CA2228387A1 - Circuit arrangement for supplying the base bias voltage of current source transistors in bipolar ic circuits - Google Patents
Circuit arrangement for supplying the base bias voltage of current source transistors in bipolar ic circuits Download PDFInfo
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- CA2228387A1 CA2228387A1 CA002228387A CA2228387A CA2228387A1 CA 2228387 A1 CA2228387 A1 CA 2228387A1 CA 002228387 A CA002228387 A CA 002228387A CA 2228387 A CA2228387 A CA 2228387A CA 2228387 A1 CA2228387 A1 CA 2228387A1
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
- G05F3/00—Non-retroactive systems for regulating electric variables by using an uncontrolled element, or an uncontrolled combination of elements, such element or such combination having self-regulating properties
- G05F3/02—Regulating voltage or current
- G05F3/08—Regulating voltage or current wherein the variable is dc
- G05F3/10—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics
- G05F3/16—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics being semiconductor devices
- G05F3/20—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations
- G05F3/30—Regulators using the difference between the base-emitter voltages of two bipolar transistors operating at different current densities
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
- G05F3/00—Non-retroactive systems for regulating electric variables by using an uncontrolled element, or an uncontrolled combination of elements, such element or such combination having self-regulating properties
- G05F3/02—Regulating voltage or current
- G05F3/08—Regulating voltage or current wherein the variable is dc
- G05F3/10—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics
- G05F3/16—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics being semiconductor devices
- G05F3/20—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations
- G05F3/22—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations wherein the transistors are of the bipolar type only
- G05F3/222—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations wherein the transistors are of the bipolar type only with compensation for device parameters, e.g. Early effect, gain, manufacturing process, or external variations, e.g. temperature, loading, supply voltage
- G05F3/227—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations wherein the transistors are of the bipolar type only with compensation for device parameters, e.g. Early effect, gain, manufacturing process, or external variations, e.g. temperature, loading, supply voltage producing a current or voltage as a predetermined function of the supply voltage
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- Power Engineering (AREA)
- Control Of Electrical Variables (AREA)
- Semiconductor Integrated Circuits (AREA)
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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
DeEcription Circuit arrangemen' for supplying the base bias voltage of current source transistors in bipolar IC circuits.
For current source transistors of the kind that freguently appear in integrated bipolar circuits, the reguired base bias voltage is often obta;ne~ with the aid of a bandgap reference circuit. Bandgap reference cir-cuits, as are disclosed for example in Tietze, Schenk:
Ealbleiter-Schaltungstechnik ~Semiconductor circuitry~, 5th edition, Berlin Heidelberg New York 1980, Figs. 16.29 and 16.30, and 9th edition, Berlin Heidelberg New York Tokyo 1991, Figs. 18.29 to 18.31, generate per se a voltage of, $or example, approximately 1.2 V which is constant independently of the temperature and of resis-tance tolerances. In integrated bipolar circuits, how-ever, current source transistors reguire a base bias voltage which has a specific depen~nce with regard to the temperature and the resistance tolerances, namely such that the current supplied by the current sources causes a constant voltage drop across the load resistors through which the current flows. Such a dep~n~nce is eff~ected in practice with the aid of a correspQ~;ngly modified bandgap reference circuit. In order then to decouple individual circuit sections that are supplied wit'h the base bias ~oltage from one another and in order not to load the bandgap circuit to an excessively great extent, the base bias voltage is passed to the individual circuit blocks via distributor circuits. This circuit principle, which is customary in practice, is illustrated in FIG. 1, in which the modified bandgap reference circuit is designated by B and two distributor circuits are designated by V.
Such a distributor circuit may have the circuit structure sketched in FIG. 2; a number of additional resLstors that are not essential for a further under-8tal~; ng are not illustrated in FIG. 2. The distributor circuit V sketched in FIG. 2 essentially comprises an GR g5 P 1707 P la input ~tage E, an GR '35 P 1707 P 2 invertor J, which is independent of fluctuations in the supply voltage, and an output driver A. The input stage E ie formed by a traneietor T4, to which the input volt:age Uin ie applied, and an identical traneietor T3, 5 whic-h i8 connected upstream of said transistor T4 in a seri.es circuit. The invertor J (disclosed in principle for instance in DE-C3-2 533 199, Figure 1) ie formed by a series circuit comprising a first transistor Tl and an identical, second transietor T2 which ie provided with a 10 collector resistor Rl and an ~n;tter resietor R2. The output driver A (diecloeed in principle for example in DE-C'3-2 849 231 and DE-C2-2 849 153) is formed by an emitter follower T6, R6 and an identical traneietor T5 which ie connected in seriee with the traneietor T6 of 15 saidL emitter follower. The distributor circuit V converts an input voltage U$n into an output voltage UOUt of identical magnitude:
On the one hand, UV = UBE1 + UR1 + U8E6 + UOUt (1) and, on the other hand, IJV = UBE5 + UBE3 + UBE2 + ~R2 UBE4 + Uin; (2) where UBEj designates the base-emitter voltage of a jth traneietor Tj. Under the condition8 UBE1 = UBE2' UBE3 = UBE4 and IJBE5 = UBE6 and al80 ~R1 = UR2~ which can be fulfilled 25 by correspon~l;ng dimensioning of the transietore and of the reeistore (Rl = R2), UOUt = Uin reeulte from thie.
Various types of reeistors are available in modern semiconductor technologies. Thue, in Siemens B6HF
technology, for example, three different types of reeie-30 tore having different eheet reeietances are used, whichresietor typee behave differently as a function of the temperature and may have different variatione in the course of manufacture. If a modified bandgap circuit ie adapted to euch a reeietor type, then the GR l95 P 1707 P 3 volltage drop (IJRc' IJRE in FIG- 1) across reE~i8tor8 of thi8 type will be constant, but across resistors of the other typos will be dependent on the temperature and on para-meter variations that are governed by fluctuations in the mamlfacturing process.
