Stabilized current and voltage reference sources

Abstract: Various voltage and current sources which are substantially independent of the positive supply rail are provided, some of which are also temperature independent. The basic NPN-type transistor circuit common to all provided sources generally comprises: a cross-coupled current stabilizer means having first and second cross-coupled transistors where the emitter area of the first transistor is larger than the emitter area of the second transistor, a third transistor having an emitter coupled to the col­ lector of the second cross-coupled transistor, a fourth transistor arranged as a diode and having a base coupled to the base of the third transistor and an emitter coupled to the collector of the first transistor; a first resistor coupled between the emitter of the first cross-coupled transistor and the negative rail; a second resistor coupled between the positive rail and the collector of said third transistor; a fifth transistor having its base and emitter coupled to the base and emitter of the second cross-coupled transistor to act as a current mirror thereof; and a sixth transistor coupled between the positive rail and the col­ lector of the fifth current mirror transistor and in cas­ code relationship therewith. A current source is further created by coupling the base of an additional transistor to the emitter of the fifth transistor. Additional tran­ sistors and resistors are utilized in accord with various embodiments of the invention to provide multiple current sources, and voltage and current sources which are sta­ bilized with respect to temperature.

Description: The invention relates to a voltage/current source connected between a positive and a negative voltage supply rail, comprising: a cross-coupled current stabilizer means comprising first and second bipolar cross-coupled transistors each having an emitter, where the emitter area of said first transistor is larger than the emitter area of the second transistor, a third bipolar transistor having an emitter coupled to a collector of said second transistor, a fourth transistor arranged as a diode and having a base coupled to a base of said third transistor, an emitter coupled to a collector of said first transistor and a collector coupled to the positive rail, the emitter of the second transistor being coupled to the negative rail, a first resistor coupled between the emitter of the first transistor and the negative rail, a second resistor coupled between the positive rail and a collector of the third transistor, a fifth transistor having a collector coupled to the positive rail, said first to fifth bipolar transistors being all of like polarity, a current mirror means for mirroring a current flowing in one of said cross-coupled transistors, an emitter of the fifth transistor being coupled to an output of the current mirror means Such a voltage/current source is known from United States Patent US 4,491,780, figure 3. This invention broadly relates to solid state integrated current and voltage reference sources which are independent of supply line voltages. More particularly, this invention relates to a stabilized current or a stabilized voltage reference source where the provided current or voltage is both temperature compensated and independent of supply line voltage changes. In providing a current or voltage source, it is desirable that the output current or voltage vary as little as possible regardless of the change in temperature or supply voltage. It is also desirable to avoid the use of PNP transistors in the circuit as the fabrication of precision PNP transistors has proved difficult. With the foregoing in mind, various current and voltage sources have been proposed. A prior art voltage source which is substantially temperature independent is seen in Figure 1. The circuit of Figure 1 basically comprises an amplifier, two transistors QA1 and QB1, and two resistors RA1 and RB1. In reviewing the operation of the circuit of Figure 1, it is important to recall that the base-to-emitter voltage (V be ) of an NPN transistor is given approximately as: V be = (kT/q) 1n(I c /I s ) (1) where k is Boltzmann's constant, q is the electric charge, T is the absolute temperature (kT/q sometimes being referenced as V T ), I c is the collecter current, and I s is the transistor saturation current which is proportional to the emitter area (or "width"). Since the amplifier of Figure 1 causes the currents I CA and I CB to be nearly equal, upon balancing the voltages, and in accord with equation (1), I CB is found to be equal to (V T /R B ) 1nK BA where the QB to QA emitter area ratio K PA has no significant dependence on V CC , T, or processing parameters. As a result, the output voltage V o is given by: V o = R A (I CA + I CB ) + V beA ≅'2(R A /R B )V T 1nK BA + V T 1n (I CA /I SA ) (2) Those skilled in the art will immediately appreciate that equation (2) is of the bandgap type with the first term having a positive, largely linear coefficient of temperature C T and the second term having a negative largely linear coefficient of temperature C T due to the strong