JPS63316930A - D/a converter - Google Patents

Abstract

PURPOSE:To dispense with adjustment by a manual operation and the setting of an adjusting means, by driving the load of a light emitting element, etc., by the output signal of a D/A converter, and performing the offset adjustment of the D/A converter and that of a signal transmission line from the D/A converter to the load automatically by detecting the presence/absence of the output current of the load. CONSTITUTION:The output signal V5 of a voltage comparator 6 is varied to a level '0' or a level '1' according to the light emission or the stoppage of the light emission of a LED. A CPU12 in a control part 11 reads the output signal V5, and supplies a signal to convert a level to the level '0' when it is the level '1' to a second D/A converter 7. As a result, the output signal V6 of the converter 7 is supplied to the reference terminal of a first D/A converter 1, then, the gain control of the converter 1 is performed. Furthermore, the level of the output signal V3 of the second D/A converter 7 changes, then, the gain control of a third amplifier circuit 4 is performed. Thus, since the offset of not only the D/A converter 1 but the signal transmission line to a driving circuit 3 is adjusted automatically based on the presence/absence of the output current of the LED, it is possible to make manual adjustment and the adjusting means for the offset unnecessary.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a D/A converter, and is particularly suitable for application to a device that drives a light emitting element based on a digital signal and records image information. be.

(Prior art) Regarding D/A converters, see "Design of rA-D/D-A conversion circuit" (Published on May 20, 1981, CQ Publishing Journal, P.
125 et seq.), which are well known to those skilled in the art.

The above-mentioned D/A converter can be used in a wide variety of ways.
As shown in the figure, it may also be used to drive a light emitting element (LED). The main points of the circuit operation will be described below. A digital signal φ, which is image information, is supplied to the D/A converter 1,
The analog-converted output signal is current-voltage crossed by an I/V converter. VR, is for gain adjustment, and the output signal of l/V converter 2 is sent to an operational amplifier (
After being amplified by OP2 (hereinafter abbreviated as OP), it is supplied to the transistor Q1 that constitutes the drive circuit 3. The drive circuit 3 operates an LED, which is a light emitting element, in response to an output signal from OP2, and exposes a photosensitive material (not shown) to record image information.

In the image recording apparatus using the above-mentioned D/A converter, it is necessary to cause the LED to emit light accurately in response to the digital signal φ, but it has the following problems.

(Problems to be Solved by the Invention) That is, the D/A converters OP, OP2 each have an offset voltage. Therefore, the digital signal φ
If this is done manually, a current corresponding to the offset voltage will flow through the LED, resulting in heavy recording of the information of the digital signal φ.

In order to solve the above problem, a variable resistor number VR2 for offset adjustment is provided, but even if the VR2 is adjusted, readjustment must be performed due to temperature changes or changes over time. That is, the offset adjustment had to be performed manually each time data was input, which was extremely troublesome.

The purpose of the present invention is to solve the above problems, and D.
An object of the present invention is to eliminate offset adjustment of a signal transmission path including a /A converter and a D/A converter.

(Means and effects for solving the problems) The above object of the present invention is to drive a load such as a light emitting element using an output signal of a D/A converter, and to detect the presence or absence of an output current of the load. This is achieved by automatically adjusting the offset of the D/A converter and the signal transmission path from the D/A converter to the load.

In other words, when an offset occurs in the D/A converter or signal transmission path, causing the load to be driven unnecessarily, or when undesired driving that does not correspond to the digital signal supplied to the D/A converter occurs. , since this is detected and automatic adjustment is performed, manual adjustment and installation of adjustment means become unnecessary.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Note that FIG. 1 is a circuit diagram of an exposure LED drive circuit using a D/A converter.

The D/A converter 1 includes a CPU (
Central Processing Unit)
A digital signal φ (image information) is supplied from 12 through an interface 13 .

