JPS5830768B2 - Kijiyunden Atsuhendou Hosei Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an A-D converter that changes an analog quantity of electricity into a digital value.
The present invention relates to a converter, and more specifically, to a reference voltage fluctuation correction circuit used in a comparative A-D converter.

A comparison type A-D converter compares the analog quantity of electricity, which is the quantity to be measured, with the analog quantity of electricity corresponding to a preset digital value, and converts the analog quantity to digital based on the digital value when both analog quantities of electricity match. It converts it into a value.

That is, set an appropriate number in the numerical setting device, generate a voltage proportional to the value in a DA converter, compare the generated voltage of the DA converter with the analog input voltage to be measured, and check that the input voltage and generated voltage match. The number of numerical setting devices is increased until the

Conventionally, in a D-A converter using such an A-D conversion method, a reference voltage source such as a constant voltage circuit that generates a constant voltage is used to generate a voltage corresponding to a set value. Since constant voltage circuits are affected by fluctuations in power supply voltage and temperature changes, it is impossible to always generate an accurate constant reference voltage, and therefore various compensation circuits have been used to maintain a constant reference voltage.

However, it is extremely difficult to maintain a constant voltage even with a compensation circuit, and the use of a compensation circuit not only makes the circuit configuration extremely complex and expensive, but also requires the power consumed by these compensation circuits from mercury batteries. Portable devices such as cameras that use small-capacity batteries as a power source have many drawbacks.

In view of this point, the present invention feeds back the amount of variation in the output voltage of the reference voltage generation circuit to an amplifier that amplifies the analog quantity to be measured, and makes the amplification rate of the amplifier correspond to the amount of variation. It is an object of the present invention to provide a reference voltage correction circuit which eliminates the above-mentioned drawbacks by controlling the analog input voltage to correspond to fluctuations in the reference voltage and generating an apparently constant reference voltage at all times.

Next, a reference voltage fluctuation correction circuit for an A-D converter according to the present invention will be explained.

FIG. 1 is a circuit diagram showing the main parts of a reference voltage fluctuation correction circuit for an A-D converter according to the present invention, where R, R2 are operational amplifiers O
A resistor is connected to the input terminal of the resistor R1, and a voltage corresponding to the quantity to be measured is applied to the terminal of the resistor R1.

CdS is a photoconductive element and is connected between the inverting input terminal and the output terminal of the operational amplifier OP.

R3 is a resistor, LED is a light emitting diode, and the photoconductive elements Cd and S form a photocoupler, which is shielded by an optical shield member C as shown by the dotted line.

Vref is a reference voltage generator with a constant reference voltage Vr at the b end.
is occurring.

R, 4, R5 are voltage dividing resistors of the constant reference voltage Vr,
The base of the transistor Trl is connected to the connection point, and the voltage change of Vref is detected, and the transistor Tr1
and controls the current flowing to the light emitting diode LED.

Mountains are resistance.

Co is a comparator, one input end of which is connected to the output end of the operational amplifier OP, and a voltage corresponding to the quantity to be measured and amplified by the operational amplifier OP is applied.

The other input terminal of the comparator Co is connected to the output terminal of a DA converter RN which generates a voltage corresponding to the number of pulses stored in the register SR.

Note that the comparator Co generates an output when the voltages at both input terminals match, transmits a stop signal to the pulse generator, and disables the pulse generator.

PG is a pulse generator and is connected to register SR.

Next, the operation of the main circuit section of the reference voltage fluctuation correction circuit for an A-D converter according to the present invention will be explained using FIG.

Assuming that the output of the reference voltage generator is Vr1 under normal conditions, Vrl is divided by voltage dividing resistors R4+R5 and applied to the base of the transistor.

As a result, the transistor Tr and the light emitting diode LE
The value of the current flowing through D corresponds to Vrl, and the amount of light irradiated onto the photoconductive element CdS by the light emitting diode LED also corresponds to Vrl.

Further, the resistance value Rcds of the photoconductive slip +CdS also has a value corresponding to Vrl.

