Difference amplifier

Claim 2

A difference amplifier comprising a current source, a source of supply voltage, two pairs of transistors, means individually connecting the emitter electrodes of the first pair of transistors to the base electrodes of the second pair, respectively, means connecting the emitter electrodes of the second pair of transistors to each other and via said current source to one terminal of the supply source, first and second impedance elements, means individually connecting the collector electrodes of the second pair of transistors via respective ones of said impedances to the other terminal of the supply source, two pairs of terminals, means connecting the first pair of terminals to the base electrodes of the first pair of transistors and the second pair of terminals to the side of the collector impedances of the second transistor pair remote from the supply source, a pair of semiconductor elements individually coupled in the collector circuits of said first pair of transistors so that each semiconductor element is traversed by substantially the same current as its respective first transistor for deriving a compensation voltage by reproducing the base-emitter voltages of at least the first pair of transistors of the difference amplifier in the pn-junction of said semiconductor elements, and means for individually coupling said semiconductor elements to one pair of said terminals so as to apply said compensation voltage to said one pair of terminals in a compensating sense.

Claim 3

A difference amplifier as claimed in claim 1 further comprising a pair of compensation transistors connected in a long-tailed pair configuration to the supply source, and means individually connecting the base electrodes of the compensation transistors to the collector electrodes of the first pair of transistors.

Claim 4

A difference amplifier as claimed in claim 1 further comprising first and second compensation transistors having their emitter electrodes connected together, means connecting the side of each of the collector impedances of the second pair of transistors remote from the supply source via third and fourth respective impedance elements, from which the output voltage is derived, to the collector of a respective compensation transistor, and means connecting the emitter electrodes of the compensation transistors via a second current source to one terminal of the supply source, and means individually connecting the collector electrodes of the said first pair of transistors to the respective base electrodes of said compensation transistors.

Claim 5

A difference amplifier as claimed in claim 3 wherein said pair of semiconductor elements comprise third and fourth transistors each connected as a diode, said amplifier further comprising a third pair of transistors, and means connecting said third pair of transistors in circuit so that the collector circuit of each of the second pair of transistors includes the emitter-collector path of a transistor of said third pair of transistors, means connecting the base electrodes of the latter transistors to a point of fixed potential, and means individually connecting the collector electrodes of each of the second pair of transistors via said third and fourth transistors each connected as a diode in the pass direction to the collector electrodes of the opposite stage transistor of the first pair of transistors of the difference amplifier and furthermore to the base electrodes of the compensation transistors.

Claim 6

A difference amplifier as claimed in claim 2 further comprising means connecting the collector of each transistor of the first pair of transistors to The base of that compensation transistor whose collector is connected to the collector impedance of the opposite stage transistor of the second pair of transistors of the difference amplifier and, moreover, via at least one transistor connected as a diode in the pass direction to a point of constant potential.

Claim 7

A difference amplifier as claimed in claim 1 characterized in that each input of the first pair of transistors of the difference amplifier comprises two other transistors traversed in series by the same current, means connecting the common electrodes thereof to the base of the associated transistor of the first pair of transistors of the difference amplifier, and means for applying the signal voltage to the base of one transistor and the compensation voltage to the base of the second transistor of said two other transistors.

Claim 8

A difference amplifier as claimed in claim 6 further comprising a further pair of transistors with their base electrodes connected to a point of fixed potential, means for obtaining the compensation voltage by including in the collector circuit of each of the second pair of transistors the emitter-collector path of a further transistor, and means connecting the collector of the transistor of the second pair of transistors concerned via a transistor connected as a diode in the pass direction to the collector of the opposite stage transistor of the first pair of transistors and to the base of the associated compensation transistor.

Claim 9

A difference amplifier as claimed in claim 6 characterized in that the compensation voltage is obtained by connecting the collector of each transistor of the first pair of transistors via a transistor connected as a diode in the pass direction to a point of constant potential and, in addition, directly to the base of the associated compensation transistor.

