NL7907161A - INTEGRATED TEMPERATURE COMPENSATED VOLTAGE REFERENCE. - Google Patents

Description

* fc * J

if.O. 28,250 1

Integrated temperature-compensated voltage reference.

The invention relates to integrated voltage references. More particularly, the invention relates to improved means and methods for temperature compensations of such voltage references and to simple measures with which such references can be optimally compensated.

Integrated voltage reference circuits generally use a junction voltage source, such as a zener diode, which exhibits a significant temperature coefficient to be compensated. For many reference devices, the relationship between voltage and temperature can be approximated by:

Tdev = TK + «d-%) eq.1 where ^ dev is the terminal voltage of the device at a temperature T and Vg and Tg are constants while α is a coefficient that varies with the processing of the device.

In order to compensate with the temperature-varying voltages, the output signal of such a device 20 can be added to a compensation voltage, for example supplied by a junction source operating at a certain band gap with a temperature coefficient opposite to that of the device and with a scale factor such that the desired output voltage level is obtained. The characteristic *.

25 marks of such a compensated voltage reference device can be represented by the following relationship: 7ref = ^ ÜC ^ go - βΤ) 6> V ^ + ® (T-Tg)] eq. 2 where V ^ q is the band gap voltage, β de temperature co-efficient for a forward biased junction, a proportionality factor between the voltage reference device and the compensating device and λ an overall scale factor is required to achieve a specific voltage value.

Such an arrangement has two degrees of freedom for adjustment purposes represented symbolically by (slope) and Λ (scale factor) in the above equation (2). One possibility to adjust the direction for a given operating characteristic is to use a computer-determined algorithm to set the correct value to minimize temperature-dependent variations for the operating characteristic. a calculated value of α and then adjusting A to achieve the specified output voltage level Y ^. This procedure therefore requires two separate adjustment steps, one for each of the two degrees of freedom of the control circuit. However, experience has taught that such a procedure is undesirably complex and expensive to perform, and although such a procedure is used commercially, it does not quite satisfactorily achieve a desired behavior. There is therefore a clear need for improvement.

According to an important feature of the invention it has now been found that significantly better results can be achieved by a method in which the adjustment of a single element of the circuit of a voltage reference circuit is used for simultaneously changing the two variable factors (represented by λ and <s in equation 2), controlling the output voltage and temperature dependence of the voltage reference circuit. More specifically, according to a preferred embodiment of the invention, an adjustment resistor is used to adjust the reference output voltage to the specified value simultaneously changing one temperature compensation control circuit to obtain an optimum temperature compensation at the point where the reference output voltage equals is at the specified value.

In other words, it has been found that the two degrees of freedom used to fully adjust each voltage reference circuit can be reduced to a single degree of freedom, thereby improving the behavior of the voltage reference circuit while simplifying the manufacturing process. The reduction of the adjustment procedure to a single degree of freedom can be understood in a mathematical sense in that the variable A becomes dependent on S from the topology of the associated control circuit for the compensating 7907161 * * 3 voltage source. The dependency relationship can be expressed as follows i Tref1 λ = V '^ GÖLa% ΤβΓδ · 3 where Vreff is the specified output voltage.

5 The output voltage can be expressed as

Enter "VK + sïG0-aIK KTGO_p! R) e + Ve (I * TK>] Terg.4

The final expression then becomes equal to:

Tref = Vref '· gTS04- - 0¾ + 7erg.5 V «= TGO" ®% 10 where <S is the remaining adjustment parameter.

According to a further feature of the invention, Igjj adjustment of Vrei to the specified value becomes the term (α-ββ) equal to zero, ie p * = a, achieving the desired equality within the limits of the model.

Other objects, features and advantages of the invention will become apparent from the embodiments of the invention illustrated in the Figures and described in the following.

Figure 1 shows a simplified diagram illustrating the basic configuration of a preferred embodiment of the invention.

Figure 2 shows a schematic with details of a voltage reference circuit based on the principles illustrated in Figure 1.

Figure 5 shows in graph form the relationship between voltage and temperature at various classes of voltage sources.

Figure 1 shows a voltage reference circuit according to the invention comprising a zener diode voltage source 10 having an electrode connected to the output line 12 of an operational amplifier 14. The diode is coupled to the inverting input terminal 16 of a negative feedback path. the amplifier, which on the other hand is connected via the resistor 18 to the common or earth conductor 20.

