JPH03272211A - Apc circuit - Google Patents

Abstract

PURPOSE:To apply accurate compensation control to an optical output level fluctuation due to a temperature change by providing 1st and 2nd linear/ nonlinear conversion circuits or the like and applying linear control to an element having a nonlinear input/output characteristic with a control signal converted into another nonlinear characteristic reverse to the nonlinear characteristic. CONSTITUTION:The APC circuit is provided with a comparator 2 controlling a bias current and a pulse current supplied to a lighting section 7, 1st and 2nd linear/nonlinear conversion circuits 3, 4 switching the control of the comparator 2 from the linear control into the nonlinear control, a 1st drive circuit 5 controlling the bias current supplied to the lighting section 7 with an output of the 1st linear/nonlinear conversion circuit 3 and a 2nd drive circuit 6 controlling the pulse current fed to the lighting section 7 with an output of the 2nd linear/nonlinear conversion circuit 4. Then the element having a nonlinear input/ output characteristic is subject to linear control by a control signal whose characteristic is converted into another nonlinear characteristic reverse to the nonlinear characteristic.

Description

[Detailed Description of the Invention] [Summary] Regarding the APC circuit, the purpose is to more accurately perform compensation control of the optical output level due to temperature changes.The purpose of this invention is to input an electrical signal to be sent, create a reference voltage, and generate a data signal. A comparator that controls the bias current and pulse current applied to the light emitting section to set the optical output to a predetermined level by manually generating a voltage corresponding to the reference voltage and the optical output level. and first and second linear/nonlinear conversion circuits that switch control in the comparator from linear control to nonlinear control, and control a bias current applied to the light emitting section by the output of the first linear/nonlinear conversion circuit. and a second drive circuit that controls a pulse current applied to the light emitting section by the output of the second linear/nonlinear conversion circuit, and the element having nonlinear input/output characteristics has a nonlinear The configuration is such that linear control is performed using a control signal converted into a nonlinear characteristic having a characteristic opposite to that of the control signal.

[Industrial Field of Application] The present invention relates to an APC circuit, and more particularly to an APC circuit that uses elements with nonlinear human output characteristics.

Usually, an APC circuit (
Automatic Power Control)
detects its optical output using the backlight of the LD, converts it into a voltage value corresponding to the detected optical output, and compares it with a reference voltage value. Based on this comparison result, the bias current and pulse current applied to the LD (laser diode) are controlled. Here, the LD drive circuit is composed of an element having nonlinear characteristics, such as an FET. This control is for compensating the bias current and pulse current in order to always keep the amount of light emitted constant in order to prevent changes in the amount of light emitted due to the temperature characteristics of the LD when a temperature change occurs.

However, since the output characteristics of a drive circuit made up of FETs etc. are non-linear, if the comparison output of the comparator is directly output to the drive circuit, errors may occur due to the non-linear characteristics (
There is a possibility that control may be performed with a deviated value.

[Prior Art] FIG. 4 shows an LD drive circuit using a conventional FET, and its operation will be described below.

In the figure, first, a signal (electrical signal) to be transmitted is manually input to a reference voltage generating circuit 1. This reference voltage generation circuit 1 generates a reference voltage for comparison with a voltage corresponding to the level of optical output of an LD (laser diode) 7, and comparator 2
At the same time, the data signal is output to the second drive circuit 6. The comparator 2 compares the voltage corresponding to the level of the optical output of the LD 7 with the reference voltage manually input from the reference voltage generation circuit 1, and compensates for the increase or decrease in the optical output level due to changes in the characteristics of the LD due to temperature changes. The bias current IB and pulse current I applied to the LD7 are controlled. For control, the voltage obtained from the comparison result is applied to the source terminal of the FET 52 of the first drive circuit 5 by the buffer 52 with a gain (
1) is controlled and applied, and the voltage between the gate and source of FET 52 ■6. The bias current ■6 can be increased or decreased by changing . Similarly, the pulse current I is applied to the source terminal of the FET 62 of the second drive circuit by controlling the gain (slope) using the buffer 62 and applying the voltage obtained from the comparison result to the source terminal of the FET 62 to increase the voltage VGE between the gate and source of the FET 62. controlled by changing. Also, LD7
The voltage corresponding to the light output level is obtained by using the back light of the LD 7 that appears when the LD 7 emits light, and by receiving the hack light by the LD 8 to obtain the voltage value corresponding to the light output level.

Next, compensation for changes in characteristics due to temperature changes will be explained based on FIG. 5.

First, FIG. 5(a) shows the transfer characteristics of the N-channel FET shown in FIG. 5(C). The output current of this N-channel FET is ■. is the potential difference between its gate and source■. , controlled by . However, the output current I.

has nonlinear characteristics with respect to the potential difference VGS between its gate and source, so it is usually approximated to the nonlinear characteristics near the temperature at which the FET is used, as shown in Figure 5(b). The output current of the FET is controlled by a straight line (a straight line passing through points a and b in the figure).

[Problem to be solved by the invention]

As mentioned above, in the conventional configuration, compensation for temperature changes is controlled by a straight line (straight line connecting points a and b in the figure) that approximates the nonlinear characteristics near the temperature at which the FET is used, so the nonlinear There is a problem that if a straight line is set incorrectly near the characteristic, or if temperature compensation control is performed at a position far from points a and b, the control deviation may become extremely large. are doing.

Therefore, an object of the present invention is to more accurately perform compensation control of the optical output level due to temperature changes.

r　Means for solving problems〕 FIG. 1 shows a basic configuration diagram of the present invention.