Claim 10

A difference amplifier adapted to be energized from a source of supply voltage comprising, a current source, first and second input transistors, a pair of signal input terminals coupled to the base electrodes of said input transistors, third and fourth output transistors, means connecting the emitter of the first transistor to the base of the third transistor and the emitter of the second transistor to the base of the fourth transistor, means connecting the emitter electrodes of said third and fourth transistors together and to one terminal of the supply source via said current source, first and second impedance elements, means including said first impedance element for coupling the collector of said third transistor to the other terminal of the supply source, means including said second impedance element for coupling the collector of said fourth transistor to said other terminal of the supply source, first and second semiconductor elements each having a PN-junction, means for coupling the collector electrodes of said first and second input transistors to said other supply source terminal via said first and second semiconductor elements, respectively, so that the semiconductor elements and the respective input transistors are traversed by substantially the same currents whereby the base-emitter voltages of the input transistors are reproduced in the PN junctions of said semiconductor elements as a compensation voltage for compensating any error voltage produced by a difference in the current amplification factors of the output transistors, a pair of signal output terminals individually coupled to the collector electrodes of the output transistors, and means for applying said compensation voltages to one pair of said terminals in a compensating sense.

Claim 11

A difference amplifier adapted to be energized from a source of supply voltage comprising, a current source, first and second input transistors, a pair of signal input terminals coupled to the base electrodes of said input transistors, third and fourth output transistors, means connecting the emitter of the first transistor to the base of the third transistor and the emitter of the second transistor to the base of the fourth transistor, means connecting the emitter electrodes of said third and fourth transistors together and to one terminal of the supply source via said current source, first and second impedance elements, means including said first impedance element for coupling the collector of said third transistor to the other terminal of the supply source, means including said second impedance element for coupling the collector of said fourth transistor to said other terminal of the supply source, first and second semiconductor elements each having a PN-junction, means for coupling the collector electrodes of said first and second input transistors to said other supply source terminal via said first and second semiconductor elements, respectively, so that the semiconductor elements and the respective input transistors are traversed by substantially the same currents whereby the base-emitter voltages of the input transistors are reproduced in the PN junctions of said semiconductor elements as a compensation voltage for compensating any error voltage produced by a difference in the current amplification factors of the output transistors, a pair of signal output terminals individually coupled to the collector electrodes of the output transistors, and means for applying said compensation voltages to one pair of said terminals in a compensating sense.

Claim 12

A difference amplifier as claimed in claim 9 further comprising first and second compensation transistors with their emitter electrodes connected together and to said one supply source terminal via a current source, means for coupling the collector electrodes of said first and second compensation transistors to said first and second impedance elements, respectively, and means for individually coupLing said first and second semiconductor elements to the base electrodes of said first and second compensation transistors thereby to apply said compensation voltages thereto.

Claim 13

A difference amplifier as claimed in claim 10 wherein said collector coupling means for the output transistors comprises fifth and sixth transistors connected in series with the third and fourth transistors, respectively, and the first and second impedance elements, respectively, and means connecting the base electrodes of said fifth and sixth transistors to a point of fixed potential.

Claim 14

A difference amplifier as claimed in claim 10 further comprising means individually connecting the collector electrodes of the input transistors to the base electrodes of the compensation transistors and to a point of constant voltage via said first and second semiconductor elements, respectively.

Claim 15

A difference amplifier as claimed in claim 9 further comprising fifth and sixth transistors connected in series across the supply terminals and having a common junction connected to the base of the first input transistor, one of said input terminals being connected to the base of the fifth transistor and one of said semiconductor elements being connected to the base of the sixth transistor to apply thereto said compensation voltage, seventh and eighth transistors connected in series across the supply terminals and having a common junction connected to the base of the second input transistor, the other one of said input terminals being connected to the base of the seventh transistor and the other one of said semiconductor elements being connected to the base of the eighth transistor to apply thereto said compensation voltage.

Claim 16

A difference amplifier as claimed in claim 13 further comprising means for connecting the collector electrodes of said first and second input transistors to a point of fixed potential via said first and second semiconductor elements, respectively, and directly to the base electrodes of said sixth and eighth transistors, respectively.

Claim 17

A difference amplifier as claimed in claim 13 wherein said collector coupling means for the output transistors comprises ninth and tenth transistors connected in series with the third and fourth transistors, respectively, and the first and second impedance elements, respectively, and means connecting the base electrodes of said ninth and tenth transistors to a point of fixed potential.