dependence of I SA on T. By suitably choosing R A and R B (or the ratio thereof), V o can be made largely temperature independent. However, one disadvantage of the prior art circuit of Figure 1 is that frequency-compensation circuitry must be used with the amplifier. Also, the use of PNP transistors is difficult to avoid if the amplifier is to operate efficiently. Turning to Figure 2, a voltage/current source prior art circuit as defined in the opening paragraph is seen. This circuit is known from U.S. Patent 3,930,172. Block 10 of Figure 2 is essentially comprised of a cross coupled current stabilizer having transistors Q1, Q2, Q3 and Q4, with the collector-base junction of transistor Q1 being coupled to effectively form a diode, a resistor R1 connected between the voltage supply V CC and the collector of transistor Q1, and a resistor R3 coupled between ground and the emitters of transistor Q4. With the arrangement of block 10, which is described in detail in U.S. Patent 3,930,172, and with the balancing of the voltages, in accord with equation (1), the following is true: R₃I C2 = V be2 + V be3 - V be1 - V be4 = V T 1n(I S4 /I S2 ) + V T 1n (I S1 /I S3 ) (3a) With transistors Q1 and Q3 having equal emitter areas, V be3 V be1 due to the fact that substantially the identical current I C1 flows through both transistors Q1 and Q3. Hence, R₃I C2 ≃V T 1n(I S4 /I S2 ) = (kT/q)1nK₄₂ (3b) where the Q4 -to-Q2 emitter area ratio K₄₂ is substantially independent of V CC , T, and processing parameters. Neglecting the small variation of R₃ with T, I C2 is proportional to T but has substantially no dependence on the high voltage supply value V CC . The addition of block 12 of Figure 2 to block 10 provides a voltage reference in combination with a current source as might be suggested by Saul et al., "An 8-bit, 5ns Monolithic D/A Converter Subsystem", IEEE JSSC , Dec, 1980, pp. 1033-1039. While the provided arrangement substantially eliminates the temperature dependence of V o and uses only NPN transistors, V o is referenced to the positive rail V CC and cannot be used in applications requiring that V o be referenced to the negative rail (often ground). A similar result (temperature compensated voltage reference circuit) is also found in U.S. Patent #4,491,780 to Neidorff where the output voltage is also referenced to the positive rail. It is therefore an object of this invention to provide voltage/current sources which are independent of the voltage of the positive supply line. It is a further object of this invention to provide a temperature compensated voltage/multiple-current source which is referenced to the negative supply line. It is yet another object of this invention to provide a temperature compensated voltage/multiple-current source which includes transistors of only one type and which is referenced to the negative supply line. In accord with the objects of the invention a voltage/current source is characterized in that the base of the fifth transistor is coupled to the collector of the fourth transistor and in that the current flowing in one of said cross-coupled transistors is the collector current of the second transistor. In this configuration the current of the second transistor is mirrored to the fifth transistor. The base-emitter voltages of the second and the fifth transistors are therefore equal. The voltage at the base of the fifth transistor is equal to the sum of the base-emitter voltages of the fourth and second transistors. The voltage at the emitter of the fifth transistor is thus equal to base-emitter voltage of the fourth transistor if the base of the fifth transistor is directly connected to the collector of the fourth transistor. If the base of the fifth transistor is coupled to the collector of the fourth transistor via a resistor or another coupling element, the voltage drop across this element is determined by the current through the fourth transistor. This current is, as demonstrated above, independent on the positive supply voltage. For the same reason the base-emitter voltage of the fourth transistor is independent on the positive supply voltage. This means that the voltage at the emitter of the fifth transistor is independent on the voltage on the positive supply rail. Additional transistors and resistors are utilized in accord with various embodiments of the invention to provide a current source, a multiple current source, and voltage and current sources which are stabilized with respect to temperature. In order to create a positive supply voltage independent current source from the voltage/current source, an additional transistor is provided with its base coupled to the voltage output (emitter of the fifth transistor), and its emitter coupled to the negative rail. In arranging a temperature independent voltage source according to one embodiment, a third resistor is coupled between the base of the fifth transistor and the collector of the fourth transistor, while a fourth resistor is coupled between the additional transistor and the negative rail. If desired, a further transistor is provided with its collector coupled to the positive