JPS6327162A - Output controller for semiconductor laser array - Google Patents

Abstract

PURPOSE:To simplify circuit constitution, to reduce cost, and to make the adjustments of respective semiconductor laser outputs common with each other and simple by using a common comparator and a common counter, etc. for output controls for the semiconductor lasers. CONSTITUTION:Semiconductor laser driving circuits 8a and 8b output currents respectively proportionate to the output signals of D/A converters 16a and 16b for the plural semiconductor lasers 1a and 1b constituting a semiconductor laser array. The beam outputs of the lasers 1a and 1b are detected by a detector 9, undergo an amplifier 11, and compared with a reference signal voltage Vref by the comparator 12. This means that the beam outputs of the lasers 1a and 1b are controlled to be equal to the reference value time sequence by the circuits 8a and 8b. In this case, the photodetector 9, the amplifier 11, comparator 12, and the counter 13 are mommonly used for the output control, also, since the interval between the lasers 1a and 1b is short, variance due to positional shifting hardly occurrs. Therefore, only one reference value is necessary. As a result, the circuit constitution can be made simple, the cost is reduced, as well as the output adjustment can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an output control device for a semiconductor laser array used in a laser printer or the like.

(Prior art) Since the output intensity of a semiconductor laser is extremely unstable with respect to temperature, it is necessary to stabilize the output intensity of the semiconductor laser using a semiconductor laser output control device, etc. in an environment where the ambient temperature of the semiconductor laser changes. There is. There is a type of semiconductor laser output control device that uses a counter, and FIG. 3 shows an example of a laser printer that employs one example of this type of type.

A laser beam generated by a semiconductor laser 1 is collimated by a collimator lens 2, deflected by an optical scanning device 3 consisting of a rotating polygon mirror, and is imaged by an fθ lens 4 on the charged surface of a photoreceptor drum 5. As the spot moves repeatedly in the direction of the arrow by the rotation of the rotating polygon mirror 3, the photosensitive drum 5 rotates at the same time. A photodetector 6 is provided outside the information writing area, and detects the laser beam deflected by the rotating polygon mirror 3 to generate a synchronization signal. The signal processing circuit 7 applies an information signal to the semiconductor laser drive circuit 8, and its timing is controlled by a synchronization signal from the photodetector 6. The semiconductor laser drive circuit 8 drives the semiconductor laser 1 according to the information signal from the signal processing circuit 7, and therefore the laser beam modulated by the information signal is irradiated onto the photoreceptor drum 5 to form an electrostatic latent image. . This electrostatic latent image is developed by a developing device and transferred onto paper or the like by a transfer device. Further, the laser beam emitted backward from the semiconductor laser 1 is transmitted to a photodetector circuit 9.
The light intensity is detected by the control circuit 10, which controls the semiconductor laser drive circuit 8 in accordance with the output signal from the photodetector 9 to keep the output light amount of the semiconductor laser 1 constant.

FIG. 4 shows the semiconductor laser drive circuit 8 and the control circuit 10.
is shown in detail.

A laser beam emitted backward from the semiconductor laser 1 is incident on a photodetector 9 made of a photodiode, and the photodiode 9 outputs a current proportional to the intensity of the laser beam. This current is converted into a voltage by an amplifier 11, and a comparator 12 converts the current to the voltage S! It is compared with the lightning voltage ref. The output voltage of the comparator 12 becomes a high level or a low level depending on the magnitude relationship between both input voltages of the comparator 12, and controls the counting mode of the up/down counter 13. For example, when the intensity of the laser beam from the semiconductor laser 1 is weaker than the reference value, the output of the comparator 12 becomes a low level, and the amplifier down counter 13 enters a state in which it operates as an up counter.

When the edge detection circuit 14 applies an enable signal to the up-down counter 13 in response to the timing signal T1, the up-down counter 13 up-counts the clock signal from the oscillator 15, and its count value increases.

