JP4715469B2 - Wavelength conversion laser temperature control circuit - Google Patents

Description

  The present invention relates to a wavelength conversion laser temperature control circuit. More specifically, the present invention relates to a wavelength conversion laser capable of avoiding a decrease in the life of a Peltier device and reducing the circuit scale and operating with a single polarity and low voltage power source. The present invention relates to a temperature control circuit.

A “wavelength conversion laser” that controls the temperature of a resonator including a semiconductor laser and a nonlinear optical crystal in order to keep the light output stable is known (see, for example, Patent Document 1).
On the other hand, there is known an “electronic device drive circuit” that drives the Peltier element by controlling the ratio of the direction of the current flowing through the Peltier element by controlling the duty ratio of the periodic pulse that drives the Peltier element. (For example, refer to Patent Document 2).
Furthermore, a “low saturation output amplifier circuit” using a grounded emitter voltage amplifier circuit is known (see, for example, Patent Document 3).
JP-A-8-171106 Japanese Patent Laid-Open No. 5-204470 JP 2001-177358 A

In the conventional “wavelength conversion laser”, a specific example of the temperature control circuit is not disclosed.
On the other hand, the conventional “electronic device driving circuit” has the following problems.
(1) Although the direction of the current passed through the Peltier element is periodically switched, such frequent switching causes a decrease in the life of the Peltier element.
(2) Since a pulse generation circuit is required, the circuit scale increases. Further, if the circuit for determining the duty ratio of the periodic pulse is a digital circuit, control is performed using a programmable element, so that the circuit becomes large in terms of scale and cost.
(3) On the other hand, if the circuit for determining the duty ratio of the periodic pulse is an analog circuit, a bipolar power source is required, which is not suitable for a portable wavelength conversion laser in which the power source used is a battery.
SUMMARY OF THE INVENTION An object of the present invention is to provide a wavelength conversion laser temperature control circuit that can avoid a decrease in the life of a Peltier element and that can be operated with a single-polarity and low-voltage power supply, with a small circuit scale. is there.

  In a first aspect, the present invention is a circuit for driving a Peltier element (Q) for controlling the temperature of an optical resonator including a semiconductor laser of a wavelength conversion laser and a nonlinear optical crystal, and corresponds to a target temperature. An analog arithmetic circuit (A1) that operates with a single polarity power supply of 3 V or less based on a deviation voltage and a bias voltage (V-ref), which is a difference between the voltage (V-set) and a voltage (V-mon) corresponding to the measured temperature , A 2, A 3, A 4), a biased differential amplifier circuit pair (10) that performs proportional gain amplification and integral gain amplification, a voltage (V−P) that performs the proportional gain amplification, and a voltage that performs the integral gain amplification Based on (V-I ') and the bias voltage (V-ref), the voltage (V-I) integrated with the analog arithmetic circuit (A5) operating with a single polarity power supply of 3 V or less and the bias voltage (V -ref) based on PI control voltage A biased PI control circuit (20) that outputs V-PI) and a collector output type pair of PNP bipolar transistors (TR2, TR4) based on the control voltage (V-PI) and bias voltage (V-ref). A wavelength conversion laser temperature control circuit (100) comprising: a TEC drive circuit (30) for changing the direction of a current flowing through the Peltier element (Q) by performing a complementary operation on the low-saturation output stage of provide.

The wavelength conversion laser temperature control circuit (100) according to the first aspect is based on an analog arithmetic circuit of a PI control method based on a low-voltage bias voltage (V-ref) located approximately in the middle of the supply voltage (Vin). The control voltage (V-PI) controls the magnitude of the voltage (V-TEC-, V-TEC +) applied to the Peltier element (Q) and the direction of the current flowing through the Peltier element (Q). This eliminates the need to periodically switch the direction of the current flowing through the Peltier element (Q), thereby avoiding a decrease in the life of the Peltier element (Q). Further, since a pulse generation circuit and a digital circuit are not required, the circuit scale can be reduced. Further, by using a collector output type low-saturation output stage (LDO; Low-Drop-Out) with PNP-type bipolar transistors (TR2, TR4), the Peltier element (Q) can reach a voltage substantially equal to the supply voltage (Vin). It can be applied and can be operated with a single polarity and low voltage power source, ie a battery.
Note that PI control enables high-precision tracking to the target temperature, and accurate temperature control can be performed even in a wide use environment temperature range of about −10 ° C. to 50 ° C. outdoors. .

  According to the wavelength conversion laser temperature control circuit of the present invention, the life of the Peltier element can be avoided, the circuit scale can be reduced, and the power supply can be operated with a single polarity and a low voltage.

  Hereinafter, the present invention will be described in more detail with reference to embodiments shown in the drawings. Note that the present invention is not limited thereby.