In order to counter that, it is possible to provide a separate bandgap circuit for e~ach type of resiLstors, in other words, for example, a bandgap refer-ence circuit which i8 designed for resistors in p-doped polysilicon and generates a base voltage U0ut = Up for current sources with p-doped resistors, and a bandgap reference circuit which i8 designed for resistors in n-doped polysilicon and generates a base voltage Un for current sources with n-doped resistors. However, on the one hand, this rec~uires more chip area for the additional circuits and, on the other hand, the latter also consume more! power. Such an increased power consumption is esse!ntial particularly in the case of resistors having a low sheet resistance because in this case high currents flow if the resistors are not to a~sume exceptionally large dimensions - which, however, would in turn cost a great deal in terms of chip area.
By contrast, the invention shows a way to supply the base bias voltage of current source transistors in bipolar IC circuits without having to construct a separ-ate bandgap reference circuit for each type of resistors.
The invention relates to a circuit arrangement for supplying the base bias voltage of current source transistors in bipolar IC circuits, having a bandgap reference circuit for supplying a base bias voltage which is dependent on the temperature and on resistance toler-ances in such a way that the current supplied by the current source transistors causes a constant voltage drop across load resistors through which said current flows, and at least one distributor circuit, which is connected downRtream of said bandgap reference circuit, outputs the respective base bias voltage and has an input stage, an output driver and an GR '35 P 1707 P 4 inte~rmediate invertor, which iB formed by a series circuit which is connected to the supply voltage and com~rises a first transistor, a first resistor, a second transistor and a second resistor; according to the S inve~ntion, this circuit arrangement is characterized in that: in order to supply the base bias voltage of current source transistors of a different resistor type than that for which the bandgap reference circuit is designed, in the associated distributor or, to put it another way, conversion circuit, the second resistor is of that resis-tor type for which the bandgap reference circuit is desi.gned, and the first resistor is formed by the series circuit comprising a resistor of that very resistor type and a resistor of the other resistor type.
By virtue of the fact that a resistor is combined from two resistor elements in the distribution circuit for the base bias voltage, one of which resistor elements i~ formed from the resistor materials of the actual bandLgap circuit and the other of which resistor elements is i-ormed from the resistor materials of the resistors usedL in the transistor current sources, the base bias voltage for these current sources is converted in the dist.ribution or conversion circuit in such a way that parameter variations and different temperature responses of t.he resistor types used are compensated for.
Further special features of the invention will become evident from the following more detailed explana-tion. of the invention with reference to the drawings, in which FIG.l shows a basic circuit diagram of a circuit arrangement for supplying the base bias voltage of current source transistors in bipolar IC cir-cuits, FIG. 2 shows a simplified circuit diagram of a distribu-tor or conversion circuit cont~;ne~ therein, and FIG. 3 shows a basic circuit diagram of a circuit arrangement for supplying the base bias voltage of current source transistors of different resis-tor types;
GR !~5 P 1707 P 5 FIG.4 illustrates the structure of resistors, and FIG. 5 shows simulation results.
In the circuit arrangement for supplying the base biat3 voltage of curre!nt source transistors in bipolar IC
circuits which is illustrated diagrA~tically in a block circuit diagram in FIG. l, two distributor circuits V are comlected downstream of a bandgap reference circuit B
which is modified in the sense explained in the introduc-tion, via which distributor circuits, as is illustrated in FIG. 1 for two current source transistor circuits Q, 8uch current source transistor circuits are supplied with a base bias voltage, with the result that the current supplied by the current sources Q causes a constant volt:age drop across the load resistors RC, RE through whic:h said current flows. This has already been explained in t.he introduction; further explanations in this respect at t:his point are not necessary for an underst~n~; ng of the invention.
As has likewise already been explained in the introduction, the distributor circuit V sketched in FIG. 2 essentially comprises an input stage E formed by a transistor T4, to which the input voltage Uin is applied, and an identical transistor T3, which is con-nect.ed upstream of said transistor T4 in a series cir-cuit., an invertor J formed by two identical transistorsT1, T2, the second transistor T2 of which is provided with a collector resistor R1 and an emitter resistor R2, which invertor is independent of fluctuations in the supply volt.age, and an output driver A formed by an emitter follower T6, R6 and an identical transistor T5 which is connected in series with the transistor T6 ~f said emitter follower.
Let it now be assumed, for example, that the modified bandgap reference circuit B is designed for resistors in p-doped polysilicon and generates a base voltage of U0ut = Up for current sources with p-doped resistors. In order to supply current sources PQ in which p-doped resistors PRC, PRE are used, then, as is sketched in FIG. 3, a conventional distributor circuit V is used GR !~5 P 1707 P 6 which has the structure sketched in FIG. 2 and supplies a base bias voltage Up with which the voltage drop across p-doped resistors (PRC, PRE) fluctuates as little as posl3ible. In order to supply current sources nQ in which n-doped resistors nRC, nRE are used, on the other hand, a dist:ributor or conversion circuit V' is used which supplies a base bias voltage Un with which the voltage drop across n-doped resistors (nR~, nR~) changes as little as possible. In the distributor or conversion circuit V', whic:h again has the structure s~etched in FIG. 2, the transistors Tl and T2, T3 and T4 and also T5 and T6 are again dimensioned identically in pairs, 80 that by ec~ua~ting the expressions in Eclu. (1) and Eclu. (2) and wit~l Uin = Up~ Uout = ~n~ the relationship ~n = UP ~ (IJR2 IJRl) (3) is E~roduced.
