JPS59224931A - Temperature control circuit - Google Patents

Abstract

PURPOSE:To set a temperature change with high accuracy by providing a voltage level shift circuit between the emitter and base of two transistors(TRs) for driving current to make both the TRs conductive at all times, and bringing a dead band of temperature control to be zero. CONSTITUTION:A voltage applied from positive and negative power supply terminals 12, 13 is divided and converted into an electric signal through the decision of a current converting element 2 and a heat-sensitive element 3 of a semiconductor laser 1. This electric signal is amplified by an amplifier 8 comprising an operational amplifier 7 mainly, converted into a current signal by a voltage- current converting circuit 6, the direction of temperature fluctuation heating or cooling the element 2. Level shift TRs 31, 32 are provided between the input side of the said converting circuit 6 and TRs 4, 5 for driving heat-sensitive element to apply an output of the amplifier 8 to the base of the TR31, 32. Further, the emitter of the TRs 31, 32 is connected to the base of the TR4, 5 to make the TR4, 5 conductive at all times, bringing the dead band of temperature control of the laser 1 to zero, thereby setting temperature with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a temperature control circuit for semiconductor devices, and particularly to a temperature control circuit suitable for stabilizing the temperature of a semiconductor laser.

[Prior art]

2. Description of the Related Art In recent years, systems for transmitting images using semiconductor lasers or optical fibers, such as CATV, have been actively developed. However, a semiconductor laser has the property that its oscillation spectrum changes at a certain temperature, and noise increases rapidly. Furthermore, when transmitting the output light of such a semiconductor laser using an optical fiber, the longer the optical fiber is, the more noise increases, which causes image quality deterioration, which is important for image transmission. This has become a serious problem. In order to solve such problems, it is necessary to control the temperature of the semiconductor laser with high precision, and Utility Model Application No. 55-4567, as shown in Figure 1, has been proposed as a conventional temperature control method. ing. In this method, an electrothermal conversion element 2 for heating or cooling a semiconductor laser 1 is provided with an NPN) transistor 4 and a P
NP) Voltage-current conversion circuit 6 composed of transistor 5
The semiconductor laser 1 is heated or cooled by causing current to flow in or out.

The temperature of the semiconductor laser 1 is controlled by an electrothermal conversion element 2 using a thermosensitive element 3 such as a thermistor whose resistance value changes depending on the temperature.
This is done by controlling the current of the voltage-current conversion circuit 6 by converting and extracting the temperature change into an electrical signal and comparing this change with a reference signal vr for setting the desired temperature.

In FIG. 1, 51 and 52 are buffer transistors having the same characteristics, and 53 and 54 are resistors for supplying current to these transistors. In FIG. 1, the required temperature is set at the reference potential V
Set by r.

When the input current Vl of the voltage-current conversion circuit 6 is at a positive potential, N
A current is supplied from the PN transistor 4 to the electrothermal conversion element 2, and the element is heated. Conversely, when the input voltage y+ is at a negative potential, current flows from the electrothermal conversion element 2 into the PNP transistor 5, so that it is cooled. In this conventional example, 1.
Since almost no current flows in the NPN transistor 4 and the PNP transistor 5 when the base-emitter voltage is approximately 0.7 V or more, the input potential Vl of the voltage-current conversion circuit is ±
In the range of 0.7 square centimeters, both transistors are in the cutoff region, and current does not flow in both directions in the electrothermal conversion element 2, which has the disadvantage that temperature control is impossible.

Therefore, in this region, the semiconductor laser 1 cannot be set to the required temperature even if the reference potential vr is changed, so the semiconductor laser 1 is largely dependent on the ambient temperature.
This was a very big problem in terms of noise suppression. FIG. 2 is a graph showing the results of measuring the temperature of the input chamber iV+ of the voltage-current conversion circuit 6 and the corresponding electrothermal conversion element 2, and there is a region where the temperature cannot be set, that is, a dead zone. It is shown that.

[Purpose of the invention]

An object of the present invention is to eliminate the dead zone of a voltage-to-current conversion circuit that drives an electrothermal conversion element for heating or cooling a semiconductor device, and in particular, to heat or cool a semiconductor laser, in order to solve the drawbacks of the prior art. An object of the present invention is to provide a temperature control circuit that can be set accurately over the entire temperature range.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention connects the snow 1 voltage, which is approximately equal to the base-emitter voltage of the transistors 4 and 5 that drive the electrothermal conversion element 2, to the input of the voltage-current conversion circuit 60 and the transistors 4 and 50. By inserting the transistors 4 and 5 between the spacers, the transistors 4 and 5 are always in a conductive state, thereby eliminating a region where temperature cannot be set, that is, a dead zone.

[Embodiments of the invention]

FIG. 3(a) is a principle diagram for determining conditions for zeroing out the dead zone of the voltage-current conversion circuit 6 according to the present invention. In the figure, 12 and 13 are positive and negative power supply terminals, respectively, and input terminals 101 and 102 of the voltage-current conversion circuit 6 are voltage level shift circuits, respectively. From the same figure, the input voltage is V
1, the output voltage is Vo, the level shift voltages of the voltage level shift circuit are vLl, vL2, and the base-emitter voltages of the transistor 4.5 are VBN, VBP, then the following equation holds true. That is, V Ll +V L2 =V BN+V IIP ・
・・・・・・ To be equal to ■, V Lt −V Lz = V BN −V BP −
It must be −−−−・−■. Therefore, ■ and 0
From the formula, yt, t, VLI are VLI==:■BN, ■
If L2=vBP is selected, va=Vs .

FIG. 3(b) shows a basic embodiment of the voltage-current conversion circuit according to the present invention, in which the voltage level shift circuit 10
1,102 as transistor 3: L, 32, resistor 33~3
It consists of 6. The level shift voltage utilizes the base-emitter voltages of transistors 31 and 32, and these voltages may be selected to be equal to the base-emitter voltage of transistor 4.5. However, in reality, it is difficult to make all the voltages between the pace emitters the same, so the voltage effect of the resistors 34 and 35 can be used to correct the difference in voltage between the pace emitters. In this method, the output voltage Vo
When is at zero potential, the current flowing through transistors 4 and 5 can be set to several mA, and transistors 4.
It becomes possible to keep the conduction constant. Note that the operation of heating or cooling the electrothermal conversion element is the same as in the case of FIG.

That is, when the input voltage Vl of the voltage-current conversion circuit is positive, a current is supplied from the transistor 4 to the electrothermal conversion element 2 to heat it, and when the input potential Vl is negative, a current is supplied from the electrothermal conversion element 2 to the transistor 5. Current flows in and cools down.

FIG. 4 shows an embodiment of the I@ degree control circuit according to the present invention. First, the resistance value of the thermosensitive element 2 is determined according to the temperature of the electrothermal conversion element 2, and the voltage supplied from the positive and negative power supply terminals 12, 13 is divided according to the ratio with the resistor 23, and an electric signal is generated. is converted to

This electrical signal is input to an amplifier 8 consisting of an operational amplifier 7 and resistors 21 and 22, and is amplified.

Next, this amplified signal is converted into a current by a voltage-current conversion circuit 6, and the electrothermal conversion element 2 is heated or cooled depending on the direction of the temperature fluctuation.

For example, if the ambient temperature first changes and the temperature of the electrothermal conversion element 2 rises above the required set temperature, then the heat-sensitive cord 2
Since the resistance value of the amplifier 8 decreases, the input voltage of the amplifier 8 increases. This increase in input voltage works in the direction of decreasing the differential voltage with respect to the reference temperature setting terminal vr.

is amplified by the operational amplifier 7, and the voltage-current conversion circuit 6
The emitter current of the transistor 4 in the transistor 4 is reduced compared to the initial state. This means that the current flowing into the electrothermal conversion element 2 is reduced compared to the initial state, and as a result, the temperature can be stabilized. Similarly, when the temperature of the electrothermal conversion element 2 decreases, the temperature deviation is stabilized by the reverse operation. Note that the temperature of the electrothermal conversion element 2 is determined by the relationship between the reference voltage Vr and the input voltage v of the voltage-current conversion circuit 6, if the values of the resistors 21.22 are R21 and R22. / R21) V r”
・・・−・ Because of the relationship ■, the output voltage ■o is ■
According to the formula, V6 = (1+ R22/ Rgt) V
r, and can be uniquely set by the reference voltage.

Also, the deviation of the set temperature can be reduced by increasing the loop gain.

0.0, IC or less, and an extremely high-precision temperature control circuit without a dead zone can be implemented. Figure 5 shows an embodiment of the temperature control circuit according to the present invention, in which the temperature changes linearly with respect to the reference voltage, and no dead zone is observed, which clearly shows the effectiveness of the present invention. I understand.

〔Effect of the invention〕

As described above, according to the present invention, heating and
In a voltage-current conversion circuit for controlling cooling, a voltage level shift circuit having a voltage approximately equal to the rise voltage between the pace emitters of a current driving NPN) transistor and a PNP transistor is connected to the NPN) transistor and PNP transistor, respectively.
NP) By inserting the transistor between the base of the transistor and the voltage-to-current conversion circuit to keep both transistors in a conductive state, the dead zone for temperature control can be reduced to zero, and the temperature can be adjusted to any temperature using the reference voltage. can be set accurately (9). The present invention provides a very effective means for suppressing noise caused by semiconductor laser mode hops and preventing image quality deterioration when transmitting broadband analog signals such as images using semiconductor lasers and optical fibers. do.

[Brief explanation of the drawing]

Fig. 1 is a connection diagram of a conventional temperature control circuit, Fig. 2 is a measurement result of electrothermal conversion element control temperature, and Fig. 3 is a basic connection diagram of a voltage-current conversion circuit which is the basis of the temperature control circuit according to the present invention. FIG. 4 is a connection diagram showing the configuration of an embodiment of the temperature control circuit according to the present invention, and FIG. 5 shows the electrothermal conversion element control temperature and the current flowing through the electrothermal conversion element at that time in the embodiment according to the present invention. FIG. 3 is a diagram showing measurement results. 1... Semiconductor laser, 2... Current conversion element, 3...
- Heat sensitive element, 4, 5... Electrothermal conversion element drive transistor, 7... Operational amplifier, 31.32... Level shift transistor, 34.35... Level shift resistor, 6... Voltage -Current conversion circuit, 8...Amplifier, 1
01゜102...Level shift circuit. (10) Figure 1! fJ Z To figure Force electric reaction Th (TI) 3 mouth (α) V“ 1 (b) Vsu

Claims (1)

[Claims] 1. An electrothermal conversion element capable of both heating and cooling depending on the polarity of the injected current, a temperature-electrical conversion circuit that detects the temperature of the electrical conversion circuit and converts it into an electrical signal, and converts the electrical signal into a reference signal. In a temperature control circuit comprising a comparator circuit for comparison, and a voltage-to-current conversion circuit whose input terminal is connected to the output terminal of the comparator circuit, includes NPN and PNP transistors, and drives the electrothermal conversion element with current, - A temperature control circuit characterized by comprising a voltage-to-current conversion circuit comprising separate voltage level shift circuits inserted between the input terminal of the current conversion circuit and the pace terminal of the NPN and PNP transistors. .