Now when the output of the reference voltage generator Vref is Vr1, CdS
If the resistance value of is Rcdsl, the gain of the operational amplifier OP is −(&dsl/R1) l, and the comparator Co
If the measured quantity is eo, then l is input to one input terminal of the .

A voltage of (Rcdsl/R4) is applied.

The number of pulses generated by the pulse generator PG is stored in the register SR, and the number of pulses is stored in the register SR.
The voltage is converted into a voltage at , and transmitted to the other input terminal of the comparator Co.

The voltage output from the DA converter RN is transferred to the register SR.
and the reference voltage from the reference voltage generator Vref.

That is, since the D-A converter converts each pulse into a constant voltage depending on the magnitude of the reference voltage Vr of the reference voltage generator Vref, the voltage output from the D-A converter RN depends on the number of pulses and the reference voltage. It is proportional to the voltage.

As mentioned above, since the output of the D-A converter and the amplified voltage value of the measured quantity are input to the input terminal of the comparator, when these two are compared and both input voltages match, the comparator Co
generates an output and stops the pulse generator.

Now suppose that the reference voltage is Vrl, and the above e.

Suppose that the number of pulses is 01 for the DA converter to output the same voltage as (Rcds 1/R1).

In other words, assuming that the relationship is 6° - (Rcds1/R1)2Vr1nO, the output of the reference voltage generator Vref will increase from Vrl due to the obvious cause (because of this, Vr2
When the base potential of the transistor Tr1 increases, the light emitting diode LED1 and the transistor T
The current flowing through rl decreases.

As a result, the illuminance of the light emitting diode LED also decreases, and the resistance value of the photoconductive element CdS becomes higher than Rcds 1 < Reds
It becomes 2.

As mentioned above, the gain of the operational amplifier OP is -(Rcds/R
1), when Vr changes from Vrl to Vr2, the gain of operational amplifier OP increases (Rcds
2/R1)', and the voltage at the output terminal of the operational amplifier OP is the measured quantity l.

Even if the reference voltage is the same, if the reference voltage increases, high < e
o I (Rcds 2/R1), and conversely becomes lower when the reference voltage decreases.

On the other hand, since the output of the DA converter RN is also proportional to the reference voltage, when the reference voltage increases from Vr1 to Vr2, Vr
Even if the number of pulses n1 is the same as in the case of 1, it becomes Vr2n1 and increases.

Therefore, when the output of the DA converter RN is the number of pulses n1, V
Even if r2n1, the amplified value t20 of the voltage to be measured
(Rcds 2 / Rt) is also 4° (Rcd
s 1 / Rt ) is higher than I, so it is possible to have the relationship Vr2nt = 6o (Rcds2/Rt), and the same voltage to be measured l.

When , the same number of pulses can be obtained regardless of variations in the reference voltage.

FIG. 2 shows an embodiment in which the reference voltage fluctuation correction circuit for an A-D converter according to the present invention is applied to a photometric A-D converter, where EA is a power supply, SWa is a power switch, and SWb is a shutter release. The switch R1, which is turned on in the second stage of
R2 is a voltage dividing resistor, and the resistance value of R1 is the same as that of R2.

OPl is an operational amplifier with an almost infinitesimal output impedance and serves as a voltage follower.

Dl is a photodetector for TTL photometry, OF2 is an operational amplifier l
D2 is a log diode connected between the inverting input terminal and the output terminal of the operational amplifier OP2, forming a photometry and logarithmic compression circuit (2).

R4-R8 are resistors, OF3 is an operational amplifier, and a light guide card +CdS is connected between its inverting input terminal and output terminal, and the CdS forms a photocoupler with a light-emitting diode LED, which will be described later, and outputs light from the light-emitting diode LED. It forms a multiplier whose gain can be varied depending on the situation.

OF, is an operational amplifier that forms an operational amplifier with resistors R9 to R1□, and combines the photometry signal from the photometry circuit ■ with D-A, which will be described later.
The outputs from the converters are summed and amplified, and the summed signal is transmitted to one input terminal of the comparator OP5.

The comparator OP5 determines If I I depending on the magnitude of the input signal.
I or II Outputs OII.

