ES2471671A1 - Differential temperature sensor with immunity to thermal interferences - Google Patents

Abstract

The invention relates to an electronic circuit designed so as to be built into a semiconductor crystal that can provide an electric magnitude at the output thereof depending on the temperature difference between two areas of the surface of said semiconductor crystal, simultaneously demonstrating a high rejection of potential thermal interferences from other areas of the same crystal. Figure 1 shows the graphical representation of the electronic circuit. It has two supply inputs (5) and (6), and a node (1) as an output. Furthermore, the figure shows various internal devices (2), (3), and (4), the temperatures of which directly influence the value of the electric magnitude of the output node.

Description

DIFFERENTIAL TEMPERATURE SENSOR WITH IMMUNITY A THERMAL INTERFERENCES

Technical sector

The present invention relates to an electronic circuit with electrical output magnitude dependent on the temperature difference of two zones of the semiconductor crystal in which it is integrated, and which at the same time presents a great rejection of possible thermal interference from other areas of the same crystal The sector of the technique to which it refers is that of electronic instrumentation for measuring temperature in integrated circuits.

State of the art

In the sector of the electronic instrumentation technique there are so-called differential temperature sensors [1]. They are circuits with applications in the realization of temperature measurements in integrated circuits. Its operation is that the output voltage (or current) varies proportionally to the temperature difference of two of its devices, called temperature transducers. These sensors are normally used in test applications and characterization of integrated circuits, such as those described by patents [2], [3], since the operation of any electronic circuit causes a power dissipation and this in turn a temperature variation in its vicinity. Therefore, a temperature measurement near this circuit can provide information on possible anomalies and characteristics thereof. Compared to the classical methods of verification of integrated circuits based on the measurement of electrical quantities, the use of temperature as observable has the main advantage that the circuit under measurement is not electrically charged, which is of vital importance for example in high frequency circuits.

[1] Eduardo Aldrete-Vidrio, Diego Mateo and Josep Altet, “Differential Temperature

Sensors Fully Compatible With a 0.35-μm CMOS Process ”, IEEE TRANSACTIONS ON COMPONENTS AND PACKAGING TECHNOLOGIES, VOL. 30, NO. 4, DECEMBER 2007.

[2] Patent number 2294888. Procedure for determining the electrical characteristics of integrated analog circuits.

[3] Patent number 2332688. Heterodyne procedure for temperature measurements.

Explanation of the invention

Differential temperature sensors are used to measure the temperature variations caused by the operation of a circuit, and from these measurements, extract electrical characteristics of the circuit. These differential sensors have the advantage of having a high sensitivity to differential temperature variations caused by power dissipation due to circuits located in the same semiconductor crystal - (8) in Figure 2 - than the sensor, and very low sensitivity at temperature variations that equally affect the entire semiconductor crystal, such as variations in ambient temperature. The state of the art of differential temperature sensors shows architectures based on differential amplifiers, for example, two bipolar coupled by emitter, bipolar that would make temperature transducers. One of the two bipolar would be located in the area of the surface of the semiconductor crystal whose temperature is considered reference - for example, (2) in figures 1 and 2 -, while the other - for example (3) in the figures 1 and 2 - would be located in the vicinity of the device or circuit whose temperature variation with respect to the reference is object of measurement - (1) in Figure 2 -. The advantage of this method of obtaining information of the circuit under measure is that it is electrically non-invasive, something that is especially beneficial in high-performance circuits such as high-frequency analogs. A possible drawback of a classic differential temperature sensor would be due to the fact that the measurement transducer (cited as (3) in Figures 1 and 2) would not be influenced solely by the temperature variations of the circuit under measurement - (1 ) in figure 2 - if not that it could also be influenced by temperature variations of other devices or integrated circuits in the same glass and that are also in the vicinity of the measurement area - (7) in figure 2 -. The present invention proposes a solution to solve this possible thermal interference, without modifying the arrangement of the devices or circuits generating said thermal interference.

If we call h the area whose temperature variation with respect to that of the reference zone wants to be measured - (1) in Figure 2 -, and s the area where we place the transconducting device of the sensor in charge of measuring it

- (3) in Figure 2 -, generically you can write:

ΔTs = aΔTh

where a is the coefficient of thermal coupling between the hys zones, and whose value depends on parameters such as the physical properties of the material over which all the circuitry is integrated and the distance between both zones, lTh is the desired temperature variation measure, and lTs is the temperature variation that exists in the area where the sensor transconductor is located, temperature variations always with respect to the reference zone of the differential sensor.

