JPH01105614A - Signal converter - Google Patents

Abstract

PURPOSE:To combine both the functions of an A-D converter and time width- analog voltage converter precisely and accompanied with little rise of cost, and at the same time, to obtain a signal converter with a perfectly isolated built-in A-D converting function by using a constitution element in common in a device using the A-D converter and the time width-analog voltage converter. CONSTITUTION:A first analog-digital converter to convert the analog voltage Ex to be converted, into a digital signal is constituted of a voltage-time width conversion circuit VT, a gate control circuit GC, a gate G, a counter COU and a micro-processor muP. Besides, a second analog-digital converter to convert the analog voltage EX' to be converted, into the potentially isolated digital signal, is constituted of the voltage-time width conversion circuit VT; a photoisolator PI, the gate control circuit GC, the counter COU and the microprocessor muP. First and second analog-digital converters are automatically switched by a selector switch SW controlled by the micro-processor muP.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a signal converter in which an analog-to-digital converter and a time width-to-analog voltage converter are constructed using common components.

[Conventional technology]

A well-known analog-to-digital converter (hereinafter simply referred to as an A-D converter) uses a voltage-to-time width conversion circuit composed of an integrator and digitally counts the obtained time width signal. It is being On the other hand, a circuit is also known in which a voltage-to-time width conversion circuit similarly using an integrator is used as a time-to-analog voltage converter, and an analog voltage is obtained from the time width signal. A-D converter and time width in one device as a signal converter (voltage generator)
There are some that have a built-in analog voltage converter, but as mentioned above, the re-converter has many common parts.

Further, in such a signal converter, it may be necessary to insulate the voltage-time width conversion circuit and the digital conversion section that constitute the AD converter.

[The interlayer point that the invention attempts to solve]

The present invention provides a high-precision signal converter that requires an A-D converter, a time-width-to-analog voltage converter, and an isolated A-D converter, by making the components common, thereby making the whole This has been realized with an extremely simple configuration and at low cost.

[Means for solving problems]

In order to achieve the above object, the present invention includes a first voltage-time width conversion circuit, a comparator 1 that compares the output of an integrator in the first voltage-time width conversion circuit with a reference voltage. A digital conversion circuit including the microprocessor that controls the sequence of the entire circuit and calculates a correction coefficient, an isolator for insulating the state control signal and driving each switch in the second voltage-time width conversion circuit, and Ill.
This circuit consists of a sample and hold circuit that samples and holds the output of the integrator in the voltage-time width conversion circuit. Examples will be described in detail below.

〔Example〕

FIG. 1 is a block diagram of an embodiment of a signal converter according to the present invention. In FIG. 0, VT is a voltage-time width conversion circuit. In this conversion circuit, EX is the analog voltage to be converted, 81 to S3 are switches, ±Es are positive and negative reference voltage sources, ING is amplifier A, input resistor R, and feedback resistor C.
It is an integrator consisting of The voltage Ex is passed through the switch S1, and the reference voltage ±Es is passed through the switch S2. are respectively applied to the integrator ING via S3. S4 is a switch for resetting the capacitor C, CPI is a comparator that uses zero volts as a reference voltage and compares the output of the integrator ING, and SD is a switch drive logic. AS and BS are control signals that control the states of the switches 81 to S3, and these signals are given from a microprocessor that will be described later. VT' is a voltage-time width conversion circuit having the same configuration as the voltage-time width conversion circuit VT;
The same parts as T are given the same reference numerals with a ``゛'' and their explanation will be omitted. PI is a photo isolator, and conversion circuit VT'
In the case, the state control signals As of the switches 81 to S3,
BS is applied to the switch drive logic SDL' via this array.

