SOLUTION: A comparator 2 receives output voltage Vsen of a sensor and reference voltage Vref as inputs, amplifies the difference between the voltages Vref and Vsen and outputs an output voltage Vad. Voltages in four stages are prepared for the voltage Vref of a reference voltage selector 3 and one of them is outputted selectively in accordance with a signal from an arithmetic means 4. Switching the voltage Vref from a lower voltage over to a higher one, the means 4 reads the voltage Vad, selects the voltage Vref so that the voltage Vad be a recognizable value and determines the voltage Vsen by computation from the voltages Vref and Vad at that time. According to this constitution, the output voltage Vsen of the sensor can be detected with high resolution by a simple construction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit for amplifying output signals of various sensors. For example, it amplifies output signals of a moisture detection sensor for transfer paper used in copying machines, printers and the like. It can be used for an amplifier circuit for

[0002]

2. Description of the Related Art Conventionally, there is known a technique of recognizing a detection value of a sensor by reading an analog output signal of the sensor with an analog-digital converter (hereinafter referred to as an A / D converter) of an arithmetic unit. In the A / D converter, the resolution of a signal to be read (read voltage per bit) is generally high in proportion to the number of bits.

[0003]

In the prior art, an A / D converter with high resolution is required when the change in the output signal of the sensor with respect to the change in the object to be detected by the sensor is small. A high A / D converter not only complicates the structure, but also increases the price exponentially.
On the other hand, in order to correct such a problem as described above, the output signal of the sensor is amplified to increase the voltage per bit of the A / D converter. In this case, the A / D converter is used. Since it is necessary to individually adjust the voltage input to the input voltage range of the A / D converter, this operation becomes extremely complicated.

The present invention solves the problems of the prior art as described above, and without using a special A / D converter, has a simple structure and at a low cost, with a high resolution of the output signal of the sensor. The purpose is to obtain a detectable amplification circuit.

[0005]

In order to achieve such an object, the present invention provides an amplifier circuit for amplifying and outputting an output signal of a sensor, and a comparator for comparing the output signal of the sensor with a reference signal, A reference signal selector for switching the reference signal supplied to the comparator, and the reference signal selector switches the reference signal according to the output signal of the comparator.

Further, in an amplifier circuit for amplifying and outputting the output signal of the sensor, a comparator for comparing the output signal of the sensor with a reference signal, and a reference signal selector for switching the reference signal supplied to the comparator. And a gain setting means for setting the gain of the comparator, and the step of switching by the reference signal selector is made larger than the gain of the comparator.

Further, a current-voltage converter for converting the output current of the light-receiving element into a voltage, a reference voltage selector for generating a reference voltage, a comparator for comparing the output voltage of the current-voltage converter with the reference voltage, and an analog An analog-digital converter that converts the output signal of the comparator given as a signal into a digital signal, and the reference voltage selector makes the output signal of the comparator a value that can be recognized by the analog-digital converter. As described above, the reference voltage is switched and the magnitude of the detection signal of the light receiving element is detected by adding the reference voltage to the output signal of the comparator.

[0008]

EXAMPLES The present invention will be described in detail below based on examples. FIG. 1 is a schematic configuration diagram of an amplifier circuit to which the present invention is applied.

In FIG. 1, the output signal Vsen of the sensor and the reference signal Vref are input to the input terminal of the comparison 2.
In this embodiment, both the output signal of the sensor and the reference signal are given as voltage. Therefore, in the following description, the reference signal may be referred to as the reference voltage, which has substantially the same contents. The comparator 2 is configured as a well-known non-inverting amplifier, amplifies the difference between the reference voltage Vref and the sensor output signal Vsen, and outputs the signal Vad. The output signal Vad of this comparator is calculated by the calculating means 4
A / built in the one-chip microcomputer
It becomes the input of the D converter.

