EP2560066A1 - Method for adjusting a reference voltage according to a band-gap circuit - Google Patents

Abstract

The method adjusts a reference voltage (V REF) of an electronic circuit based on a band-gap voltage (V1) provided by a band-gap first stage (11). The band-gap stage (11) comprises in a series connection between two terminals of a supply voltage source, a current source (P1) connected to a first branch, which comprises a first configurable resistor ( R1 a) in series with a first diode (N1), and at a second branch, which comprises a second configurable resistor (R1b) connected to a complementary resistor (R2) in series with a second diode (N2). Band-gap voltage is supplied to a connection node between the current source and each branch. The current source is a PMOS transistor (P1) controlled by an output voltage of a first operational amplifier (A1) of a current control loop. The appropriate binary word (M1) for configuring the configurable resistors (R1a, R1b) is determined on the basis of four band-gap voltage values measured at two different temperatures (T1, T2) and two resistive values of the resistances configured by the same first binary word and the same second binary word different from the first binary word.

Description

The invention relates to a method for adjusting a reference voltage of an electronic circuit provided with a band-gap stage.

The invention also relates to an electronic circuit for implementing the method of adjusting a reference voltage.

The production of electronic circuits comprising a band gap stage to provide a reference voltage is generally well known. This reference voltage must in principle be set to be independent of the temperature.

As represented in figure 1 such a band-gap type electronic circuit 1 is composed of a diode, such as a bipolar transistor N1 mounted in the form of a diode, which is crossed by a direct current Ic generated by a current source Sc to define a voltage diode V _BE . Generally this diode voltage V _BE decreases with an increase in temperature, and conversely increases with a decrease in temperature. The current source Sc and the diode-connected bipolar transistor N1 are connected in series between two terminals of a DC supply voltage.

Since the diode voltage V _BE varies inversely with the variation of the temperature, a generator 2 of a voltage K · U _T , whose voltage K · U _T varies inversely with the diode voltage V _{BE, is also provided} . This voltage K · UT is added in an adder 3 to the diode voltage to provide a reference voltage V _REF , which is equal to V _BE + K · UT _· The factor K is thus adapted so as to obtain a reference voltage V _REF independent of the temperature. For this, it is necessary that dV _BE / dT be equal to -K · dU _T / dT _· The reference voltage V _REF , which may be a band-gap voltage, is of a value substantially equal to 1.22 V at 0 ° C. The thermodynamic tension U _T , which is equal to k · T / q, is about 23.5mV at 0 ° C, where k is the Boltzmann constant, T is the temperature in Kelvin, and q is the load of an electron in absolute value.

Generally for an electronic circuit band-gap type as represented in figure 1 , a default value of the factor K to have a reference voltage V _REF independent of the temperature is fixed during the design of the electronic circuit. This factor K influences the absolute reference voltage, as well as the temperature dependence of the first order. During the adjustment of the absolute value of the reference voltage, the variation of the factor K also influences the temperature stability. Since the method of manufacturing such an electronic circuit may vary for adjustment of the reference voltage, it may result in suboptimal temperature stability. This leads to a variation of one electronic circuit to another with a reference voltage, which is not entirely independent of the temperature, which is a drawback.

For example, the patent application US 2006/0043957 A1 which describes such an electronic circuit provided with a band-gap type stage. In this patent application, it is particularly described a way to adjust the temperature coefficient. To do this, it is performed measurements of the voltage at different temperatures to calculate the slope and thus adjust the reference voltage generated. This band-gap stage therefore provides a precise reference voltage following various measurements of adjustment of the temperature coefficient. However, the adjustment method requires several measurement steps in order to derive the precise adjustment parameters of the reference voltage, which is a drawback. In addition, the adjustment of the reference voltage is highly dependent on variations in the manufacturing parameters of the electronic circuit, which constitutes another drawback.

The purpose of the invention is therefore to overcome the drawbacks of the state of the art by providing a method of adjusting a reference voltage on the basis of an electronic circuit provided with a band-gap stage, which is simple to implement. The method makes it possible to easily adjust the reference voltage generated independently of the variations of the manufacturing parameters of said electronic circuit, and by suppressing the temperature dependence of the first order.

For this purpose, the invention relates to a method for adjusting a reference voltage of an electronic circuit provided with a band-gap type stage, which comprises the characteristics defined in the independent claim 1.

Particular steps of the method of adjusting a reference voltage are defined in dependent claims 2 to 6.

An advantage of the method of adjusting a reference voltage according to the invention lies in the fact that a band-gap voltage is measured at two different temperatures for two resistance values trimmed by two binary words. The appropriate calibration binary word of one or two configurable band-gap resistors is determined based on the four band-gap voltage values to obtain a band-gap voltage independent of the temperature.

Another advantage of the method of adjusting a reference voltage is that the level of the reference voltage can thus be adjusted precisely in a second step on the basis of the adjusted band gap voltage. The reference voltage adapted to the desired level is also independent of any temperature variation.

