Wideband differential amplifier

• US 4,075,574 A
• Filed: 07/15/1976
• Issued: 02/21/1978
• Est. Priority Date: 10/16/1975
• Status: Expired due to Term

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Gilbert, Barrie
• Primary Examiner(s): Mullins, James B.
• Application Number:
  US05/705,634
• Time in Patent Office: 586 Days
• Field of Search: 330/22, 330/30 D, 330/38 M, 330/40, 330/149
• US Class Current: 330/257
• CPC Class Codes: H03F 1/3211 in differential amplifiers
• CPC Class Codes: H03G 1/0005 Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal

Abstract

A wideband differential amplifier comprises a pair of differentially connected control devices, for example transistors, having a pair of semiconductor junction input devices coupled thereto for receiving complementary input currents. The input devices exhibit logarithmic characteristics substantially compensating for nonlinear properties of the pair of differentially connected control devices, whereby a linear rather than a nonlinear amplified current output is produced. Multipliers, cascaded amplifiers, and other useful circuit configurations are provided.

Claims

1. A differential amplifier comprising:

a pair of control devices respectively provided with an output terminal, a control terminal, and a common terminal, and

a pair of input devices coupled respectively to said control terminals and receiving input current for providing thereacross the input applied to each said control device, said input devices each having at least input terminals and common terminals, said input devices having logarithmic characteristics substantially matching that of the pair of control devices for producing a linear output at said output terminals,

and means coupling together the common terminals of said pairs of devices to a common current connection,

wherein said pair of control devices comprises a pair of transistors having their emitter terminals interconnected and wherein said input devices each comprise semiconductor means including a semiconductor junction for receiving input currents and providing thereacross the input applied to the base terminals of said transistors, common terminals of the semiconductor junction means being connected to the emitter terminals of said pair of transistors,

wherein said input devices comprise diodes having their cathodes connected to the emitter of said pair of transistors,

wherein the emitters of said transistors have a junction area A times the junction areas of said diodes to provide an amplifier having a gain of A.

2. A differential amplifier comprising:

a pair of control devices respectively provided with an output terminal, a control terminal, and a common terminal, and

a pair of input devices coupled respectively to said control terminals and receiving input current for providing thereacross the input applied to each said control device, said input devices each having at least input terminals and common terminals,

said input devices having logarithmic characteristics substantially matching that of the pair of control devices for producing a linear output at said output terminals,

and means coupling together the common terminals of said pairs of devices to a common current connection,

wherein said pair of control devices comprises a pair of transistors having their emitter terminals interconnected and wherein said input devices each comprise semiconductor means including a semiconductor junction for receiving input currents and providing thereacross the input applied to the base terminals of said transistors, common terminals of the semiconductor junction means being connected to the emitter terminals of said pair of transistors,

wherein said input devices comprise diode-connected transistors having their emitters connected to the emitters of said pair of transistors,

wherein the emitters of the pair of transistors have emitter areas A times the emitter areas of said diode-connected transistors to provide an amplifier having a gain of A, the base resistances of said transistors being inversely proportional to said areas.

3. A cascaded differential amplifier comprising:

a pair of amplifier input terminals,

an amplifier common current terminal,

a plurality of circuits each providing a current output linearly proportional to the circuit'"'"'s input current while being characterized by a logarithmic operating characteristic relating voltage in said device to input current, each said circuit including at least one semiconductor device exhibiting a logarithmic voltage in response to current input and a second semiconductor device providing an output current linearly related to said input current, each of said circuits having an input terminal, an output terminal, and a common terminal,

means coupling a first pair of said circuits to be driven by said amplifier input terminals,

and means coupling further pairs of said circuits with input terminals of circuits of each further pair receiving currents from the common terminals of circuits of the preceding pair, with the last pair having common terminals thereof connected to said amplifier common current terminal.

4. The amplifier according to claim 3 wherein each of said circuits comprises a transistor having a semiconductor junction device coupled across the base-emitter junction thereof.

5. The amplifier according to claim 4 wherein the emitter of said transistor has a junction area A times the area of said semiconductor junction to provide a stage gain of A.