The output of the operational amplifier OP1 provides a midpoint voltage to the operational amplifier OP2 of the photometric circuit (2), and also provides a voltage for comparison to one input terminal of the comparator OP5.

Vref is a reference power supply that provides a reference voltage Vr for the DA converter, which will be described later, and also connects the transistor Tr1 with a resistor R15.
A base potential is applied via +R16 to control the output of the transistor.

Further, the transistor Trl is the light emitting diode LED.
and control its output light.

GC is gate control chic and comparator OP5 mentioned above
A control signal is transmitted to the storage register SR and shift register R by the output of the comparator OP5.
At the time of I II, a reset signal is transmitted to the storage register SR.

The storage register SR has bits FF1 to FF4 and stores the contents of each bit.

SW1 to SW4 are switching circuits made of semiconductor elements, and are controlled and switched by the storage register SR.

The resistance value of RN is determined by a circuit network such as a ladder circuit in conjunction with the switching circuit, converts the reference voltage Vr into a value corresponding to the resistance value, and transmits it to the input terminal of the operational amplifier OP.

FIG. 2 is an explanatory diagram of the operation of the A-D conversion system, and shows the operation when the subject light information voltage (3) is IIV.

E in the figure.

is the voltage applied to the input terminal of the comparator OP5 shown in the second figure, and V5-Vd is a comparator.

The voltage to be compared, El, is applied to the other input terminal of OF5.
indicates the output of comparator OP5.

Next, the operation of the second illustrated embodiment of the reference voltage fluctuation correction circuit for an A-D converter according to the present invention will be explained.

When the power switch SW5 is turned on, a resistor R1 is connected to the input terminal of the operational amplifier OP forming a voltage floor circuit.
, R2 to apply the divided voltage E, 73S, and E to the output terminal.

is transmitted. The voltage E. is the operational amplifier O of the photometry circuit■
It is transmitted to one input terminal of P2 and the comparator OP5, and applies a midpoint voltage to the operational amplifier OP2, thereby activating the operational amplifier OP2.

The midpoint potential applied to the operational amplifier OP2 is the midpoint potential E since it is applied from the power supply EA via the voltage floor circuit.

varies at a constant rate with respect to variations in the power supply voltage EA.

Next, by pressing a shutter button (not shown), the switch swb is turned on in the first step of the operation, and voltage is supplied to the subsequent circuit.

When the object light is received by the light receiving element D1 of the photometry circuit (■), an object light information voltage V5 corresponding to the object light is generated between the input terminals of the operational amplifier 'OP2, and this voltage (5) is logarithmically compressed by the photometry circuit (■). and is transmitted to the negative input terminal of operational amplifier OP3.

On the other hand, the reference power supply Vref generates a constant reference voltage Vr at the same time as the switch Swb is turned on, and applies a constant voltage to the base of the transistor Tr1 via voltage dividing resistors R15 and R16, so that the output of the transistor Trl is a value corresponding to the reference voltage.

Therefore, a constant current corresponding to Vr flows through the light emitting diode LED, and the light output of the LED corresponds to Vr4, and irradiates the photoconductive slip element CdS.

The resistance value of the photoconductor CdS is inversely proportional to the light output from the incident LED, and since the light output of the LED is inversely proportional to the reference voltage Vr, the resistance value of CdS is proportional to the reference voltage Vr3. becomes.

Furthermore, since the gain of the operational amplifier OP3 is proportional to the resistance value of CdS, the gain of the operational amplifier OP3 is also proportional to the reference voltage.

Therefore, the object light information (5) transmitted to the negative input terminal of the operational amplifier OP3 is amplified by a value O proportional to the reference voltage in the operational amplifier OP3, and transmitted to the negative input terminal of the operational amplifier OP4.

On the other hand, when the switch SWb is turned on, the first bit FF1 of the storage register SR has a logical value II.
I II is set, the switching circuit SW1 corresponding to the bit FF1 is turned on, and the reference power supply Vr
The reference voltage Vr output from ef is transmitted to the circuit network RN via SWl, and the output -Vd corresponding to the resistance value of the circuit network RN determined by the Switznung circuit is applied to the operational amplifier O.
Applied to the negative input terminal of P.