rail, its emitter coupled to the third resistor, and its base coupled to the collector of the third transistor. A multiple-current source is created by the use of a plurality of transistors and resistors arranged in an identical manner to and in parallel to the additional transistor and fourth resistor. If desired, additional transistors in cascode relationship may be added between the positive and negative rails with the base of the first cross-coupled transistor coupled to the base of one of the cascoded transistors, the base of the fourth transistor coupled to the base of the other cascoded transistor, and the coupled emitter and collector of the cascoded transistors coupled to the base of the additional transistor. A temperature independent multiple-current source may be obtained by taking the afore-summarized basic current source, adding a diode coupled between the collector of the fourth transistor-diode and the collector of the third transistor, and by adding another transistor with its collector and emitter coupled about the fourth resistor and its base coupled to the emitter of the third transistor. Of course, with the provided circuitry, and as will be described in detail hereinafter, the resistances and the transistor emitter areas should be carefully chosen to obtain desired results. Also, advantageously, all of the transistors are NPN-type transistors. A better understanding of the invention, and additional advantages and objects of the invention will become apparent to those skilled in the art upon reference to the detailed description and the accompanying drawings, wherein Figure 1 is a circuit diagram of a substantially temperature independent voltage source of the prior art; Figure 2 is another circuit diagram of a current/voltage source of the prior art; Figure 3a is a circuit diagram of a positive supply voltage independent voltage/current source of the invention; Figure 3b is a circuit diagram of a preferred temperature and positive voltage supply independent voltage source and positive voltage supply independent current source of the invention; Figure 4 is a circuit diagram of one embodiment of a positive supply voltage independent multiple current source of the invention; Figure 5a is a circuit diagram of a preferred temperature independent current source of the invention; and Figure 5b is a circuit diagram of an alternative embodiment of the output circuitry of the preferred temperature independent current source of the invention. Turning to Figure 3a, a circuit diagram of the preferred voltage/current source of the invention is seen. At the core of the circuit, a cross-coupled current stabilizer means is provided comprising first and second cross-coupled transistors T1 and T2, and third and fourth transistors T3 and T4. The emitter of transistor T3 is coupled to both the collector of cross-coupled transistor T2 and the base of cross-coupled transistor T1, while the emitter of cross-coupled transistor T4 is likewise coupled to both the collector of cross-coupled transistor T1 and the base of cross-coupled transistor T2. As indicated in Figure 3a, transistors T3 and T4 are arranged with common bases, transistor T4 is arranged as a diode having its base coupled to its collector, and transistor T1 is provided with an emitter area p times larger than the emitter area of T2. The emitter of cross-coupled transistor T2 is preferably connected to the negative rail (ground), while the emitter(s) of cross-coupled transistor T1 is coupled to the negative rail through resistor R1. The collector of transistor T3 is coupled to the positive rail (Vcc) via resistor R2. The collector of transistor T4 also may be coupled to Vcc via resistor R2. It should be noted that transistors T1, T2, T3 and T4, as well as all the transistors to be recited hereinafter are preferably of the same polarity: preferably NPN-type. Also, it should be noted that all of the transistors, unless otherwise indicated, preferably have substantially identical emitter areas, i.e. emitter areas equal to the emitter area of transistor T2. Completing the voltage source arrangement, transistors T5 and T6 are arranged in cascode relationship. Transistor T5 has an emitter coupled to the negative supply rail, a base coupled to the base of transistor T2, and a collector coupled to the emitter of transistor T6 and to the voltage output. In this arrangement, transistor T5 acts as a current mirror in conjunction with transistor T2, with the collector current of transistor T2 being the current mirror input current, and the collector current of transistor T5 being the current mirror output current. Transistor T6 has a collector coupled to the positive supply rail, and a base coupled to the collector of transistor T4. Turning to Figure 3b, the circuitry of Figure 3a, including transistors T1-T6, and resistors R1 and R2 are left intact, and an additional resistor R3 and an additional transistor T7 are provided. Resistor R3 couples the collector-base of transistor T4 to the base of cascode transistor T6, while transistor T7 has its base coupled to the collector of transistor T3, its collector coupled to the