The count output of the up/down counter 13 is converted into an analog quantity by a digital/analog converter 16 and input to the semiconductor laser drive circuit 8. The semiconductor laser drive circuit 8 drives the semiconductor laser 1 based on the information signal from the signal processing circuit 7, and changes its drive current in accordance with the output of the digital/analog converter 16. Therefore, as the count value of the 7-up down counter 13 gradually increases, the intensity of the laser beam from the semiconductor laser 1 gradually increases, and the output of the amplifier 11 increases. When the output of the comparator 12 is inverted from low level to high level, the edge detection circuit 14 detects the rising edge of the output of the comparator 12 and turns off the enable signal to the up/down counter 13. Therefore, the up/down counter 13 becomes disabled and holds its count value, so that the magnitude of the driving current of the semiconductor laser 1 is maintained as it is. Next, the edge detection circuit 14 is activated by the timing signal T.
When the disable state of the up/down counter 13 is released, if the output of the comparator 12 is at a high level (if the output intensity of the semiconductor laser is strong), the up/down counter 13 operates as a down counter and receives the clock signal from the oscillator 15. is counted down and the count value decreases. Therefore, the output of the digital/analog converter 16 decreases, the drive current of the semiconductor laser 1 decreases, and the output of the amplifier 11 decreases. Then, when the output of the amplifier 11 becomes smaller than the reference voltage Vref and the output of the comparator 12 is inverted from high level to low level, the edge detection circuit 14 detects the falling edge of the output of the comparator 12 and inverts the up/down counter 13. Disable.

Therefore, the up/down counter 13 maintains the current value, and the magnitude of the driving current of the semiconductor laser 1 is maintained as it is. Here, the edge detection circuit 14 releases the disabled state of the up/down counter 13 using the timing signal T□, and disables the up/down counter 13 only when the output of the comparator 12 is inverted from a low level to a high level. With this configuration, when the output of the comparator 12 is at a low level and the disable state of the amplifier down counter 13 is released by the timing signal T, when the output of the comparator 12 is reversed from low level to high level, the up The down counter 13 becomes disabled and holds the count value.

When the output of the comparator 12 is at a high level and the disable state of the up counter 13 is released by the timing signal T□, when the output of the comparator 12 changes from high level to low level, the amplifier down counter 13 is disabled. With the output of the comparator 12 remaining released, it operates as an up-counter. and semiconductor laser 1
When the g dynamic current increases and the output of the comparator 12 is inverted from a low level to a high level, the edge detection circuit 14 detects the rising edge and disables the up/down counter 13 to hold the count value. The print end signal generated by detecting the rising edge of the frame synchronization signal is used as the timing signal T, and the drive current of the semiconductor laser 1 is adjusted every time frame recording is completed.

Further, a system has been considered in which a semiconductor laser array is used in place of the semiconductor laser 1 in the laser printer, and a semiconductor laser output control device as shown in FIG. 4 is provided for each semiconductor laser constituting the semiconductor laser array.

However, in this method, since a semiconductor laser output control device is provided for each semiconductor laser, the circuit configuration becomes complicated and expensive, and the optical output of each semiconductor laser must be adjusted separately, which is troublesome.

(Objective) It is an object of the present invention to provide a semiconductor laser array output control device that can improve the above-mentioned drawbacks, simplify the circuit configuration, reduce costs, and simplify the adjustment of semiconductor laser light output. .

(Yokonari) The present invention comprises a photodetector for detecting the optical output of a semiconductor laser array, a comparator for comparing the output signal of the photodetector with a reference signal, and a counter controlled by the output signal of the comparator. , a plurality of latch circuits into which the outputs of the counters are respectively input, a plurality of digital/analog converters that convert each output signal of the plurality of latch circuits into analog quantities, and a plurality of digital/analog converters. It has a plurality of semiconductor laser driving circuits that respectively flow a current proportional to each output signal to each semiconductor laser of the semiconductor laser array, and a control means, and the control means controls the semiconductor laser according to the surface input signal of the comparator. The lights are turned on in time order so that the difference is always zero.

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

FIG. 1 shows an embodiment of the invention. In this embodiment, a photodetector 9, an amplifier 11, a comparator 12, and a counter 13 for output control are made common to a plurality of semiconductor lasers la and lb constituting a semiconductor laser array in the laser printer described above.

Now, when the semiconductor laser control signal T is input.

The edge detection circuit 17 clears the counter 13, and at the same time causes the latch command circuit 18 to release the latch of the latch circuit 19a and put the latch circuit 19b into the holding mode.

The output signal of the comparator 12 is input to the up/down terminal of the counter 13 via the edge detection circuit 17, and the oscillator 1
The clock signal from 5 is counted up or down, and the count value is converted into an analog quantity by the digital/analog converter 16a through the latch circuit 19a. The semiconductor laser drive circuit 8a passes a current proportional to the output signal of the digital/analog converter 16a to the semiconductor laser 1a, and the optical output of the semiconductor laser 1a is detected by the photodetector 9.
It is detected by the comparator 12 via the amplifier 11 and compared with the reference signal voltage Vref. Therefore, the semiconductor laser 1a
The optical output of the comparator 12 is controlled so that the difference between the two inputs of the comparator 12 becomes zero.

