GB2366627A

GB2366627A - Method and apparatus for temperature control

Info

Publication number: GB2366627A
Application number: GB0022229A
Authority: GB
Inventors: Lee Smethurst
Original assignee: Bookham Technology PLC
Current assignee: Lumentum Technology UK Ltd
Priority date: 2000-09-11
Filing date: 2000-09-11
Publication date: 2002-03-13
Also published as: GB0101749D0; GB2366629A; GB0022229D0

Abstract

A circuit 200 configured to refine the control of a device temperature, comprising: means 202 for sensing a temperature of the device; and means 204, 206 for varying a current supplied to a heat source 116 or heat exchanger packaged within the device, by an associated temperature controller 100, in accordance with the sensed temperature. This invention provides an apparatus and method for controlling the temperature of a device to remain within a narrower range, with regard to a desired temperature than is currently achievable. This is achieved by means of an additional control circuit which may be utilised alongside currently available systems.

Description

2366627 METHOD AND APPARATUS FOR TEMPERATURE CONTROL This invention

relates to the control of temperature. More specifically, this invention relates to the control of the.temperature of electrical, electronic or optical devices in order to provide high levels of stability to those devices.

Optical devices and analogous electrical and electronic devices often require to be operated under very stable temperature conditions. When heating alone is used to correct the temperature of operation, the temperature of the 10 device is usually set to be a little higher than the ambient temperature. For example, the operating temperature may be 75'C for a device operating in an external environment which temperature ranges from OC to 70'C. When a thermo electric cooler is used, the operating temperature may be either side of ambient.

Often, the temperature of such a device must be controlled to remain within 0.20C of the required temperature of operation (i.e. 750C), and preferably within 0.10C. In addition to this, the temperature control system must be able to accommodate wide and rapid external fluctuations within the ambient temperature 20 range.

At present, the control of the temperature of a device, for the sake of example, an optical device, is achievable within a range of approximately:L-1'C of the temperature required for the correct operation of the device. Such a degree of 25 control is acceptable for a device comprising optical waveguides formed in silica (Si02) on a substrate of silicon (Si), for example.

However, the above degree of control is insufficient for the control of the temperature of optical devices comprising optical waveguides formed in silicon.

30 Such devices include arrayed waveguide gratings used in multiplexers and demultiplexers for use in dense wavelength division multiplexing (DWDM), for example. If such a degree of control is utilised, the temperature will deviate too far from the ideal operating temperature of the device, and degradation in the performance of the device will ensue. There is thus a problem in the provision of a sufficient degree of control for optical devices utilising silicon waveguides and the like, and analogous electrical and electronic systems which require a similarly stable operating temperature.

With the foregoing in mind, the present invention aims to provide a finer degree of temperature control than is currently available utilising prior art temperature control circuitry and apparatus. This invention provides a means of improving the sensitivity of temperature control of an already installed temperature

10 control device.

In accordance with the present invention, there is provided a circuit configured to refine the control of a device temperature, comprising:

means for sensing a temperature of the device; and 15 means for varying a current supplied to a heat source or heat exchanger, packaged within the device, by an associated temperature controller, in accordance with the sensed temperature.

The use of such a circuit provides the ability to fine tune a current supplied 20 to a heater or heat source which is utilised to control the temperature of a device with which it is packaged. Such fine tuning enables the temperature of the device to be controlled to be within a range which is much narrower than that which is achievable with many installed systems.

25 In accordance with a preferred embodiment of the present invention the means for sensing a temperature comprises one or more resistive temperature detectors (RTD) or thermistors.

Preferably, the means for sensing the temperature of the device is 30 packaged within the device. Preferably, the circuit is packaged with the associated temperature controller and is connected thereto. Alternatively, the circuit may be packaged with the device which temperature is to be controlled.

In accordance with a preferred embodiment of the present invention, the means for varying the current supplied comprises:

a temperature control circuit -connected to the means for sensing a temperature of the device; and 5 a current degradation circuit connected to the input of the heat source or heat exchanger packaged within the device.

