JPH0421110A - Accurate temperature control device - Google Patents

Abstract

PURPOSE:To obtain a compact device hardly influenced by noise and capable of easily executing arithmetic processing by driving a heating/cooling means based upon an output signal from a crystal temperature (temp.) sensor and highly accurately controlling the temp. of an object to be controlled. CONSTITUTION:Output signal from a reference oscillator 3 and an oscillator 2 are beaten down by a mixer 4. Then, the output signal of the mixer 4 is multiplied by a certain number and a difference between the frequency bands of the reference oscillator 3 is found out, beaten down and inputted to a frequency counter 8 through an LPF 7. A CPU 11 inputs data from the counter 8, calculates a current temp. based upon a set sensor coefficient, compares the calculated current temp. with an objective temp., and drives a Peltier element 9 by PID control. Namely, the direction and size of the current inputted to the element 9 can be controlled and the object to be controlled can be set up to the objective temp. value. Thus, the temp. of the object to be controlled can be highly accurately controlled over a long period, arithmetic processing can easily be executed and the device can be made compact.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a precision temperature control device used in fields where extremely high precision temperature control is required, such as temperature control of LDs for optical communications, etc. The present invention relates to a precision temperature control device that uses a heating/cooling element such as a Beltier element to heat and cool an object to be temperature controlled to control its temperature.

(Prior Art) In recent years, as electronics technology has become more sophisticated, there has been a strong demand for stabilization of output signals from semiconductor elements and the like. In particular, in a laser diode that outputs laser light for the purpose of coherent communication, it is necessary to stabilize the temperature within a range of approximately ±5/1000° C. in a normal temperature atmosphere.

Conventionally, in order to control the temperature of the laser diode as mentioned above, a thermistor was used as a temperature sensor.
The output value of this thermistor is compared with a predetermined target value, and the Beltier element is driven based on the comparison result, and heat is generated in the Beltier element.

Temperature control devices that perform absorption are known. The temperature control device using this thermistor sensor is
Since the thermistor sensor can be easily miniaturized, the entire control device can be miniaturized, which has the advantage that the entire system can be miniaturized.

(Problem to be Solved by the Invention) However, in the temperature control device using the thermistor sensor as described above, the temperature drift of the thermistor sensor is extremely large, and the temperature of the laser diode can be controlled with high accuracy over a long period of time. This made it difficult to perform highly reliable coherent communication. Furthermore, since the thermistor sensor outputs a level signal, it has the disadvantage that it is susceptible to noise and is difficult to perform arithmetic processing on.

The present invention was made in view of these circumstances, and
The purpose of the present invention is to provide a compact precision temperature control device that can control the temperature of a temperature-controlled object with high precision over a long period of time, has an output signal from a sensor that is not easily affected by noise, and is easy to process. It is something.

(Means for Solving the Problems) The precision temperature control device of the present invention uses a crystal temperature sensor as a temperature sensor, and drives a heating and cooling means based on an output signal from the crystal temperature sensor to increase the temperature of a temperature controlled object. It is characterized by highly accurate control. That is, the precision temperature control device of the present invention includes a crystal temperature sensor that measures the temperature of a temperature-controlled object and outputs a frequency signal according to the measured temperature, and a crystal temperature sensor that adjusts the frequency of the output signal of the crystal temperature sensor at a predetermined timing. A counter that counts with
a calculation means for determining the current temperature of the temperature controlled object based on the pressure from the counter and outputting a signal according to the difference between the current temperature and the target temperature; and a calculation means for controlling the temperature based on the output signal from the calculation means. The apparatus is characterized by comprising a heating and cooling means for heating or cooling the temperature controlled object so that the temperature of the object becomes the target temperature.

(Function) According to the above configuration, a crystal temperature sensor is used as the temperature sensor. Crystal temperature sensors have extremely high accuracy and stability, and in particular, temperature drift over time is about two orders of magnitude smaller than that of thermistors. Further, since the output signal of the crystal temperature sensor is a frequency signal, it is more resistant to noise than a thermistor which uses a level signal as an output signal, and it is extremely easy to perform digital processing using a CPU or the like afterwards. Furthermore, extremely small crystal temperature sensors have recently been developed, which are comparable to the case where a thermistor is used as a temperature sensor in terms of miniaturizing the device.