In contrast to the conventional distributor circuit V, the difference between the voltage drops across the resistors Rl and R2 is used in the conversion circuit V' for the purpose of matc~;ng the base biaLs voltage to the different types of resistors. In the exa~le, this is done by producing the resistor R2 comF~letely from p-doped silicon and the resistor Rl in a ~eries circuit partly made of p-doped silicon and partly made of n-doped silicon. Given infinitesimal deviations of both types of resistors from their target values, Rl and R2 are identical, thereby affording, according to Eclu. (3), Un = Up (3a).
If solely the n-doped resistors vary for example to ~higher values, then the voltage drop UR1 become~
greater than the voltage drop UR2; according to Eclu. (3), therefore, the voltage Un will be less than Up, 80 that with the base bias voltage, reduced in this way, of the current sources (nQ) with n-doped re~istors (nRC, nRE), the voltage drops across the latter remain constant. The same stabilizing effect occurs when the n-doped resistorl3 vary to smaller value~3. If, on the other hand, solely the p-doped resistors vary to higher values, then the voltage UR2 becomes greater than the voltage ~JRl~ because the resil3tance of the resistor R2 increasos to a greater extent than the resistance of the resistor Rl. According to Equ. (3), therefore, the voltage Un will be greater than the voltage Up, which, owing to the variation of the p-do]ped resistors to larger values, is reduced by the bandgap circuit. As a result, the voltage Un then remains constant, given corresp~n~;ng dimensioning.
The same stabilizing effect is achioved with othe:r combinations of resistor variations (both types of resi~3tors vary in the same direction or in opposite directions); as a result, different temperature responses of the two types of resistors are also inherently compon-sated for.
With regard to the following more comprehensive cons:ideration of the circuit arrangement, let it again be assumed that the modified bandgap reference circuit B is dimen~3ioned for current sources with p-doped resistors and s~enerates a base voltage Up for current sources with p-doped resistors; the base bias voltage Up generated is then dependent on the temperature and on fluctuations of the p-doped resil3tors, 80 that it is possible to write Up = Up (T, xp), where T is the temperature and the factor xp expresses the variation of the p-doped resistors. The temperature response of the resistors will be disregarded in the following consideration, since it is cont~ine~
implicitly in the variations.
The t:otal derivative of the base bias voltage Up is ~Up ~Up dUp = dT+ - dzp. (4) ~T ~xp On account of the dimQnisioning of the bandgap circuit B, the voltage drops across p-doped resistors remain constant in the event of changes in temperature and in the event of resistor variations; the partial derivatives will in this case be - = kT (5a) ~T
and ~Up = kx. (5b) ~xp In customary bipolar technologies, kT has a value of about -1...-2 mV/R and kx has a value of about -25...
-30 mV. In order that the voltage across the emitter resii~tor remains constant, the emitter current must change by dI = -I dx in the event of a resistor change dx. Using the exponential law for the emitter current I = I8.e (~/UT)~ dI = (I/UT) .dU, and consequently dU = _UT. dx. The distributor circuit or, to put it anotller way, converter circuit V~ generates from the voltege Up the voltage Un in accordance with Un=Up + f(T,xp~xn)~ (6) which produces the total derivative ~Un ~Un ~Un dUn = dUp + - dT + - dx + - dx (7) If the voltage drops across n-doped resistors are now al80 intended to be constant in the event of change~
in t~mperature and in the event of resistor variations, then the following must also hold true for Un , dUn = kTdT + kxdXn~ (8) If the expressions of Equ. (7) and Equ. (8) are eguated with one another and Equ. (4) i8 used with Equ.
(5a) and Equ. (5b) then ~Un ~Un ~Jn kTdT+kxdxp+ - dT+ - dxp+ - dxn=kTdT+kxdxn~ (9) is obtained. This equation is satisfied when the follow-ing conditions are fulfilled:
~Un = O (lOa) ~T
~U
n kx ( lOb) ~xp 15 ~U
n ~ (lOc) n The condition (lOa) means that the temperature response of the current source transistors is compensated for solely by the bandgap circuit B (and not by the conversion circuit V ); the condition (lOb) means that the conversion circuit V~ reverl3es the voltage correction effected as a result of a ~ariation (xp) of p-doped resil3tors; and fulfilling the condition (lOc) effects a voltage correction as a result of a variation (xn) of n-doped resistors.
There will now follow a consideration of a conversion circuit V (in FIG. 3) which has the structure sketched in FIG. 2 and in which the resistor Rl i8 composed of a p-doped resistor and an n-doped resistor.
In order to be able to calculate the voltage difference UR2 UR1 in Equ. (3) it is necessary to know the current flowing through the resistors Rl and R2. It results from the mesh Uv - Ts - T3 - T6 ~ U2 ~ T4 ~ ~in' given ~in = ~p' as GR "5 P 1707 P 10 I (R2) = 8E ( P ~BE) (11) The following is th~s obtained from Equ. (3) U = _ U + (~ -2~BE)- (12) The bias voltage Uv can advantageously be derived from a plurality of base-emitter voltages, with the result that the term (Uv - 2 UBE) can be expressed by m UBE; a practical value for m is 2. 5.
The resistor R2 made of p-doped polysilicon varies by the factor xp :
R2 = xp R; (13) the resistor R1, a fraction (1-~) of which is produced from p-doped silicon and the fraction ~ of which is produced from n-doped silicon, varies according to the relationship R1 = ~ )xp+~xnlR. (14) Insertion into Equ. ( 12) thus yields Un = ~ ) +~ n ~ Up+~ ~ 1- n ~ mUB~. (15) With a given division ratio ~, U~ is consequently a function of Up, xp, xn and - by way of the temperature dependence of the base-emitter voltage - also of T.