The output -■ is added together with the object optical information voltage Vs by the operational amplifier OP4 and transmitted to the negative input terminal of the comparator OP5.

Assuming that the combined photographic information voltage VS is IIV, when the bit FF1 of the storage register SR is set to 1, the output Vd of the network RN is generated by the operation of a known ladder circuit.

This -Vd and object information voltage ■S are operational amplifier OP4
and the added value and the bias voltage E.

are compared by comparator OP5.

Vs is IIV - Vd is - 23■, so the added value is 3■
becomes.

On the other hand, E. is the ground potential, so ■S−■d＞Eo
Then, the ant comparator OP5 generates an output +I □ I", which is transmitted to the gate control logic GC to hold the contents of bit FF1 of the storage register SR, and FF1-1 is determined.

At the same time, the control signal is transferred from FF1 to FF22 of shift register R by the output of gate control logic GC, and the theoretical value I+11! is transferred to bit FF2 of storage register SR. is set, and by the same operation as described above, the output -Vd of the circuit network RN becomes -(23+22)■, which is added to VS by the operational amplifier OP4 to obtain the voltage E.

compared to As a result, Vs-va<Eo, so the output of comparator OP5 is! I I If, the output is transmitted to the gate control logic GC, the gate control logic GC is controlled, a reset signal is transmitted to the bit FF2 of the storage register SR, and the content of the bit FF2 is determined to be II OII.

Thereafter, FF3=1 and FF421 are determined in the same manner, and the contents of the storage register SR are set to 1.0°1.1.

The above-described operation converts analog subject information into digital values.

If the reference voltage of the reference power supply Vref fluctuates and becomes higher due to some reason in the series of processes described above, the voltage value transmitted to the circuit network RN also increases, and the same digital value as above is stored in the storage register SR. Even at this time, the output -Vd transmitted to the negative input terminal of the operational amplifier OP4 has a larger value -(Vd-1-JVd) than in the above case.

On the other hand, since the gain of the operational amplifier OP3 is proportional to the reference voltage Vr, the object light information Vs is also transmitted to the operational amplifier OP4 with a larger value (■S + JVS) than in the above case. Since they are added by the width filter OP4, if the reference voltage variation AVd corresponds to the gain variation (Vs) caused by the operational amplifier OP3, the same digit value as in the above case is stored in the storage register SR, and the reference voltage is Appropriate A-D conversion is always performed without being affected by voltage fluctuations.

As described above, in the reference voltage fluctuation correction circuit of the A-D converter according to the present invention, the amount of fluctuation in the output voltage of the reference voltage generation circuit and the analog amount to be measured are fed back to the amplifier that amplifies the amount of fluctuation in the output voltage of the reference voltage generating circuit. By making the amplification factor of the device correspond to the amount of variation, the analog input voltage is made to correspond to the variation in the reference voltage, and an apparently constant reference voltage is generated at all times, which makes it difficult to generate a reference voltage. This has great effects in the reference voltage fluctuation correction circuit of an AD converter, such as being able to perform proper A-D conversion at all times without providing a circuit compensation circuit.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the reference voltage fluctuation correction circuit of the present invention, FIG. 2 is a circuit diagram showing an embodiment applied to photometry of the present invention, and FIG. 3 is a circuit diagram of the embodiment of the present invention applied to photometry. It is an operation explanatory diagram explaining an operation. LED... Light emitting diode, CdS...
・Photoconductive element, Trl...transistor, V
ref...Reference voltage generation circuit, OP, OPl,
OP2...Operational amplifier, C09OP5...
...Comparator.

Claims (1)

[Claims] 1. In an analog-to-digital converter having a digital-to-analog converter that converts a digital value into an analog value corresponding to a reference voltage, an amplifier that amplifies the analog measured value and an amplifier that detects the amount of variation in the reference voltage and converts the amount of variation ( A detection circuit that generates an output corresponding to this and a control circuit that controls the amplification rate of the amplifier based on the output of the detection circuit are provided, and the amplification rate of the amplifier is made to correspond to the amount of variation in the reference voltage. A reference voltage fluctuation correction circuit characterized in that: