JPH0468812B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention relates to a temperature compensation circuit using thermistors, and in particular, to a temperature compensation circuit using two thermistors, and determining the equivalent value of the temperature when the temperature rises or falls above a certain temperature. The present invention relates to a temperature compensation circuit having a characteristic that resistance increases or decreases.

(b) Problems with the Prior Art FIG. 1 is a diagram showing an example of a temperature compensation circuit using a conventional thermistor, where a represents the circuit diagram and b represents its temperature characteristics. In the figure, R1 and R2 are resistors, respectively, and Th is a thermistor.

As is well known, the resistance value of the thermistor Th decreases as the temperature increases. Therefore, when creating a circuit like a in Figure 1, the relationship between the combined resistance R between terminals α and β and temperature T is as shown in b in Figure 1. Within a certain temperature range, the temperature T increases. At the same time, the combined resistance R decreases approximately linearly, and its slope can be changed by appropriately selecting the resistances R1 and R2. This characteristic was used to perform various types of temperature compensation.

However, in a conventional circuit using only one thermistor as shown in Figure 1a above, the combined resistance R only decreases approximately linearly as the temperature T increases, so it is difficult to perform various temperature compensations. Not enough.

Therefore, a circuit configuration was devised that not only changes the combined resistance linearly, but also changes the tendency of the combined resistance to change at a certain temperature.

FIGS. 2a to 2h are diagrams for explaining the example. In the figure, R3 and R4 are resistors, respectively, and Th is a thermistor.

Now, in a of Figure 2, when a constant voltage is applied between terminals 1 and 2 and the temperature is changed, the relationship between the output voltage V1 between terminals 3 and 2 and temperature T is expressed as b.
Shown below. As the temperature rises, the resistance value of the thermistor Th decreases, and the output voltage V1 decreases.

On the other hand, in c of FIG. 2, a constant voltage is similarly applied between terminals 4 and 5, and the relationship between the output voltage V2 between terminals 6 and 5 and temperature T when the temperature is varied is shown in d. As the temperature increases, the thermistor Th
The resistance value of V2 decreases, and the output voltage V2 increases. At this time, due to the relationship between the resistance values of resistor R3, resistor R4, and thermistor Th, curved points are created in the temperature T and output voltage V1, V2 curves, and broken line characteristics are shown at b, d, etc. in Fig. 2. However, it actually changes along a curve as shown by the dotted line. A broken line is used to clearly indicate changes in characteristics.

If a parallel resistor R5 is attached to the thermistor Th as shown in e of FIG. 2, the output voltage V1 curves in the opposite direction to b as shown in f. Further, when a parallel resistance R5 is attached to the thermistor Th as shown in g in FIG. 2, the output voltage V2 curves in the opposite direction to d as shown in h.

By connecting resistors in series and parallel to one thermistor in this way, it is possible to provide an inflection point in the change in the combined resistance value with respect to temperature. However, in reality, this is still insufficient, and there are cases where it is necessary for the combined resistance value to change from increasing to decreasing or from decreasing to increasing after a certain temperature.

FIG. 3a is a diagram showing an example of a circuit configuration that achieves the above object, in which R6 and R7 are resistors, respectively.
Th1 and Th2 are thermistors, respectively. Third
FIG. 3B is a diagram illustrating the operation of the circuit shown in FIG. 3A.

In Fig. 3a, a constant voltage is similarly applied between terminals 7 and 8, and how the output voltage V3 between terminals 9 and 8 changes depending on the temperature T is calculated in a third manner.
b in the figure shows. That is, when the temperature is low, if the resistance R7 is set to be larger than the value of thermistor Th2, the resistance R7 and thermistor Th2
The amount of change in the combined resistance is the resistance R6 and thermistor Th
1, so as the temperature T increases, the output voltage V3 increases as shown in Figure 3b.
will also increase. However, when a certain temperature is exceeded, the resistance R7
Since the amount of change in the combined resistance of R7 and thermistor Th2 is mainly controlled by the amount of change in thermistor Th2, the amount of change in the combined resistance of resistor R7 and thermistor Th2 is larger than the amount of change in the combined resistance of resistor R6 and thermistor Th1, Output voltage V3 decreases. As a result, characteristics as shown in FIG. 3b are obtained.

FIG. 4a shows another example, and FIG. 4b shows a valley-shaped characteristic, which is opposite to the mountain-shaped characteristic shown in FIG. 3b.

By using two thermistors in this way, connecting a series resistor to one and connecting a parallel resistor to the other, and connecting both in series, it is possible to
As shown in FIG. 4b, a characteristic is obtained in which the combined resistance either increases or decreases when the temperature becomes higher or lower than a certain value. By utilizing this characteristic, it is possible to compensate for the temperature characteristic of a compensated means such as a circuit or a circuit element, which has a characteristic that becomes maximum or minimum at a certain temperature.

However, temperature characteristics can only be compensated using a thermistor circuit having this type of configuration only when the thermistor circuit is effectively used as a bias circuit. That is, the power supply voltage is supplied to both ends of the circuits shown in FIGS. 3a and 4a, and the midpoint (terminal 9 in FIG. 3a,
In Figure 4a, it is effective if the temperature characteristics can be compensated for by taking out the bias voltage from the terminal 12), but this type of bias correction does not compensate for the temperature characteristics of all circuits or circuit elements. Therefore, it is not something that can be compensated for.

For example, a laser diode generally includes a laser element and a photodiode as a monitor element that detects and outputs the optical output of the laser element. When using this laser diode, the optical output of the laser element is detected by a monitor element, and this is fed back to control the optical output of the laser element.