Zener diode 10 is formed as part of a chip of an integrated circuit together with associated drivers as shown in Figure 2. The chip will further contain 790 71 6 t 4 of the circuits (not shown) containing the generated stabilized need reference voltage as will be described in the following. Preferably, the zener diode is configured as a device with a so-called buried layer, for example, a device as described in detail in U.S. Patent Application 801,410 filed May 27, 1977 also of applicant · The potential of the non-inverting connection 22 of the amplifier 14 is determined by a control circuit 10 which is generally indicated by 24 and which is provided with a second voltage source. This circuit contains the series-matched transistors and Q2 each with an emitter resistor and R2 · The collector of Q2 is connected to the output line 12 and the emitter-15 resistor is connected to the ground wire. A three-resistance voltage divider 26, 28, 30 is provided for fixing the base voltages of the transistors Q / | and Q2 ° P for sDT certain voltage levels as will be described further below.

The feedback circuit of the operational amplifier 14 ensures that the input terminals 16 and 22 will have the same potential so that the amplifier output voltage 7q can be regarded as the sum of the diode voltage 7 ^ and the voltage supplied to the non-inverting-25. the terminal 22. It is noted that because of the particular bridge type of the circuit shown, the voltage at the terminal 22 also depends on the output voltage 7q. However, this dependence is not a requirement according to the invention, other types of circuits can also be used to combine the zener voltage with the compensation voltage.

The output reference voltage 7q can be considered as a function of the values of the circuit elements and the significant parameters still to be discussed.

A detailed derivation of this relationship is provided in the appendix at the end of this description. As shown in this derivation, the output voltage can be written as: V. + {ψ- - 1) bebe

Tn = a K1 equ. U

40 0 1 -f * »2e- 7 90 7 1 6 f * -¾ 5 where V is the Zener diode voltage and 7 ^ e is the base-emitter voltage (of either either Q2)» while further 6 is the proportionality factor for the base voltage of ^ (ie Y ^ 2 = & Vq) »S is the proportionality factor for 5 the base voltage of and B ^, B2 are resistance values.

By determining a group of relations for a zero-1 temperature coefficient, the derivative of equation 1A can be taken to the temperature and equated to zero giving:

10 E2 oC

= Λ + y compare 2A

where ^ is defined as ^ Υ ^ θ, ^ ethereal is approximately equal to (Y ^ Q - where as previously described equals ^ 7 ^; and 7go is the band gap voltage.

For deriving further necessary requirements for zero temperature coefficient conditions, equation 1A can be further elaborated as:

~ T + (Tgo-ZD

20 VQ - ^ - compare YES

E1 in which and are constants (see equ. 1) and T is the temperature of the device.

Equation 3A can be further developed using eq. 2A yielding: x \ + * (¾ -%)

T0 (^) = ---- T7— compare 4A

1 - £ + e (1 + - * -) where YK are "%" an f constants.

Determining the derivative of equation 4A to <Λ and equating it to zero gives: T60 6

ψ - ï ^ "T-i ♦ € - Verg-5A

When this relationship is determined, 7q will be independent of ff. That is, the driver circuit will achieve the desired results regardless of the particular zener diode being used.

Since the determined parameters must be valid for each a, a further relationship for € - and ó can be put on 790 7 1 6 f 6 ί · * by assuming α = 0 in equation 4A:

YK

tt “= 1 - ζ + € comp. 6A

v0

Equations 5 & and 6A can be solved for & and ^:

5 ^ = (VG0 "(Γ% ^ 0 compare 7A

"Yir

ς) = 1 + β - equ. 8A

These relationships are derived from. obtain a zero-tipperature coefficient at a given output voltage. In the same manner, however, modified relationships can be derived for other types of temperature coefficient control depending on adjusting the output voltage to a specified value. For example, there are applications in which a certain non-zero temperature coefficient of the specified reference voltage is required, for example, to adapt the behavior of the reference circuit to the properties of another circuit. In addition, the control function described herein can be used in applications where 20 different output voltages are required for individual units of a group, each of the output voltages having a correspondingly different temperature coefficient requirement. The manner in which the invention is applied will thus depend on the particular application problem to be solved.

In the case of the circuit of Figure 1 in which the circuit is used to achieve a zero temperature coefficient, the numerical values for € and & can be obtained by entering experimentally determined values for Vg and Tg in equations 7 & 8A together with; the known value for V ^ Q, a calculated value for jf (assuming the definition in equation 1A with a known value for & e nested value for Vq.

Vg and Tg are determined experimentally by voltage-temperature measurements on a large number of buried layer zener diodes and typical extrapolated values are:

Vg = 4.7 ^ and Tg = -383 ° K. The value of VfeeQ is 0.655 at Tq = 300 ° K. Assuming a specified value Vq = 10, the proportionality factors become: 790 7 1 6 i 7 - - G = 0.1960 - β = 0.7220 ...