Preferably, the temperature control circuit comprises either a Proportional Integral (PI) controller or a Proportional Integral Differential (PID) controller.

In accordance with a further preferred embodiment of the present invention, the current degradation circuit comprises means for bleeding away a proportion of the current that is supplied to the heat source by the associated temperature controller. The proportion of that current which is bled away will depend upon the sensed temperature.

Also in accordance with the present invention there is provided a method of controlling and refining a temperature controller, thereby providing greater control of the temperature of a device requiring strict temperature control, comprising:

20 utilising a temperature control circuit to control the current provided, by the temperature controller, to a heat source or a heat exchanger packaged with the device, thereby narrowing the achievable range of control of the device from a first range to a second range.

25 Preferably, the first range is about VC around a desired temperature.

Preferably, the second range is about 0.2"C around a desired temperature. Still more preferably, the second range is about 0.1C around a desired temperature.

Preferably, the desired temperature is higher than ambient temperature and typically 75C for a resistive heater system.

A specific embodiment of the present invention is now described, by way of example only, with reference to the accompanying drawings, in which:Figure I is a representation of.a prior art temperature control system;

5 Figure 2 is a block diagram illustrating a temperature control system in accordance with the present invention; and Figure 3 is a circuit diagram illustrating one realisation of the system of Figure 2.

10 Figure 1 shows a prior art temperature control circuit, which is currently available, suitable for controlling the temperature of devices to within 1 OC of a required temperature. This circuit is suitable for the control of devices such as optical waveguides created in silica POO on a substrate of silicon (Si), and is currently utilised therefor.

The prior art temperature controller 100 comprises two temperature sensors

102 in the form of resistive temperature detectors (RTDs) or thermistors connected in series between a positive voltage supply rail and ground. The temperature sensors 102 are packaged with a device which temperature requires control. The 20 sensors 102 are connected to the positive input of a first operational amplifier 104, the output of which is connected to the negative input thereof, and to a second operational amplifier 106 via a resistance (R1) 108. Typically a digital to analog converter (D/A) 110 is connected to the positive input of the second operational amplifier 106. The digital to analog converter may be within a source of reference 25 voltage (not shown) comprised within or connected to the prior art circuit. Thus, a reference voltage is provided therethrough to the second operational amplifier.

The output of the second operational amplifier 106 is fed back, via a resistance (R2) 112, to the negative input thereof, and is also connected to the 30 base of a bipolar junction transistor 114. The collector of the transistor is connected to the positive voltage supply rail and the emitter of the transistor 114 is connected to ground via a heat source or heater 116. The heat source or heater is also packaged with the device which temperature requires controlling.

The controller 100 is a proportional differential type control circuit which senses a temperature of a device and utillses a reference voltage to create a current to drive a heater in order to balance a sensed temperature and a required 5 temperature. However, wavelength drift due to ambient temperature fluctuations prevents such a controller from achieving an accuracy of control of any greater than 10C, as has already been stated.

With reference to Figure 2 of the accompanying drawings, a temperature 10 controller 200 according to the present invention comprises a number of elements which, when combined with a prior art temperature controller 100, provide a narrower band of control to a device which requires temperature control. These elements include temperature sensor means 202 which are preferably one or more resistive temperature detectors (RTDs). A combination of two such

15 detectors is known to provide greater sensitivity than a single such detector. However, other devices such as one or more thermistors may equally be applied. The elements referred to above further include a temperature control circuit 204 and a current degradation circuit 206.

20 These circuit elements may be located in different manners. For example, the temperature control circuit 204 and current degradation circuit 206 may be packaged with the device which temperature is to be controlled. Alternatively, they may be external thereto. However, the temperature sensor means 202 must be located within the device requiring control. For example, if the control system for 25 the present invention is to be utilised in an optical device comprising waveguides formed in silicon (Si), the temperature sensor means 202 should be located on the silicon (Si) itself. A further alternative location configuration is the packaging of the respective elements with a prior art control system, which may or may not be packaged with the device.

