EP0376787B1 - Temperature controller for the characteristics of an integrated circuit - Google Patents

Description

The present invention relates to a device for controlling the temperature of monolithic integrated circuits, more particularly those which are produced on fast materials of group III-V such as GaAs.

The temperature behavior of circuits made on III-V substrates is one of the important parameters for the user. It must therefore be taken into account by the designer of the circuit, either by providing an accessible control electrode, or by producing on the circuit a device making it possible to correct the variations as a function of the temperature of the characteristic or characteristics of the circuit to be stabilized. .

In the prior art, methods external to the circuit are described, whether it is a question of regulating the ambient temperature, or of a servo comprising a variable element depending on the temperature, generally correcting a parameter of the circuit by a voltage. .

This is the case, for example, of the voltage temperature control system described in patent GB-A-960,015. The temperature variation is detected by a bridge in which two resistors have a variable value with temperature, but this system, intended for ferrite core memories, is not integrated into the circuit it controls.

US-A-4,723,108 describes a system integrated on the chip of the circuit to be checked, but its principle is different from that of the present invention.

According to this document, a first current mirror uses the threshold voltage variation of a transistor as a temperature detector, to provide at the output of a second current mirror, a single variable voltage which makes it possible to act to compensate for the effects of temperature variation.

The temperature control device according to the invention associates the control circuit with the circuit to be stabilized, in a single circuit produced in a homogeneous integrated circuit technology, microwave on Gallium Arsenide for example. The manufacture of the two circuits side by side on the same substrate uses the standard stages of the technological process of the integrated circuit sectors. The temperature is detected directly on the substrate and is used to control a correction voltage.

This technology must include at least two types of resistive elements, with different temperature coefficients. It is then possible to produce a divider bridge associating these two types of elements, capable of supplying a variable voltage as a function of temperature. The device to be monitored must itself have the possibility of compensating for its thermal drifts with a DC voltage, such as, for example, the gate bias voltage to control the gain of a field effect transistor amplifier.

More precisely, the invention relates to a device for controlling the temperature of the characteristics of an integrated circuit, carried by a substrate, this device, produced on the same substrate as the circuit to be stabilized, being characterized in that it comprises a divider bridge formed by four resistors (R₁ - R₄), supplied between two stable voltages (DC₁ - DC₂), these resistors being, in groups of two (R₁ + R₄), (R₂ + R₃) mounted diagonally from the bridge, opposite temperature coefficients, and delivering at their midpoints (A, B) two control voltages, which move in opposite directions with temperature.

• figure 1 : schéma électrique du détecteur intégré sur la pastille de circuit intégré,
• figure 2 : schéma électrique d'une structure différentielle fournissant des tensions complémentaires fonction de la température,
• figure 3 : courbes de résistances en fonction de la température, pour les capteurs de mesure
• figure 4 : courbes de réponses de la structure de la figure 2, en fonction de la température.

The invention will be better understood from the more detailed description which now follows of an exemplary embodiment, in conjunction with the attached figures which represent:

• Figure 1: electrical diagram of the integrated detector on the integrated circuit chip,
• Figure 2: electrical diagram of a differential structure providing additional voltages as a function of temperature,
• figure 3: resistance curves as a function of temperature, for measurement sensors
• Figure 4: response curves of the structure of Figure 2, as a function of temperature.

The measurement sensor of the control device according to the invention comprises two resistors R1 and R2 mounted as a voltage divider bridge, supplied at its two terminals by external DC voltage generators, stable in temperature, DC1 and DC2; one of these two voltages can be in OV potential of the circuit (ground).

avec
T₀ = 20°C
R₁₀ = R₁ pour T = 20°C
De même :

$\text{R₂ = [1 + α₂ (T-T₀)] R₂₀}$

Pour simplifier les expressions, posons

${\text{β}}_{\text{T}}\text{= 1 + α₁ (T-T₀)}$

${\text{γ}}_{\text{T}}\text{= 1 + α₂ (T-T₀)}$

   La tension de sortie Vc1 du pont diviseur est variable en fonction de la température, et permet de contrôler le circuit.Resistors R1 and R2 have different thermal coefficients α1 and α2. The variation in resistance as a function of temperature can be written:

$\text{R₁ = [1 + α₁ (T - T₀)] R₁₀}$

with
T₀ = 20 ° C
R₁₀ = R₁ for T = 20 ° C
Similarly:

$\text{R₂ = [1 + α₂ (T-T₀)] R₂₀}$

To simplify the expressions, let’s pose

${\text{β}}_{\text{T}}\text{= 1 + α₁ (T-T₀)}$

${\text{γ}}_{\text{T}}\text{= 1 + α₂ (T-T₀)}$

The output voltage Vc1 of the divider bridge is variable according to the temperature, and allows to control the circuit.

Soit un transistor à effet de champ, dont la dérive en température peut être compensée en modifiant sa tension grille de OV (à 80°C) à -0,3 V (à -40°C).

$\text{T₁ = - 40°C → VC1 (T₁) = -0,3 V}$

$\text{T₂ = + 80°C → VC1 (T₂) = 0V}$

On peut écrire :

   Le choix de la valeur de DC1 permet de calculer la valeur de DC2 et le rapport des résistances R1 et R2 . La valeur de ces résistances est déterminée par la consommation acceptable dans le circuit contrôlé par rapport à la consommation dans le circuit de commande.The calculation of the resistances of the divider bridge is done using the following equations:

Or a field effect transistor, whose temperature drift can be compensated by modifying its gate voltage from OV (at 80 ° C) to -0.3 V (at -40 ° C).