Amplification degree of the comparator (hereinafter referred to as gain)
G is set to 4 times. Further, in this embodiment, the reference voltage Vref output from the reference voltage selector 3 is 4
It is prepared as a step voltage. FIG. 2 shows this point. As is clear from FIG. 2, specifically, 0
(V), 1.25 (V), 2.5 (V), 3.75
Four voltages of (V) are prepared as reference voltages.
The reference voltage selector receives the 2-bit output from the port P1 of the arithmetic means, that is, 4 of 00, 01, 10, 11.
One of the four reference voltages is selected and output according to a signal that can take one of four states.

A circuit diagram of the reference voltage selector 3 is shown in FIG.
As is apparent from the above, the reference voltage selector 3 is configured as a general adder circuit using an operational amplifier, and is supplied with the 2-bit signal from the P1 port of the arithmetic means as an input, as described above. One of the four reference voltages is selected and output according to the state of.

The A / D converter built in the arithmetic means has 8 bits and converts the output signal Vad of the comparator 2 into the power of 2 or 256 voltage steps and reads it. A
The input voltage range of the / D converter is set to the same voltage as the output range of the comparator (0 (V) to 5 (V)), and A /
The output signal Vad per bit of the D converter is about 0.0
It becomes 195 (V). Further, in the present embodiment, since the gain of the comparator 2 is set to 4 times as described above,
The resolution of the sensor output signal Vsen in the A / D converter is about 0.0048 (V) / 1 bit. Therefore, the resolution of the sensor output signal Vsen is 4 when the gain G = 1.
To double. However, the voltage range of the sensor output signal Vsen that can be recognized by the A / D converter is ¼ (V) which is ¼ when the gain G = 1 (0 to 1.25 (V)).
become.

Thus, although the resolution is generally improved, the reading range (detection range) is narrowed,
In this embodiment, as shown in FIG. 4, the reference voltage Vref is switched to the same four stages as the gain of the comparator,
It is configured to achieve the same reading range (detection range) as when the gain G = 1. For example, the reference voltage Vref
Is 0 (V), the range of the sensor output signal Vsen from 0 to 1.25 (V) can be recognized by the A / D converter. Further, when the reference voltage number 3 is selected, the reference voltage Vref becomes 2.5 (V), and the sensor output signal Vsen in the range from 2.5 to 3.75 (V).
Can be recognized by the A / D converter.

V which is the output signal of the comparator in the calculating means 4
Read operation of ad is shown in the flowchart of FIG. Here, while switching the reference voltage from low voltage to high voltage,
The sensor output signal Vad is read by the A / D converter, and the reference voltage is selected so that the read Vad has a recognizable value (5 (V) or less). When Vad is within the recognizable range, the value of the sensor output signal is calculated from Vad and the reference voltage at that time.

In this way, by correcting the read data in the A / D converter by the bias amount of the reference voltage Vref, A / of the voltage step (1024 steps = 256 * 4) of the gain times of the comparator. The sensor output signal can be detected with the same resolution as that of the D converter. That is, in the present embodiment, the reference voltage Vref is equally divided into the same steps as the gain, and the reference voltage is switched according to the sensor output signal Vsen, so that even if an A / D converter with few bits is used, the resolution is wide and high. The sensor output signal in the range is detected.

Next, another embodiment will be described with reference to FIGS. 6 to 8. The main difference from the above-described embodiment is that the switching step of the reference voltage selector is made larger than the gain of the comparator. This simplifies the configuration of the circuit that generates the reference voltage, and makes it possible to obtain a more inexpensive amplifier circuit.

In this embodiment, the case where an optical sensor is used as the sensor has been described. PD in 6 figures
The photo diode as a light receiving element labeled as "" receives light from a light emitting element (not shown). The output signal output from the light receiving element PD appears as a current, which is converted into a voltage by the operational amplifier OP1 to form a sensor output signal Vsen, which is connected to one input of the operational amplifier OP2 forming a comparator. The operational amplifier OP2 constitutes a non-inverting amplifier as in the above-mentioned embodiment. Operational amplifier OP
The reference voltage Vref is input to the other input of 2.