The operation of the system of the present invention will now be described. A prior art temperature controller 100 is utilised to provide a coarse temperature control, i.e. within VC of a desired temperature of a device. Utilising the previous example, the controller 100 provides a current to its associated heater or heat source 116 to retain the device temperature within the range 75:t 1 OC. The system of the present invention operates alongside the prior art controller 100 to subtract a proportion of the current supplied to the heat source 116. The amount 5 of current subtracted depends upon the temperature sensed by the system 200. This provides fine tuning to the temperature controller 100, thus enabling control of the device within a range of:t 0. 1 C of a required temperature, e.g. 75 0. 1 OC.

To clarify this point further, as the device temperature drops below a 10 desired temperature, a current is supplied to a heat source located within the device in order to counteract the drop. This current provides control within VC of the desired temperature. As the temperature increases toward the desired temperature + 0. 1 "C, current is drawn away from the heat source by the system of the present invention to prevent that temperature being exceeded. Similarly, as 15 the temperature drops toward the desired temperature - 0.1"C, the current drawn away from the heat source is reduced and may be made zero, in order that the device temperature does not drop therebelow.

A specific realisation of the system 200 of the present invention is now 20 described with reference to Figure 3 of the drawings. As may be seen, the circuit 300 comprises all of the elements of the system, as described above. The first of these, the temperature sensor means 202, is depicted as a sub-module of the circuit 300. The temperature sensor means 202 is in the form of a resistive temperature detector (RTD) 302 which is connected between ground and a 25 positive voltage supply, via a resistance 304. The RTD may have a resistance of approximately 100Q at OOC. The resistance 304 may be of approximately 1.2kQ. The positive voltage supply is provided by a voltage reference source, which may be a MAX6025 source produced by Maxim. The voltage supply is of approximately 2.5v in magnitude.

Connected to the sensor 302 and the positive voltage supply via the resistance 304, is a first operational amplifier 306. This connection is made via the operational amplifier's positive input. The output of the first operational amplifier is connected to the negative input thereof, to a negative input of a second operational amplifier 308 via a resistance 310, which may be of approximately 100ko, and to the positive input of a third operational amplifier 312, via a resistance 314, which may be of approximately 20kQ. All operational amplifiers 5 within the circuit shown in Figure 3 may be LM6248 operational amplifiers produced by National Semiconductors.

Returning to the second operational amplifier 308, the positive input thereof is connected to the negative input of a fourth operational amplifier 316, the output 10 of which is fed back to the negative input thereof, and is also connected to the positive input of the third operational amplifier 312, via a resistance 318, which may be of approximately 20kQ. The positive input of the fourth operational amplifier 316 is connected to a moveable contact of a variable resistance 320. The variable resistance 320 is connected between the positive voltage supply and 15 ground. The variable resistance 320 thereby provides a reference voltage to the positive input of the fourth operational amplifier 316, the magnitude of which depends upon the location of the moveable contact.

Returning again to the second operational amplifier 308, the output thereof 20 is fed back via a capacitance 322, which may be of approximately 22PF, to the negative input thereof. The output is also connected, via a resistance 324, which may be of approximately 20kf), to the negative input of the third operational amplifier 312.

25 The output of the third operational amplifier 312 is fed back to the negative input thereof via a resistance 326, which may be of approximately 68kc). It is also connected to the current degradation sub-module 206.

The current degradation sub-module 206 comprises a depletion or 30 enhancement mode metal oxide semi-conductor field effect transistor (DE

MOSFET) 328, the gate of which is connected to the output of the third operational amplifier 312. The drain of the DE MOSFET 328 is connected or connectable to the input of a heat source 116 associated with a temperature control circuit 100, via a resistance 330, which may be of approximately 1000, providing coarse control to a device, and the source is connected either to ground or to a negative voltage supply rail. The MOSFET may be a MTD20NO6HDL MOSFET produced by Motorola.