The dimen~ioning of the circuit is based on the target valu/es xn = 1 and xp = 1 at which the compensation is intended to be exact; at this point xn = 1, xp = 1 is also called the development point.
At the development point xn = 1, xp = 1, the partial derivatives according to Equ. (lOa, lOb, lOc) can now be written as GR '35 P 1707 P 11 ~n ~UB~
= ~ ~ - 116a) ~T~T
n -m~B~) (16b) ~xp ~Jn +~(~p m~BE) (16c) Xn According to Equ. 15, Un dopends on Up with the factor (1-~)+~ - , with the rosult that, in general, d~ )+~ ~ ~1 ; at the development point, however, owin,g to ~ =1 , the derivative d~ )+~1 1 and is thu~ as required (in Equ. (6)). tGiven n~l this requirement is no longer fulfilled exactly; the 15 conversion circuit operates more accurately the better the condition is fulfilled]. The partial derivative with respect to temperature is zero, which corresponds to the requirement from Equ. (lOa). In order to fulfill ths conditions of Equ. (lOb, lOc), ~ must be chosen to be ~ = (17) ~Jp - mUBE
If a value of approximately -0.75 V is assumed for the expression Up - mUB~ and ~x = -30 mV is set, then ~ must be equal to 0.04. This can be achieved with a resistor Rl which is realized by a series circuit of 4% n-doped resistor material and 96% p-doped resistor material.
In the exemplary ~mhodiments considered here, therefore, the resistor Rl of the distribution or conver-sion circuit V' must be composed to the extent of 4% of that material for which the modified bandgap GR !~5 P 1707 P 12 reference circuit B i8 not designed and to which it must therefore be matched by the conversion circuit B'.
If polysilicon resistors having different doping materials are involved, then the resistor R1 must be realized by two series-connected resistors of the two types. In order not to form any asymmetries with regard to the contact holes, the resistor R2 should also be conE~tructed from a series circuit of two resistors, which are both composed of the resistor material of the bandgap reference circuit B.
In Siemens B6HF technology, it is also possible to produce a further type of resistor from hea~ily p-doped silicon, in that during the course of production, a m;sk which is placed over resistors that are to be doped weakly in comparison therewith is omitted. If the banclgap reference circuit B is constructed with weakly (p~) p-doped resistors and the base bias voltage is to be matched by means of a conversion circuit V' to current sources with hea~ily p-doped resistors, then the resistor R1 can be constructed as a series circuit comprising a heavily (p+) and a weakly (p~) p-doped resistor in a very simF,le manner with the aid of a mask which covers only part of the resistor. This also becomQs evident from FIG. 4, in which the respective mask is designated by M
for the two resistors R1 and R2 which are provided with contacts R. In its right-hand part, the resistor R1 is then heavily p-doped and has a sheet resistance of, for example, 60 ohms/square, whereas it is weakly p-doped in its left-hand part (just like the entire resistor R2) and ha~ a sheet resistance of, for example, 1000 ohms/square.
FIG. 5 shows a simulation result in two diagrams, in the upper diagram the voltage drop across a heavily p-doped resistor (p+-type resistor) and in the lower diagram the voltage drop across a weakly p-doped resistor (p~-type resistor) being illustrated against the vari-ation factor of the pt-type resistance for different temperatures (temp) and variation values (xr) of the weakly p-doped resistor material GR .'95 P 1707 P 13 (p~-type resistor) (u~ed in the bandgap reference circuit B). The voltage drop fluctuate~ by less than 12 mV, in which case it should be noted that the voltage drop across the wea~ly p-doped resistors already fluctuate~ by 8 mtr on account of shortcomings of the bandgap reference.
For current source transistors of the kind that freguently appear in integrated bipolar circuits, the reguired base bias voltage is often obta;ne~ with the aid of a bandgap reference circuit. Bandgap reference cir-cuits, as are disclosed for example in Tietze, Schenk:
Ealbleiter-Schaltungstechnik ~Semiconductor circuitry~, 5th edition, Berlin Heidelberg New York 1980, Figs. 16.29 and 16.30, and 9th edition, Berlin Heidelberg New York Tokyo 1991, Figs. 18.29 to 18.31, generate per se a voltage of, $or example, approximately 1.2 V which is constant independently of the temperature and of resis-tance tolerances. In integrated bipolar circuits, how-ever, current source transistors reguire a base bias voltage which has a specific depen~nce with regard to the temperature and the resistance tolerances, namely such that the current supplied by the current sources causes a constant voltage drop across the load resistors through which the current flows. Such a dep~n~nce is eff~ected in practice with the aid of a correspQ~;ngly modified bandgap reference circuit. In order then to decouple individual circuit sections that are supplied wit'h the base bias ~oltage from one another and in order not to load the bandgap circuit to an excessively great extent, the base bias voltage is passed to the individual circuit blocks via distributor circuits. This circuit principle, which is customary in practice, is illustrated in FIG. 1, in which the modified bandgap reference circuit is designated by B and two distributor circuits are designated by V.
