JPS6088329A - Photometry circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention] (Four branches (dimensions ψf) F41'; Light is a σ1 optical circuit used in photographing equipment 69, etc., and sometimes a 1llll 1-element circuit that integrates the photocurrent from the light receiver with a capacitor. It is something to do.

(Prior art) In this device, both ends of the capacitor are turned on by turning on a switching element, so that the device is exposed to the light receiving surface. Upon exposure, this switching element is turned off and the photocurrent starts charging the canopy.Using the fact that the charging voltage is proportional to the total exposure, the amount of exposure to the light-receiving surface is adjusted (11).
] has been established. However, 1. Usually, a semiconductor element is used as this switching element, and its ON voltage cannot be made zero, and its offset changes depending on the current flowing. Further, when an amplifier is used to amplify the voltage of the canopy, and the amplifier has an offset voltage, there is a problem in that a non-negligible side light error is generated together with the offset voltage when the switching element is in the ON state.

In contrast, conventionally, in order to reduce the offset of switching elements and amplifiers, expensive and complicated elements and amplifiers have been used.

(Purpose) The present invention was made in view of the above drawbacks of conventional circuits, and an object of the present invention is to provide a photometric circuit that can always calibrate offset voltages of switching elements and amplifiers, regardless of the magnitude or fluctuation of the offset voltages. shall be.

(Example) The present invention will be explained below based on Examples.

FIG. 1 shows an example of the photometric circuit of the present invention applied to the control of a flashlight emitting device. In the figure, reference numeral 1 denotes a light receiving element such as SK, which is connected between two inputs of an operational amplifier 4 as an amplifying means. A capacitor 2 is connected between the inverting input and the output of the operational amplifier 4. Reference numeral 3 denotes a switching element such as a transistor, which is connected in parallel with the capacitor 3, and whose control terminal is connected to the control circuit 8. 5 is a comparator as an arithmetic means; its non-inverting input is connected to the output of the operational amplifier 4, and its inverting input is connected to the D/
The output of the A converter 7 is connected to the terminal 6b of the analog switch 6 and the control circuit 8.
connected to. The analog switch 6 has its control terminal 6a
When the control terminal 6b is at low level, the terminals 6b-6c are conductive, and when the control terminal 6b is at the low level, the terminals □b-5c are non-conductive.The terminal 6a is connected to the control circuit 8, and the terminal 6C is connected to the control circuit 8. The light amount control circuit of the flash light emitting device 12 is connected to [0]. The light quantity control circuit 10 has the function of immediately stopping the flash light emitting device if it is emitting light when a positive pulse is input through the analog switch 6. Reference numeral 7 denotes a 1)/A converter serving as a setting means, which converts the digital input from the control circuit 8 into an analog value, and inputs its output to the inverting input terminal of the comparator 5 as a reference value. 8 is a control circuit, and a release switch 9
Based on the input from switching element 3, analog switch 5. The synchro circuit of the D/A converter/flash light emitting device 12 is controlled as shown in FIG. The synchro circuit 11 is a circuit that causes a flash tube or the like in a flash light emitting device to emit light in response to a control signal from the control circuit 8. Further, in FIG. 1, numerals 1 to 8 are located outside the flashlight emitting device, but part or all of these may be located inside the flashlight emitting device. Further, the flash light emitting device σ mentioned here may be a known device for emitting light from a xenon tube or the like.

One embodiment of the present invention has the above-described configuration, and its operation will be explained below with reference to Figure 2. First, before time T1 when the release is performed, the control voltage of the switching element 3 is at a high level and the switching element 3 is turned on, as shown in FIG. 2(b). Also, Figure 2 (c
), the control terminal 6a of the analog switch 6 is at a low level, and there is no conduction between 6b and 6c of the analog switch 6. As a result, a voltage is generated at the output of the operational amplifier 4 that depends on the operational amplifier 40 offset) and the ON voltage of the switching element 30. During this time, the output voltage of the comparator 5 is input to the sight control circuit 1o. There's nothing to do. In this state, control circuit 8, IVk
The converter 7 and comparator 5 work as follows.

f lx If the output of the comparator 5 is at a high level, the control circuit 8 is set to 1)/A converter 70
The input is increased by 1 pin, and if the output of the comparator 5 is at a low level, the input of the 8-digit D/A converter 7 is decreased by 1 pin. In this way, the output voltage of the value converter 7 finally becomes equal to the output voltage of the operational amplifier 4 with an error of 1 bit or less. .

If the resolution of the D/A converter 7 is set sufficiently small, this value can be considered to be equal to the output of the operational amplifier 4.

At time TI, when the release switch 9 is turned on, the control circuit 8 operates as shown in FIG. 2 (L)) and (C).

As shown in (d), the control terminal of the switching element 3 is set to a low level, the switching element 3 is turned off, and the control terminal 6a of the analog switch 60 is set to a high level, so that the terminals 6b to 6C are connected equally. At the same time, ㅅA converter 7
The input to the comparator 5 is increased by a certain bit difference ΔV from the previous value, and the inverting input potential of the comparator 5 is changed by ΔV.

