JPS63282622A - Photometer - Google Patents

Abstract

PURPOSE:To enable the time of an A/D conversion of fall in a desired range by comparing a photometric output with a reference voltage and changing cover a measuring range depending on the result of a comparison. CONSTITUTION:A photoelectric transducer SPD converts its photometric quantity to electric signals. An operational amplifier OPA and a negative feed back capacitor C1 constitute an integrating circuit. A comparator COP compares the integrated output of the amplifier OPA and a reference voltage Vr with each other. At the same time, the integrating circuit conducts an integration for a prescribed time and, when the integrated output of the amplifier OPA exceeds the reference voltage Vr, outputs a signal to a changeover circuit X to make capacitors C1 and C2 parallel and change over a range to 'high'. When an integration time has elapsed, the capacitors C1 and C2 are discharged by a signal from a microcomputer K and by a constant current from a constant voltage source V5 and a comparator COP' detects that the integrated output of the amplifier OPA becomes zero. Thus, the discharge time of the integrating circuit are counted by clock pulses whereby a photometric value is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an optical measurement device, and particularly to an apparatus for capturing a plurality of optical information as digital data.

Conventional technology: Normally, when optical information is captured as digital data, the analog signal of the optical information is converted into digital data.
As the -D converter, one using a dual slope A-D converter is known because it can perform A-to-back conversion with high accuracy.

However, conventional dual-slope A-to-digital converters have had the disadvantage of slow A-to-D conversion speeds and the inability to convert multiple analog signals at once.
Furthermore, when the input signal fluctuates in the range of 0 to 0, for example, there is a problem that the time required for A-D2 conversion varies greatly.

Therefore, in order to increase the speed of A-D conversion, a triple ramp method, a cascade integration method,
Methods such as the Quadraphasis method have been proposed, but these methods increase the speed without reducing accuracy by switching the amount of discharge per clock during discharge. These perform full-range A-D conversion with a constant minimum resolution, but it is not necessarily necessary to perform full-range A-D conversion with a constant minimum resolution; for example, 16-bit A-D conversion
-For D conversion, the minimum resolution is 1.24.8, 16.3
In some cases, a converted value of 10 bits is desired as 2.64, and in such a case, A-D conversion will be performed with unnecessary precision. Furthermore, with the above-mentioned A-D conversion method, the discharge current is switched during the discharge time, but there is a problem in that it is difficult to adjust the timing to synchronize the counting clock with the timing at which the discharge current is switched. There is a point.

C. Problems to be solved by the invention The present invention is a double integral type A-D that solves the above problems.
The purpose of this paper is to propose an optical measurement device using a converter.

21 Means for Solving Problems In a light measuring device, there is provided a photometric means that outputs a signal corresponding to the amount of received light, a discrimination circuit that determines within which range the output of this photometric means falls, and a an integrating means for integrating the signal for a certain period of time; a discharging means for discharging the integrated charge of the integrating means with a current corresponding to the determination result of the discriminating circuit; The device includes a counter that counts the time until a value is reached, and a processing device that takes in data from the discrimination circuit and the counter.

E, 11: The present invention is characterized in that the minimum resolution of A-D conversion is determined based on the photometric output, and the discharge current is switched based on the determination result. It is.

In the present invention, a signal corresponding to the amount of received light is outputted from a photometric means, and the intensity of this output signal is discriminated by a discriminating circuit, and at the same time, it is integrated for a certain period of time by an integrating means. The integrated charge integrated by the integrating means is discharged with a current corresponding to the determination result of the above-mentioned discriminating circuit, and the time from the start of the discharging operation until the integrated charge of the above-mentioned integrating means reaches a predetermined value is counted using clock pulses, and this calculation is performed. Treat numerical values as digital signals. According to the above judgment result, when the amount of received light exceeds the range, the discharge current is switched to a larger value to speed up the discharge base of the integrating circuit. - The time required for conversion can be made approximately the same.

Note that the words "integration" and "discharge" used here refer to, for example, when a capacitor is used as the integration means, the capacitor is charged from a short-circuited state to a potential corresponding to the time-integrated value of the photometric signal.
After that, the capacitor is not only discharged to lower the voltage of the capacitor, but also the capacitor is precharged to a predetermined level (for example, power supply voltage) and then charged to a level corresponding to the time integral value. Then, the capacitor may be charged so that the potential changes in the pre-charging direction (this corresponds to the discharging mentioned in the gist of the invention), and furthermore, the integrating operation by the above charging or discharging may be performed. The subsequent discharging operation pumps more charge into the charged capacitor so that the voltage is increased to the integral level. The potential of the capacitor may be increased to a predetermined level, or the discharged capacitor may be discharged such that the voltage is reduced to an integral value level, and the charge may be further released to lower the potential of the capacitor to a predetermined level.