This reference voltage Vref is a digital-analog converter (hereinafter referred to as a D / A converter) built in a microcomputer (CPU) which is an arithmetic means. With such a circuit configuration, a comparator is provided. OP2 amplifies the difference between the reference voltage Vref and the sensor output signal Vsen four times and outputs it as Vad. In this embodiment,
The reference voltage Vref is switched to eight stages which is twice the gain of the comparator as shown in FIG. The output voltage Vad of the comparator at each reference voltage Vref overlaps like the hatched portion in FIG. As a result, the reference voltage Vr
The entire range (0 to 5 (V)) of the sensor output signal Vsen can be read without setting the steps of ef at equal intervals.

According to the above embodiment, the reference voltage Vref
In order to make each step evenly spaced, it was necessary to finely adjust the voltage of each step or a relatively expensive component, but in this embodiment, by overlapping each step, The circuit for generating the voltage becomes simpler. In the same manner as described with reference to FIG. 5 in the previous embodiment, the signal Vad is read by the arithmetic means while switching the reference voltage Vref from a low voltage to a high voltage.
Reading with the / D converter.

[0020]

As described above, claims 1 to 3 of the present application
According to the invention described, a simple structure and at a low price,
It is possible to obtain an amplifier circuit that can detect the output signal of the sensor with high resolution.

[0021]

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of the present invention. FIG.
4 is a table showing reference voltages in the first embodiment. FIG. 3 is a circuit configuration diagram of the reference voltage selector of the first embodiment. FIG. 4 is a graph showing the relationship between Vsen and Vad in the first embodiment. FIG. 5 is a flow chart showing the operation of selecting the reference voltage. FIG. 6 is a circuit configuration diagram of the second embodiment according to the present invention. FIG. 7 is a table showing reference voltages in the second embodiment. FIG. 8 is a graph showing the relationship between Vsen and Vad in the second embodiment.

[0022]

[Explanation of symbols]

 1 sensor 2 comparator 3 reference voltage selector 4 computing means

[Procedure amendment]

[Submission date] January 24, 1996

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

[Title of Invention] Amplifier circuit

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of the present invention.

FIG. 2 is a chart showing reference voltages in the first embodiment.

FIG. 3 is a circuit configuration diagram of a reference voltage selector of the first embodiment.

FIG. 4 is a graph showing the relationship between Vsen and Vad in the first embodiment.

FIG. 5 is a flowchart showing a reference voltage selecting operation.

FIG. 6 is a circuit configuration diagram of a second embodiment according to the present invention.

FIG. 7 is a table showing reference voltages in the second embodiment.

FIG. 8 is a graph showing the relationship between Vsen and Vad in the second embodiment.

[Explanation of reference numerals] 1 sensor 2 comparator 3 reference voltage selector 4 computing means

Claims (3)

[Claims] 1. An amplifier circuit for amplifying and outputting an output signal of a sensor, comprising: a comparator for comparing the output signal of the sensor with a reference signal; and a reference signal selector for switching a reference signal supplied to the comparator. And an amplifier circuit, wherein the reference signal selector switches the reference signal according to an output signal of the comparator. 2. An amplifier circuit for amplifying and outputting an output signal of a sensor, comprising: a comparator for comparing the output signal of the sensor with a reference signal; and a reference signal selector for switching a reference signal supplied to the comparator. An amplifier circuit comprising: gain setting means for setting the gain of the comparator, wherein the step of switching by the reference signal selector is made larger than the gain of the comparator. 3. A current-voltage converter for converting the output current of the light-receiving element into a voltage, a reference voltage selector for generating a reference voltage, and a comparator for comparing the output voltage of the current-voltage converter with the reference voltage. And an analog-digital converter for converting the output signal of the comparator given as an analog signal into a digital signal, and the reference voltage selector has a value that the output signal of the comparator can be recognized by the analog-digital converter. An amplifier circuit, wherein the reference voltage is switched as much as possible, and the magnitude of the detection signal of the light receiving element is detected by adding the reference voltage to the output signal of the comparator.