JPH0534756A - A/d converter for camera - Google Patents

Abstract

PURPOSE:To provide an A/D converter which is reduced in scale and inexpensive. CONSTITUTION:The integration type A/D conversion circuit is divided to a logic part such as a counter and an analog part such as an integration circuit. An INT in a figure 1 is the analog part consisting of an integration capacitor C1, a memory capacitor C2, a comparator CMPI or the like. The analog part is provided in a peripheral circuit such as an interface circuit or an amplifier circuit. On the other hand, the logic part such as the counter assumes the role thereof by the counter or software which already exists in a CPU. By such constitution, the A/D conversion device which is reduced in scale and inexpensive is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an A / D conversion device for a camera.

[0002]

2. Description of the Related Art Recently, a one-chip microcomputer (hereinafter referred to as "microcomputer") has been used as a sequence control circuit of a camera.
Is abbreviated) is commonly used. Therefore, in a camera that handles many analog quantities (values) such as photometric values and distance measurement values, an A / D conversion circuit that converts these analog quantities (values) into digital quantities (values) that can be processed by a microcomputer is provided. It is essential.

Therefore, conventionally, for example, (1) a microcomputer having a built-in A / D conversion circuit such as a successive approximation A / D conversion circuit is used. (2) An A / D conversion circuit such as an integration type A / D conversion circuit is also integrated in a dedicated IC in which peripheral circuits such as an interface circuit or an amplifier circuit are integrated. Was used.

[0004]

However, when the former method is used, the microcomputer becomes expensive and the operating power supply voltage range of the microcomputer becomes narrow, so that the power supply circuit becomes large in scale and expensive. There is a problem that the dedicated IC becomes large in scale and expensive when the latter method is used.

The present invention has been made in view of these points, and provides a small-scale and inexpensive A / D conversion circuit.

[0006]

The A / D conversion circuit according to the present invention employs an integration type A / D conversion circuit, which is divided into a logic part such as a counter and an analog part such as an integration circuit. The former plays the role of an existing counter and software in a microcomputer for sequence control, and the latter is provided in a peripheral circuit such as an interface circuit or an amplifier circuit.

[0007]

Therefore, the increase in the electric circuit by mounting the A / D conversion circuit is limited to the analog section such as the integration circuit, and it is possible to realize a very small and inexpensive A / D conversion circuit as a whole. It will be possible.

[0008]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of an integral type A / D conversion circuit to which the present invention is applied. The integration type A / D conversion circuit includes an integration unit [INT] and a microcomputer [CPU]. The integrating unit [INT] is a buffer circuit [OP1, D1] for transmitting the voltage of the integrating capacitor [C1], the memory capacitor [C2], and the integrating capacitor [C1] to the memory capacitor [C2], and the memory capacitor [OP]. C2]
[CMP1], which compares the voltage of the capacitor with the voltage of the integrating capacitor [C1], and the reference current [CC for the first integration
1], a measured current input terminal [AIN], a changeover switch [SW1] for switching the integrated current to the integrating capacitor [C1], a first discharging switch [SW2] for discharging the integrating capacitor [C1], and a memory. It is composed of a second discharge switch [SW3] for discharging the capacitor [C2]. The changeover switch [SW1], the first discharge switch [SW2], and the second discharge switch [SW3] are controlled by the microcomputer [CPU].
It should be noted that the analog amount (value) of A / D-converted object brightness information or distance information is converted into a current and input to the measured current input terminal [AIN].

Next, the actual operation will be described with reference to the voltage waveforms of the respective parts shown in FIG. 2 and the flow chart shown in FIG.

First, in step 1, prior to the integration operation, the first and second discharge switches [SW2, SW3] are turned on to discharge the residual charge of the integration capacitor [C1] and the memory capacitor [C2], Initial voltage setting of both capacitors is performed (timing in FIG. 2). Also,
The changeover switch is set to the reference current side (A) for the next first integration.

