Temperature controlling apparatus and oscillation apparatus

It is desired to even further attempt to stabilize temperature in oscillator such as OCXOs (Oven Controlled Crystal Oscillators). A temperature controlling apparatus is provided. The temperature controlling apparatus includes: a temperature sensor; a power supply circuit that supplies, to a first heater, power corresponding to a difference between a target value and a detected value obtained from the temperature sensor; and a second heater that is provided at a position such that thermal conduction therefrom to the temperature sensor is faster than that from the power supply circuit, and changes power consumption of the second heater according to power consumption of the power supply circuit.

The contents of the following Japanese patent application(s) are incorporated herein by reference:NO. 2017-061975 filed on Mar. 27, 2017.

BACKGROUND

1. Technical Field

The present invention relates to a temperature controlling apparatus and an oscillation apparatus.

2. Related Art

An oscillator using a crystal blank or the like has an oscillation frequency that varies depending on temperature. Because of this, there is an OCXO (Oven Controlled Crystal Oscillator) that keeps temperature constant by incorporating a heat source in the oscillator (please see Patent Document 1, for example). Because the OCXO attains approximately constant temperature of a crystal blank even if the ambient temperature varies, it can keep the oscillation frequency constant, independent of the temperature characteristic of the crystal blank. Accordingly, OCXOs are in some cases used to generate reference clocks of communication infrastructures (backbone networks, wireless base stations, etc.) that require stricter frequency accuracy than that of TCXOs (Temperature Compensated Crystal Oscillators).

Patent Document 1: Specification of United States Patent Application Publication No. 2016/0285460

It is desired to even further attempt to stabilize temperature in oscillators such as OCXOs like the one explained above.

SUMMARY

Therefore, it is an object of an aspect of the innovations herein to provide a temperature controlling apparatus and an oscillation apparatus, which are capable of overcoming the above drawbacks accompanying the related art. The above and other objects can be achieved by combinations described in the claims. A first aspect of the present invention provides a temperature controlling apparatus including: a temperature sensor; a power supply circuit that supplies, to a first heater, power corresponding to a difference between a target value and a detected value obtained from the temperature sensor; and a second heater that is provided at a position such that thermal conduction therefrom to the temperature sensor is faster than that from the power supply circuit, and changes power consumption of the second heater according to power consumption of the power supply circuit.

A second aspect of the present invention provides an oscillation apparatus including: the temperature controlling apparatus according to the first aspect; and an oscillation circuit controlled to be at a target temperature by the temperature controlling apparatus.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1shows a first configuration example of an oscillation apparatus100according to the present embodiment. The oscillation apparatus100includes an oscillation circuit200and a temperature controlling apparatus300. The oscillation apparatus100controls, by means of the temperature controlling apparatus300, the oscillation circuit200to be at a target temperature, and oscillates the oscillation circuit200at a predetermined target oscillation frequency. The oscillation apparatus100is an OCXO (Oven Controlled Crystal Oscillator), as one example.

The oscillation circuit200oscillates a resonator by supplying oscillation energy, and outputs, to the outside, an oscillation frequency signal. The oscillation circuit200may have a resonator connected outside an integrated circuit400, and the resonator may be provided with a crystal blank or the like between two electrodes. The oscillation frequency of the oscillation circuit200may vary according to the temperature of the oscillation circuit200.

The temperature controlling apparatus300controls the oscillation circuit200to be at a target temperature, and adjusts variation in the oscillation frequency of the oscillation circuit200. The temperature controlling apparatus300has a temperature sensor310, a power supply circuit320, a first heater330and a second heater340.

The temperature sensor310may detect the internal temperature of the oscillation apparatus100, the temperature of the oscillation circuit200or the temperature of the first heater330, and output a sense voltage corresponding to the detected value. The temperature sensor310may detect the temperature around a crystal blank of the oscillation circuit200or the first heater330, for example. The temperature sensor310may be a temperature sensor device incorporated into the integrated circuit400, and may be a diode, for example.

The power supply circuit320is connected to the temperature sensor310, and outputs power corresponding to the difference between the detected value obtained from the temperature sensor310and a target value. The power supply circuit320has a target setting circuit322, a difference circuit324and a current output circuit326.

The target setting circuit322outputs a target value corresponding to a target temperature. The target setting circuit322can set the target temperature of the oscillation circuit200at the time of factory shipment or according to a user input, for example, and outputs a voltage or current corresponding to the target temperature.

The difference circuit324may have a negative input connected to the target setting circuit322and a positive input connected to the temperature sensor310. The difference circuit324may amplify and output the difference between the target value obtained from the target setting circuit322and the detected value obtained from the temperature sensor310. The difference circuit324may be a differential amplifier circuit, as one example.