SW is the comparator CP of the voltage-time width conversion circuit VT, VT'
A selector switch that changes the output of CPI and CPI'.
The output of CPI' is directly applied to the changeover switch SW, and the output of CPI' is applied to the changeover switch SW via the isolator PI. CF2 is a comparator, which uses +Es as a reference voltage to convert voltage to time width conversion circuit VT.
Compare the outputs of the integrator ING at . G is gate,
CL is a clock pulse, GC is a comparison! This is a gate control circuit that receives the output of 1cP2 and the output of comparator CPI or CP1' and controls clock pulses CL&If passing through gate G. COU is a counter that counts the clock pulses CL that have passed through the gate G. μP controls the sequence of the entire circuit and calculates a correction coefficient based on the output of the counter COU.
A microprocessor that provides correction coefficients to The voltage-time width conversion circuit VT, the gate control circuit GC, the gate G, the counter COU, and the microprocessor μP constitute a first analog-to-digital converter that converts the analog voltage Ex to be converted into a digital signal. or,
Analog voltage Ex' to be converted by voltage-time width conversion circuit VT', isolator PI, gate control circuit GC, gate G, counter COU, and microprocessor μP
A second analog-to-digital converter is configured to convert the signal into a potential-isolated digital signal. 1st. Second
The switching of the analog-to-digital converter is automatically performed by a changeover switch SW controlled by the microprocessor μP.

SH is a sample switch consisting of a sample switch S5, a hold capacitor C8, and a buffer amplifier BA.
A hold circuit whose input terminal is a voltage-time width conversion circuit V
It is connected to the output terminal of the integrator ING that constitutes T.

The output end of the sample-and-hold circuit SH is connected to a terminal UT from which the output voltage Eo is taken out. In the signal converter having such a configuration, the operation of the analog-to-digital converter will first be explained with reference to FIG. 2 as follows.

By connecting the changeover switch SW to the terminal a, the voltage-time width conversion circuit VT is connected to the gate control circuit GC. In this case, the comparator CP2 is controlled by the gate control circuit GC.
The output of is prohibited, and only comparator CPI functions. State III control signals AS, BS are generated by the microprocessor μP and applied to the switch drive logic SD.

As a result, the switches 81 to S3 are driven.

Here, at time t1 in FIG. 2, for example, the switch S1 in the voltage-time width conversion circuit VT is turned on, so that the analog voltage Ex to be converted is applied to the integrator ING, and the integrator output increases.

After the switch S1 is turned on for a certain period of time T1,
It turns off at time t2. At the same time, switch S
2 is turned on, the reference voltage element Es with the opposite polarity to Ex is applied to the integrator ING and integration begins, and the gate G is opened by the output of the gate Il's circuit GC, and the clock pulse CL is applied to this gate. through the counter COU
is added to and counted. The output of the integrator ING decreases and when its value crosses the zero level, the comparator CPI detects this and closes the gate G. As is well known, the period T2 from time t2 to time t3 when the output of the integrator NG crosses the zero level corresponds to the value of the analog voltage Ex to be converted, and the clock pulse CL passing through the gate G during this T2 period
The counted value of the counter C○U corresponds to the analog voltage Ex to be converted. The counted value of the counter COU is taken into the microprocessor μP, subjected to special calculations, and then outputted from the microprocessor μP as a digital signal.

Here, if you want to convert the analog voltage to be converted into a digital signal while insulating the voltage-time width conversion circuit VT and the digital conversion section composed of a microprocessor μP, etc., set the changeover switch SW to the terminal side. Connected. The switch state control signals AS and BS obtained from the microprocessor μP are applied to the switch drive logic SD' via the photo-isolator PI, and the output terminal of the comparator CPI' is selected by the change-over switch SW via the photo-isolator PI. Gate control circuit GC
connected to. In such a configuration, the analog-to-digital conversion operation is exactly the same as when the voltage-time width conversion circuit VT is selected, but the voltage-time width conversion circuit VT
When ' is selected, the voltage-time width conversion circuit VT' to which the analog voltage Ex' to be converted is input is electrically separated from the digital conversion section.

