EP0842461A1

EP0842461A1 - Circuitry for supplying the base bias voltage of current source transistors in bipolar ic circuits

Info

Publication number: EP0842461A1
Application number: EP96924768A
Authority: EP
Inventors: Reinhold Unterricker
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1995-08-01
Filing date: 1996-07-24
Publication date: 1998-05-20
Anticipated expiration: 2016-07-24
Also published as: DE59601894D1; CA2228387A1; EP0842461B1; ES2134629T3; DE19528209C1; WO1997005537A1; ATE180067T1

Abstract

In order to supply the base bias voltage of bipolar IC current source transistors with a band gap reference circuit that supplies a temperature-dependent and resistance tolerance-dependent base bias voltage so that the current supplied by the current source transistors causes a constant voltage drop in the load resistances through which the current flows, the base bias voltage is supplied by a distributor circuit connected downstream of the load resistances and having an input stage, an output driver and an intermediate inverter composed of a first transistor, a first resistance, a second transistor and a second resistance mounted in series and connected to the supply voltage. In order to supply the base bias voltage to current source transistors having another type of resistance than that for which the band gap reference circuit is designed, the corresponding distributor or converter circuit has a second resistance of the same type as that of the resistance for which the band gap reference circuit is designed, and a first resistance composed of a resistance of this same type connected in series to the other type of resistance.

Description

description

Circuit arrangement for the basic bias supply of current source transistors in bipolar IC circuits

For current source transistors, as are often found in integrated bipolar circuits, the required base bias is often obtained with the aid of a bandgap reference circuit. Bandgap reference circuits, e.g. from Tietze, Schenk: Semiconductor circuit technology, 5th ed. Berlin Heidelberg New York 1980, Figs. 16.29 and 16.30, and 9th ed., Berlin Heidelberg New York Tokyo 1991, Figs. 18.29 to 18.31, are known per se a constant voltage of, for example, about 1.2 V regardless of the temperature and resistance tolerances. In integrated bipolar circuits, however, a base bias is required for current source transistors, which has a certain dependency with regard to the temperature and the resistance tolerances, namely in such a way that the current supplied by the current sources causes a constant voltage drop across the load resistors through which this current flows. Such a dependency is brought about in practice with the aid of a correspondingly modified bandgap reference circuit. In order to then decouple individual circuit parts supplied with the base bias voltage and to avoid stressing the bandgap circuit too much, the base bias voltage is routed to the individual circuit blocks via distributor circuits. This circuit principle, which is common in practice, is shown in FIG. 1, in which the modified bandgap reference circuit is denoted by B and two distributor circuits by V.

Such a distributor circuit can have the circuit structure outlined in FIG. 2, some additional resistances which are not essential for further understanding not being shown in FIG. The distributor circuit V outlined in FIG. 2 essentially consists of an input stage E, a of variations in the supply voltage independent inverter J and an output driver A. The input stage E is formed with ei¬ nem with the input voltage applied Uj_ _n transistor T ₄ and an upstream him in a series circuit chen same transistor T3. The inverter J (known in principle from DE-C3-2 533 199, FIG. 1) is provided with a series connection of a first transistor T 1 and the same, provided with a collector resistor R; L and an emitter resistor R ₂ second transistor T2 formed. The (known in principle e.g. from DE-C3-2 849 231 and DE-C2-2 849 153)

Output driver A is formed with an emitter follower Tg, Rg and an identical transistor T5 connected in series with its transistor Tg. The distributor circuit V is an input voltage _U in an equally large output voltage U _out at:

It is on the one hand

U _v = U _BE1 + U _R1 + U _BE6 + U _0Ut (1)

and on the other hand

U _v = U _BE5 + U _BE3 + U _BE2 + U _R2 _{-U BE4} + 1 ^; (2)

where UgEj denotes the base-emitter voltage of a jth transistor Tj. Under the conditions U EI = ^U BE2, ^U BE3 ^{= U} BE ₄ ^unα ^ ^U _B E ₅ = ^U _B E ₆ and U _R1 = U, which must be met by appropriate dimensioning of the transistors and resistors (R ^ = R ₂ ) _R2 results from U _out = U _in .