The current output circuit326may have a first transistor327, and the first transistor327may have the gate connected to an output of the difference circuit324, and the source and drain respectively connected between a power source potential VDD, and the first heater330and the second heater340. The current output circuit326outputs, to the first heater330and the second heater340, current corresponding to an output of the difference circuit324. The current output circuit326may increase output current if detected temperature is lower than the target temperature, and decrease output current if detected temperature is higher than target temperature. The first transistor327may be a bipolar transistor, a power MOSFET or a power transistor such as an IGBT, for example.

The first heater330is connected between an output of the current output circuit326and a reference potential, and is supplied, from the current output circuit326, with power corresponding to the difference between the detected value obtained from the temperature sensor310and the target value. The reference potential may be a ground potential VSS, for example. The first heater330is arranged near the oscillation circuit200, and for example is arranged very close to a resonator of the oscillation circuit200or is arranged such that a plurality of the first heaters330sandwich a resonator. The first heater330may consume power from the current output circuit326to generate heat, thereby controlling the oscillation circuit200to be at the target temperature. The first heater330may be any heater as long as it generates heat by current being flowing therethrough, and may have a transistor such as an NMOS transistor or a PMOS transistor, for example. Also, the first heater330may be a metal wire or the like such as a nichrome wire. The first heater330may not be included in the temperature controlling apparatus300.

The second heater340is connected between an output of the current output circuit326and a reference potential, and connected to the power supply circuit320in parallel with the first heater330. The second heater340is provided at a position such that thermal conduction therefrom to the temperature sensor310is faster than that from the power supply circuit320, and changes power consumption of the second heater340according to power consumption of the power supply circuit320. The second heater340consumes power according to the difference between the detected value obtained from the temperature sensor310and the target value, and generates heat. The second heater340has a second transistor342that has: the drain and source that are connected between an output of the current output circuit326and a reference potential; and the gate connected on the side of the output of the current output circuit326. The second transistor342may be a MOS transistor, a bipolar transistor or the like. If the second transistor342is a bipolar transistor, the emitter, collector and base are connected corresponding to the source, drain and gate. As one example, in the oscillation apparatus100of the first configuration example, the second transistor342is an NMOS transistor, and in this case, the reference potential is the ground potential VSS.

The oscillation apparatus100of the present embodiment can suppress, by means of the second heater340, thermal hunting (thermal oscillation) in which heat-generation of the current output circuit326is inevitably detected by the temperature sensor310. Also, because suppression of thermal hunting is realized only by adding the second heater340constituted by one type of transistor or the like, the area for the second heater340does not require much space, and wiring also can be minimized because complicated wire connections are not necessary. Also, the oscillation apparatus100requires no more than a solid ground pattern with a single wire allowing large current to flow through the first heater330and the second heater340. As a result of this, it is possible to prevent heat from escaping, which may result in unstable heat control, as observed if extra and excessive conductivity patterns are prepared, and heat control becomes more stable.

Here, thermal hunting is explained in detail.FIG. 2shows an oscillation apparatus500of a comparative example. The oscillation apparatus500of the comparative example does not include the second heater340in the oscillation apparatus100of the present embodiment.

First, because the first transistor327supplies current to flow through the first heater330, the first transistor327itself generates heat. Accordingly, as shown inFIG. 2, the temperature sensor310receives heat from the first transistor327and heat from the first heater330. Here, if temperature detected by the temperature sensor310is low, in order to raise the temperature of the first heater330, the power supply circuit320increases current to flow through the first transistor327, and increases current to flow through the first heater330. At this time, in the region indicated with broken lines A inFIG. 4, current of the first transistor327increases, but the inter-source-drain voltage of the first transistor (the inter-emitter-collector voltage in the case of a bipolar transistor) lowers; therefore, the power consumption of the first transistor327decreases, and the amount of heat to be transferred from the first transistor327to the temperature sensor310decreases. Because as a result of this, the amount of heat that the temperature sensor310receives from the first transistor327decreases before the amount of heat that the temperature sensor310receives from the first heater330increases, the temperature sensor310might detect a temperature fall at least temporarily. Accordingly, if in the temperature controlling apparatus300, the amount of current to flow through the first transistor327is increased to raise the temperature, a positive feedback occurs in which the temperature detected by the temperature sensor310lowers, and furthermore current to flow through the first transistor327is inevitably increased.