After waiting for a predetermined time in step 2, in step 3 the first and second discharge switches [SW2, SW3].
Are turned off at the same time to start the first integration (timing in FIG. 2). This first integration is based on the reference current [CC
1] is used to charge the integration capacitor [C1] for a predetermined time (tc) to obtain a reference voltage for the second integration described later. Specifically, when the voltage of the integrating capacitor [C1] rises, the voltage of the memory capacitor [C2] also rises due to the buffer circuit [OP1, D1]. Then, the voltage of the integrating capacitor [C1] after the lapse of a predetermined time (tc) is held by the memory capacitor [C2] and becomes the reference voltage at the time of the second integration.

Step 4 waits for the first integration time (tc). In step 5, the first discharge switch [S
By turning on W2] again, the integration capacitor [C
1] is discharged, and the voltage of the integrating capacitor [C1] is initialized again (timing in FIG. 2). At this time, the memory capacitor [C2] is connected to the comparator [CMP
1] has a very high input impedance and the discharge blocking diode [D1] causes the voltage of the integrating capacitor [C1] to change to the second voltage at the end of the first integration, that is, immediately before the first discharge switch [SW2] is turned on again. Hold as the reference voltage for integration.

In preparation for the second integration, the change-over switch [SW1] is switched from the reference current side (A) at the time of the first integration to the measured current input side (B).

After the stabilization wait in step 6, the second discharge switch [SW2] is turned off in step 7 to start the second integration by the measured current, and the timer is started in step 8 (timing in FIG. 2). ).

Then, in steps 9 and 10, R /
Wait for signal B to become “H.” Integrating capacitor [C] after the first integration held in memory capacitor [C2].
1] becomes equal to the second integrated voltage, and the comparator [CMP1] is inverted, so that the R / B signal becomes “L”.
When it changes from "H" to "H" (or timing in FIG. 2), the timer is stopped in step 11, and the timer value (tx or tx 'in FIG. 2) in step 12.
To store. However, tx is a timer value when IIN is large, and tx ′ is a timer value when it is small.

Now, assuming that the capacitance of the integrating capacitor [C1] is CC1, the current value of the reference current [CC1] is ICC1, the measured current value is IIN, and the first integration time is tc, R from the start of the second integration. Since the first and second integrated voltages are the same, the time tx until the / B signal inversion is iccc1 × tc / cc1 = IIN × tx /
CC1 Therefore, tx becomes tx = tc × ICC1 / IIN, which is inversely proportional to the measured current value (IIN). Therefore,
The measured current value (IIN) can be known by measuring tx. That is, the measured current value (IIN), which is an analog value, can be represented by the digital value tx.

In the present embodiment, the timer for measuring tx is started in step 8, and the inversion of the R / B signal is detected in steps 9 to 11 to stop the timer. The digital value of the measured current value can be obtained from the value of the timer at this time.

The configuration of the A / D conversion circuit described above can be applied to an integrated circuit in which a microcomputer and an analog circuit are mixed on the same chip.

[0020]

As described above, A / to which the present invention is applied
In the D converter, the increase of the electric circuit by mounting the A / D converter circuit is limited only to the analog section such as the integration circuit, so that a very small and inexpensive A / D converter circuit is realized as a whole. It becomes possible to do.

[Brief description of drawings]

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

FIG. 2 is a timing chart showing a switching operation and a voltage waveform of each part.

FIG. 3 is a flowchart showing an operation sequence of the A / D conversion circuit of the present invention.

[Explanation of symbols]

INT integration section CPU microcomputer

Claims (2)

[Claims] 1. A first control for controlling a photographing sequence of a camera
Second I that integrates the IC and interface circuit and amplifier circuit
In a camera having C, an analog section such as an integrating circuit and a logic section such as a counter section are provided, and the analog section is provided in the second IC and the logic section is provided in the first IC. Characteristic camera A /
D converter. 2. The A / D conversion device for a camera according to claim 1, wherein the sequence control IC is a one-chip microcomputer.