positive supply rail, and its emitter coupled to the base of transistor T6. As will be discussed hereinafter, the current source circuitry includes an additional resistor (R4) beyond the transistor (T8) shown in Figure 3a. With the provided voltage source arrangements of Figures 3a and 3b, the following relationship is obtained: V be4 + V be2 = V be3 + V be1 + I₁R1 (4) where I₁ is the current through transistor T₁. Because a substantially equal current (which is approximately equal to V cc - {3V be /R₃}) flows through both transistors T3 and T2 (ignoring base currents), the base-emitter voltage drop of transistors T3 and T2 are substantially equal as the emitter areas of transistors T3 and T2 are equal. Hence, relationship (4) may be simplified to V be4 = V be1 + I₁R1. Because substantially equal current also flows through transistors T4 and T1, in accord with equation (1): V be4 - V be1 = (kT/q) ln{I₁pi s /I₁i s } = (kT/q)ln(p) (5) where i s is the saturation current of transistor T2. Combining simplified relationship (4) with equation (5), it is seen that: I₁ = (1/R1){ (kT/q) ln(p)} (6) Thus, for Figure 3a, the voltage at the base of transistor T6 is determinable as V be2 + V be4 , while for Figure 3b, the voltage at the emitter of T7 is then determinable as V be2 + V be4 + (R3/R1) {(kT/q) ln(p)} . As a result, in either case, when the supply voltage varies, the current through the transistor T2 varied and causes V be2 to vary, which results in a variation of the voltage at the base of transistor T6. However, with the provision of transistors T5 and T6, the voltage output can be decoupled from changes in the supply voltage, and in the case of Figure 3b can be made to be as substantially temperature independent. As aforementioned, transistor T5 is arranged to provide a current mirror in conjunction with transistor T2 (i.e. the transistors are arranged in parallel). As a result, whatever current mirror input current flows through transistor T2, a substantially equal current mirror output current flows through transistor T5. Also, because transistors T5 and T6 are in cascode relationship, whatever current flows through transistor T5 is pulled from and through transistor T6. Hence, the base-emitter voltage drop across transistor T6 is substantially equal to the base-emitter voltage drop across transistor T2. With the voltage output being located at the emitter of transistor T6, for Figure 3a: V out = V be2 + V be4 - V be6 (7a) while for Figure 3b, V out = V be2 + V be4 + (R3/R1) {(kT/q)ln(p)} - V be6 (7b) With V be2 equal to V be6 , relationships (7a) and (7b) respectively simplify to: V out = V be4 (8a) V out = V be4 + (R3/R1) {(kT/q)ln(p)} (8b) Relationships (8a) and (8b) are completely independent of reliance on the positive supply voltage Vcc and hence are stabilized. Moreover, with respect to Figure 3b and relationship (8b), by adjusting R3 properly (given a particular R1 and emitter width ratio p), the output voltage may be arranged to be the bandgap voltage of silicon which is temperature independent. In providing a current source for Figure 3a, an additional transistor T8 is added to the provided voltage source, while in Figure 3b, transistor T8 and resistor R4 are added to the provided voltage source. The base of transistor T8 is connected to the voltage source output (i.e. the emitter of transistor T6) while the emitter of transistor T8 is coupled to ground via resistor R4 (for Fig. 3b). The collector of transistor T8 is considered the current source output node. If a multiple current source is desired, a plurality of additional transistors or transistors and resistors arranged in the same manner as and in parallel to transistor T8 and resistor R4 can be provided. With the same emitter areas and resistances, the provided current sources will provide equal currents. Or, if desired, by arranging the emitter areas and resistances as desired, binary weighted currents, decimally weighted currents, or other desired outputs could be provided. In both the Figure 3a and Figure 3b embodiments of the single current source, the emitter area of T8 is set to be equal to the emitter area of transistor T2, while in Figure 3b, the resistance of R4 is set to the resistance of R3. Alternatively, if the width of transistor T8 is half that of T2, the resistance of resistor R4 should be twice that of resistor R3. Regardless, it will be appreciated with respect to the provided current source arrangements as opposed to the voltage source arrangements, that the added transistors T8 (and resistor R4) add additional temperature dependence. The temperature dependence can be eliminated, however, as will be discussed hereinafter with respect to Figure 5. Turning to Figure 4, a multiple current source is provided which permits heavy loading of the current source by the output circuits. The core of the cross-coupled current stabilizer means comprised of transistors T11, T12,T13 and T14, with resistors R11 and R12 is identical to the arrangement of that of Figure 3b. Likewise, resistor R13 and transistor T17 are arranged identically to resistor R3 and transistor T7, as is transistor T16 