Such a distributor circuit may have the circuit structure sketched in FIG. 2; a number of additional resLstors that are not essential for a further under-8tal~; ng are not illustrated in FIG. 2. The distributor circuit V sketched in FIG. 2 essentially comprises an GR g5 P 1707 P la input ~tage E, an GR '35 P 1707 P 2 invertor J, which is independent of fluctuations in the supply voltage, and an output driver A. The input stage E ie formed by a traneietor T4, to which the input volt:age Uin ie applied, and an identical traneietor T3, 5 whic-h i8 connected upstream of said transistor T4 in a seri.es circuit. The invertor J (disclosed in principle for instance in DE-C3-2 533 199, Figure 1) ie formed by a series circuit comprising a first transistor Tl and an identical, second transietor T2 which ie provided with a 10 collector resistor Rl and an ~n;tter resietor R2. The output driver A (diecloeed in principle for example in DE-C'3-2 849 231 and DE-C2-2 849 153) is formed by an emitter follower T6, R6 and an identical traneietor T5 which ie connected in seriee with the traneietor T6 of 15 saidL emitter follower. The distributor circuit V converts an input voltage U$n into an output voltage UOUt of identical magnitude:
On the one hand, UV = UBE1 + UR1 + U8E6 + UOUt (1) and, on the other hand, IJV = UBE5 + UBE3 + UBE2 + ~R2 UBE4 + Uin; (2) where UBEj designates the base-emitter voltage of a jth traneietor Tj. Under the condition8 UBE1 = UBE2' UBE3 = UBE4 and IJBE5 = UBE6 and al80 ~R1 = UR2~ which can be fulfilled 25 by correspon~l;ng dimensioning of the transietore and of the reeistore (Rl = R2), UOUt = Uin reeulte from thie.
Various types of reeistors are available in modern semiconductor technologies. Thue, in Siemens B6HF
technology, for example, three different types of reeie-30 tore having different eheet reeietances are used, whichresietor typee behave differently as a function of the temperature and may have different variatione in the course of manufacture. If a modified bandgap circuit ie adapted to euch a reeietor type, then the GR l95 P 1707 P 3 volltage drop (IJRc' IJRE in FIG- 1) across reE~i8tor8 of thi8 type will be constant, but across resistors of the other typos will be dependent on the temperature and on para-meter variations that are governed by fluctuations in the mamlfacturing process.
In order to counter that, it is possible to provide a separate bandgap circuit for e~ach type of resiLstors, in other words, for example, a bandgap refer-ence circuit which i8 designed for resistors in p-doped polysilicon and generates a base voltage U0ut = Up for current sources with p-doped resistors, and a bandgap reference circuit which i8 designed for resistors in n-doped polysilicon and generates a base voltage Un for current sources with n-doped resistors. However, on the one hand, this rec~uires more chip area for the additional circuits and, on the other hand, the latter also consume more! power. Such an increased power consumption is esse!ntial particularly in the case of resistors having a low sheet resistance because in this case high currents flow if the resistors are not to a~sume exceptionally large dimensions - which, however, would in turn cost a great deal in terms of chip area.
By contrast, the invention shows a way to supply the base bias voltage of current source transistors in bipolar IC circuits without having to construct a separ-ate bandgap reference circuit for each type of resistors.
The invention relates to a circuit arrangement for supplying the base bias voltage of current source transistors in bipolar IC circuits, having a bandgap reference circuit for supplying a base bias voltage which is dependent on the temperature and on resistance toler-ances in such a way that the current supplied by the current source transistors causes a constant voltage drop across load resistors through which said current flows, and at least one distributor circuit, which is connected downRtream of said bandgap reference circuit, outputs the respective base bias voltage and has an input stage, an output driver and an GR '35 P 1707 P 4 inte~rmediate invertor, which iB formed by a series circuit which is connected to the supply voltage and com~rises a first transistor, a first resistor, a second transistor and a second resistor; according to the S inve~ntion, this circuit arrangement is characterized in that: in order to supply the base bias voltage of current source transistors of a different resistor type than that for which the bandgap reference circuit is designed, in the associated distributor or, to put it another way, conversion circuit, the second resistor is of that resis-tor type for which the bandgap reference circuit is desi.gned, and the first resistor is formed by the series circuit comprising a resistor of that very resistor type and a resistor of the other resistor type.
By virtue of the fact that a resistor is combined from two resistor elements in the distribution circuit for the base bias voltage, one of which resistor elements i~ formed from the resistor materials of the actual bandLgap circuit and the other of which resistor elements is i-ormed from the resistor materials of the resistors usedL in the transistor current sources, the base bias voltage for these current sources is converted in the dist.ribution or conversion circuit in such a way that parameter variations and different temperature responses of t.he resistor types used are compensated for.
Further special features of the invention will become evident from the following more detailed explana-tion. of the invention with reference to the drawings, in which FIG.l shows a basic circuit diagram of a circuit arrangement for supplying the base bias voltage of current source transistors in bipolar IC cir-cuits, FIG. 2 shows a simplified circuit diagram of a distribu-tor or conversion circuit cont~;ne~ therein, and FIG. 3 shows a basic circuit diagram of a circuit arrangement for supplying the base bias voltage of current source transistors of different resis-tor types;
GR !~5 P 1707 P 5 FIG.4 illustrates the structure of resistors, and FIG. 5 shows simulation results.
In the circuit arrangement for supplying the base biat3 voltage of curre!nt source transistors in bipolar IC
circuits which is illustrated diagrA~tically in a block circuit diagram in FIG. l, two distributor circuits V are comlected downstream of a bandgap reference circuit B
which is modified in the sense explained in the introduc-tion, via which distributor circuits, as is illustrated in FIG. 1 for two current source transistor circuits Q, 8uch current source transistor circuits are supplied with a base bias voltage, with the result that the current supplied by the current sources Q causes a constant volt:age drop across the load resistors RC, RE through whic:h said current flows. This has already been explained in t.he introduction; further explanations in this respect at t:his point are not necessary for an underst~n~; ng of the invention.
As has likewise already been explained in the introduction, the distributor circuit V sketched in FIG. 2 essentially comprises an input stage E formed by a transistor T4, to which the input voltage Uin is applied, and an identical transistor T3, which is con-nect.ed upstream of said transistor T4 in a series cir-cuit., an invertor J formed by two identical transistorsT1, T2, the second transistor T2 of which is provided with a collector resistor R1 and an emitter resistor R2, which invertor is independent of fluctuations in the supply volt.age, and an output driver A formed by an emitter follower T6, R6 and an identical transistor T5 which is connected in series with the transistor T6 ~f said emitter follower.