$\text{T₁ = - 40 ° C → VC1 (T₁) = -0.3 V}$

$\text{T₂ = + 80 ° C → VC1 (T₂) = 0V}$

We can write :

The choice of the value of DC1 makes it possible to calculate the value of DC2 and the ratio of the resistors R1 and R2. The value of these resistors is determined by the acceptable consumption in the controlled circuit compared to the consumption in the control circuit.

The values of the supply voltages DC1 and DC2 can then be used as a posterior adjustment means of the temperature control device.

Let us now consider a complete control device, sensor and shaping circuit, of such differential structure as shown in FIG. 2: it is integrated into the same chip of semiconductor material as the circuit to be controlled in temperature. The temperature, detected directly on the substrate, is used to control the gain of a differential structure providing additional voltages which are functions of temperature.

Thus, an amplifier can be stabilized by controlling a stage of this amplifier with automatic gain control. A bigrille field effect structure can also be controlled if the control voltage is applied to the second grid. An oscillator can be stabilized in temperature by applying a control voltage to a varactor in the circuit. Other applications may be concerned from the moment when the controlling voltage can be applied to a gate of a transistor or else to a diode.

The differential structure of Figure 2 has two parts: a first part which detects temperature variations and a second part which formats the signal intended for the control of the circuit to be controlled in temperature.

The temperature variations are detected with a resistance bridge balanced at T₀ (20 ° C for example) and which provides a voltage proportional to the temperature as it varies. This bridge is formed on the one hand by the resistors R1 and R2, supplied between DC1 and the ground, and on the other hand the resistors R3 and R4, supplied in the same way. The bridge resistors have opposite temperature coefficients, mounted diagonally.

Resistors R1 to R4 have the same value at T₀ but opposite temperature coefficients: R1 and R4 have the same coefficient and are made for example of titanium (positive temperature coefficient), while R2 and R3 are made for example of tantalum and have a negative temperature coefficient, opposite to that of R1 and R4. The variations of these resistances, with temperature, are shown in Figure 3.

In this type of bridge, the potentials at midpoints A and B, equal to the equilibrium at T₀, move in opposite directions, which increases the value of the output signal.

The second part of the device is a differential structure with transistors. The load of the two channels is active and can therefore be adapted to the circuit to be temperature compensated.

The transistors T2 and T3 are supplied, through the current source T1, between DC1 and ground: the unbalance voltages at points A and B of the resistance bridge are applied to the gates of T2 and T3. The load transistors T4 and T7 are used to obtain the correct operating point at T₀. The transistors T 5 and T6, controlled by the voltages DC3 and DC4, make it possible to control the gain of this differential circuit as a function of the circuit to be stabilized. The output voltages are supplied at points V2 and V3, common to T2 / T5 and T3 / T6 respectively. The voltage V2, applied for example to the gate of a transistor of the circuit to be controlled - which is integrated on the same chip - makes it possible to stabilize it the characteristics if the temperature changes.

The response of the circuit, as a function of the temperature, is given in FIG. 4. The curves V2 and V3 (solid line) correspond to a balanced response because DC3 = DC4. We can move the balance by varying one of the DC3 or DC4 voltages, which then gives, for example, the dotted curve V3: DC3 ≠ DC4.

The simplified differential structure presented on the diagram of principle can be designed more completely so as to obtain a response V2 or V3 linear, parabolic, logarithmic, etc ... according to the circuits to stabilize. The diagrams of these shaping circuits are known art in logic design.

The advantage of this new device is its full compatibility with the stages of production of the microwave channels. The circuit is small and can be installed alongside a transistor or a varactor in the microwave circuit to be stabilized in temperature.

Claims (3)

1. Device for the temperature control of the characteristics of an integrated circuit, carried by a substrate, this device, made on the same substrate as the circuit to be stabilized being characterized in that it includes a divider bridge formed by four resistors (R₁ - R₄), which is fed between two stable voltages (DC₁ - DC₂), these resistors having, in groups of two mounted on the diagonals of the bridge (R₁ + R₄) (R₂ + R₃), with opposite temperature coefficients, and delivering at their midpoints (A, B) two control voltages which evolve in opposite directions with temperature.
2. Device according to Claim 1, characterized in that it furthermore includes a differential circuit for shaping the control signals, formed by two first transistors (T₂, T₃) and their load transistors (T₄, T₇), fed with the measurement bridge feed voltages (DC₁, DC₂), by means of a current source (T₁), the unbalancing voltages of the bridge being applied to the gates of the two first transistors (T₂, T₃) and the output voltages (V₂, V₃) being gathered at the common points between the first transistors (T₂, T₃) and their load transistors (T₄, T₇).
3. Device according to Claim 2, characterized in that, in order to adjust the gain of the differential circuit on the basis of the integrated circuit to be stabilized, it furthermore includes two adjusting transistors (T₅, T₆) mounted in parallel with the load transistors (T₄, T₇), adjusting voltages (DC₃, DC₄) being applied to the gates of the adjusting transistors (T₅, T₆).

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