relative to transistor T6. However, two additional transistors T19 and T20 are added to the circuit, and transistor T15 is arranged differently than transistor T5 of Figure 3b. Thus, transistor T19 is connected in parallel with cross-coupled transistor T11 and resistor R11 with the base of transistor T19 being connected to the base of cross-coupled transistor T11, and the emitter of transistor T19 being coupled to ground. The collector of transistor T19 is coupled to the base of transistor T15 (which is otherwise arranged as transistor T5 of Figure 3b), as well as to the emitter of cascode transistor T20. The base of transistor T20 is coupled to the base of transistor T14, and the collector of transistor T20 is coupled to the positive voltage rail Vcc. Loading the voltage output V out are a plurality of transistors with resistors coupling their emitters to the negative rail. As seen in Figure 4, a first set of transistors T18a and T18b with resistors R14a and R14b are shown as providing current outputs from the voltage output obtained at the junction of transistors T15 and T16. However, if desired, and as shown in phantom, one or more additional blocks of multiple current source output circuitry can be provided such as by providing transistors T25 and T26 in parallel with transistors T15 and T16 and by providing transistors T28a, T28b... and resistors R24a, R24b... therewith. With the provided arrangement of Figure 4, the base to emitter voltage of transistor T15 is determined as: V be15 = V be12 + V be14 - V be20 (9) Because transistor T11 has a large emitter area and a resistor R11 attached to its emitter, and because transistor T19 has its base coupled to the base of transistor T11, the current through transistors T19 and T11 can be arranged to be equal. Hence, the current through transistor T20 can be equal to the current through transistor T14. With the emitter areas of transistors T14 and T20 being equal, the base emitter voltage drops across the two transistors are substantially equal, and relationship (9) reduces to V be15 = V be12 . As a result, the current through transistor T15 varies in the same manner as the input current through transistor T12. With transistors T15 and T16 in cascode relationship, the current through transistor T16 likewise varies in the same manner as the current through transistor T12. Hence, the output voltage V out is equal to V be14 + (R13/R11) {(kT/q)ln(p)} , and represents the same stabilized voltage which is seen at the voltage output in Figure 3b. Again, the output currents flowing through the various output transistors and resistors can be controlled as desired, but are still somewhat temperature dependent. The multiple current source arrangement of Figure 4 permits heavier loading on the output as transistors T19 and T20 decouple the loading of the multiple current sources from the stabilized cross-coupled circuit T11, T12, T13, T14. Transistor T17 operates as a current gain stage and supplies current to the base of the multiple output current sources (T16, T26...) and resistor R13. In this way, the operation of the basic stabilizer is not influenced by the output loading. Turning to Figure 5a, a temperature-independent, positive rail-independent current source is seen. Again, the core cross-coupled current stabilizer circuit including cross-coupled transistors T31 and T32, and transistors T33 and T34 are provided with resistor R31 coupling the emitter of transistor T31 to ground. Also, as with Figures 3b and 4, a resistor R32 is provided which couples the collector of transistor T33 with the positive rail, and cascoded transistors T35 and T36 are arranged with transistor T35 mirroring the current through transistor T32, and the voltage output being at the emitter of transistor T36. However, instead of using a resistor such as R3 or R13, and a transistor such as T7 and T17, a transistor-diode T37 is provided with its emitter coupled to the collector-base of transistor T34, and its collector-base coupled to the base of transistor T36 as well as to resistor R32. Also, preferably an additional transistor T44 is provided with its collector coupled to a node between the output transistor T38 and its associated emitter resistor R34, its base coupled to the collector of transistor T32, and its emitter coupled to the negative rail. With the provided arrangement of Figure 5a, a voltage variation in the positive rail will cause a variation in current through transistor T32 which is mirrored by transistor T35 and hence by transistor T36 which is in cascode relationship with transistor T35. As a result, the output voltage at the emitter of transistor T36 is equal to 2V be34 (i.e. V be32 + V be34 + V be37 - V be36 ) when V be34 = V be37 . The 2V be34 voltage is applied to the base of transistor T38 having degeneration resistor R34 coupling its emitter to the negative rail. Without transistor T44 connected, a voltage drop equal to approximately V be34 is generated across degeneration resistor R34 thereby giving the current through R34 a negative temperature coefficient. With transistor T44 connected, the base-emitter voltage of transistor