For this purpose, the invention also relates to an electronic circuit provided with a band-gap stage for implementing the method for adjusting a reference voltage, which comprises the characteristics defined in the independent claim 7.

Particular embodiments of the electronic circuit are defined in the dependent claims 8 to 16.

• la figure 1 citée ci-devant représente de manière simplifiée un circuit électronique du type band-gap de l'état de la technique,
• la figure 2 représente une forme d'exécution d'un circuit électronique muni d'un étage du type band-gap permettant le mise en oeuvre du procédé d'ajustement d'une tension de référence indépendante de la température selon l'invention, et
• la figure 3 représente un graphique représentant la variation de la tension fournie de l'étage band-gap du circuit électronique en fonction de la température relative à la mise en oeuvre du procédé d'ajustement d'une tension de référence selon l'invention.

The aims, advantages and characteristics of the method of adjusting a reference voltage, and the electronic circuit for its implementation will appear better in the following description on the basis of at least one non-limiting embodiment illustrated by the drawings on which:

• the figure 1 cited above represents, in a simplified manner, an electronic circuit of the band-gap type of the state of the art,
• the figure 2 represents an embodiment of an electronic circuit provided with a band-gap stage allowing the implementation of the method of adjusting a reference voltage independent of the temperature according to the invention, and
• the figure 3 represents a graph representing the variation of the voltage supplied from the band-gap stage of the electronic circuit as a function of the temperature relative to the implementation of the method of adjusting a reference voltage according to the invention.

In the following description, all elements of the electronic circuit for implementing the method of adjusting a reference voltage, which are well known to those skilled in this technical field will be reported in a simplified manner.

The figure 2 represents an embodiment of an electronic circuit, which comprises at least a band-gap first stage 11 to provide a band-gap voltage V1, and a second adaptation stage 12 of the reference voltage V _REF on the basis of band-gap voltage V1. In a first step of the adjustment process, the band gap voltage V1 is adjusted to be independent of any variation in temperature. In a second step of the adjustment method, the reference voltage V _REF can be adapted to a desired level for the supply of other electronic components. However the tension Band gap V1 can also be used as a reference voltage for other electronic components. This reference voltage does not vary in temperature, if the band-gap voltage has been adjusted in the first stage according to the adjustment method of the present invention, as explained below.

In a simple configuration of the electronic circuit with the band-gap first stage, it can be provided at least one current source P1, a resistor R1 a configurable by a binary word M1, and a diode-shaped element, such as a bipolar transistor mounted diode N1. The current source, the resistor and the junction diode are connected in series between two terminals of a not shown power supply source. The current source P1 is preferably connected to the high potential terminal of the supply voltage source, while the diode N1 is preferably connected to the low potential terminal of the supply voltage source. The band-gap voltage V1, which can define, in this case, a reference voltage, is therefore supplied to the connection node between the current source P1 and the configurable resistor R1a. However, this band-gap voltage can also be supplied to the connection node between the current source P1 and the diode N1, if the configurable resistor R1a is directly connected to the low voltage terminal of the supply voltage source. This band gap voltage V1 is thus the addition of the diode voltage of the transistor N1 and the voltage generated by the current flowing through the resistor R1 a.

The electronic circuit is generally formed in a semiconductor substrate, such as silicon Si or gallium arsenide GaAs. With an increase in temperature, the value of the resistor R1a increases, while the diode voltage N1 decreases, and conversely with a decrease in temperature. It must therefore be determined the binary word M1 in such a way that the band gap voltage V1 supplied at the output of the first stage 11 is independent of the variation of the temperature. As explained below in particular with reference to the figure 3 , the process adjusting the reference voltage makes it possible to determine the appropriate binary word M1 for configuring the resistor R1a. The method for adjusting the reference voltage or band gap voltage V1 makes it possible to suppress the first-order temperature dependence as briefly explained with reference to FIG. figure 1 by adapting the factor K.

According to the adjustment method of the present invention, band-gap voltage V1 must be measured at a first temperature T1 and at a second temperature T2 in a temperature range enabling operation of the electronic circuit. This temperature range can be for example between -40 ° C to at least 85 ° C depending on the technology used to achieve the integration of the electronic circuit. For example, a first temperature T1 at 0 ° C. and a second temperature T2 at 60 ° C. can be selected, but other temperatures can also be chosen for the adjustment method according to the invention.

Preferably, the two measurement temperatures T1 and T2 can be chosen on either side of a median temperature value in the operating temperature range of the electronic circuit. This also minimizes the effects of the second order (bell effect). In principle, they must also be sufficiently far apart from each other without approaching each limit of the temperature range so as to avoid amplifying measuring inaccuracies.

The band-gap voltage V1 is measured at both temperatures at a first resistance value R1a and a second resistance value. First two band-gap voltage values V1 are advantageously measured at the first temperature T1 for the two resistance values R1 a successively configured by the two binary words M1. Then two second band-gap voltage values V1 are measured at the second temperature T2 for the two resistance values R1 a successively configured by the two binary words M1. The four values of the band-gap voltage can be stored in means storing a microprocessor unit, which can be integrated in the same integrated circuit as the electronic circuit or simply connected to the electronic circuit.

It may also be provided to store in a test file during production, the two band-gap voltage values V1 of the two resistance values at the first temperature T1. This file can be reused when testing the two band-gap voltage values at the second temperature T2 so as to allow the final calculation of the factor K. The production test stores the measurement results of the two band-gap voltage values at the first temperature associated with each circuit. Under these conditions, it is not necessary to provide the electronic circuit with a non-volatile memory.

In a variant of the method, two values of the band gap voltage V1 can be measured with the first resistance value R1a configured by a first binary word M1, at the two measurement temperatures T1 and T2. Then, two other values of the band gap voltage V1 can also be measured with the second resistance value R1 a configured by a second binary word M1 at the two temperatures T1 and T2. The four values of the band gap voltage V1 can be stored in the storage means of the microprocessor unit.

On the basis of the four values band-gap voltage V1 stored, it is directly possible to calculate the appropriate binary word to configure said resistor R1a. Once the resistor R1a is configured by the appropriate binary word M1, the band gap voltage V1 is independent of any variation in temperature. This makes it possible to adjust the temperature stability of the first order. The binary word M1 configuring the configurable resistors can be a binary word of at least 4 bits, and preferably can be 7 bits or more. The current I supplied by the current source can also be adapted as a function of the value of the band-gap voltage to have a band-gap voltage level V1 determined taking into account the value of the configured resistor R1 a.

It should also be noted that it is possible to determine the band-gap voltage variation slopes for the two resistance values R1a configured by the two different M1 bit words, in order to determine the appropriate M1 binary word. However, in this case, the equations of the measurement temperature values must be taken into account, which complicates the method of adjusting the reference voltage. Moreover, for identical slopes of any measured electronic circuit, the same binary word is always obtained, which does not make it possible to benefit from a good temperature adaptation.

Subsequently in a second step, the reference voltage V _REF can be adapted in the second stage 12 of the electronic circuit. This reference voltage V _REF can be precisely adjusted to a higher value or a lower value for example to 0.8 V, or also to a value identical to that of the band gap voltage V1, as explained in more detail below. As the band-gap voltage adapted in the first stage 11 of the electronic circuit, may be different from one circuit to the other of the same circuit board of integrated circuits or different integrated circuit boards, it is necessary to adapt the reference voltage desired in the second stage 12.

In a more complete configuration illustrated by the figure 2 the first band-gap stage 11 is first composed of a current source P1, which is produced by means of a PMOS transistor P1. The source of the PMOS transistor P1 is connected to a high potential terminal of a not shown power supply source, while the drain is connected to a first configurable resistor R1a and a second configurable resistor R1b. To make the PMOS transistor P1 conductive, the gate of this PMOS transistor P1 is controlled by an output voltage of a first operational amplifier A1 of a current control loop. Thus a controlled current I is supplied by this PMOS transistor P1 to the first and second configurable resistors R1a and R1b. A first current I _a passes through the first resistor R1 has while a second current I _b passes through the second resistor R1 b. The band-gap voltage V1 of the first stage output 11 is defined at the connection node between the PMOS transistor P1 and each configurable resistor R1a and R1b.

In a first branch, the first resistor R1 a is connected on one side to the drain of the PMOS transistor P1 and on the other hand to a first diode, which is preferably a first diode-connected bipolar transistor N1. This first transistor mounted diode N1 is composed of n bipolar elementary transistors. This first bipolar transistor may be a PNP transistor with the base and the collector connected to the low potential terminal of the supply voltage source. Thus the PMOS transistor P1, the first resistor R1a and the first diode-connected bipolar transistor N1 are connected in series between the terminals of the supply voltage source.

In a second branch, the second resistor R1b is connected on one side to the drain of the PMOS transistor P1 and on the other hand to a complementary resistor R2, which is then connected to a second diode. This second diode is preferably a second bipolar transistor mounted diode N2. This second diode-mounted transistor N2 is composed of m bipolar elementary transistors. This second bipolar transistor may be a PNP transistor with the base and the collector connected to the low potential terminal of the supply voltage source. Thus the PMOS transistor P1, the second resistor R1b, the complementary resistor R2 and the second diode-connected bipolar transistor N2 are connected in series between the terminals of the supply voltage source.

The number m of bipolar elementary transistors of the second branch is greater than the number n of elementary bipolar transistors of the first branch. In an advantageous embodiment of the electronic circuit, the number n of elementary bipolar transistors for the diode N1 may be chosen equal to 1, while the number m of elementary bipolar transistors of the diode N2 may be chosen equal to 24. This choice comes from a good pairing sought with central symmetry during the placement of the elementary transistors on the integrated circuit of the electronic circuit. The bipolar elementary transistor of the diode N1 is disposed in the center of the 24 elementary bipolar transistors of the diode N2 to give a structure in the form of a square.

The two configurable resistors R1a and R1b may be similar and configured by the same binary word M1 provided through a configuration bus connected to the microprocessor unit. Each configurable resistor can be composed in series of a base resistor and a resistor network. The resistors of the network can be short-circuited each by means of a respective switch activated by a respective bit of the binary word M1. The values of a part of the resistances of the network may be weighted by power of 2 or be each of the same value, for example chosen between 15 and 20 kOhm. Preferably, each configurable resistor can vary from 1.8 MOhm (base resistance) to 4.03 MOhm. The default value of each configurable resistor, which is adjusted for example to the design, can be set at 2.94 MOhm. The complementary resistance R2 may be of a fixed value of the order of 420 kOhm. Naturally, other values of resistances can be provided so as to obtain a band gap voltage V1 of the order of 1.22 V at 0 ° C.

It should be noted that instead of the first and second bipolar transistors mounted in PNP-type diode N1 and N2, it may be envisaged to use first and second bipolar transistors mounted in NPN-type diode N1 and N2. In this case, the emitter of each transistor is connected to the low voltage terminal of the supply voltage source, while the base and the collector are connected to the first resistor R1 a for the first transistor and to the resistor complementary R2 for the second transistor.

As mentioned above, the current I, which is supplied by the PMOS transistor P1 to the resistors R1a, R1b, R2 and to the diodes N1 and N2, is determined in the current control loop. To do this, the positive input of the first operational amplifier A1 receives a first comparison voltage value Vp at the connection node between the first configurable resistor R1 a and the first PNP transistor mounted in diode N1. The negative input of the first operational amplifier A1 receives a second comparison voltage value Vm at the connection node between the second configurable resistor R1b and the complementary resistor R2. The output of this first operational amplifier A1 controls the gate of the PMOS transistor P1 so as to control the current passing through the first configurable resistor R1a and the current _Ib passing through the second configurable resistor R1b.

The first stage 11, which provides band-gap voltage V1, thus makes it possible to adjust the temperature stability of the first order. On the other hand, the second stage 12 makes it possible to adjust the value of the desired reference voltage V _REF without modifying the temperature stability by means of a simple adjustment of the offset, as explained hereinafter in more detail.

où Vp correspond à la tension de diode V_BE du premier transistor PNP monté en diode N1, qui est formé de n transistors bipolaires élémentaires. Le facteur K pour l'ajustement de la stabilité en température du premier ordre est donc R1a·In(m/n)/R2.The value of the band gap voltage V1, which is output from the first stage 11, is defined by the following equation: $$\mathrm{V}\mathrm{1}\mathrm{=}\mathrm{Vp}\mathrm{+}\mathrm{R}\mathrm{1}\mathrm{at}\mathrm{\cdot }\ln \left(\mathrm{m}\mathrm{/}\mathrm{not}\right)\mathrm{\cdot }{\mathrm{U}}_{\mathrm{T}}\mathrm{/}\mathrm{R}\mathrm{2}$$

where Vp corresponds to the diode voltage V _BE of the first N1 diode-mounted PNP transistor, which is formed of n elementary bipolar transistors. The factor K for adjusting the first-order temperature stability is therefore R1a · In (m / n) / R2.

It is therefore easy to calculate the factor K to be able to obtain a band-gap voltage V1, which is stable in temperature by applying the equation K = (V1-Vp) / U _T. It is clear that this result can vary from one electronic circuit to another depending on the variations of the manufacturing process. The configurable resistor R1 and also the configurable resistor R1b thus allow adjustment of the factor K.

As shown in figure 3 if the value of these configurable resistors varies from a minimum value to a maximum value by the configuration bit word M1 to i bits, the variation of the band gap voltage V1 as a function of the temperature is represented by the lines _pb and p _m . For a maximum value of the configurable resistors, it is possible to measure a first band gap voltage value V _1HT1 at a first temperature T1, and a second band gap voltage value V _1HT2 at a second temperature T2. The slope of the line p _m for a maximum value of the configurable resistors is a positive slope, which means that the band-gap voltage increases with an increase in temperature. For a minimum value of the configurable resistors, it is possible to measure a first band gap voltage value V _1LT1 at a first temperature T1, and a second band gap voltage value V _1LT2 at a second temperature T2. The slope of the line p _b for a minimum value of the configurable resistors is a negative slope, which means that the band-gap voltage decreases with an increase in temperature.

For the adjustment of the factor K, it is therefore sufficient to measure two band-gap voltage values V1 at two different temperatures. This makes it possible to be able to determine the appropriate binary word M1 for configuring the resistors R1a and R1b of the figure 2 , in order to obtain a value of band-gap voltage V1 independent of the temperature. The band-gap voltage V1 independent of the temperature is shown by the line p _n in broken lines at the figure 3 . This line p _n is parallel to the axis x relative to the temperature.

In a practical case of determining the appropriate binary word, the configurable resistors are configured between the minimum and maximum values. They are configured at a first resistive value by a first binary word and at a second resistive value by a second binary word. The first resistive value may for example be greater than the second resistive value. The first straight line p ₁ relative to the first resistive value is represented with a positive slope, while the second right p ₂ is represented with a negative slope. However, it is also quite possible to have both positive slopes or both negative slopes for determining the correct binary word. It is, however, imperative that the electronic circuit be designed to have a positive slope with a maximum configurable resistance value and a negative slope with a minimum configurable resistance value. This is necessary to determine the appropriate binary word of zero temperature variation of the band gap voltage.

A first band-gap voltage value V _11T1 can be measured at the first temperature T1 with the first resistive value of the configurable resistors. A first band-gap voltage value V _12T1 can be measured at the first temperature T1 with the second resistive value of the configurable resistors. A second band-gap voltage value V 11 _T2 can be measured at the second temperature T2 with the first resistive value of the configurable resistors. Finally, a second band-gap voltage value V _12T2 can be measured at the second temperature T2 with the second resistive value of the configurable resistors. The four band-gap voltage values are stored in storage means of the microprocessor unit for the determination of the appropriate binary word.

The binary word M1 suitable for i bits for the configuration of the resistors R1a and R1b is therefore given by the following equation: $$\mathrm{M}\mathrm{1}\left[\mathrm{i}\mathrm{-}\mathrm{1}\mathrm{:}\mathrm{0}\right]\mathrm{=}\left({\mathrm{2}}^{\mathrm{i}}\mathrm{-}\mathrm{1}\right)\mathrm{<figure-callout\; id="12"\; label="\cdot \; V"\; filenames="imgf0001.png"\; state="\{\{state\}\}">\cdot \; </figure-callout>}\left({\mathrm{V}}_{}\right)\left({\mathrm{}}_{\mathrm{12}\mathrm{T}\mathrm{1}}\mathrm{-}{\mathrm{<figure-callout\; id="12"\; label="V"\; filenames="imgf0001.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{12}\mathrm{T}\mathrm{2}}\right)\mathrm{/}\left({\mathrm{<figure-callout\; id="11"\; label="V"\; filenames="imgf0001.png"\; state="\{\{state\}\}">V</figure-callout>}}_{11\mathrm{T}\mathrm{2}}\mathrm{-}{\mathrm{<figure-callout\; id="12"\; label="V"\; filenames="imgf0001.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{12}\mathrm{T}\mathrm{2}}\mathrm{-}{\mathrm{<figure-callout\; id="11"\; label="V"\; filenames="imgf0001.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{11}\mathrm{T}\mathrm{1}}\mathrm{+}{\mathrm{<figure-callout\; id="12"\; label="V"\; filenames="imgf0001.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{12}\mathrm{T}\mathrm{1}}\right)$$

It should be noted that the aforementioned formula is based on a very good differential non-linearity (DNL) and a very good integral non-linearity (INL). Between the values of V _1HT1 and V _1LT1 , likewise between the values of V _1HT2 and V _1LT2 , all the adjustment steps (LSB) must be, if possible, equal to one another. If the function V1 = f (M1) is not linear, the formula above must in principle be adapted to this non-linearity.

Differential nonlinearity focuses on the adjustment steps. This differential non-linearity is the ratio between each adjustment step and the theoretical pitch. For an adjustment ranging from 0 to 15 (16 steps), which is coded on 4 bits, there is a theoretical pitch of 1. To characterize such a means, it can be measured the value of each step and made a comparison by relation to the theoretical result. For a theoretical step (LSB = 1) of the succession of 0, 1, 2 to 15, a succession of 0, 1.1, 1.9, 3.2 is measured up to 15 for example. For each step, the differential nonlinearity is calculated and gives DNL (0) = 0, DNL (1) = (1.1 - 0) / LSB - 1 = 0.1, DNL (2) = (1.9 - 1.1) / LSB - 1 = - 0.2, DNL (3) = (3.2 - 1.9) / LSB - 1 = 0.3 and so on. Thus the differential non-linearity (DNL) of this system is the maximum absolute value between all the DNL (i) steps that are defined by the formula (f (i) - f (i-1)) / LSB-1.

Integral non-linearity (INL) represents the accumulation of differential non-linearity (DNL). This complete non-linearity brings out the drift of the adjustment function with respect to the theoretical curve. For each step, this gives INL (0) = DNL (0) = 0, INL (1) = DNL (0) + DNL (1) = 0.1, INL (2) = DNL (0) + DNL (1) + DNL (2) = -0.1, INL (3) = DNL (0) + DNL (1) + DNL (2) + DNL (3) = 0.2 and so on. The integral nonlinearity (INL) of this system is the absolute maximum value between all INL (i).

If the differential non-linearity of such a system is bad, it means that the steps have a distribution around the theoretical value with a wide standard deviation. Bad integral non-linearity means that the adjustment curve gradually deviates from the theoretical curve. On portions of the curve, the average value of the steps is not equal to the theoretical value of the steps. It also means that on this portion, the average value of the DNL (i) is not equal to 0.

For a DNL less than 0.5, this means that the system is monotonous and of good quality. For a DNL greater than 0.5, it is necessary to analyze each step. For an INL smaller than 0.5, this means that the adjustment function never deviates from the theoretical curve by more than 0.5 LSB. This sets a very good result.

For the determination of the reference voltage of the electronic circuit, the adjustment range of the factor K must always be wide enough to obtain a variation slope of the band gap voltage V1 always positive for Kmax and always negative for Kmin. The binary word M1 of configuration is therefore minimal for Kmin and maximum for Kmax. With a minimum value Kmin, each configurable resistor R1a and R1b can have a value of 1.8 MOhm. On the other hand with a maximum value Kmax, each configurable resistor R1a and R1b can have a value of 4.03 MOhm.

It should be noted that an optimal K factor does not necessarily give an optimal result in absolute value. This is due in particular to variations in the manufacturing process of the electronic circuit.

With the method of adjusting the reference voltage and in particular the band-gap voltage according to the invention, it is possible to carry out a direct calculation with two pairs of band-gap voltage values to be measured. Two first band-gap voltage values are measured with resistors configured with two different binary words at a first temperature T1. Both measurements are made in very close time periods and with a first stable temperature T1. The junction temperature of the diodes N1, N2 thus does not have time to change. Then two second band-gap voltage values are measured with the resistors configured by the two binary words at a second temperature T2. Again, both measurements are made in very close time periods and with a second stable T2 temperature. By operating in this manner to determine the four band-gap voltage values, each absolute temperature value does not need to be selected very precisely.

As indicated above, it can also be envisaged to calculate the temperature variation slopes of the band gap voltage V1. This measurement method requires a precision of the absolute temperature for the first and second measurement temperatures. This measurement method is difficult to put into practice in the production of electronic circuits. Thus, this method does not offer a very great advantage for the determination of the appropriate binary word in order to provide a band-gap voltage independent of the temperature.

It can still be planned to calculate the fixed slopes. This only makes sense if it is not possible to store the measurement results in a file or non-volatile memory. The calculation of the slope is done during the characterization phase of the design and then is fixed for all the integrated circuits according to the characterization.

The adjustment of the absolute value of the reference voltage V _REF at the output of the electronic circuit is carried out by the second stage 12. In this second stage, a second operational amplifier A2 is connected as a voltage follower to receive the band voltage as input. -gap V1 of the first stage 11. This voltage follower makes it possible not to influence the adaptation of the band gap voltage V1 in the first stage 11. A third configurable resistor R3 is provided to enable the voltage to be lowered before the amplification unit. This third resistor R3 is connected between the output of the voltage follower A2 and the low potential terminal of the supply voltage source. The third resistor R3 comprises a bottom part and a top part, which can be configured by means of a second matching bit word M2 supplied through an offset bus. This binary word can also be a binary word of at least 4 bits, preferably 7 bits or higher. The lower part of the third resistor R3 may be equal to 1.66 MOhm, while the upper part may be configured by the binary word to vary from 0 to 720 kOhm.

The amplification unit comprises a third operational amplifier A3, whose positive input is connected to an intermediate portion configured of the third resistor R3. This amplification unit is gain-fixed by fourth and fifth resistors R4 and R5. The fourth resistor R4 is connected between the negative input and the output of the third operational amplifier A3. This fourth resistance can be chosen at a value of 862 kOhm. The fifth resistor R5 is connected between the negative input of the third operational amplifier and the low potential terminal of the supply voltage source. This fifth resistor R5 can be chosen at a value of 1.57 MOhm. According to this configuration of the electronic circuit, no voltage is defined negative. Thus the third amplifier A3 must be mounted with a positive gain.

In an alternative embodiment of the second stage 12 of the electronic circuit, the third operational amplifier A3 can be mounted as a voltage follower without the fourth and fifth resistors. The upper part of the third resistor R3 can be adjusted for example to the design to a value of 363 kOhm.

As the band-gap voltage V1 may be greater than the desired reference voltage V _REF , it is necessary to have an overall gain of the second stage smaller than 1. The band-gap voltage V1 may be of the order of 1.22 V, while the reference voltage V _REF can be set to 0.8 V. To do this, the band gap voltage V1 is reduced by the resistive divider formed by the third configurable resistor R3 before entering the unit. of final amplification with the third amplifier A3 of the second stage.

The method of adjusting the reference voltage in the second stage 12 can be done in several ways depending on the chosen design of the second stage. If the differential and integral linearities of the second stage adjustment set are good (<1 LSB), this adjustment of the reference voltage can be done simply. It can be measured a minimum value and a maximum value. Then it can be calculated the binary adjustment word M2, so that it is proportional to the difference between the two measures min and max, and the target value sought. If there is only differential linearity that is good, the adjustment of the reference voltage can be done with the use of a dichotomy method. On the other hand, if the linearity is not guaranteed, it is necessary to carry out a refined search following the execution of the process by dichotomy. For all the selected possibilities of adjusting the reference voltage V _REF in the second stage 12, the adjustment bit word M2 must be determined to configure the third resistor R3 to obtain the desired target value. This binary adjustment word M2 may of course be different from an electronic circuit to another electronic circuit, since the stabilized band-gap voltage V1 at the output of the first stage may be different from one circuit to the other.

From the description that has just been given, several variants of the method for adjusting a reference voltage of an electronic circuit can be devised by those skilled in the art without departing from the scope of the invention defined by the claims. The current source can be connected to the low potential terminal of the supply voltage source, while the series arrangement of the junction diode with the configurable first-stage band-gap resistor can be connected to the potential high terminal of the supply voltage source. The first and second configurable resistors of the first band gap stage of the electronic circuit can each be separately configured to a different resistive value.

Claims (16)

A method of adjusting a reference voltage (V _REF ) of an electronic circuit, which is provided with a band-gap stage (11), the band-gap stage (11) comprising in a series connection between two terminals of a supply voltage source, at least one current source (P1), a first configurable resistor (R1a) and a first diode (N1), the band-gap type stage providing a band-gap voltage (V1), which is defined by the voltage generated by the current flowing through the configurable resistor and the diode, the reference voltage being obtained on the basis of the band-gap voltage supplied by the band-type stage gap, the process comprising the steps of: measuring a first band gap voltage (V _11T1 ) with a first resistance value configured by a first binary word (M1) at a first temperature (T1) selected from an operating temperature range of the electronic circuit, measuring a second band-gap voltage (V _12T1 ) with a second resistance value configured by a second binary word (M1) at the first temperature (T1), measuring a third band-gap voltage (V _11T2 ) with the first resistance value configured by the first binary word (M1) at a second temperature (T2) different from the first temperature and in the operating temperature range of the electronic circuit, measuring a fourth band gap voltage (V _12T2 ) with the second resistance value configured by the second binary word (M1) at the second temperature (T2), and determining a suitable binary word (M1) to configure the configurable resistor based on the four measured band-gap voltage values, in order to obtain a band-gap voltage independent of the variation in temperature. A method of adjusting a reference voltage (V _REF ) of an electronic circuit, which is provided with a band-gap stage (11), the band-gap stage (11) comprising in a series connection between two terminals of a supply voltage source, at least one current source (P1), a first configurable resistor (R1a) and a first diode (N1), the band-gap type stage providing a band-gap voltage (V1), which is defined by the voltage generated by the current flowing through the configurable resistor and the diode, the reference voltage being obtained on the basis of the band-gap voltage supplied by the band-type stage gap, the process comprising the steps of: measuring a first band gap voltage (V _11T1 ) with a first resistance value configured by a first binary word (M1) at a first temperature (T1) selected from an operating temperature range of the electronic circuit, measuring a second band-gap voltage (V _11T2 ) with the first resistance value configured by the first binary word (M1) at a second temperature (T2) different from the first temperature and in the operating temperature range of the electronic circuit, measuring a third band-gap voltage (V _12T1 ) with a second resistance value configured by a second binary word (M1) at the first temperature (T1), measuring a fourth band gap voltage (V _12T2 ) with the second resistance value configured by the second binary word (M1) at the second temperature (T2), and determining a suitable binary word (M1) to configure the configurable resistor based on the four measured band-gap voltage values, in order to obtain a band-gap voltage independent of the variation in temperature. Method according to one of claims 1 and 2, characterized in that the first, second, third and fourth band-gap voltages measured are successively stored in storage means of a microprocessor unit. Process according to one of Claims 1 and 2, characterized in that the first measurement temperature (T1) and the second measurement temperature (T2) are selected on either side of a median temperature of the temperature range. operation of the electronic circuit. Method according to one of the preceding claims, characterized in that the appropriate binary word (M1) for configuring the configurable resistor (R1a) is determined on the basis of the formula of the i-bit binary word: $$\mathrm{M}\mathrm{1}\left[\mathrm{i}\mathrm{-}\mathrm{1}\mathrm{:}\mathrm{0}\right]\mathrm{=}\left({\mathrm{2}}^{\mathrm{i}}\mathrm{-}\mathrm{1}\right)\mathrm{\cdot }\left({\mathrm{V}}_{\mathrm{12}\mathrm{T}\mathrm{1}}\mathrm{-}{\mathrm{V}}_{\mathrm{12}\mathrm{T}\mathrm{2}}\right)\mathrm{/}\left({\mathrm{V}}_{11\mathrm{T}\mathrm{2}}\mathrm{-}{\mathrm{V}}_{\mathrm{12}\mathrm{T}\mathrm{2}}\mathrm{-}{\mathrm{V}}_{\mathrm{11}\mathrm{T}\mathrm{1}}\mathrm{+}{\mathrm{V}}_{\mathrm{12}\mathrm{T}\mathrm{1}}\right)$$

where V _11T1 is the band-gap voltage measured at the first resistive value of the configurable resistor and at the first temperature (T1), V _11T2 is the band-gap voltage measured at the first resistive value of the configurable resistor and at the second temperature (T2), V _12T1 is the band-gap voltage measured at the second resistive value of the configurable resistor and at the first temperature (T1), and V _12T2 is the band-gap voltage measured at the second resistive value of the resistor configurable and at the second temperature (T2). Method according to one of the preceding claims, wherein the electronic circuit comprises a second stage (12) for adapting the level of the reference voltage (V _REF ) on the basis of the band-gap voltage (V1), this second stage comprising a second operational amplifier (A2) connected as a voltage follower for receiving as input the band-gap voltage of the band-gap first stage (11), a third configurable resistor (R3), which can be configured by a second word binary (M2), being connected between an output of the second operational amplifier (A2) and a low potential terminal of a supply voltage source, and an amplification unit connected to an intermediate portion configured of the third resistor to output the adapted reference voltage (V _REF ), characterized in that the reference voltage is adapted after the band-gap voltage (V1) has been adapted in the first stage of the band type. gap (11), by configuring the third resistor (R3) by a second binary word by means of a dichotomy method so as to determine the appropriate second binary word (M2) to configure the third resistor. Electronic circuit for implementing the method of adjusting a reference voltage (V _REF ) according to one of the preceding claims, the reference voltage being obtained on the basis of a band-gap voltage (V1) supplied by a band-gap first stage (11), characterized in that the band-gap first stage comprises, in a series connection between two terminals of a supply voltage source, a current source (P1 ) connected to a first branch, which comprises a first configurable resistor (R1 a) in series with a first diode (N1), and a second branch, which comprises a second configurable resistor (R1b) connected to a complementary resistor (R2) in series with a second diode (N2), the band-gap voltage being supplied to a connection node between the current source and each branch. Electronic circuit according to Claim 7, characterized in that the current source is composed of a MOS transistor (P1), the gate of which is controlled by an output voltage of a first operational amplifier (A1) of a control loop. controlling the current in the MOS transistor, in that a positive input of the first operational amplifier (A1) is connected to a connection node between the first configurable resistor (R1a) and the first diode (N1) to receive a first voltage of comparison (Vp), and in that a negative input of the first operational amplifier (A1) is connected to a connection node between the second configurable resistor (R1b) and the complementary resistor (R2) to receive a second comparison voltage ( vm). Electronic circuit according to one of claims 7 and 8, characterized in that each configurable resistor (R1a, R1b) is configured by a respective binary word. Electronic circuit according to claim 9, characterized in that the two configurable resistors (R1a, R1b) are configured by the same first binary word. Electronic circuit according to claim 7, characterized in that the first diode (N1) is a first bipolar transistor mounted diode, and in that the second diode (N2) is a second bipolar transistor mounted diode. Electronic circuit according to claim 11, characterized in that each diode-mounted bipolar transistor is a PNP type transistor. Electronic circuit according to Claim 11, characterized in that the first diode-mounted bipolar transistor (N1) is composed of n elementary bipolar transistors, and in that the second diode-connected bipolar transistor (N2) is composed of m bipolar elementary transistors. the integer number m being larger than the integer n, which is at least 1. Electronic circuit according to Claim 13, characterized in that the electronic circuit is an integrated circuit, in that the first diode-mounted bipolar transistor (N1) comprises a bipolar elementary transistor, and that the second diode-connected bipolar transistor ( N2) comprises 24 elementary bipolar transistors, which are formed around the elementary bipolar transistor of the first diode so as to constitute a structure in the form of a square. Electronic circuit according to Claim 7, characterized in that it comprises a second stage (12) for adapting the level of the reference voltage (V _REF ) on the basis of the band-gap voltage (V1), this second stage comprising a second operational amplifier (A2) connected in voltage follower for receiving at the input the band-gap voltage of the first stage (11), a third configurable resistor (R3), which can be configured by a second binary word (M2), being connected between an output of the second operational amplifier ( A2) and a low potential terminal of the supply voltage source, and an amplification unit connected to a configured intermediate portion of the third resistor for outputting the adapted reference voltage. Electronic circuit according to claim 15, characterized in that the amplification unit comprises a third operational amplifier (A3), a positive input of which is connected to a configured intermediate portion of the third resistor (R3), a fourth resistor (R4 ) connected between a negative input and an output of the third operational amplifier (A3), and a fifth resistor (R5) connected between the negative input of the third operational amplifier and a low potential terminal of the supply voltage source, the fourth and fifth resistors for setting the gain gain of the third operational amplifier (A3).

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