The changes in the potential of these capacitors are only relative, and the point is that the change within a certain period of time corresponds to the photometric value, and then the time required for the change to reach a certain level by charging or discharging with a certain current is counted. However, it is preferable to change the level of the integrating means in the opposite direction during the discharge operation and during the integration (this is the concept of the so-called double slope), since errors during reciprocation can be compensated for.

Embodiment FIG. 1 shows an apparatus according to an embodiment of the present invention, and FIG. 2 is a time chart illustrating its operation. In this embodiment, the SPD measures light using a photoelectronic conversion element such as a photodiode and converts the measured amount into an electrical signal. OPA is an operational amplifier. Capacitor C1 is directly connected between the inverting terminal and the output terminal of operational amplifier OPA, and capacitor C2
is the capacitor C via the range selection switch SW3.
1 in parallel. The operational amplifier OPA and negative feedback capacitors CI and C2 form an integral circuit.
The switch SWI is a reset switch connected in parallel with the capacitors C1 and C2. The switch S w 2 is an integration start and end switch connected between the photodiode SPD and the inverting terminal of the operational amplifier OPA. COP is a comparator that connects the integral output of the operational amplifier OPA to its child terminal and the reference voltage Vr to one terminal, compares the integral output of the operational amplifier OPA with the reference voltage Vr, and determines whether the integral output of the operational amplifier OPA exceeds the reference voltage Vr. 3w3 in case
The closing signal of C is output to switching circuit X, and the integrating capacitor is
Switch the range from low to high by connecting I and C2 in parallel. The switching circuit X opens and closes the switch Sw3 according to the range signal from the comparator COP, and outputs the range signal to the microcomputer K. R1 and R2 are resistors for adjusting the reverse charging current, and are connected to the constant voltage source VS via the inverting terminal of the operational amplifier OPA and the switch S w 4 or 3w5, and when the switch S w 4 or 3w5 is closed, C1, Reverse charge C2. Cop' is a comparator that detects that the integral output of the operational amplifier OPA becomes 0 due to this reverse charging, and outputs this detection signal to the microcomputer K. The microcomputer controls the opening and closing of each switch based on each input signal, counts the reverse charging time to the integrating circuit using clock pulses, and calculates the photometric value from the counted value. The DSP displays measurement data such as photometric values calculated by a display circuit.

Prior to light intensity measurement, switch SW1. SW2 and SW3 are all closed, and SW4. SW5 is opened and capacitor C
1, the residual charge of C2 is discharged, and then the switch SW
1. Light intensity measurement starts by opening SW3.

At the same time as the light intensity measurement starts, the microcomputer starts measuring the integration time. The photometric signal detected by the photodiode SPD is immediately integrated by an integrating circuit composed of an operational amplifier OP'A and a negative feedback capacitor C1,
The integrated output of the operational amplifier OPA is compared with the reference voltage Vr at the comparator COP, and when the integrated output of the operational amplifier OPA exceeds the reference voltage Vr, a high signal is output from the comparator COP to the switching circuit X, setting the measurement range to the high state. do. This high signal closes SW3, and after a predetermined integration time has elapsed, the microcomputer K ends the first integral action, closes switch SW4 or SW5, and the reverse charging circuit enters the operating state and the display goes high. Set it to the state. By closing 3w3, capacitor C2 is connected in parallel with C1 in the integrating circuit, and the integrated charge is held by 01 and C2. In other words, the measurement range has been switched to high.

The integration is completed by opening the switch SW2.

When S W 2 is opened, the output of the integrating circuit consisting of the operational amplifier OPA and the capacitor C1 or the parallel connection of C1 and 02 holds the integrated output at that time. The held integral output is reduced by the constant current reverse charging of capacitors C1 and C2 by closing S w 4 or 3w5. The microcomputer uses clock pulses to count the time until the integrated charge becomes O during reverse charging at this time, and the counted value is taken as the measured value. This counted value is corrected at the measurement range and the photometric value is calculated by the microcomputer.

When the switch SW2 is opened, the integrating circuit holds the integral output at that time, as described above.

When switch SW4 or SW5 is closed, one terminal of operational amplifier OPA is connected to constant voltage source Vs via resistor R2 or R1, and current 1=Vs/(R2
Alternatively, a constant current determined by R1) flows into the capacitors CI and C.
Reverse charge the 2nd class. That is, capacitor C1 or C1 and C
The output of the operational amplifier OPA decreases linearly from the value when the switch SW2 is open. When the output of the operational amplifier OPA becomes 0, the comparator Detect with cop' and switch SW
4 or from the time SW5 is closed, the output of the operational amplifier OPA becomes O.
The light amount value is digitized by counting clock pulses by a microcomputer during the time until switch SW4. SW5
Which of the two is to be closed depends on whether or not the range has been changed during the light amount integration.

Further, the embodiment shown in FIG. 1 will be explained in detail. switch S
W1 to SW5 are all semiconductor analog switches. The switching circuit X is a flip-flop that has a preset terminal, a clear terminal, and a clock input terminal, and the Q output is inverted at the rising edge of the preset input, and the Q output becomes low due to the clear input. is high, and when the comparator COP changes from low to high, the Q output becomes low, and this low signal closes the switch SW3. First, we will discuss the case where the light intensity is large and the range is changed during measurement.
4. Both SW5 are open.