Specifically, it is assumed that in the oscillation apparatus500of the comparative example, the power source voltage is Vdd [V], the voltage of the output terminal IOUT of the current output circuit326is Vo [V], the amount of output current that flows through the current output circuit326and the first heater330is Io [A], and the resistance of the first heater330is Rh [Ω]. In this case, the voltage Vo of the output terminal IOUT is expressed by the equation Vo=Rh×Io. Also, the power Pt [W] and Ph [W] consumed by the current output circuit326and the first heater330are expressed as follows:
Pt=Io(Vdd−Vo)=Io(Vdd−Rh×Io)  (Equation 1)
Ph=Vo×Io=Rh×Io2(Equation 2)

Accordingly, the internal temperature Ti [° C.] of the oscillation apparatus500when it is heated by the output current Io is expressed as follows if it is assumed that the package thermal resistance (the thermal resistance between the integrated circuit400and the first heater330, and the outside air) of the oscillation apparatus500is θa [° C./W], and the ambient temperature is Ta [° C.]. It is assumed that temperature increase of the integrated circuit400all approximates the one due to current Io.
Ti=Ta+θa(Pt+Ph)=Ta+θa×Io×Vdd(Equation 3)

As a specific example, it is assumed that in the oscillation apparatus500of the comparative example, Vdd=3 V, Rh=10Ω, θa=150° C./W and Ta=−40° C.FIG. 3shows internal temperature [° C.] of the oscillation apparatus500, power consumption Pt [W] of the current output circuit326, and power consumption Ph [W] of the first heater330in relation to output current of the current output circuit326.FIG. 4shows power consumption Pt [W] of the current output circuit326.

As shown inFIGS. 3 and 4, along with increase in the output current, the internal temperature and the power consumption of the first heater330increase, but the region A of a negative slope (the range where output current is 150 to 300 mA inFIGS. 3 and 4) occurs to the power consumption of the current output circuit326. The region A is one of causes of thermal hunting. The region A shown inFIG. 4shows that if output current of the current output circuit326is increased to heat the oscillation circuit200, heat-generation of the current output circuit326decreases. This shows that, neglecting heat-generation of the first heater330outside the package of the integrated circuit400and considering only the current output circuit326, the thermal feedback loop system becomes a positive feedback.

Also, a second cause of thermal hunting is that the speed of thermal conduction to the temperature sensor310is slower for the first heater330than for the current output circuit326.

As shown inFIG. 2, the first heater330is connected outside, a substrate and the like are arranged in a thermal conduction path to the temperature sensor310, and this inhibits thermal conduction from the first heater330to the temperature sensor310. Therefore, it takes time for heat to reach from the first heater330to the temperature sensor310. On the other hand, because the thermal conduction path from the current output circuit326to the temperature sensor310is thermal conduction within the single integrated circuit400, the thermal conduction is fast. The stability of the thermal feedback loop system in such an oscillation apparatus500is shown using an AC analysis simulation result using specific numerical values.

Respective simulation conditions are as follows: the power source voltage Vdd=3 V; the resistance Rh of the first heater330=10Ω; the package thermal resistance θa of the oscillation apparatus500=150° C./W, the ambient temperature Ta=−40° C.; and the output current Io=200 mA. The conditions are equivalent to conditions where thermal hunting occurs (region A) inFIG. 4. In this case, the internal temperature of the oscillation apparatus500is:
Ti=−40° C.+150° C./W×(3V×200 mA)=50° C.

Furthermore, in addition to these conditions, it is assumed about the time constants of thermal conduction that the thermal conduction time constant of thermal conduction from the current output circuit326to the temperature sensor310is τt=10 ms, and the thermal conduction time constant of thermal conduction from the first heater330to the temperature sensor310is τh=10 s. Also, parameters of the temperature controlling apparatus300are as follows: the gain of the temperature sensor310=10 mV/° C. (positive temperature characteristic); the gain of the difference circuit324=60 dB; and the transconductance gm of the current output circuit326=800 mA/V. In the oscillation apparatus500, a thermal feedback loop, output of the temperature sensor310→control of the current output circuit326→change in the output current Io→detection by the temperature sensor310→output of the temperature sensor310→ . . . , is formed.FIG. 5shows an open-loop gain characteristic and phase characteristic of the thermal feedback loop.

As shown inFIG. 5, the gain characteristic has two poles. The first pole corresponds to the thermal conduction time constant=10 s of thermal conduction from the first heater330, and is observed at the frequency 16 mHz (=1/(2π+10 s)). The second pole corresponds to the thermal conduction time constant=10 ms of thermal conduction from the current output circuit326, and is observed at the frequency 16 Hz (=1/(2π×10 ms)). InFIG. 5, the phase of frequency where gain=0 dB is −90 deg. That is, the phase margin is −90 deg, and this indicates that thermal hunting occurs.