When a transmission signal is input to the reference voltage generation circuit 1, the data signal is inputted to the second drive circuit, and a predetermined reference voltage is generated and outputted to the comparator 2. The ratio V, device 2 compares the input reference voltage and the voltage value corresponding to the output level of the LD, and according to the comparison result, controls the control signal for controlling the drive current of the LD into the first and second linear/nonlinear signals. Output to the conversion circuit. The first and second linear/nonlinear conversion circuits convert the manually input control signal into a nonlinear signal corresponding to the nonlinear characteristics of the FET, and output the signal to the first drive circuit and the second drive circuit. The first drive circuit linearly controls the bias current using a nonlinear control signal input manually, and the second
The drive circuit operates to linearly control the pulse current using a manually inputted nonlinear control signal.

[Effect]

According to the present invention, a control signal applied to a drive circuit having nonlinear characteristics that controls the optical output level of an LD is converted into a nonlinear signal that is opposite to the nonlinear 1.7 characteristic of the drive circuit, and then the control signal is applied to the drive circuit. By applying this, substantially linear control is possible.

〔Example 〕

A detailed description will be given below based on the embodiments shown in the drawings.

The linear/nonlinear conversion circuit 3゜4, which is the main part of the present invention, is
The linear/nonlinear conversion circuit 3L4 shown in FIG.
The explanation will be given by replacing 1 with the linear/nonlinear conversion circuit 3.4 in FIG.

- An explanation will be given below using an example of a drive circuit using an FET. Since the nonlinear characteristics of the FET have quadratic function characteristics, the linear/nonlinear conversion circuit performs control by converting the constraint signal into a square root characteristic that is opposite to the quadratic function characteristics.

The circuit operation is the same as the conventional circuit except for linear/nonlinear circuits 31 and 41. In the nonlinear circuit 3゜4, the manually inputted control signal is sent to the square root calculation circuit 3.
5.45 (linear/nonlinear conversion circuit) is manually operated.

The square root calculation circuits 3 and 4 are connected to the feedback circuit of the operational amplifier.
y = f (eo)'' is connected to form a square root calculation circuit, and its operation is performed by human power (C8), while its output (co) is as shown in the following equation. It is.

e r + f (eo) RR e□・= f(eo) eo == f −'(ei) In other words, if the signal f(eo) is a quadratic function, the output (
The signal appearing at ``e,'' becomes ``eo...Jet J.

Therefore, the input control signal is outputted to the level shift circuits 36 and 46 by the square root calculation circuit to obtain a nonlinear characteristic that is opposite to a linear characteristic, that is, a control signal as shown in FIG. 3. In the level shift circuit, the operating point a of the input nonlinear control signal is
A shift value is determined so as to match the operating point of the nonlinear signal of the drive circuit, and the incoming signal is shifted according to the shift value, and the drive amount F! A nonlinear control signal is output to @36.46. The driving circuits 36 and 46 substantially linearly control the driving current of the LD using control signals having opposing nonlinear characteristics.

Hereinafter, a description will be given of controlling a drive circuit having non-linear characteristics using the opposing non-war characteristics.

r(x) - nonlinear characteristic a of FET - position x of operating point - nonlinear characteristic f (z) with inverse characteristic to FET - control information, f(x) - b (x+a)2 ... (1 )x=JZ
-, a...(2) Substitute (2) into equation (1) f(z) =b L'Z-a+a)" f(z) -b L'Z) 2=bZ...( 3) As shown in the above equation, when an element or circuit having a square root characteristic (nonlinear) is controlled by a control signal converted to a square root characteristic (nonlinear), both nonlinear characteristics are canceled and a linear characteristic is obtained.

Therefore, when the nonlinear characteristic to be controlled is controlled by the opposite nonlinear characteristic, linear operation can be performed.

〔effect〕

As described above, according to the present invention, it has become possible to linearly operate a drive circuit having nonlinear characteristics, and it has become possible to accurately perform compensation control of the optical output level due to temperature changes.

[Brief explanation of drawings]

Fig. 1 is a diagram of the principle of the present invention, Fig. 2 is an embodiment of the main part of the present invention, Fig. 3 is a diagram showing square root characteristics, Fig. 4 is a conventional APC circuit diagram, and Fig. 5 is a diagram of an N-channel FET. In the diagrams showing transfer characteristics, ■... Reference voltage generation circuit 2... Comparator 3.4...
・Linear/nonlinear conversion circuit 5.6...Drive circuit 7.8...Laser diode 31.41...Square root conversion circuit 32.42...Level shift circuit 51.61...Buffer 52.62 ...FET

Claims (1)

[Claims] In an electric/optical conversion circuit using an element with nonlinear input/output characteristics, a reference voltage generation circuit that receives an electric signal to be sent, generates a reference voltage, and outputs a data signal. (1) and
A bias current (I_B) and a pulse current (I_P) are applied to the light emitting section (7) in order to input a voltage corresponding to the reference voltage and the optical output level and set the optical output to a predetermined level.
a comparator (2) that controls the comparator (2), first and second linear/nonlinear conversion circuits (3) and (4) that switch the control of the comparator (2) from linear control to nonlinear control; The drive circuit (1) controls the bias current (I_B) applied to the light emitting section (7) by the output of the linear/nonlinear conversion circuit (3).
5) and a second drive circuit that controls a pulse current (I_P) applied to the light emitting part (7) by the output of the second linear/nonlinear conversion circuit (4), An APC circuit characterized in that linear control is performed using a control signal obtained by converting an element having a nonlinear characteristic to a nonlinear characteristic opposite to the nonlinear characteristic.