Different types of resistors are available in modern semiconductor technologies. For example, in Siemens B6HF technology, three different types of resistance with different surface resistances can be used, which behave differently depending on the temperature and which can have different variations during manufacture. If one adapts a modified band gap circuit to such a resistance type, then the Voltage drop (URQ, URE in ^FIG D may be constant ^on resistors of this type, but on resistors of the other types may depend on the temperature and on parameter variations due to production process fluctuations.

To counter this, a separate bandgap circuit can be provided for each type of resistor, for example a band gap reference circuit designed for resistors in p-doped polysilicon, which has a base voltage U _out = U _p for current sources with p-doped Generates resistors, and a band gap reference circuit designed for resistors in n-doped polysilicon, which generates a base voltage U _n for current sources with n-doped resistors. However, on the one hand, more chip area is required for the additional circuits and, on the other hand, more power is also consumed by them. Such an increased power consumption is particularly important in the case of resistors with a low sheet resistance, because high currents flow here, provided the resistors are not to have exceptionally large dimensions, which would in turn cost expensive chip area.

The invention, on the other hand, shows a way to supply a base bias for current source transistors in bipolar IC circuits without having to set up a separate bandgap reference circuit for each type of resistor.

The invention relates to a circuit arrangement for the basic bias supply of current source transistors in bipolar IC circuits, with a bandgap reference circuit for supplying a base bias dependent on the temperature and resistance tolerances in such a way that the current supplied by the current source transistors arrives load resistors through which this current causes a constant voltage drop, and at least one downstream distribution circuit with an input stage, an output driver and a corresponding intermediate inverter, which is formed with a series circuit of a first transistor, a first resistor, a second transistor and a second resistor connected to the supply voltage; This circuit arrangement according to the invention is characterized in that for the base bias supply of current source transistors of a different type of resistor than the one for which the bandgap reference circuit is designed, in the associated distributor or, in other words, conversion circuit, the second resistor is of the resistance type for which the bandgap reference circuit is designed, and the first resistance is formed by the series connection of a resistance of this same resistance type and a resistance of the other resistance type.

The fact that a resistor made up of two partial resistors is combined in the distribution circuit for the base bias voltage, one of which is formed from the resistive materials of the actual bandgap circuit and the other of which is made up of the resistive materials of the resistors used in the transistor current sources Base bias for these current sources implemented in the distribution or conversion circuit in such a way that parameter variations and different temperature characteristics of the resistance types used are compensated for.

Further special features of the invention will become apparent from the following detailed explanation of the invention with reference to the drawings. 1 shows a basic circuit diagram of a circuit arrangement for basic bias supply of current source transistors in bipolar IC circuits, FIG. 2 shows a simplified circuit diagram of one contained therein

Distributor or converter circuit and FIG. 3 shows a basic circuit diagram of a circuit arrangement for basic bias voltage supply of current source transistors of different resistance types; 4 illustrates the structure of resistances, and FIG. 5 shows simulation results.

In the circuit arrangement for basic bias supply of current source transistors in bipolar IC circuits, shown schematically in a block diagram in FIG. 1, a bandgap reference circuit B modified in the sense explained at the outset is followed by two distributor circuits V via which, as shown in FIG 1 for two current source transistor circuits Q, such current source transistor circuits are supplied with a base bias, so that the current supplied by the current sources Q causes a constant voltage drop at the load resistors R _Q , RE through which they flow. This has already been explained at the beginning; Further explanations at this point are not necessary for understanding the invention.

As was also explained at the beginning, the distributor circuit V sketched in FIG. 2 essentially consists of an input stage E formed with a transistor T ₄ , which is supplied with the input voltage ^u in, and an identical transistor T _{3 connected} upstream of it in a series circuit , one with two identical transistors T] _, T ₂ , the second transistor T _{2 of which is provided} with a collector resistor R _j and an emitter resistor R ₂ , formed and independent of fluctuations in the supply voltage inverter J and one with an emitter follower Tg, Rg and one Output driver A formed in series with the same transistor T5 connected to the same transistor Tg.