Here, normally, the phase lag caused by one pole is 90°. However, the phase lag due to pole=16 mHz ofFIG. 5is not 90° but 180°. This is because about frequency components exceeding 16 mHz, the gain of a negative feedback path from the first heater330to the temperature sensor310decreases, and then the positive feedback path from the current output circuit326to the temperature sensor310becomes dominant. Because the negative feedback for DC frequency turns the positive feedback after 16 mHz, this is equivalent to the phase being lagged by 180° (=the polarity reverses).

Under the above-mentioned conditions, a transient response simulation of output current and internal temperature was performed.

FIG. 6shows a transient response simulation result of output current of the current output circuit326.FIG. 7shows a transient response simulation result of internal temperature of the oscillation apparatus500. At the time of the simulation, the upper limit of output current of the current output circuit326was set to 1 A. As shown inFIGS. 6 and 7, it can be seen that both output current and internal temperature did not stabilize, and thermal hunting occurred. In the thermal hunting, the current output circuit326shows a behavior of periodically switching ON/OFF.

As a reference, the gain characteristic and phase characteristic in a case where the respective conditions are as follows were investigated: the power source voltage Vdd=3 V; the resistance Rh of the first heater330=10Ω; the package thermal resistance θa of the oscillation apparatus500=150° C./W, the ambient temperature Ta=−40° C.; and the output current Io=100 mA. In this case, the internal temperature of the oscillation apparatus500is:
Ti=−40° C.+150° C./W×(3V×100 mA)=5° C.
The condition of Io=100 mA is a region where thermal hunting does not occur (a region outside the region A) inFIG. 4.

FIG. 8shows an open-loop gain characteristic and phase characteristic of a thermal feedback loop under the reference conditions. InFIG. 8, the phase margin is 90 deg, and this indicates that the system is stable. Also, inFIG. 8, change from a negative feedback to a positive feedback (180°−phase lag) at pole=16 mHz did not occur either.

Here, in the oscillation apparatus100of the present embodiment shown inFIG. 1, the second heater340can attain a thermal feedback which is a negative feedback and improve the temperature stability by compensating change in power consumption corresponding to decrease in power of the current output circuit326of the power supply circuit320. For example, if the power supply circuit320increases power supplied to the first heater330, and power consumption of the power supply circuit320decreases, the second heater340preferably keeps constant or increases (un-decreases) the total power consumption of the power supply circuit320and the second heater340.FIG. 9shows power of the current output circuit326, power of the second heater340, and their total power in the oscillation apparatus100of the present embodiment. As shown inFIG. 9, by compensating, with the power of the second heater340, the region of the power of the current output circuit326after the peak and where the slope becomes negative, the slope of the total power can be made positive or zero after the peak. Thereby, it is possible to prevent the power of the current output circuit326from decreasing irrespective of the output current being increased and to prevent the thermal feedback from inevitably turning a positive feedback, which are causes of thermal hunting.

In the oscillation apparatus100according to the present embodiment inFIG. 1, the temperature sensor310, the power supply circuit320, the second heater340and the oscillation circuit200may be provided in the single integrated circuit400, and the first heater330may be connected outside the integrated circuit400. Because thermal conduction time constant also affects temperature stability, in comparison with thermal conduction from the current output circuit326, thermal conduction from the second heater340preferably reaches the temperature sensor310simultaneously or faster, for the sake of temperature stabilization. Because the temperature sensor310, the power supply circuit320and the second heater340provided in the single integrated circuit400are linked in a single substrate, thermal conduction time constants of the second heater340and the power supply circuit320become approximately the same. Also, in terms of thermal conduction time constant, the second heater340is more preferably arranged closer to the temperature sensor310than the power supply circuit320is. The integrated circuit400may be an LSI, a multi-chip module, or the like.

Here, operation of the oscillation apparatus100of the present embodiment is as follows: according to detected temperature of the temperature sensor310, current of the current output circuit326increases, voltage of the output terminal IOUT rises, gate voltage of the second heater340rises, the amount of current from the drain of the second heater340to its source increases, and the amount of heat generation of the second heater340increases. That is, according to increase in current of the current output circuit326, the amount of heat generation of the second heater340also increases. Therefore, by appropriately selecting parameters, it is possible to make the slope of the total power of the current output circuit326and the second heater340always positive in relation to increase in current of the current output circuit326. In the following, one example of parameters for making the slope of the total power positive is shown with a simulation result using the oscillation apparatus100of the present embodiment.