The first amplifier 2 converts the output current of the D/A converter 1 into a voltage, and is a resistor R that supplies a reference voltage to OP.
1, R2, a feedback resistor R3, and a phase compensation capacitor C1.

The third amplifier 4 performs differential amplification between the output signal V2 of the first amplifier 2 and the output signal v3 of the second D/A converter 7, which will be described later, and is composed of an OP3 and a feedback resistor R4. ing.

The second amplifier 5 outputs a signal V corresponding to the output signal V3 of the third amplifier 4, and this output signal V.

is supplied to the transistor Q1 forming the drive circuit 3 via the resistor R6. Note that the resistor R5 converts the output current I of the drive circuit 3 into a voltage and supplies the voltage to the inverting input terminal of OP2.

The drive circuit 3 drives the LED, which is a light emitting element, in response to the output signal V4, and the transistor Q1 controls the current of the LED connected in parallel to the emitter resistor R7. Note that the diode D1 is provided as a clipper.

The output current of the drive circuit 3 is fed back to the second amplifier 5, and at the same time is supplied to the voltage comparison circuit 6.
It is compared with the voltage divided by Rs. Drive circuit 3
The output current of is obtained when the LED is driven, but becomes 0 when it is not driven.

Therefore, the output signal v5 of the voltage comparison circuit 6 changes in level to 0 or 1 as the LED emits light or stops emitting light.

The CPU 12 in the control unit 11 uses the interface 1
The second D/A converter 7 reads the output signal V, which is supplied via the interface 15, and supplies a signal to be converted to a level 0 in the case of level 1 to the second D/A converter 7 via the interface 15. At the same time, a digital zero value is supplied via the interface 13.

As a result, the output signal V6 of the second D/A converter 7 is supplied to the first D/A converter reference terminal, and the output signal V6 of the second D/A converter 7 is supplied to the first D/A converter reference terminal.
Adjust the gain of A converter 1.

Further, the level of the output signal V of the second D/A converter 7 changes, and the gain of the third amplifier circuit 4 is adjusted.

Depending on the presence or absence of the output current of the LED, the first D/A converter 1
In addition, the offset of the signal transmission path up to the drive circuit 3 is automatically adjusted, eliminating the need for manual offset adjustment and adjustment means.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible.

For example, an LED may be placed in the collector path of transistor Q1.

(Effects of the Invention) According to the present invention, the light emitting element is driven by the output signal of the D/A converter, and the presence or absence of a current for driving the light emitting element is detected, and the D/A converter and the D/A converter Since the structure is configured to automatically adjust the offset from the device to the light emitting element drive circuit, there is no need to provide an offset adjustment means in the output signal transmission path of the D/A converter, reducing the number of adjustment steps, and reducing temperature changes in characteristics over time. Unnecessary light emission of the LED due to the change can be reduced, and the reliability of the device can be improved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a D/A converter to which the present invention is applied and an exposure LED drive circuit showing an example of its use, and FIG. 2 is a circuit diagram showing a conventional example of the exposure LED drive circuit. 1.7... D/A converter, 2.4.5... amplifier,
3... Drive circuit, 6... Voltage comparator, 11... Control section.

Claims (1)

[Claims] The first D converts the digital image signal into an analog signal.
/A converter, a first amplifier that amplifies the output signal of the first D/A converter, and converts a digital signal to an analog signal to perform offset adjustment of the first D/A converter, a second D/A converter that supplies one output signal to the first D/A converter, and the other output signal of the first amplifier and the second D/A converter. a third amplifier for comparison and amplification, a second amplifier for amplifying the output signal of the third amplifier, and a light emitting element that emits light based on the output signal of the second amplifier, corresponding to a drive current of the light emitting element. a voltage comparator that compares the output voltage with a reference voltage; and a voltage comparator that reads the output voltage of the voltage comparator and supplies a digital zero value to the first D/A converter depending on the level, and also sets the read value to zero. A D/A converter comprising: a control unit that supplies a digital signal to the second D/A converter.