If instead of having a single source of heat in the vicinity of h, on the contrary there are more sources of heat, these can also cause a variation of the temperature in the measuring device and therefore can be considered as sources of heat interfering In Figure 2, a single interfering source has been considered, indicated as (7), but in a generic way there may be more thermal interference to be considered for the measurement being carried out. Considering n interfering heat sources, in this case the above equation should be written:

ΔT = a ΔT + a ΔT + � + a ΔT

s 1 h12 h2 n hn

where ai is the thermal coupling between each hi zone where a power dissipating source is found and the thermal sensing zone s. One of the

zones hi is considered the zone whose temperature variation is to be measured, for example h1, and the rest, for example h2 to hn, zones whose temperature has also varied because they are dissipative devices that cause thermal interference on the zone s. The objective of the thermal sensing technique using integrated temperature sensors is to estimate lTh1 from

of the measure lTs, the coefficients ai and also the value of the interfering temperature increases lThi should be known, with i between 2 and n. The coefficients ai can be estimated a priori from the layout of the circuit by computational simulation, but the interfering temperature increases will generally be unpredictable.

The present invention proposes to eliminate the effect of interfering temperatures by using more than one sensor device - in Figure 2 a single extra sensor device has been considered, indicated as (4) -. Thus, assuming the use of m sensor devices (in addition to the

reference, indicated as (2) in figure 2), the above equation is transformed into a system of m equations:

ΔTs1

ΔTh

aa .. a

1112 1

n

ΔTs2

.

.

ΔTh

to . .. to

21 2 2

n

=

. ...

. ...

.

.

.

mn ΔThn

to . .. to

m1

ΔTsm

where aij is the thermal coupling between the source j (of a total of n) and the sensor device i (of a total of m). In this way it is immediate that, by ensuring that m is equal to or greater than an, and assuming the thermal coupling matrix is known, by measuring the vector of temperature variations lTs = [lTs1, lTs2, ..., lTsm] it is possible to determine the temperature increase sought (for example lTh1, but it could be any other), eliminating the effect of interfering temperature increases.

Description of the drawings

Figure 1 shows the symbol of the electronic circuit object of the present invention. It has two power inputs (5) and (6), and as output it has a node (1). In addition, it has several internal devices, at least 3. The figure shows 3 - (2), (3) and (4) -, without limiting the present invention to the use of a larger number, the temperatures of which will influence directly on the value of the electrical magnitude of the output node.

Figure 2 schematically shows a semiconductor crystal (8) in which there is an electronic circuit or device (1) whose temperature variation we want to measure by including a temperature sensor integrated in the same crystal, sensor whose elements more Significant are a temperature sensitive device located near the circuit to be measured and indicated as (3) in Figure 2, and a device responsible for measuring the reference temperature of the integrated circuit and indicated as (2) in Figure 2. In the same figure 2 has included a circuit or device that dissipates power in the vicinity of the circuit to be measured - indicated as (7) in the figure -, and that causes an increase in temperature in (3) considered as interference. And an extra temperature sensitive device is also included, (4) in Figure 2, forming part of the same temperature sensor together with (3) and (2).

Figure 3 shows an inverting amplifier formed by an amplifier transistor MA (1) and its resistive load RLOAD (7). The temperature of the transistor MA is the objective of the measurement, and the RLOAD resistive load acts as a thermal interference by generating a temperature increase in the area of the semiconductor glass that will also affect the measurement sensor by thermal coupling.

Figure 4 shows a possible transistor level implementation of the circuit of Figure 1, object of the present invention. The indications (1) to (6) of figure 4 correspond to those of figure 1: the two supply nodes (5) and (6), the output (1) (in this case in voltage mode and also indicated with Vout), and the temperature sensing devices that in this implementation are the bipolar transistors Qref (2) (which is responsible for sensing the reference temperature of the semiconductor crystal die, and that is usually located in a place of the surface of the die away from any heat source), and the bipolar Qs1 (3) and Qs2 (4) (corresponding to (3) and (4) in Figure 1 and also in Figure 2), all interconnected by coupling from emitter to differential torque mode, Qref on the one hand and the rest on the other. All MOS transistors perform functions of active loads and current mirrors, to end up generating the output voltage Vout (1).

Description of preferred applications

As a preferred application, the one described in Figures 1, 2, 3 and 4 is shown. Figure 1 shows the symbol of the temperature differential sensor object of the present invention, and in Figure 4 a possible implementation is shown at the level of transistor of said circuit. An electronic circuit is described in Figure 3 which is used in the preferred application as a circuit to be characterized by temperature measurements, without limiting the use of the differential sensor object of the present invention to the temperature measurement caused by other electronic circuits. The circuit described in Figure 3 is an inverting amplifier formed by an amplifier transistor MA (1) and its resistive load RLOAD (7), the first being the object of measurement, and the resistive load (7) the device that acts as a source of interfering temperature. And finally, Figure 2 shows a possible distribution on the surface of the semiconductor glass of the heat sources corresponding to the circuit of Figure 3, so that in Figure 2 (1) it corresponds to the transistor MA of Figure 3 and ( 7) to the RLOAD load of the same figure. Also shown in Figure 2 are the sensor devices of the temperature sensor of Figure 4, so that (2), (3) and (4) of Figure 2 correspond to transistors (2), (3) and (4) of Figure 3. The transconducting device responsible for the reference temperature is considered - Qref in Figure 4

(2) and also represented in Figure 2 (2) - is far enough away to not be influenced by any heat source.

From the distribution presented in Figure 2, the following equations can be obtained:

ΔT = a ΔT + a ΔT

s1 11h1 12h2 ΔTs2 = a21ΔTh1 + a22ΔTh2

where lTs1 is the temperature increase in the measuring zone s1 and lTs2 is the temperature increase in the measuring zone s2; lTh1 the temperature increase caused by the transistor object of the MA measurement in the area of the semiconductor glass where it is located and lTh1 the temperature increase caused by the RLOAD load resistance in the area of the glass where it is located and considered as interfering; a11 and a12 the thermal coupling coefficients of the MA and RLOAD devices respectively up to the area where the device Q1 and a21 are located and a22 the thermal coupling coefficients of the MA and RLOAD devices respectively up to the area where the device Q2 is located. Assuming that these four coefficients are known, either by experimental measurement or by simulation, it is immediate to obtain from the measurement of lTs1 and lTs2 the temperature increase object of the measurement, in this case lTh1, despite the increase in temperature interference caused by resistance:

to -a

22 12

ΔT = ΔT + ΔT

h1s1 s2

(aa - aa) (aa - aa)

11 22 2112 11 22 2112

Specifying to the extent that it will in fact be done with the sensor, and assuming that its output is in voltage mode just like the sensor presented in the present invention, the system of equations becomes the following:

ΔV = S (a ΔT + a ΔT)

s1 T11h1 12h2

ΔV = S (a ΔT + a ΔT)

s2 T21h1 22 h2

where ST is the differential sensitivity of the temperature sensor (of units V / �C), and where it has been considered without loss of generality that the two transconductors Q1 and Q2 of Figure 4 are sized and polarized in the same way, therefore providing equal ST sensitivity.

In this way, the procedure for estimating the temperature increase caused by the transistor MA of the amplifier of Figure 3 in the vicinity of its position, being polarized and dissipating power both it and its RLOAD load resistance (which would act as an increase generator of interfering temperature on the temperature sensor), consists of polarizing the sensor and successively activating each of its m transconducting devices, and measuring in each case the sensor output. In the present case, Q1 would first be activated (with Q2 deactivated) and the corresponding variation of the sensor output, lVs1, would be measured. Then Q1 would be deactivated (for example, putting its base-to-ground voltage) and Q2 would be properly polarized, measuring the corresponding variation of the sensor output, lVs2. The estimation of the temperature variation of MA due to being the polarized amplifier would be:

to -a

22 12

ΔT = ΔV + ΔV

h1s1 s2

S (aa - aa) S (aa - aa)

T 11 22 2112 T 11 22 2112 eliminating the interfering effect of the power dissipation of the RLOAD load.

Claims (3)

 Claims 1.- An electronic circuit integrated in a semiconductor crystal die characterized in that the variation in its electrical output magnitude depends on the temperature difference between two zones of said crystal, being able at the same time not to depend on the temperature increases that take place in other areas of the same semiconductor crystal. By having m-1 interfering temperature sources, and assuming an output sensor in voltage mode (it could be in current mode), it is possible to obtain at the sensor output a measure proportional only to the objective temperature difference of the lTh1 measurement and independent of interfering temperatures: ΔT = αΔV + α ΔV + ++ α ΔV h1 1s1 2s2 m sm where lVsi are the values obtained at the sensor output by activating only each of its m temperature measuring devices, and ai are coefficients that depend on the thermal couplings between the interfering sources and the m devices of the sensor and The sensitivity of the sensor.

2.

 An electronic circuit according to claim 1 can be output in lVout voltage mode or in lIout current mode.

3.

 An electronic circuit comprising a differential pair formed by:

a) in one of the two branches of said pair, a bipolar transistor responsible for providing the circuit with the dependence of the circuit's output on a reference temperature, b) and on the other branch of the differential pair, not another single transistor but m bipolar transistors in parallel and properly located on the surface of the semiconductor crystal. And characterized in that if m is 1 the circuit would behave like a classic differential temperature sensor, and for values of m greater than 1 the circuit can eliminate m-1 interfering temperature variations. Figure 1 Figure 2 Figure 3 Figure 4