The conditions of the oscillation apparatus100are as follows: the power source voltage Vdd=3 V; the resistance Rh of the first heater330=10Ω; the package thermal resistance θa of the oscillation apparatus100=150° C./W; the ambient temperature Ta=−40; the thermal conduction time constant τt of thermal conduction from the current output circuit326to the temperature sensor310=10 ms; the thermal conduction time constant τnd of thermal conduction from the second heater340to the temperature sensor310=10 ms; the thermal conduction time constant τh of thermal conduction from the first heater330to the temperature sensor310=10 s; the gain of the temperature sensor310=10 mV/° C. (positive temperature characteristic); the gain of the difference circuit324=60 dB; the transconductance gm of the first transistor327of the current output circuit326=800 mA/V; and the threshold Vth of the second transistor342of the second heater340=0.65 V.

The results of simulation under these conditions are shown inFIGS. 10 to 13.

FIG. 10shows a relationship between output current of the current output circuit326and gate voltage of the second heater340(NMOS). Current of the current output circuit326is branched into the first heater330and the second heater340, and the NMOS gate voltage of the second heater340monotonically increases as the amount of current of the current output circuit326increases.

FIG. 11shows current of the first heater330and current of the second heater340in relation to output current of the current output circuit326. As current of the current output circuit326increases, the NMOS gate voltage Vg of the second heater340rises, and current of the second heater340increases. Also, current from the current output circuit326is divided into current the amount of which is proportional to the square of (Vg−Vth) and which flows to the second heater340and the rest of the current which flows to the first heater330. By attaining a relationship of current like the one shown inFIG. 11, the second heater340can make its power consumption smaller when current flows therethrough than the first heater330does when current flows therethrough. Thereby, with the first heater330, it is possible to control the oscillation circuit200to be at a target temperature efficiently. That is, because by arranging the first heater330very close to an external resonator, and making the power of the first heater330higher than the power of the second heater340, heat from the first heater330can be kept from escaping to the other portions and transferred to the external resonator, so the external resonator can be controlled to be at a target temperature.

FIG. 12shows power consumption of the current output circuit326, power consumption of the second heater340, and the total power of them in relation to output current of the current output circuit326. Power consumption of the current output circuit326increases and has a positive slope at an initial period during which the amount of current is small, and shows a negative slope at the latter half (the region where ≥200 mA). On the other hand, power consumption of the second heater340is increasing along with increase in the amount of current of the current output circuit326. Thereby, the total of power consumption of the current output circuit326and power consumption of the second heater340shows a positive slope over the entire region. Accordingly, in the oscillation apparatus100according to the present embodiment, the thermal feedback becomes stable, and thermal hunting can be prevented.

Next, a second configuration example of the oscillation apparatus100according to the present embodiment is explained.FIG. 13shows a second configuration example of the oscillation apparatus100according to the present embodiment. Explanation of configurations which are approximately the same as the configurations of the oscillation apparatus100of the first configuration example shown inFIG. 1is omitted. The oscillation apparatus100of the second configuration example is the same as the oscillation apparatus100of the first configuration example in terms of configurations and operation. However, a second heater344has a PMOS transistor346, and the PMOS transistor346has the drain and source connected between an output of the current output circuit326and the power source potential VDD. Also, the first heater330is connected between an output of the current output circuit326and the power source potential VDD, and a current output circuit328has an NMOS transistor329having the drain and source connected between the ground potential VSS, and the first heater330and the second heater344. The NMOS transistor329may be a bipolar transistor, a power MOSFET or a power transistor such as an IGBT.

In the oscillation apparatus100of the second configuration example, according to sense voltage of the temperature sensor310, output current of the power supply circuit320increases, power consumption of the first heater330increases, voltage at the output terminal IOUT lowers, current flowing through the PMOS transistor346increases, and the second heater340generates heat. Thereby, the oscillation apparatus100of the second configuration example can suppress thermal hunting. Also, the oscillation apparatus100of the second configuration example requires no more than a solid power source pattern with a single wire allowing large current to flow through the first heater330and the second heater344. As a result of this, it is possible to prevent heat from escaping, which may result in unstable heat control, as observed if extra and excessive conductivity patterns are prepared, and heat control becomes more stable.

In the oscillation apparatus100according to the present embodiment, values of sense voltage of the temperature sensor310may have a positive or negative slope in relation to temperature. The temperature sensor310may be connected to an input of the difference circuit324with the polarity thereof being switched depending on whether the temperature sensor310shows a positive slope or a negative slope. For example, in the oscillation apparatus100of the first configuration example, if the temperature sensor310shows a negative slope, an output of the temperature sensor310may be connected to a negative input of the difference circuit324, and on the other hand, an output of the target setting circuit322may be connected to a positive input.