It is now assumed, for example, that the modified bandgap reference circuit B is designed for resistors in p-doped polysilicon and generates a base voltage U _out = U _p for current sources with p-doped resistors. To supply current sources PQ, in which p-doped resistors PRc, P ^ E are used, a conventional distributor circuit V is then used, as is outlined in FIG. set which has the structure outlined in FIG. 2 and which supplies a base bias U _p with which the voltage drop across p-doped resistors (PRc / PRE) fluctuates as little as possible. In contrast, for supplying current sources ⁿ Q, in which n-doped resistors ⁿ RQ, ⁿ R-£ are used, a distributor or conversion circuit V is used, which supplies a base bias voltage U _n with which the voltage drop occurs n-doped resistors ( ⁿ Rc, ^Π RE) change as little as possible. In the distributor or conversion circuit V, which in turn has the structure outlined in FIG. 2, the transistors Ti and T ₂ , T3 and T ₄ and T5 and Tg are again dimensioned identically in pairs, so that by equating them in Eq. (1) and Eq. (2) standing expressions and with Uj_ _n = U _p , U _ou t = U _n the relationship

U _n = U _p + (U _R2 -U _R1 ) (3)

results.

In contrast to the conventional distribution circuit V the difference in the dropping at the resistors Rl and _R2 for adjusting the voltages Basisvor- εpannung used to verεchiedenen resistor types in the Umsetzεchaltung V. In the example, this is done in that the resistor R _{2 is} made entirely of p-doped silicon and the resistor Ri is made in a series circuit partly from p-doped silicon and partly from n-doped silicon. If deviations of both resistance types from their target values vanish, Ri and R _{2 are the} same, so that according to Eq. (3)

U _n = U _p (3a)

becomes.

If the n-doped resistors alone scatter, for example, to higher values, the voltage drop URI becomes greater than the voltage drop UR ₂ ; the voltage U _n is therefore in accordance with Eq. Be (3) is smaller alε up, so that with the thus reduced base bias voltage of the current sources (Q ⁿ⁾ with n-doped Wider¬ stands ⁽ⁿ Rc, ^Π RE) ^d i ^{e at} these sloping kon¬ stresses remain constant. The same stabilizing effect occurs when the n-doped resistors scatter to smaller values. If, on the other hand, the p-doped resistors scatter to higher values, the voltage U & ₂ becomes greater than the voltage UJ _Q because the resistance value of the resistor R ₂ increases more than the resistance value of the resistor Ri. According to Eq. (3) the voltage becomes U _{n should} therefore be greater than the voltage U _p , which is reduced to larger values by the bandgap circuit because of the scattering of the p-doped resistors. With appropriate dimensioning, the voltage U _n then remains constant.

The same stabilizing effect is achieved with other combinations of resistance scattering (both types of resistance scatter in the same or in the opposite direction); Therewith different temperature changes of the two types of resistance are inherently compensated.

For the following, in-depth consideration of the circuit arrangement, it is again assumed that the modified band gap reference circuit B is dimensioned for current sources with p-doped resistors and generates a base voltage U _p for current sources with p-doped resistors; The generated base bias U _p then depends on the temperature and on fluctuations of the p-doped resistors, so that Up = U _p (T, x _p ) can be written, in which T is the temperature and the factor x _{p is} the scatter of the p-doped resistors. The temperature response of the resistors should be disregarded in the following consideration, since it is implicit in the scatter. The complete differential of the base bias U _p iεt

Due to the dimensioning of the bandgap circuit B, the voltage drops across p-doped resistors remain constant with changes in temperature and with resistance scattering; the partial differentials in this case

and

(5b)