As will be appreciated, the above circuit 300 comprises proportional 301a, adder 301b and integral 301c elements and as such is based upon a PI- type control circuit. The circuit 300 utilises a reference voltage to balance a temperature sensed by RTD 302 with a required temperature defined by 10 resistance 320 and produces an output representative of the requirements to achieve the desired balance. The output is supplied to the gate of the MOSFET 328 which is thus caused to draw current away from the heat source 106 associated with the temperature controller 100. This current is intended to drive the heat source 106, but by the drawing off of a proportion thereof, over- 15 compensation by the temperature controller is prevented and temperature control within a narrower band, i.e. 74.90C to 75.1 OC, is achievable.

The amount of current bled away from the heat source is proportional to the output of the temperature sensor 302 and the output characteristics of the 20 MOSFET. The MOSFET output characteristics dictate that the drain current increases exponentially as the voltage applied across the gate and source increases. Therefore, as the sensed temperature increases, a larger voltage will be applied across the gate and source of the MOSIFET, thereby causing a larger current to be drawn off by the drain of the MOSFET.

It will be appreciated that, although this invention has been described with reference to a particular configuration of temperature control circuit, it is equally applicable to any control circuit utilising a current to drive a device intended to compensate for variations of a specific quality around a desired value thereof, and 30 these are therefore within the scope of this invention as defined by the claims.

Additionally, although this invention has been described with reference to the provision of heat to a device in order to control its temperature, it applies equally to the removal of heat, i.e. cooling. For example, if a device requires to be controlled to operate at a temperature below OOC and the ambient temperature ranges from OC to 30'C, a heat exchanger may be provided in the place of the heat source described. The heat exchanger may be triggered to remove heat from 5 the device by the provision of a current configured to restore a balance of a sensed temperature and a required temperature.

It will of course be understood that this invention has been described above by way of example only, and that modifications of detail can be made within the 10 scope of this invention.

Claims

1 A circuit configured to refine the control of a device temperature, comprising:

means for sensing a temperature of the device; and means for varying a current supplied to a heat source or heat exchanger, packaged within the device, by an associated temperature controller, in accordance with the sensed temperature.

10

2. A circuit as claimed in claim 2, wherein the means for sensing a temperature comprises one or more resistive temperature detectors (RTDs) or thermistors.

3. A circuit as claimed in either of claims 1 or 2, wherein the means for sensing the temperature of the device is packaged with the device.

4. A circuit as claimed in any preceding claim, wherein the circuit is packaged with the associated temperature controller, and is connected thereto.

5. A circuit as claimed in any preceding claim, wherein the circuit is packaged with the device which temperature is to be controlled.

6. A circuit as claimed in any preceding claim, wherein the means for varying the current supplied comprises:

a temperature control circuit connected to the at least one temperature sensor; and a current degradation circuit connected to the input of the associated controller heat source or heat exchanger packaged within the device.

30

7. A circuit as claimed in claim 6, wherein the temperature control circuit comprises either a Proportional Integral (PI) controller or a Proportional Integral Differential (PID) controller.

8. A circuit as claimed in either of claims 6 or 7, wherein the current degradation circuit comprises means for bleeding away a proportion of the current that is supplied to the heat source by the associated temperature controller.

9. An optical device comprising a circuit according to any preceding claim.

10. An optical device as claimed in claim- 9, wherein the device is an arrayed waveguide grating, a multiplexer or a demultiplexer.

10

11. A method of controlling and refining a temperature controller, thereby providing greater control of the temperature of a device requiring strict temperature control, comprising:

utilising a temperature control circuit to control the current provided, by the temperature controller, to a heat source or a heat exchanger packaged with the 15 device, thereby narrowing the achievable range of control of the device from a first range to a second range.

12. A method as claimed in claim 11, wherein the first range is about t VC around a desired temperature.

13. A method as claimed in either of claims 11 or 12, wherein the second range is about - 0.2C around a desired temperature.

14. A method as claimed in either of claims 11 or 12, wherein the second range is about t 0. 1 OC around a desired temperature.

15. A method as claimed in any of claims 12 to 14, wherein the desired temperature is approximately 750C.

16. A circuit substantially as hereinbefore described with reference to and as shown in Figures 2 and 3 of the accompanying drawings.

17. A method substantially as hereinbefore described with reference to and as shown in Figures 2 and 3 of the accompanying drawings.