Subsequently, by suitable selection of resistors 26, 28 and 30, base voltages T1e1 and Y1e2 are set at 1.960 and 7.220 Volts, and the circuit shown in FIG.

1 will show optimum temperature compensation when one or the other emitter resistor R ^ or S2 is set to achieve the specified output voltage of 10 Volts. Which resistor R ^ or R2 is applied depends on whether the initial measured output voltage is above or below 10 Volts.

For a series of experimentally measured values of α for a large number of units of the class Zener diodes used in an integration process as described above, the corresponding values for I / R / j are approximately determined. Referring to equation 25., the measured values for α corresponding to measured zener voltages V ^ (at 300 ° K) are equal to 6.0 and 6.6, showing that: the minimum of R2 / B ^ = 1.966 (for Vz = 6.0) the maximum of R2 / R ^ = 2.426 (for Vz = 6.6).

Figure 2 shows details of a preferred embodiment of the circuit according to the invention shown in Figure 1, which circuit has already been substantially described above. In Figure 2, Q ^ 2 and the basic elements of the operational amplifier 14. The zener diode Dg has Kelvin terminals with power and direction electrodes essentially at the same potential. One electrode is connected to the inverting input terminal 16 and the other is connected to the common lead 20 through a resistor R ^ (reference 18 in Figure 1). The transistors correspond to Q2 and in Figure 1, the resistors R ^ g and R ^ g correspond to the resistors R2, R ^ and the resistors R, ^, 35 and correspond to the resistors 26, 28 and 30.

The amplifier circuit of Figure 2 is in principle designed as a symmetrical balance configuration. supplies the collector current to Q ^ 2 and §113 · Re collector of receives the emitter currents of Q ^ 2 and ^ 113 and 40 adjusts a total correct current. The 790 7 1 6 1 J% 8 base of is controlled via the voltage translation transistor Q ^ g and the adjustment resistor B ^ q via current from the left collector of and Q> | ^ jo ζ ^ η buffer transistors. The current in Q ^ q9 5 is controlled by Q ^ q5 ^ which is adapted to provide equal flows. The current of Q ^ o4 · passes through ^ 106 which is matched to Q ^ y, so that the current of Q ^ y and the current of will be equal and equal to the current of Although the base currents of Q > | 09 and Q> j> j4 may also exhibit errors, such errors are balanced with respect to ^ 113 »so that they tend to be eliminated due to circuit symmetry.

^ 103 feeds any additional power required by 15 ^ 115? ^ 116 * ^ 111 provides protection for the output buffer Q ^ q. The left emitter is used to start the circuit.

Figure 3 graphically illustrates the voltage-temperature relationships discussed above to the hanii of Figure 1 for achieving optimum temperature compensation by adjusting the reference output voltage to its specified value. The graph shows two straight lines and Z% indicating the limit values for the variance range of the measured voltage-temperature characteristics for a large number of buried layer zener diodes. The slope of these lines (et /] and represent the derivative of the voltage-temperature relationship described in the above. Additional polarization of these lines (and lines for intermediate values not shown) to the left results in a cut in a common area centered around a certain voltage% and an associated temperature Tg. (It should be noted that for the measured values shown herein, the intersection takes place at a temperature below the absolute zero point so that there is no physical opposite to it and which is of significance only for the design) With a common intersection and at least approximately rectilinear characteristics, the voltage-temperature characteristic of this zener diode class of 40 voltage sources, as already noted above, can be represented by: 7aev = + «( i - iK) where α indicates the slope of each curve.

Furthermore, in Figure 3, two additional straight lines 5 and J2 are shown as representing the limits of the range of the voltage-temperature characteristics for the voltage combined with the zener voltage and derived from the compensating voltage source 24 provided with a band gap junction. These lines also intersect and the control circuit of the compensating voltage source is designed such that this intersection is at a temperature Tg, ie on the same vertical line as the common intersection of the zener characteristics Z ^ and Z2 ·

The control circuit is further designed such that the common intersection at the compensation voltage Vj has a magnitude such that when combined Vj and 7K the composite voltage will be equal to the specified reference output voltage, in this case 10 Volts. note such adjustment of the reference voltage 20 to provide the specified output voltage of 10 Volts, in fact changing the slope of the compensating voltage source line within the range between and J2, the final adjusted slope of the curve will automatically be obtained with an inverse adjustment -25 sing (i.e. complementary relationship) to the slope of the characteristic line Z ^ of the respective zener diode which forms the base source in the voltage reference circuit. The temperature coefficient of the voltage reference circuitry will therefore be optimally equal to zero or very close to it due to the adjustment of the output voltage to the specified value.