T44 must be equal to the voltage drops across the base-emitter junction of transistor T31 and resistor R31. Hence, the collector current of transistor T44 is substantially equal to the collector currents of transistors T31 and T34 which have a positive temperature coefficient. Adding the currents through transistor T44 and the current through resistor R34 together results in an output current with an adjustable temperature coefficient. In order to create an output current which is substantially independent of temperature, the value of resistor R34 can be chosen to be approximately equal to the bandgap voltage of silicon divided by the output current (V gap /I out ). By adjusting R31 properly, a desired output current is obtained. Figure 5b shows an alternative manner of arranging the output circuitry of Figure 5a to create a temperature-independent current source. Thus, instead of providing transistor T44 in the previously discussed manner, two transistors T54a and T54b are provided in cascode relationship. Transistor T54a has its base coupled to the emitter of transistor T36 as well as to the base of transistor T38, its collector coupled to the collector of transistor T38 (i.e. to the current source output), and its emitter coupled to the collector-base of transistor T54b. The emitter of transistor T54b is coupled to the negative rail. In a similar manner to the output arrangement of Figure 5a, the temperature coefficient of the current flowing through transistors T54a and T54b may be balanced with the temperature coefficient of the current flowing through transistor T38 and resistor R34 to provide the substantially temperature independent current source. With respect to both Figures 5a and 5b, a multiple current source which is independent of temperature may be obtained. In Figure 5a, a plurality of transistors can be connected with their bases coupled to the base of transistor T38 and their emitters coupled to resistors which are coupled to the negative rail. Likewise, a plurality of transistors such as transistor T44 can be coupled to the base of transistors T31 and T44 with their collectors coupled to the emitters of their respectively associated output transistors and their emitters coupled to the negative rail. The current outputs can be made temperature independent by carefully choosing the values of their respective degeneration resistors. Of course, resistor R31 must likewise be chosen carefully. In a similar manner to the creation of multiple current sources from the output circuitry of Figure 5a, multiple current sources can be created with the output circuitry of Figure 5b. For each desired current source three additional transistors and one degeneration resistor are used and arranged in a similar manner to transistors T54a, T54b, and T38, and resistor R34 of Figure 5b. Thus, two additional transistors having coupled bases and coupled collectors would have their bases coupled to the base of transistor T38 (their collectors not being coupled to the collector thereof). An additional transistor arranged as a diode would couple the emitter of one transistor to the negative rail, while the degeneration resistor would couple the emitter of the other transistor to the negative rail.

Claims: A voltage/current source connected between a positive and a negative voltage supply rail, comprising: a cross-coupled current stabilizer means comprising first (T1) and second (T2) bipolar cross-coupled transistors each having an emitter, where the emitter area of said first transistor (T1) is larger than the emitter area of the second transistor (T2), a fourth transistor (T4) arranged as a diode and having a base coupled to a base of a third bipolar transistor (T3) and a collector coupled to the positive rail, the emitter of the second transistor (T2) being coupled to the negative rail, a first resistor (R1) coupled between the emitter of the first transistor (T1) and the negative rail, a second resistor (R2) coupled between the positive rail and a collector of the third transistor (T3), a fifth transistor (T6) having a collector coupled to the positive rail, said first to fifth bipolar transistors being all of like polarity, a current mirror means for mirroring a current flowing in one of said cross-coupled transistors, an emitter of the fifth transistor (T6) being coupled to an output of the current mirror means, characterized in that the base of the fifth transistor (T6) is coupled to the collector of the fourth transistor (T4), in that said mirrored current flowing in one of said cross-coupled transistors is the collector current of the second transistor (T2), in that the emitter of the third transistor (T3) is coupled to a collector of said second transistor (T2) and in that the emitter of the fourth transistor (T4) is coupled to a collector of said first transistor (T1). A voltage/current source according to Claim 1, wherein: said current mirror means comprises a sixth bipolar transistor (T5) in conjunction with said second cross-coupled transistor (T2), said sixth transistor (T5) having a base coupled to a base of said second cross-coupled transistor (T2), an