Let it now be assumed, for example, that the modified bandgap reference circuit B is designed for resistors in p-doped polysilicon and generates a base voltage of U0ut = Up for current sources with p-doped resistors. In order to supply current sources PQ in which p-doped resistors PRC, PRE are used, then, as is sketched in FIG. 3, a conventional distributor circuit V is used GR !~5 P 1707 P 6 which has the structure sketched in FIG. 2 and supplies a base bias voltage Up with which the voltage drop across p-doped resistors (PRC, PRE) fluctuates as little as posl3ible. In order to supply current sources nQ in which n-doped resistors nRC, nRE are used, on the other hand, a dist:ributor or conversion circuit V' is used which supplies a base bias voltage Un with which the voltage drop across n-doped resistors (nR~, nR~) changes as little as possible. In the distributor or conversion circuit V', whic:h again has the structure s~etched in FIG. 2, the transistors Tl and T2, T3 and T4 and also T5 and T6 are again dimensioned identically in pairs, 80 that by ec~ua~ting the expressions in Eclu. (1) and Eclu. (2) and wit~l Uin = Up~ Uout = ~n~ the relationship ~n = UP ~ (IJR2 IJRl) (3) is E~roduced.
In contrast to the conventional distributor circuit V, the difference between the voltage drops across the resistors Rl and R2 is used in the conversion circuit V' for the purpose of matc~;ng the base biaLs voltage to the different types of resistors. In the exa~le, this is done by producing the resistor R2 comF~letely from p-doped silicon and the resistor Rl in a ~eries circuit partly made of p-doped silicon and partly made of n-doped silicon. Given infinitesimal deviations of both types of resistors from their target values, Rl and R2 are identical, thereby affording, according to Eclu. (3), Un = Up (3a).
If solely the n-doped resistors vary for example to ~higher values, then the voltage drop UR1 become~
greater than the voltage drop UR2; according to Eclu. (3), therefore, the voltage Un will be less than Up, 80 that with the base bias voltage, reduced in this way, of the current sources (nQ) with n-doped re~istors (nRC, nRE), the voltage drops across the latter remain constant. The same stabilizing effect occurs when the n-doped resistorl3 vary to smaller value~3. If, on the other hand, solely the p-doped resistors vary to higher values, then the voltage UR2 becomes greater than the voltage ~JRl~ because the resil3tance of the resistor R2 increasos to a greater extent than the resistance of the resistor Rl. According to Equ. (3), therefore, the voltage Un will be greater than the voltage Up, which, owing to the variation of the p-do]ped resistors to larger values, is reduced by the bandgap circuit. As a result, the voltage Un then remains constant, given corresp~n~;ng dimensioning.
The same stabilizing effect is achioved with othe:r combinations of resistor variations (both types of resi~3tors vary in the same direction or in opposite directions); as a result, different temperature responses of the two types of resistors are also inherently compon-sated for.
With regard to the following more comprehensive cons:ideration of the circuit arrangement, let it again be assumed that the modified bandgap reference circuit B is dimen~3ioned for current sources with p-doped resistors and s~enerates a base voltage Up for current sources with p-doped resistors; the base bias voltage Up generated is then dependent on the temperature and on fluctuations of the p-doped resil3tors, 80 that it is possible to write Up = Up (T, xp), where T is the temperature and the factor xp expresses the variation of the p-doped resistors. The temperature response of the resistors will be disregarded in the following consideration, since it is cont~ine~
implicitly in the variations.
The t:otal derivative of the base bias voltage Up is ~Up ~Up dUp = dT+ - dzp. (4) ~T ~xp On account of the dimQnisioning of the bandgap circuit B, the voltage drops across p-doped resistors remain constant in the event of changes in temperature and in the event of resistor variations; the partial derivatives will in this case be - = kT (5a) ~T
and ~Up = kx. (5b) ~xp In customary bipolar technologies, kT has a value of about -1...-2 mV/R and kx has a value of about -25...
-30 mV. In order that the voltage across the emitter resii~tor remains constant, the emitter current must change by dI = -I dx in the event of a resistor change dx. Using the exponential law for the emitter current I = I8.e (~/UT)~ dI = (I/UT) .dU, and consequently dU = _UT. dx. The distributor circuit or, to put it anotller way, converter circuit V~ generates from the voltege Up the voltage Un in accordance with Un=Up + f(T,xp~xn)~ (6) which produces the total derivative ~Un ~Un ~Un dUn = dUp + - dT + - dx + - dx (7) If the voltage drops across n-doped resistors are now al80 intended to be constant in the event of change~
in t~mperature and in the event of resistor variations, then the following must also hold true for Un , dUn = kTdT + kxdXn~ (8) If the expressions of Equ. (7) and Equ. (8) are eguated with one another and Equ. (4) i8 used with Equ.
(5a) and Equ. (5b) then ~Un ~Un ~Jn kTdT+kxdxp+ - dT+ - dxp+ - dxn=kTdT+kxdxn~ (9) is obtained. This equation is satisfied when the follow-ing conditions are fulfilled:
~Un = O (lOa) ~T
~U
n kx ( lOb) ~xp 15 ~U
n ~ (lOc) n The condition (lOa) means that the temperature response of the current source transistors is compensated for solely by the bandgap circuit B (and not by the conversion circuit V ); the condition (lOb) means that the conversion circuit V~ reverl3es the voltage correction effected as a result of a ~ariation (xp) of p-doped resil3tors; and fulfilling the condition (lOc) effects a voltage correction as a result of a variation (xn) of n-doped resistors.