Note that conventional crystal temperature sensors were large and had poor accuracy compared to current ones, so it was unthinkable to use such crystal temperature sensors for temperature control of laser diodes for coherent communication. However, in recent years, the size of crystal temperature sensors has been significantly reduced and the accuracy has improved, so the inventors of the present application focused on this point and created the present invention.

(Embodiments) Hereinafter, embodiments of the precision temperature control device of the present invention will be described with reference to the drawings. The device in this drawing is a temperature controlled object (
A crystal oscillator 1 that measures the current temperature of a laser diode for coherent communication, and an oscillator 2 that outputs a signal with a frequency corresponding to the measured value of this oscillator 1. ), a reference oscillator 3 that outputs a constant frequency wave with a frequency slightly higher than the average frequency of the output signal from the oscillator 2;
A mixer 4 beats down the output signal from the oscillator 2 by taking the difference in frequency between the output signal from the oscillator 2, a multiplier 5 that multiplies the output signal from the mixer 4, and an output signal from the multiplier 5 and the reference oscillator 3. A mixer 6 beats down the output signal from the multiplier 5 by taking the frequency difference between the two, a low-pass filter 7 cuts high-frequency components of the output signal from the mixer 6, and the frequency of the signal passing through the low-pass filter 7 is counted. A frequency counter 8 that calculates how much the current temperature of the temperature controlled object deviates from the target temperature based on the count value read by the counter 8,
After this, the CP calculates the drive current to the Peltier element 9 in order to set the temperature controlled object to the target temperature, and outputs digital data corresponding to this current value to the D/A converter 10.
A Peltier element 9 that heats and cools the temperature controlled object according to the drive current based on the output data from the UII and the CPU II.
and circuit sections such as a rectifier circuit 12 for applying a drive current to the Peltier element 9, a transformer 13, and a switch circuit 14.

The above-mentioned crystal oscillator 1 changes the resonant frequency according to temperature changes, and uses a crystal plate cut out by the Y-cut method, and the temperature coefficients of the first, second, and third orders are each, for example, 7.802X. 10'/”C.

1.048 XIO°END/'C2 and 1.091 X
10-''/'C3. Table 1 shows the specifications of this crystal oscillator 1.

Table 2 The oscillation circuit 2 described above is for oscillating the frequency signal from the crystal oscillator 1, and its specifications are shown in Table 2. Note that the distance from the crystal oscillator 1 to this oscillation circuit 2 is 15 cm or more.

As shown in the table, the crystal temperature sensor consisting of the crystal oscillator 1 and oscillation circuit 2 has an aging characteristic (change over time) of ±0.0.
Excellent, less than 1℃/year, and oscillation frequency is 25~30MH
Since the frequency displacement per 1 degree Celsius in z is 80 ppm or more, high resolution can be ensured.

Further, the multiplier 5 is extremely compact and includes an amplifier section made of a UB type HCMOS logic IC and an LC filter. The reason for providing this multiplier 5 is as follows. That is, as mentioned above, depending on the crystal temperature sensor, 80 ap at a frequency of 25 to 30 MHz.
A change of H/”C or more can be obtained. For example, at 25MHz, 8
At 0 ppm/'C, the change is 2 KHz/°C. When this frequency is counted by the frequency counter 8, in the case of a 1 second gate (1/2000) 'C becomes the resolution of 1 count. However, when performing temperature control with high precision, it is necessary to set the gate to about (1/10) seconds.
If you use the above signal as is, the resolution of 1 count will be (
1/200)°C, the original signal frequency is multiplied by 9 using this multiplier 5, and even at the (1/10) second gate, the resolution of one count is (1/1g).
QQ) ``C is secured.

Further, the mixer 4.6 performs a subtraction process between the output signal frequency from the oscillator 2 or the multiplier 5 and the output signal frequency from the reference oscillator 3 to perform beatdown. That is, the output signal frequency from the oscillator 2 described above is as high as 25 to 30 MHz, and if this frequency is further multiplied by 9, digital ICs such as the frequency counter 8 used for signal processing will become expensive. Therefore, beatdown is performed using the output signal from the reference oscillator 3 to increase the amount of change. As a result, signal processing can be performed without using an expensive digital IC, and the causes of errors can be minimized and the actual sensitivity can be improved. In addition, in order to minimize the cause of error, a highly stable crystal oscillator (-1
±0 at 0 to +40°C. O4ppm) is used.

Furthermore, DBM (double balanced modulator) is used as the mixers 4 and 6 mentioned above.

Next, the arithmetic processing by the CPU II mentioned above will be explained. This CPU II receives data from the frequency counter 8 and sets sensor coefficients (reference temperature, frequency data at reference temperature).

The current temperature is calculated based on the first-order and second-order frequency temperature coefficients, etc.). This calculated current temperature is compared with the target temperature, and PID control is performed based on the comparison result. P
ID constants and the like are input from a keyboard connected to the CPU II. Thereafter, the digital data obtained by PID control is converted by the D/A converter 10 into an analog quantity for driving the Beltier element 9.

In addition, the above-mentioned Bertier element 9 heats and cools the temperature controlled object, and whether heating or cooling, that is, heat release or heat absorption, is determined by the direction of the input current, and the amount of heat released or absorbed. is proportional to the magnitude of the current.

Therefore, by controlling the direction and magnitude of the current input to this Beltier element 9 and controlling the amount of heating and cooling of the temperature-controlled object by the Beltier element 9, it is possible to set the temperature-controlled object to the target temperature value. It becomes possible. Note that since the internal resistance value of the Beltier element 9 also changes due to temperature changes, it is necessary to drive the Beltier element 9 with a constant current source in order to further improve temperature control.

In the device of this embodiment, in order to achieve miniaturization and high efficiency, the constant current source is constructed using a switching method as shown in the drawings. Further, in response to the polarity reversal of the polarity signal output from the CPU II, the direction of the driving current of the Beltier element 9 is reversed by the high power FET 16, so that the current can be sent to the Beltier element 9 with high resolution. In addition,
In order to obtain this drive current, a rectifier circuit 12, a transformer 13, and a switching FET element 14 are provided.

In this way, this example device uses a small crystal temperature sensor with excellent stability and accuracy, and uses a method that beats down the detection signal and then multiplies it to improve resolution and shorten the measurement time interval, resulting in high accuracy. This makes it ideal as a temperature control device for laser diodes intended for coherent communication.

Note that the above-described embodiment apparatus can be modified in various configurations. For example, if the use does not require beatdown processing or multiplication processing, it is also possible to omit the mixer 4.6, the reference oscillator 3, the multiplier 5, etc. Further, when a multiplier 5 is provided, an optimal value may be selected as the multiplier.

Although the present invention is primarily intended for use in temperature control of laser diodes for coherent communication,
Of course, it is also possible to use it for other precision temperature control, such as temperature control of a laser diode used as a light source other than coherent communication, temperature compensation of an IC, or gas flow rate control.

(Effects of the Invention) As explained above, according to the precision temperature control device of the present invention, since a crystal temperature sensor is used as the temperature sensor, it is possible to control the temperature of the temperature controlled object with high precision over a long period of time. This makes it possible to increase the S/N ratio of the output signal from the sensor, facilitate calculation processing, and downsize the device.

[Brief explanation of drawings]

The drawing shows a circuit port showing a precision temperature control device according to an embodiment of the present invention. 1... Crystal oscillator 3... Reference oscillator 5... Multiplier 8... Frequency counter 10... D/A converter 2... Oscillator 4.6... Mixer 7... Low-pass filter 9...Peltier element 11...CPU

Claims (1)

[Claims] A crystal temperature sensor that measures the temperature of a temperature-controlled object and outputs a frequency signal according to the measured temperature, and a counter that counts the frequency of the output signal of the crystal temperature sensor at a predetermined timing. , calculation means for calculating the current temperature of the temperature controlled object based on the output from the counter and outputting a signal corresponding to the difference between the current temperature and the target temperature; A precision temperature control device comprising: heating and cooling means for heating or cooling a temperature controlled object so that the temperature of the controlled object becomes the target temperature.