However, the above-mentioned monitor elements often have temperature characteristics such that their detection sensitivity is maximum or minimum at a certain temperature, and even though the optical output of the laser element itself is constant, the detection output of the monitor element fluctuates. However, as a result, the optical output may change. In order to compensate for the temperature characteristics of the detection output of this monitor element, which is impossible with the thermistor circuit of the above configuration, a control circuit with temperature characteristics opposite to that of the monitor element is provided, and the detection output of the monitor element is input to this control circuit. It is necessary to perform temperature compensation and use the corrected output as the detection output for the optical output of the laser element.

However, in the temperature compensation circuit using the thermistor having the above-mentioned conventional configuration, it is not possible to perform temperature compensation of the detection output of the monitor element, which is the means to be compensated and has the above-mentioned temperature characteristics.

(c) Purpose of the Invention Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and provide a temperature compensation circuit using a thermistor that can add a predetermined temperature compensation to an input having temperature characteristics and output the result. With the goal.

(d) Structure of the Invention The above object is achieved by the present invention, which includes a first circuit in which a series resistance is connected to a first thermistor, a second circuit in which a parallel resistance is connected to a second thermistor, a first operational amplifier, and a second circuit in which a series resistance is connected to a first thermistor. the first operational amplifier and the second operational amplifier are connected via the first circuit or the second circuit, and the feedback circuit of the second operational amplifier is connected to the second operational amplifier; or the first circuit, and change the values of the series resistance and parallel resistance to make the temperature characteristics of the circuit opposite in polarity to the temperature characteristics of the compensated means that outputs the input voltage to the first operational amplifier. This is achieved by a temperature compensation circuit using a thermistor characterized by:

(e) Embodiment of the invention FIG. 5 is a diagram showing an embodiment of the invention, and R8 to
R13 is a resistor, and AMP1 and AMP2 are operational amplifiers.

In this example, terminal a1 and terminal a of the operational amplifier, terminal a
By connecting 2 and terminal b, terminal b1 and terminal c, and terminal b2 and terminal d, that is, terminal a
As an input resistance connected between 1 and a2, a series connection circuit of thermistor Th1 and resistor R13, terminal b
By using a parallel circuit of thermistor Th2 and resistor R14 as the feedback resistor connected between 1 and b2, temperature characteristics similar to those shown in FIG. 3b can be obtained.

In addition, by connecting terminals a1 and c, terminals a2 and terminals d, terminals b1 and a, and terminals b2 and b, respectively, a parallel connection circuit of thermistor Th2 and resistor R14 is used as an input resistor, and a thermistor is used as a feedback resistor. By forming a series connection circuit of Th1 and resistor R13, a temperature characteristic similar to that shown in FIG. 4b can be obtained.

By using the temperature compensation circuit of this embodiment configured as described above, it is possible to perform temperature compensation of the means to be compensated such as the monitor element of the laser diode mentioned above.

That is, the temperature characteristics of the temperature compensation circuit with the above configuration are
If the temperature characteristic of the monitor element is set to have an inverse characteristic, and the detection output of the monitor element is inputted to the input terminal IN of the monitor element, it is possible to obtain a corrected output whose temperature characteristic is compensated for by this temperature compensation circuit. Therefore, even if the monitor element has temperature characteristics, an output that compensates for the temperature characteristics can be obtained, so if this is used to control the optical output of the laser element, the laser Erroneous control of the optical output of the element can be prevented.

Incidentally, FIG. 6 shows actual measured values of the temperature characteristics of the temperature thermistor circuit having the configuration shown in FIG. 3a.
As shown, various curves can be obtained by changing the values of the resistors connected in series and in parallel with the thermistor. Therefore, by combining the input resistor and feedback resistor of the two operational amplifiers according to the present invention with the series circuit or parallel circuit of the thermistor and resistor, temperature compensation can be achieved for the output of circuits or circuit elements having various temperature characteristics. It becomes possible to add

(f) Effects of the Invention As explained in detail above, according to the present invention, it is possible to effectively apply temperature compensation to the output of a circuit or circuit element having a mountain-shaped or valley-shaped temperature characteristic. .

[Brief explanation of the drawing]

Figures 1a and b are diagrams showing an example of a temperature compensation circuit using a conventional thermistor, Figures 2a to h are diagrams showing another example of a temperature compensation circuit using a conventional thermistor, Figure 3a , b are diagrams showing an example of a temperature compensation circuit using two conventional thermistors, FIGS. 4a and b are diagrams showing another example of a temperature compensation circuit using two conventional thermistors, and FIG. A diagram showing the configuration of the temperature compensation circuit according to the present invention, FIG.
FIG. 3 is a diagram showing actual measured values of the circuit shown in FIG. In the figure, R1 to R14 are resistances, Th, Th1, Th
2 is a thermistor, and AMP1 and AMP2 are operational amplifiers.

Claims (1)

[Claims] 1 comprising a first circuit in which a series resistance is connected to a first thermistor, a second circuit in which a parallel resistance is connected to a second thermistor, a first operational amplifier and a second operational amplifier, An operational amplifier and a second operational amplifier are connected via the first circuit or the second circuit, and the second circuit or the first circuit is connected to the feedback circuit of the second operational amplifier, and the second operational amplifier is connected in series. A temperature compensation circuit using a thermistor, characterized in that the temperature characteristics of the circuit are made opposite in polarity to the temperature characteristics of a compensated means that outputs an input voltage to a first operational amplifier by changing the values of a resistance and a parallel resistance.