Next, the operation of the time width to analog voltage converter will be explained. In this case, the changeover switch SW is connected to the terminal a side, and the inhibition of the comparator CP2 is released, so that it operates together with CPl. The sequence is as shown in Figure 2.
Analog-to-digital conversion operation (2) and time width-voltage conversion operation (2) are performed in combination. Note that during the operation (2), the voltage-time width conversion circuit VT' operates in the same manner as VT, but this does not pose any particular problem. When the switch S3 is turned on at time t4, the reference voltage (-) Es is applied to the integrator ING, and the integrator output increases from the zero level to (+) Es as shown by the solid line. The zero level is detected by comparator CP1 and (
+)Es is detected by comparator CP2. C.P.I.
The output of CF2 is applied to the gate control circuit GC, and during this period the gate G! l1la, and the clock pulse CL is counted by the counter COU. The count value of counter COU is taken into microprocessor μP. The microprocessor μP turns on the switch S4 after a predetermined time has elapsed since the output of the integrator ING reaches (+)Es, and turns on the integrator ING.
After resetting, the switch is turned off, and the reference voltage (-) Es is integrated again by the integrator ING.

Here, the time To is preset using the preset terminal of the counter COU. The integrator ING integrates the reference voltage (-) Estc again after being reset, but when the integration time reaches To, the switch S3 is turned off and
The microprocessor μP has a sample and hold circuit SH
Switch S5 is turned on to sample the output of integrator ING, and the value is held by capacitor C8.

This held voltage is taken out via the buffer amplifier BA as an analog voltage Eo corresponding to the time width.

In this case, the value of the integration time constant C-R of the integrator ING may fluctuate, and the fluctuation immediately causes the output voltage Eo
This appears as an error. In the voltage generator of FIG. 1, by correcting this variation, the output voltage Eo becomes unaffected by changes in the integration time constant CH. This will be explained as follows. That is, the integrator ING is
In the 0 part of the figure, the integral output is less than zero (+
)Es until the reference voltage (-)E! g is integrated, and the integration time Ts is determined by the following formula.

-(1/CR)f:%(-Es)dt=EsE's (
Ts/CR)=Es,'', Ts=CR...(1) Now, as mentioned above, the time To(=K
(setting value)・Ts...calculated by μP) is preset, but the sample/hold circuit S at that To time
The output Eo of H is obtained by the following formula.

E o = −(1/CR) /c#(−E s) d
t= E s (T o / CR)
・= (2) From equation (1), equation (2) becomes Eo=Es (To/Ts) = −Es ・・・(3)(
3) As is clear from the equation, the output voltage EO is not affected by the integral time constant CH. The dotted line at the 0 part in Figure 2 shows this graphically, and as the integral time constant CR fluctuates, T
Even if s becomes T s ′ and T Oh”T o ′, the output voltage Eo remains unchanged.

[Effects of the present invention]

As explained above, in the present invention, in a device using an A-D converter and a time width-to-analog voltage converter, by using common components, it is possible to achieve both functions with high precision and with almost no increase in cost. It is possible to have both.

Moreover, at the same time, it is possible to obtain a signal converter with a built-in completely isolated A-D conversion function.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram of an embodiment of a signal converter according to the present invention,
FIG. 2 is a diagram for explaining the operation of FIG. 1. VT, VT'...voltage-time width conversion circuit, ING. ING'...Integrator, CPI, CPI', CF2...
・ . Comparator, SW...changeover switch, GC...gate control circuit, G...gate, COU...counter, μP
...Microprocessor, SH...Sample and hold circuit. Figure 2

Claims (1)

[Claims] The analog voltage to be converted or the positive and negative reference voltages are respectively switched by a switch driven by a state control signal obtained from a microprocessor, and one of them is integrated by an integrator, and then the output of the integrator and the zero level are connected to a comparator. first and second voltage-time width conversion circuits, which are compared by
a changeover switch that switches the outputs of both voltage-time width conversion circuits; a second comparator that compares the output of the integrator in the first voltage-time width conversion circuit with a reference voltage; and the pair of voltage-time width conversion circuits. A comparator in the conversion circuit and a counter that counts clock pulses that have passed through a gate controlled by the output of the second comparator, and the output of this counter is given to control the sequence of the entire circuit and calculate a correction coefficient. A digital conversion circuit including a microprocessor, an isolator for insulating the state control signal and driving each switch in the second voltage-time width conversion circuit, and an integrator in the first voltage-time width conversion circuit. A signal converter consisting of a sample and hold circuit that samples and holds the output.