Although a preferred embodiment of the invention has been described in detail above, it will be appreciated that the preferred embodiment is shown merely as an illustration of the principles of the invention without limiting the invention. It will be clear that the invention can be used to compensate for various types of base voltage sources and that the compensation means can use various types of compensating voltage sources cooperating with the basic 790 7 1 6 1 4 V-10 voltage source. In addition, a wide variety of control circuits can be used to implement the basic concepts of the invention. Within the scope of the invention, the person skilled in the art will be able to apply the invention for a large number of different application cases.

Appendix

Since the input terminals of amplifier 14 have the same potential, the following equality can be noted: -r T0 - T, - "Tb · - ij (6T0 - 7be>

R 'R

15 -5T0 + e. jji. T0 = vz - Tbe + vbe

R R

v0 Ό - <S + € jq) - + (jq - 1) vbe 20 • T + (yr -1> Tbe

* z g1_ compare. 1A

ü 17 ^ “ti + ^ 17 25 .. ^ dV„ E ~ dVv «y__3_ Γ _- + (- - -n _ £ ®ί

dT V0 "1 _ ^ + ^ E2 L dT + 'kE1 |; dT J

Rp dVz / dT d! T0 50 “1 =" d? Be / dï where 3j W ~ = 0 R2 ^ d7z / dT; 'if = 1 "4Tbe / ai 55 if ïz = YK α (T -TK) d7z TT = *.

40 if 7be '7S0 ”ƒ 1 7907161 11 h Vbe = -r dTz 5 r

Ro ^ = 1 + t

Enter in equation 1A before and 1 ^ / ^ 1 leTer'b: 10 _ vK + (1 - V ♦ <7> - pn ° "1 - it 6 (1 t L) work out the counter: h -«% + J TS0 so the voltage as a function of a is: 15 Vr + a (IsO - IK) 70 = _f VK, Ικ, i = constant equ. 4-1 1- £ + 6 (1 + ~) take derivative to α: 20 V 7 - 37o Il .-- ^ + £ + 1p »] (“ ^ “%) - + e (~ fr-%) 3 ^ ^ [1 - <S + 1 (1 W ^ ^ derivative equal to zero draws:

^ <f · = = 1 -J + e equ. 5A

7907161

Claims (5)

1. Temperature compensated integrated reference signal source, characterized by a first signal source which supplies a first signal, which signal follows a signal temperature characteristic with a first slope; a second signal source which supplies a second signal which signal is combined with the first signal to provide the compensated reference output signal responsive to the first and second signals, which second signal follows a signal temperature characteristic with a second slope; a control circuit which interacts with the second signal source and includes adjusting means to vary this second signal to correspondingly change the composite reference output signal to the specified value; which control circuit is provided with means under control of said control means for varying said second slope when said second signal is changed to provide a predetermined temperature coefficient for the composite signal when the signal is adjusted to its specified value . 2. Device according to claim 1, characterized in that the control circuit is for supplying an effective zero temperature coefficient for the composite signal when it is set to its specified value. 5. Device according to claim 2, characterized in that said driving circuit is for producing an effective inverse adjustment between the two said slopes when said composite signal reaches its specified value in order to achieve a zero temperature coefficient at this particular level . 35 4-. Apparatus according to claim 1, characterized in that the first-mentioned signal source is provided with a zener diode and the second signal source is provided with means for producing a compensating signal, which signal is a function of the base-emitter 4-0 voltage of a semiconductor junction. 7907161 ai ~ 5. Device according to claim, characterized in that said control means are provided with a variable resistance in series with said junction. 6. A method of temperature compensating the signal of an integrated signal source by coupling a second signal source which supplies a second signal to generate a reference signal which depends on both the first and the second signal, the signal temperature characteristics of the two signals have the opposite sign in order to eliminate the temperature effects in said reference signal, which method of improving the temperature compensation of the reference signal at a specific value is characterized by adjusting a circuit element coupled to the said second signal source such that the second signal is varied thereby bringing the reference signal to the specified value and controlling by means of the adjustment of this switching element the slope of the characteristic signal-temperature curve for said second signal in order to obtain a predetermined be create some relationship between the influence on said reference signal of the temperature characteristic of the first and second signals 25 in order to obtain a preselected temperature coefficient for said reference signal when the reference signal is set to its specified value. 790 7 1 6 1