FIG. 1 is a block diagram of a wavelength conversion laser temperature control circuit 100 according to the first embodiment.
The wavelength conversion laser temperature control circuit 100 includes a biased differential amplifier circuit pair 10, a biased PI control circuit 20, and a TEC (ThermoElectricCooler) drive circuit 30.
The TEC is a thermo module that controls the temperature of an optical resonator including a semiconductor laser of a wavelength conversion laser and a nonlinear optical crystal, and includes a Peltier element Q and a temperature sensor M. The temperature sensor M is, for example, a thermistor.
The wavelength conversion laser temperature control circuit 100 operates with the supply voltage Vin from the battery B.

In the biased differential amplifier circuit pair 10, the deviation voltage “V-set−V” which is the difference between the voltage “V-set” corresponding to the target temperature and the voltage “V-mon” corresponding to the measured temperature detected by the temperature sensor M. The biased differential amplifier circuit 11 for the P control is multiplied by the proportional gain “m” by adding the bias voltage “V-ref” to the “−mon”, and the P control output voltage “V-P” is output. In addition, the biased differential amplifier circuit 12 for I control multiplies the voltage obtained by adding the bias voltage “V-ref” to the deviation voltage “V-mon-V-set” whose polarity is changed, and the integral gain is multiplied by “n”. Output the previous voltage "V-I '".
As will be described later, the bias voltage “V-ref” is a reference voltage that determines the magnitude of the drive voltage “V-TEC−, V-TEC +” applied to the Peltier element Q and the direction of the current flowing through the Peltier element Q. It is.

In the biased PI control circuit 20, the I control output voltage “V-I” obtained by integrating the pre-integration voltage “V-I ′” in the biased integration circuit 21 and the P control output voltage “V-P” are added, and extra. By subtracting the added bias voltage “V-ref”, the control voltage “V-PI” is output.
Note that the biased integrating circuit 21 can be easily configured as an inverted type by using a pair of deviation voltages whose polarity is changed in the biased differential amplifier circuit pair 10.

  In the TEC drive circuit 30, the control voltage “V-PI” and the bias voltage “V-ref” are compared by the low saturation output circuit 31, and the drive voltages “V-TEC-” and “V-TEC +” are compared according to the comparison result. Is output.

FIG. 2 is a specific example of the biased differential amplifier circuit pair 10 and the biased PI control circuit 20.
The amplifiers A1 to A5 are analog arithmetic circuits that operate with a single polarity power supply of 3V or less.
In the biased differential amplifier circuit pair 10, the amplifiers A1 and A3 constitute a biased differential amplifier circuit 11 for P control.
V-P = m (V-set-V-mon) + V-ref (1)
It is.
The amplifiers A2 and A4 form a biased differential amplifier circuit 12 for I control.
V-I '= n (V-mon-V-set) + V-ref (2)
It is.

In the biased PI control circuit 20, the amplifier A 5 constitutes a biased integration circuit 21. By applying inversion type integration using the bias voltage “V-ref” to the equation (2),
V-I = 1 / (Cl.R2) .∫ {n (V-set-V-mon)} dt + V-ref (3)
It is.
By adding equations (1) and (3) and subtracting the bias voltage “V-ref”,
V-PI = m (V-set-V-mon) + 1 / (C1.R2) .∫ {n (V-set-V-mon)} dt + V-ref (4)
It is.

  The integral term in equation (4) indicates that the deviation voltage “V-set−V-mon” increases as the deviation between the voltage corresponding to the target temperature and the voltage corresponding to the measured temperature increases. The control voltage “V-PI” is changed in the direction of decreasing “V-set-V-mon”.

FIG. 3 is a specific example of the TEC drive circuit 30.
The amplifiers A6 to A9 are analog arithmetic circuits that operate with a single polarity power supply of 3V or less.
The supply voltage Vin to the transistors TR2, TR4, TR5 and TR7 is a single polarity power supply of 3V or less.

When the measured temperature is higher than the target temperature, the control voltage “V-PI” becomes smaller than the bias voltage “V-ref”, so that the output voltage of the amplifier A6 swings to the supply voltage side, and the amplifier A7 , The output voltage of the amplifier A8 becomes close to “L”, and the output voltage of the amplifier A9 becomes “H”. As a result, the transistors TR1 and TR2 are turned on by dropout corresponding to the output voltage of the amplifier A6, the transistors TR7 and TR8 are turned on, the transistors TR3, TR4, TR5 and TR6 are cut off, and the drive voltage “V-TEC -"Becomes the voltage according to the output voltage of the amplifier A6, the drive voltage" V-TEC + "becomes almost 0, and the drive current flows from the" V-TEC- "side to the" V-TEC + "side in the Peltier element Q .
When a drive current flows from the “V-TEC-” side to the “V-TEC +” side in the Peltier element Q, the Peltier element Q absorbs heat. Thereby, control temperature (measurement temperature) falls and it approaches target temperature.