In common bipolar technologies, kp has a value of approximately -1 ...- 2 mV / K and k _x a value of approximately -25 ...- 30 mV. So that the voltage at the emitter resistor remains constant, the emitter current must change by a change in resistance dx by dl = -I dx. With the exponential law for the emitter current I = I _Ξ -e ^(u / ^u τ ⁾ dl = (I / U _τ ) -dU, thus du = -U _τ -dx. The distributor circuit or, in other words, converter circuit V generates the voltage U _n from the voltage U _{p in} accordance with

U _n = U _p + f (T, x _p , x _n ), (6)

which results in complete differential

dU _n = dU _{p +} ^ dT ₊ - ^ dx _{p +} ^ dx _n (7) δT öx _p dx _n

results

If the voltage drops at n-doped resistors should also be constant with changes in temperature and resistance scattering, then U _n must also apply

dU _n = k _τ dT + k _x dx _n . (8th) If one puts the expressions of Eq. (7) and Eq. (8) equal to each other and uses Eq. (4) with Eq. (5a) and Eq. (5b), we get

This equation is fulfilled if the following conditions are met:

1F ^{= 0} ' ^(10a)

—- ^ = - k _x , (10b) dx _p

- ^ - = + k _x . (10c) dx _n

Condition (10a) means that the temperature response of the

Current source transistors are compensated only with the bandgap circuit B (and not with the conversion circuit V); condition (10b) means that the conversion circuit V cancels the voltage correction caused by a scatter (x _p ) of p-doped resistors, and with the fulfillment of the

Condition (10c) is a voltage correction caused by a scattering (χ _n ) of n-doped resistors.

Let us now consider a conversion circuit V (in FIG. 3) of the structure outlined in FIG. 2, in which the resistor R _{i is} composed of a p-doped resistor and an n-doped resistor. The voltage difference UR ₂ -URI in Eq. (3) To be able to calculate, one must know the current flowing through the resistors Ri and R ₂ . It results from the mesh U _v - T ₅ - T ₃ - Tg - U ₂ - T ₄ - U-j_ _n with ^u in = ^u p ^z u _T U _V -3U _BE - (U _P -U _BE ) HK2) - - ^• (11)

With this one obtains from Eq. (3)

R, -R

".-f" p ⁺ 1 (U _V -2U _BE ). (12)

The bias voltage U _v can advantageously be derived from a plurality of base-emitter voltages, so that the term (U _v - 2 -ÜBE) can be expressed by m-UßE, a practical value for m iεt 2.5 .

The resistor R ₂ made of p-doped polysilicon scatters with the factor Xp:

R ₂ = Xp-R; (13)

the resistance Ri, which is made to a fraction (1-μ) of p-doped silicon and the fraction μ of n-doped silicon, scatters according to the relationship

R ₁ = [(l-μ) x _p + μx _n ] R. (14)

In G1. (12) used results in

U _n is consequently a function of Up, x _p , x _n and - via the temperature dependence of the base-emitter voltage - also of T.

The dimensioning of the circuit is based on the target values x _n = 1 and Xp = 1, at which the compensation should be exact; this point x _n = 1, x _p = 1 is also called the development point.

At the development point x _n = 1, x _p = 1, the partial differentials can be calculated according to Eq. (10a, 10b, 10c) now write as ÖU _g δU

= μ -0 BE (16a) dτ dτ

dυ ⁵ - = + μ (U _p - mU _BE ) (16c) dx _n

off, so that in general —- = (l-μ) + μ— ≠ l; in the development dU _p x _p point, however, because of - = 1, the differential is - - = (l- μ) + μ- = lx _p dU _p 1 and thus as it is required (in Eq. (6)) . [At - ≠ l

Xp this requirement is no longer exactly met; the conversion circuit works the more precisely the better the condition is fulfilled.] The partial derivative according to the temperature is zero, which is the requirement from Eq. (lθa) corresponds. In order to meet the conditions of Eq. (10b, 10c) must satisfy μ

μ = K (17)

U _p -mU _BE

to get voted. If one assumes a value of approx. -0.75 V for the expression Up - mUgE and sets k _x = -30 mV, then μ = 0.04. This can be achieved with a resistor Ri, which is realized with a series connection of 4% n-doped resistor material and 96% p-doped resistor material.