(Fig. 2 (h)) Furthermore, as shown in Fig. 2 (d), a short positive pulse is sent to the synchro circuit 11, and the flash light emitting device 1
2 to emit light. (Fig. 2 (g)) The flash light from the flash light emitting device is irradiated onto the subject, and the reflection yC from the subject is photoelectrically converted by the light receiving element 1, a current proportional to the received light intensity flows, and this current charges the capacitor 2. do. Then, when the charging voltage exceeds ΔV (time T2), the comparator 5
The output of the FT control circuit 10 changes from a low level to a high level, and a positive pulse is manually applied to the optical ft control circuit 10, and as a result, the flash light emission stops. Incidentally, this flash light emission time, that is, (T 2- T
I) is, for example, several tens to several 17 m5ec.0 As explained above, by using the device of the present invention, terms that depend on the on-voltage of the switching element and the onocent voltage of the amplifier are detected before entering the photometric operating state. Therefore, even if these exist, there will be no error, and highly accurate photometry can be performed.

FIG. 3 is a diagram for explaining the control circuit 8 in FIG. 2 in more detail, and its operation will be explained with reference to the timing diagram of FIG. 4 as well.

8-1, 8-1', 8-2 are one-shot circuits, 8
-3 is an associate down counter, 8-4 is a clock generator, 8-5 is a latch circuit, 8-6 is an OR circuit, and 8-7 is an inverter, which are connected as shown in Fig. 91.

Therefore, as shown in Figure 4, the one-shot circuit 8-1 operates in synchronization with the release signal at time T'1 and outputs a pulse with a pulse width ΔT.0 While this pulse is at a high level, the OR gate output is Counter 8 because it becomes high level
-3 is not in the count-up state, clock generator 8-
The output of 4 is counted and a count amplifier corresponding to Δ■ is performed. One-shot circuit 8-1'.

8-2 both indicate the falling edge of the one-shot circuit 8-1 (time T
1), and the synchro circuit 11 operates according to the output of the circuit 8-2 and starts emitting light.Also, the analog switch 6 is turned on and the switching element 3 is turned off. In this embodiment configured as shown in FIG. This error may be stored.

FIG. 5 is a diagram showing an example of such a configuration. In FIG. 0, the same reference numerals as in FIGS. 1 to 4 indicate the same elements. 13 is a control circuit, 14 is a sample hold circuit as a setting means, and 15 is a power supply for generating ΔV.

With this configuration, the circuit configuration can be extremely simplified.

Until the output of the release switch 9 is obtained, the output 13a of the control circuit 13 is at a high level, and since the element 3 is turned on, the charge in the capacitor 2 is discharged.

Further, while the level of signal 13a is at high level, sample and hold circuit 14 samples and holds the error component output of amplifier 4.

When the release switch 9 is turned on, the control circuit 13
The output 13a of is at a low level, the element 3 starts charging the 0FFL capacitor, and the sample and hold circuit holds the value immediately before release. Therefore, the sampled and held error voltage and ΔV are added and input to the inverting input of the comparator 5.

Therefore, the reference voltage on which the ON voltage of the switching element 3 and the offset of the amplifier 40 are superimposed is compared with the charging voltage of the capacitor, and based on this, the timing of stopping light emission (dimming) of the flash light emitting device is controlled.

Incidentally, in the above embodiment, an example of a circuit for measuring reflected light from flash light emission was given as a photometric circuit, but the present invention is not limited to this. Needless to say, it can also be used as a photometric circuit. In the above explanation, the comparator 5 is used as an example of the calculation means, but the present invention is not limited to those that perform such a discrimination operation, but can be applied to any device that processes photometric values along with various parameters. (Effects) As explained above, according to the present invention, the ON voltage of the switching element, the offset of the amplifier, etc. before the photometry operation are detected and stored, and the side light information is stored in the memory. Since the data is calculated, highly accurate photometry is possible.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a first embodiment of the present invention, Fig. 2 is a typing chart thereof, Fig. 3 is a diagram showing a detailed example of a control circuit, Fig. 4 is a diagram showing timing in the control circuit, and Fig. 5 is a diagram showing a detailed example of a control circuit. The figure shows a second embodiment of the present invention. 01. Light receiving element such as SPC 2. Capacitor 3. Swinging element such as transistor 4. Operational amplifier as amplifying means 5. Arithmetic means Comparator as 6.
Analog switch 7...1)/A converter as a setting means 8...Control circuit 9...Release switch 10...Light amount control circuit 11...Synchro circuit 12...Flash light emitting insufflation 14. ...Sample and hold circuit as a rectangle setting means. TT T2 T3 Figure 17'Tr Tt T3

Claims (1)

[Claims] Capacitor for charging photocurrent, switching means for discharging the charge of the capacitor, rJiJ capacitor 7
an amplifying means for amplifying the evening voltage, an arithmetic means for calculating the output of the amplifying means with reference 1, and an oil switching means for increasing the voltage of the amplifying means while discharging the charge of the capacitor. and a setting means for setting the sales increase according to the output VC.