emitter coupled to an emitter of said second cross-coupled transistor (T2), and a collector coupled to said emitter of said fifth transistor (T6), wherein said collector of said second cross-coupled transistor (T2) is an input of said current mirror. A voltage/current source according to Claim 1 or 2, further comprising: a third resistor (R3) coupling said base and collector of said fourth transistor (T4) to a base of said fifth bipolar transistor (T6). A voltage/current source according to Claim 3, further comprising: a seventh bipolar transistor (T7) of like polarity having an emitter coupled to a base of said fifth transistor (T6), a base coupled to said collector of said third transistor (T3), and a collector coupled to said positive rail. A voltage/current source according to Claim 3, wherein: said third (T3), fourth (T4), and fifth (T6) transistors have emitter areas substantially equal to the emitter of said second (T2) transistor. A voltage/current source according to Claim 1,2,3,4 or 5, characterized by at least one eighth bipolar output transistor (T8) of like polarity, each eighth output transistor (T8) having a base coupled to said emitter of said fifth transistor (T6), and each eighth output transistor (T8) having a collector with a node coupled thereto acting as a current source. A voltage/current source according to Claim 6, further comprising: at least one fourth resistor (R4), each fourth resistor (R4) coupling an emitter of one eighth output transistor (T8) to said negative rail. A voltage/current source according to Claim 7, wherein: said at least one eighth output transistor (T8) comprises a plurality of output transistors and said at least one fourth resistor (R4) comprises a corresponding plurality of fourth resistors (R4). A voltage/current source according to Claim 7, further comprising: an ninth bipolar transistor (T20) of like polarity having a base coupled to a base of said fourth transistor (T4, T14), a collector coupled to said positive rail and an emitter coupled to a base of said sixth transistor (T5, T15), and a tenth bipolar transistor of like polarity (T19) having a collector coupled to said base of said sixth transistor (T5, T15), a base coupled to said base of said first cross-coupled transistor (T1, T11), and an emitter coupled to said negative rail. A voltage/current source according to Claim 9, further comprising: one or more stages coupled to said emitter of said ninth transistor (T20) and said emitter of said seventh transistor (T7, T17), each stage comprising a plurality of transistors (T26,T25,T28) and at least one resistor (R24) arranged in a manner identical to an arrangement of said fifth transistor (T6), said sixth transistor (T5), said at least one eighth transistor (T8), and said at least one fourth resistor (R4). A voltage/current source according to Claim 17 or 10, wherein: said eighth output transistors (T8) and said fourth resistors (R4) are chosen for each transistor-resistor couple such that an index of the emitter area of said eight output transistor (T8) multiplied by the resistance of said fourth resistor (R4) provides a substantially identical value for each said couple to provide substantially equal current outputs. A voltage/current source according to Claim 7 or 10, wherein: said eighth output transistors (T8) and said fourth resistors (R4) are chosen for each transistor-resistor couple such that an index of the emitter area of said eight output transistor (T8) multiplied by the resistance of said fourth resistor (R4) provides a value which is a binary power of another transistor-resistor couple to provide substantially binary weighted current outputs. A voltage/current source according to Claim 6, further comprising: an eleventh bipolar transistor (T37) of like polarity arranged as a diode having an emitter and a collector coupled to the collector of said fourth transistor (T34) and the base of the fifth transistor (T36) respectively, at least one twelfth bipolar transistor (T44) of like polarity for each eighth transistor (T38), each twelfth transistor (T44) having a base coupled to said collector of said first cross-coupled transistor (T31), a collector coupled to said emitter of its corresponding eighth output transistor (T38), and an emitter coupled to said negative rail. A voltage/current source according to Claim 13, wherein: said at least one fourth resistor (R4) is chosen to have a resistance substantially equal to the bandgap voltage of silicon divided by an output current flowing to a collector of a respective eighth transistor (T8), A voltage/current source according to Claim 13, the at least one twelfth transistor (T44) being replaced by an at least one thirteenth bipolar transistor (T546) of like polarity for each of said eighth transistors (T38), said thirteenth transistor having a base and a collector coupled to an emitter of said eighth transistor, and an emitter coupled to said negative rail.

Inventors: VAN DE PLASSCHE RUDY JOHAN, VAN DE PLASSCHE, RUDY JOHAN
Applicants: PHILIPS NV, N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1989
Main classification: G05F3
IPC codes: G05F3