When the measured temperature is lower than the target temperature, the control voltage “V-PI” becomes larger than the bias voltage “V-ref”, so that the output voltage of the amplifier A6 is swung to the 0 side, and the amplifier A7 The output voltage changes to the supply voltage side, the output voltage of the amplifier A8 becomes “H”, and the output voltage of the amplifier A9 becomes “L”. As a result, the transistors TR3 and TR4 are turned on by dropout corresponding to the output voltage of the amplifier A7, the transistors TR5 and TR6 are turned on, the transistors TR1, TR2, TR7 and TR8 are cut off, and the drive voltage “V-TEC -"Becomes almost 0, the drive voltage" V-TEC + "becomes the voltage according to the output voltage of the amplifier A7, and the drive current flows from the" V-TEC + "side to the" V-TEC- "side in the Peltier element Q .
When a drive current flows from the “V-TEC +” side to the “V-TEC-” side in the Peltier element Q, the Peltier element Q generates heat. As a result, the control temperature (measured temperature) rises and approaches the target temperature.

  In the low saturation output circuit 31, since the transistors TR2 and TR4 in the output stage are collector output types of PNP bipolar transistors, the base can be driven with a voltage lower by 0.6V than the supply voltage Vin. As a result, the saturation voltage between the emitters and collectors of the transistors TR2 and TR4 can be reduced as compared with a circuit in which Darlington connection is performed using NPN bipolar transistors. That is, it can be avoided that a large dropout occurs at the output stage and the voltage applied to the Peltier element Q is insufficient, and a voltage close to the supply voltage Vin can be applied to the Peltier element Q. Accordingly, it is possible to operate with a single polarity and low voltage power source.

According to the wavelength conversion laser temperature control circuit 100 of the first embodiment, the following effects can be obtained.
(1) Since it is not necessary to periodically switch the direction of the current flowing through the Peltier element Q, it is possible to avoid a decrease in the life of the Peltier element Q.
(2) Since no pulse generation circuit or digital circuit is required, the circuit scale can be reduced.
(3) By using a collector output type low saturation output stage with PNP type bipolar transistors TR2 and TR4, a voltage substantially equal to the supply voltage Vin can be applied to the Peltier element Q. It becomes possible to operate.
(4) By adopting PI control, it is possible to follow the target temperature with high accuracy, and accurate temperature control can be performed even in a wide use environment temperature range of about -10 ° C to 50 ° C outdoors.

  The wavelength conversion laser temperature control circuit of the present invention can be used for a portable battery-driven wavelength conversion laser.

1 is a configuration block diagram illustrating a wavelength conversion laser temperature control circuit according to Embodiment 1. FIG. 3 is a circuit diagram illustrating a specific example of a biased differential amplifier circuit pair and a biased PI control circuit of the wavelength conversion laser temperature control circuit according to the first embodiment. FIG. FIG. 3 is a circuit diagram illustrating a specific example of a TEC drive circuit of the wavelength conversion laser temperature control circuit according to the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Biased differential amplifier circuit pair 20 Biased PI control circuit 30 TEC drive circuit 100 Wavelength conversion laser temperature control circuit A1-A9 Analog arithmetic circuit TR2, TR4 PNP type bipolar transistor Vin Supply voltage

Claims (1)

A circuit for driving a Peltier element (Q) for controlling the temperature of an optical resonator including a semiconductor laser of a wavelength conversion laser and a nonlinear optical crystal,
P control output with proportional gain amplification of the voltage obtained by adding the bias voltage (V-ref) to the deviation voltage , which is the difference between the voltage (V-set) corresponding to the target temperature and the voltage (V-mon) corresponding to the measured temperature a voltage (V-P) first the biased differential amplifier circuit for outputting (11), a voltage obtained by adding a bias voltage (V-ref) to said difference voltage obtained by rearranging the polarity and integral gain amplifier, before integration A biased differential amplifier circuit pair (10) comprising a second biased differential amplifier circuit (12) for outputting a voltage (V-I ') ;
The I control output voltage (V-I) obtained by integrating the voltage (V-I ') after the integral gain amplification by the biased integration circuit (21) is added to the voltage (V-P) after the proportional gain amplification. and, by subtracting the bias voltage (V-ref), comprising a the biased PI control circuit (20) for outputting a control voltage for the PI control (V-PI),
The first biased differential amplifier circuit (11), the second biased differential amplifier circuit (12), and the biased integrator circuit (21) are derived from an analog arithmetic circuit that operates with a single polarity power supply of 3V or less. Configured,
Depending on the sign of the difference between the control voltage (V-PI) and the bias voltage (V-ref) , one of a pair of collector output type low-saturation output stages using PNP-type bipolar transistors (TR2, TR4) is selected. A wavelength conversion laser temperature control circuit (100) comprising a TEC drive circuit (30) that changes the direction of a current flowing through the Peltier element (Q) by performing a complementary operation.

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