The resistance Ri of the distribution or conversion circuit V in the exemplary embodiment considered here must therefore consist of 4% of the material for which the modified band gap Reference circuit B is not designed and to which it must therefore be adapted by means of the conversion circuit V. If polysilicon resistors with different doping materials are involved, the resistor Ri must be implemented with two resistors of the two types connected in series. In order not to form any asymmetries with regard to the contact holes, the resistor R _{2 should also be constructed} from a series connection of two resistors, both of which consist of the resistance material of the band gap reference circuit B.

In Siemens B6HF technology, another type of resistor can also be produced from heavily p-doped polysilicon by omitting a mask which is placed over resistors which are weakly doped by comparison. If the bandgap reference circuit B is constructed with weakly (p ^~ ) p-doped resistors and the base bias is to be adapted to current sources with heavily p-doped resistors by means of a conversion circuit V, the resistor Ri can be very easily with the aid of a Mask, which covers only part of the resistance, as a series circuit of a high (p ⁺ ) and a low (p ^~ ) p-doped resistor. This can also be seen from FIG. 4, in which, in the case of the two resistors R 1 and R ₂ provided with contacts K, the respective mask is designated by M. The resistor Ri is then heavily p-doped in its right part and has a sheet resistance value of, for example, 60 ohms / square, while it is weakly p-doped in its left part (just like the entire resistor R ₂ ) and has a sheet resistance value of, for example 1000 ohms / square.

FIG. 5 also shows a simulation result in two diagrams, the voltage drop across a heavily p-doped resistor (p ⁺ resistor) in the upper diagram and the voltage drop across a weakly p-doped resistor in the lower diagram (p ^~ - Resistance) above the scatter factor of the p ⁺ resistance value for various temperatures (temp) and scatter values (xr) of the (in the bandgap reference circuit B „„, „„, „PCT / DE96 / 01364 O 97/05537

13)) weakly p-doped resistance material (p ^~ resistance) is shown. The voltage drop fluctuates by less than 12 mV, it should be noted that the voltage drop across the weakly p-doped resistors fluctuates by 8 mV due to inadequacies in the bandgap reference.

Claims

claims

1. Circuit arrangement for basic bias supply of

Current source transistors in bipolar IC circuits, with a bandgap reference circuit (B) for supplying a base bias voltage which is dependent on the temperature and resistance tolerances in such a way that the current supplied by the current source transistors disturbs the load current flowing through it. which causes a constant voltage drop, and at least one downstream circuit (V) with an input stage (E), an output driver (A) and an interposed inverter (J) connected to it and supplying the respective base bias voltage the supply voltage-connected series circuit of a first transistor (Ti), a first resistor (R _i ), a second transistor (T ₂ ) and a second resistor (R ₂ ) is formed, characterized in that for the basic bias voltage supply of current source transistors of another type of resistor than that for which the bandgap reference circuit (B) is designed i st, in the associated distributor or converter circuit (V) the second resistor (R ₂ ) is of the type of resistor for which the bandgap reference circuit (B) is designed, and the first resistor (Ri) is formed by the series connection of a resistor of this type of resistor and a resistor of the other type of resistor.

2. Circuit arrangement according to claim 1, characterized in that the first resistor (RD TO a fraction μ = -

U _w -mU _BE

[where k _{x is} the partial differential of that of the modified

Bandgap reference circuit (B) generated base bias according to the scattering factor of the resistance material of the modified

Bandgap reference circuit (B) iεt, U _{w is} the base bias generated by the modified bandgap reference circuit (B) iεt and m-UgE the base multiplied by a factor m The emitter voltage of the input circuit and output driver transistors of the distributor or converter circuit (V) is made of the material for which the modified band gap reference circuit (B) is not designed.

3. Circuit arrangement according to claim 1 or 2, characterized in that the second resistor (R ₂ ) is formed by the series connection of two resistors of the resistance type for which the bandgap reference circuit (B) is designed.