In this case, during the integration operation, the output voltage of the operational amplifier OPA is set to the comparison reference voltage V
r is exceeded and the switch SW3 is closed (between to and tit in FIG. 2), and then integration is continued by the parallel connection of capacitors C1 and C2, and when the integration time has elapsed, the switch SW3 is closed from the control circuit K via the interface If.
A signal is sent to switch SW2 and SW4, and switch SW2 is opened and switch SW4 is opened.
W4 is closed (at time t2 in Figure 2), so capacitors C1 and C2 discharge at a constant current of I = V s / R2, and the output voltage of operational amplifier OPA becomes T1 in Figure 2.
It takes a time of 0 and reaches O at time t4. Comparator cop' detects that the output of OPA becomes 0, and a detection signal is sent to control circuit K, which outputs switch S.
W1. SW2. SW3 closed, SW4. A signal to open SW5 is output, and a preset signal is output to the switching circuit We will discuss the case where this is not done. At this time, as shown in FIG. 2 from time t5 to time t7, switch SW3 remains open, and integration is performed only by capacitor C1. In this case, the output of switching circuit A signal for opening switch SW2 and closing switch SW5 is output to the circuit at the end of the integration time. Therefore, the capacitor C1 will be discharged by the current I = V s / R1, and the output of the operational amplifier OPA will be at the time T
2 to reach the output voltage 0. The other operations are the same as those between tO and t4 in FIG.

Next, we will discuss the selection of the values of resistors R1 and R2, and explain the flow of photoelectric conversion in 1. ! Let Q be the integral during a certain time T, and fft
If IΩ・dt=F, for the same F, capacitor C1
The integrated output voltage when alone is F/C1, and C1 and C
The integrated output voltage when using parallel connection with 2 is F/(C
1+C2).

If each resistance value is determined so that the ratio of resistors R1 and R2 is R1/R2= (C1+C2>/C1), the discharge for the same amount of light when C1 is used alone and when C1 and C2 are connected in parallel The time ratio is C1 alone/C1, C2 in parallel = (C1+C2)/C1, and the discharge time is longer for C1 alone.In other words, since clock pulses of the same cycle are counted, the count value for the same light amount is In the case of C1 alone, that is, in the case of a small range, it is larger.For example, if the small range has a light intensity of 0 to 1, and the large range has a light intensity of 0 to 10, the light j11 in the small range is larger than that in the large range. This means that the amount of light is counted as 0.1, and in a large range, the amount of light is displayed as the amount of light (count) x 10. This signal multiplied by 10 is detected by the control circuit determining whether the Q output of the switching circuit χ is high at the end of A-D conversion, and when this signal is detected, the display is switched. The above calculations are performed in the control circuit to ensure that the range is appropriate. After all, even if the range is changed, the period of the clock pulse for A-D conversion of the integrated output is only one type.For different ranges with the same integrated output, the required discharge time, that is, the A-D conversion of the integrated output is required. The time is the same regardless of the range.

G. Effects As described above, the present invention discharges the integrating means that integrates the photometric signal for a certain period of time with a constant current, and the current is discharged by the integrated charge amount of the integrating means, the capacity at the time of integration, or the integration level. Since the discharge time, that is, the time required for counting can be controlled according to the switching, the time required for AD converting the integral signal can be kept within a desired range regardless of the integral value.

This means that when there are multiple photometric devices and their output signals are sequentially A-D converted and processed by a microcomputer to obtain the desired result, each A-D conversion time is limited to a predetermined range. It is easy to set the timing for starting A-D conversion, and the processing ability of the microcomputer within a certain period of time is also improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of one embodiment of the present invention, and FIG. 2 is a time chart of the above embodiment. SPD...photoelectronic conversion element, OPA...operational amplifier, cop, cop'...comparator, X...switching circuit, If...input/output interface, K/microcomputer, DSP...display circuit , Swl・
・Reset switch, S w 2...photometering start and end switch, S w 3...range selection switch,
3w4゜Sw5... Reverse charging switch, CI, C2.
・Capacitor for integrating circuit, R1, R2 ・Resistance for adjusting reverse charging current, Vr ・ Range switching reference voltage, Vs ・
・・Constant voltage source for reverse charging.

Claims (1)

[Claims] a photometric means for outputting a signal corresponding to the amount of received light; a discrimination circuit for determining within which range the output of the photometric means falls; an integrating means for integrating the signal from the photometric means for a certain period of time; and an integrating means. a discharging means for discharging the integrated charge with a current corresponding to the determination result of the discriminating circuit; a counter for counting the time from the start of discharging operation of the discharging means until the output of the integrating means reaches a predetermined value; An optical measuring device comprising a circuit and a processing device that takes in data from the counter.