There will now follow a consideration of a conversion circuit V (in FIG. 3) which has the structure sketched in FIG. 2 and in which the resistor Rl i8 composed of a p-doped resistor and an n-doped resistor.
In order to be able to calculate the voltage difference UR2 UR1 in Equ. (3) it is necessary to know the current flowing through the resistors Rl and R2. It results from the mesh Uv - Ts - T3 - T6 ~ U2 ~ T4 ~ ~in' given ~in = ~p' as GR "5 P 1707 P 10 I (R2) = 8E ( P ~BE) (11) The following is th~s obtained from Equ. (3) U = _ U + (~ -2~BE)- (12) The bias voltage Uv can advantageously be derived from a plurality of base-emitter voltages, with the result that the term (Uv - 2 UBE) can be expressed by m UBE; a practical value for m is 2. 5.
The resistor R2 made of p-doped polysilicon varies by the factor xp :
R2 = xp R; (13) the resistor R1, a fraction (1-~) of which is produced from p-doped silicon and the fraction ~ of which is produced from n-doped silicon, varies according to the relationship R1 = ~ )xp+~xnlR. (14) Insertion into Equ. ( 12) thus yields Un = ~ ) +~ n ~ Up+~ ~ 1- n ~ mUB~. (15) With a given division ratio ~, U~ is consequently a function of Up, xp, xn and - by way of the temperature dependence of the base-emitter voltage - also of T.
The dimen~ioning of the circuit is based on the target valu/es xn = 1 and xp = 1 at which the compensation is intended to be exact; at this point xn = 1, xp = 1 is also called the development point.
At the development point xn = 1, xp = 1, the partial derivatives according to Equ. (lOa, lOb, lOc) can now be written as GR '35 P 1707 P 11 ~n ~UB~
= ~ ~ - 116a) ~T~T
n -m~B~) (16b) ~xp ~Jn +~(~p m~BE) (16c) Xn According to Equ. 15, Un dopends on Up with the factor (1-~)+~ - , with the rosult that, in general, d~ )+~ ~ ~1 ; at the development point, however, owin,g to ~ =1 , the derivative d~ )+~1 1 and is thu~ as required (in Equ. (6)). tGiven n~l this requirement is no longer fulfilled exactly; the 15 conversion circuit operates more accurately the better the condition is fulfilled]. The partial derivative with respect to temperature is zero, which corresponds to the requirement from Equ. (lOa). In order to fulfill ths conditions of Equ. (lOb, lOc), ~ must be chosen to be ~ = (17) ~Jp - mUBE
If a value of approximately -0.75 V is assumed for the expression Up - mUB~ and ~x = -30 mV is set, then ~ must be equal to 0.04. This can be achieved with a resistor Rl which is realized by a series circuit of 4% n-doped resistor material and 96% p-doped resistor material.
In the exemplary ~mhodiments considered here, therefore, the resistor Rl of the distribution or conver-sion circuit V' must be composed to the extent of 4% of that material for which the modified bandgap GR !~5 P 1707 P 12 reference circuit B i8 not designed and to which it must therefore be matched by the conversion circuit B'.
If polysilicon resistors having different doping materials are involved, then the resistor R1 must be realized by two series-connected resistors of the two types. In order not to form any asymmetries with regard to the contact holes, the resistor R2 should also be conE~tructed from a series circuit of two resistors, which are both composed of the resistor material of the bandgap reference circuit B.
In Siemens B6HF technology, it is also possible to produce a further type of resistor from hea~ily p-doped silicon, in that during the course of production, a m;sk which is placed over resistors that are to be doped weakly in comparison therewith is omitted. If the banclgap reference circuit B is constructed with weakly (p~) p-doped resistors and the base bias voltage is to be matched by means of a conversion circuit V' to current sources with hea~ily p-doped resistors, then the resistor R1 can be constructed as a series circuit comprising a heavily (p+) and a weakly (p~) p-doped resistor in a very simF,le manner with the aid of a mask which covers only part of the resistor. This also becomQs evident from FIG. 4, in which the respective mask is designated by M
for the two resistors R1 and R2 which are provided with contacts R. In its right-hand part, the resistor R1 is then heavily p-doped and has a sheet resistance of, for example, 60 ohms/square, whereas it is weakly p-doped in its left-hand part (just like the entire resistor R2) and ha~ a sheet resistance of, for example, 1000 ohms/square.
FIG. 5 shows a simulation result in two diagrams, in the upper diagram the voltage drop across a heavily p-doped resistor (p+-type resistor) and in the lower diagram the voltage drop across a weakly p-doped resistor (p~-type resistor) being illustrated against the vari-ation factor of the pt-type resistance for different temperatures (temp) and variation values (xr) of the weakly p-doped resistor material GR .'95 P 1707 P 13 (p~-type resistor) (u~ed in the bandgap reference circuit B). The voltage drop fluctuate~ by less than 12 mV, in which case it should be noted that the voltage drop across the wea~ly p-doped resistors already fluctuate~ by 8 mtr on account of shortcomings of the bandgap reference.