6. A wide band differential amplifier, comprising:

a pair of differentially coupled transistors the emitters of which are coupled together to a suitable source of current, and each having a base terminal and a collector output terminal; and

a pair of input devices receiving differential input signal currents and respectively connected to the differentially coupled transistors, said input devices comprising a pair of semiconductor junction devices having junctions similar to those of said differentially coupled transistors,

said input devices having logarithmic characteristics substantially matching that of said differentially coupled transistors for producing a linear output at said output terminals.

7. An amplifier circuit in accordance with claim 6 wherein said input currents are complementally supplied in accordance with an input index, x, such that the input current applied to one said input device substantially equals (1 - x)I when the input current to the other said input device substantially equals xI, wherein I is the current complementally divided between said pair of input devices.

8. An amplifier circuit in accordance with claim 6 wherein respective terminals of said pair of input devices are connected together.

9. An amplifier circuit in accordance with claim 6 wherein said pair of input devices comprises transistors having base terminals coupled respectively to said base terminals of said pair of differentially coupled transistors and having their emitter terminals coupled together,

and amplifier means for providing current to the emitter terminals of said pair of differentially coupled transistors, said amplifier means being coupled to the commonly connected emitter terminals of said input transistor devices for adjusting the current to the emitter terminals of said differentially coupled transistors in accordance with the sum of the current provided said input device transistors.

10. An amplifier circuit in accordance with claim 6 wherein said input devices are also coupled to the output terminals of the pair of differentially coupled transistors for combining input currents with output currents at said output terminals of the differentially coupled transistors.

11. An amplifier circuit in accordance with claim 10 wherein said input devices are coupled to the output terminals of the differentially coupled transistors in phase relation for additively combining input currents with output currents at the output terminals of said differentially coupled transistors.

12. An amplifier circuit in accordance with claim 10 wherein said input devices are coupled to said output terminals in phase relation for subtractively combining the input currents with output currents at said output terminals.

13. An amplifier circuit in accordance with claim 10 wherein said input devices comprise transistors having their collector terminals interconnected with collector terminals of said differentially coupled transistors in phase relation for combining input currents with output currents.

14. An amplifier circuit in accordance with claim 13 wherein said input device transistors have their emitter terminals connected to respective base terminals of said differentially coupled transistors, the input device transistors and transistors having their collector terminals connected in additive phase relation for combining input currents with output currents from said differentially coupled transistors.

15. An amplifier circuit in accordance with claim 14 wherein said input currents are applied at the emitter terminals of said input device transistors.

16. An amplifier circuit in accordance with claim 6 further including a second pair of differentially coupled transistors;

and

a second pair of input devices coupled respectively to base terminals of the second pair of differentially coupled transistors and receiving input currents from output terminals of the first mentioned pair of differentially coupled transistors for providing across said second pair of input devices the inputs applied to each said second differentially coupled transistor,

said second pair of input devices having logarithmic characteristics substantially matching that of the second pair of differentially coupled transistors for producing a linear output therefrom.

17. An amplifier circuit in accordance with claim 16 wherein said second pair of input devices receives current substantially directly from the respective output terminals of said first mentioned pair of differentially coupled transistors free of impedance coupling elements, to provide a cascade amplifier substantially entirely composed of such differentially coupled transistors, input devices and interconnections.

18. An amplifier circuit in accordance with claim 16 wherein said second pair of differentially coupled transistors have their emitter terminals connected together,

wherein said second pair of input devices each comprise transistors having their emitter terminals connected to base terminals of said second pair of differentially coupled transistors, said emitter terminals being connected to receive input currents from output terminals of said first mentioned pair of differentially coupled transistors,

said second pair of input devices having their collector terminals connected to output terminals of a pair of said differentially coupled transistors in additive phase relation.

19. An amplifier circuit in accordance with claim 16 further including means for providing a common mode output from the output terminals of said second pair of differentially coupled transistors, and feedback means for coupling said common mode output in a negaive input sense to a pair of said differentially coupled transistors.