When the edge detection circuit 17 detects an edge of the output signal of the comparator 12, it causes the latch command circuit 19 to put the latch circuit 19a into the latched state to hold the output of the counter 13, and at the same time releases the latch of the latch circuit 19b, so that the counter 1
Clear 3. Therefore, the counter 13 is the comparator 12
The clock signal from the oscillator 15 is counted in a count mode according to the output signal of the oscillator 15, and the count value is converted into an analog quantity by the digital/analog converter 16b through the latch circuit 19b. Semiconductor laser drive circuit 8b
A current proportional to the output signal of the digital/analog converter 16b flows through the semiconductor laser 1b, and the optical output of the semiconductor laser 1b is detected by the photodetector 9 and outputted to the comparator 12 via the amplifier 11. Therefore, the semiconductor laser la, Ib
The optical output is time-sequentially controlled to a reference value by semiconductor laser drive circuits 8a and 8b. When the edge detection circuit 17 detects an edge of the output signal of the comparator 12, the latch command circuit 18 causes the latch circuit 19b to be in a latched state to hold the output of the counter 13. This completes the optical output control of the semiconductor lasers 1a and 1b, and the semiconductor laser drive circuits 8a and 8b operate the semiconductor lasers 1a and 1b using modulation signals.
Start modulating a and lb. At this time, the semiconductor laser la,
A current flows through lb according to the output signals of the latch circuits 19a and 19b. Note that since the distance between the semiconductor lasers la and 1b is very narrow, approximately 100 μm, the photodetector 9 placed behind the semiconductor laser array has almost no variation in the amount of incident light depending on the position of the semiconductor lasers la and lb, and therefore the reference value is constant. Good and easy to adjust.

FIG. 2 shows another embodiment of the invention.

In this embodiment, in the above embodiment, the precent value of the counter 13 is transferred to the multiplexer 2o and the circuit 19a.
The selection is made from the output of 19b. When the edge detection circuit 17 completes the optical output control of the semiconductor laser 1a and detects an edge of the output signal of the comparator 12, it causes the latch command circuit 18 to put the latch circuit 19a into the holding mode, and then sends the multiplexer 20 to the launch circuit 19b. The output is selected and inputted to the counter 13, and the counter 13 presets the output of the latch circuit 19b.Then, the latch command circuit 18 is made to release the latch of the launch circuit 19b, and the light output control of the -C semicentric laser 1b is started. let Further, when the edge detection circuit 17 receives the semiconductor laser control signal T, it causes the latch command circuit 18 to set the latch circuit 19b to the holding mode, and then causes the multiplexer 2o to select the output of the latch circuit 19a and pre-center the counter 13. , and then the latch command circuit 18 is connected to the latch circuit 19a.
The latch is released to start controlling the optical output of the semiconductor laser 1a. In this way, when controlling the optical output of the semiconductor lasers la and lb, by selecting the count value from the previous control from the latch circuits 19a and 19b using the multiplexer 2o and presetting it in the counter 13, the optical output of the semiconductor laser can be set to the reference value. The light output control can be started by flowing a current in a state close to that of the current state, and higher-speed control is possible compared to the case where the counter 13 is cleared at the start of the light output control as in the above embodiment.

Although the semiconductor laser array is composed of two semiconductor lasers in the above embodiment, it may be composed of three or more semiconductor lasers.

(Effects) As described above, according to the present invention, the comparators, counters, etc. for output control are made common to each semiconductor laser, so the circuit configuration can be simplified and the cost can be reduced. It also becomes possible to standardize and simplify the adjustment of laser output.

[Brief explanation of drawings]

1 and 2 are block diagrams showing each embodiment of the present invention, FIG. 3 is a diagram showing an example of a laser printer, and FIG. 4 is a block diagram showing a part of the laser printer. la, lb... Semiconductor laser, 8a, 8b... Semiconductor laser drive circuit, 9... Photodetector, 12... Comparator, 13... Counter, 16a, 16b... Digital/analog Converter, 17... Edge detection circuit, 1
8... Latch command circuit, 19a, 19b... Latch circuit. Location δ Figure 4 Figure

Claims (1)

[Claims] a light detection means for detecting the light output of the semiconductor laser array;
A comparator that compares the output signal of the photodetection means with a reference signal, a counter controlled by the output signal of the comparator, a plurality of latch circuits to which the outputs of the counters are respectively input, and the plurality of latch circuits. a plurality of digital/analog converters that convert each output signal into an analog quantity, and a plurality of digital/analog converters that flow a current proportional to each output signal of the plurality of digital/analog converters to each semiconductor laser of the semiconductor laser array. a semiconductor laser drive circuit;
A semiconductor laser array output control device comprising: control means for turning on each of the semiconductor lasers in time sequence so that the difference between both input signals of the comparator is always zero.