Claims (3)
1. A circuit arrangement for supplying the base bias voltage of current source transistors in bipolar IC
circuits, having a bandgap reference circuit (B) for supplying a base bias voltage which is dependent on the temperature and on resistance tolerances in such a way that the current supplied by the current source transistors causes a constant voltage drop across load resistors through which said current flows, and at least one distributor circuit (V), which is connected downstream of said bandgap reference circuit, outputs the respective base bias voltage and has an input stage (E), an output driver (A) and an intermediate invertor (J), which is formed by a series circuit which is connected to the supply voltage and comprises a first transistor (T1), a first resistor (R1), a second transistor (T2) and a second resistor (R2), characterized in that in order to supply the base bias voltage of current source transistors of a different resistor type than that for which the bandgap reference circuit (B) is designed, in the associated distributor or conversion circuit (V'), the second resistor (R2) is of that resistor type for which the bandgap reference circuit (B) is designed, and the first resistor (R1) is formed by the series circuit comprising a resistor of that very resistor type and a resistor of the other resistor type.
circuits, having a bandgap reference circuit (B) for supplying a base bias voltage which is dependent on the temperature and on resistance tolerances in such a way that the current supplied by the current source transistors causes a constant voltage drop across load resistors through which said current flows, and at least one distributor circuit (V), which is connected downstream of said bandgap reference circuit, outputs the respective base bias voltage and has an input stage (E), an output driver (A) and an intermediate invertor (J), which is formed by a series circuit which is connected to the supply voltage and comprises a first transistor (T1), a first resistor (R1), a second transistor (T2) and a second resistor (R2), characterized in that in order to supply the base bias voltage of current source transistors of a different resistor type than that for which the bandgap reference circuit (B) is designed, in the associated distributor or conversion circuit (V'), the second resistor (R2) is of that resistor type for which the bandgap reference circuit (B) is designed, and the first resistor (R1) is formed by the series circuit comprising a resistor of that very resistor type and a resistor of the other resistor type.
2. The circuit arrangement as claimed in claim 1, characterized in that the first resistor (R1) is composed to the extent of a fraction [where kx is the partial derivative of the base bias voltage, which is generated by the modified bandgap reference circuit (B), with respect to the variation factor of the resistor material of the modified bandgap reference circuit (B), Uw is the base bias voltage generated by the modified bandgap reference circuit (B), and m-UBE is the base-emitter 14a voltage, multiplied by a factor m, of the input circuit and output driver transistors of the distributor or conversion circuit (V')] of that material for which the modified bandgap reference circuit (B) is not designed.
3. The circuit arrangement as claimed in claim 1 or 2, characterized in that the second resistor (R2) is formed by the series circuit comprising two resistors of that resistor type for which the bandgap reference circuit (B) is designed.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19528209A DE19528209C1 (en) | 1995-08-01 | 1995-08-01 | Base bias voltage supply circuit for bipolar IC current source transistors |
| DE19528209.4 | 1995-08-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2228387A1 true CA2228387A1 (en) | 1997-02-13 |
Family
ID=7768399
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002228387A Abandoned CA2228387A1 (en) | 1995-08-01 | 1996-07-24 | Circuit arrangement for supplying the base bias voltage of current source transistors in bipolar ic circuits |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0842461B1 (en) |
| AT (1) | ATE180067T1 (en) |
| CA (1) | CA2228387A1 (en) |
| DE (2) | DE19528209C1 (en) |
| ES (1) | ES2134629T3 (en) |
| WO (1) | WO1997005537A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103905028B (en) * | 2012-12-25 | 2018-05-25 | 中芯国际集成电路制造(上海)有限公司 | Signal receiver and signal transmission apparatus |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2533199C3 (en) * | 1975-07-24 | 1981-08-20 | Siemens AG, 1000 Berlin und 8000 München | Circuit arrangement for generating an auxiliary voltage that is independent of changes in the supply voltage |
| DE2849153C2 (en) * | 1978-11-13 | 1982-08-19 | Siemens AG, 1000 Berlin und 8000 München | Circuit arrangement for generating a constant auxiliary DC voltage |
| DE2849231C3 (en) * | 1978-11-13 | 1981-12-03 | Siemens AG, 1000 Berlin und 8000 München | Circuit arrangement for compensating the internal resistance of a voltage source formed by an emitter follower |
| DE3213838A1 (en) * | 1982-04-15 | 1983-10-27 | Philips Patentverwaltung Gmbh, 2000 Hamburg | INTEGRATED CIRCUIT ARRANGEMENT WITH A VOLTAGE CURRENT TRANSFORMER |
| US4808908A (en) * | 1988-02-16 | 1989-02-28 | Analog Devices, Inc. | Curvature correction of bipolar bandgap references |
| KR920010633A (en) * | 1990-11-30 | 1992-06-26 | 김광호 | Reference voltage generation circuit of semiconductor memory device |
| US5291122A (en) * | 1992-06-11 | 1994-03-01 | Analog Devices, Inc. | Bandgap voltage reference circuit and method with low TCR resistor in parallel with high TCR and in series with low TCR portions of tail resistor |
-
1995
- 1995-08-01 DE DE19528209A patent/DE19528209C1/en not_active Expired - Fee Related
-
1996
- 1996-07-24 CA CA002228387A patent/CA2228387A1/en not_active Abandoned
- 1996-07-24 DE DE59601894T patent/DE59601894D1/en not_active Expired - Fee Related
- 1996-07-24 EP EP96924768A patent/EP0842461B1/en not_active Expired - Lifetime
- 1996-07-24 ES ES96924768T patent/ES2134629T3/en not_active Expired - Lifetime
- 1996-07-24 AT AT96924768T patent/ATE180067T1/en not_active IP Right Cessation
- 1996-07-24 WO PCT/DE1996/001364 patent/WO1997005537A1/en active IP Right Grant
Also Published As
| Publication number | Publication date |
|---|---|
| ATE180067T1 (en) | 1999-05-15 |
| DE19528209C1 (en) | 1996-08-29 |
| EP0842461B1 (en) | 1999-05-12 |
| EP0842461A1 (en) | 1998-05-20 |
| WO1997005537A1 (en) | 1997-02-13 |
| ES2134629T3 (en) | 1999-10-01 |
| DE59601894D1 (en) | 1999-06-17 |
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Legal Events
| Date | Code | Title | Description |
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| FZDE | Discontinued |