Differential amplifier for reducing input capacitance without de

Details Differential amplifier for reducing input capacitance without de Differential amplifier for reducing input capacitance without de

1994-08-02

1995-09-26

Mottola, Steven

Amplifiers

With semiconductor amplifying device

Including differential amplifier

330292, H03F 345

Patent

active

054537185

ABSTRACT:
A differential amplifier (101) includes an input circuit (20), a bias circuit (31) and an output circuit (50). In the input circuit (20), when base potentials of transistors (Q1) and (Q2) change respectively by .DELTA.V and -.DELTA.V thereby changing current flowing through the transistors (Q1) and (Q2) by .DELTA.I and -.DELTA.I, respectively, base-emitter voltages of transistors (Q5) and (Q9) equally increase by .DELTA.V in the bias circuit (31). However, since a base potential of the transistor (Q5) is fixed, an emitter potential of the transistor (Q9) drops by 2.DELTA.V, decreasing a base potential of a transistor (Q4) by 2.DELTA.V. On the other hand, since a current flowing through the transistor (Q4) changes by -.DELTA.I, a base-emitter voltage of the transistor (Q4) accordingly falls by .DELTA.V. This reduces an emitter potential of the transistor (Q4), i.e., a collector potential of the transistor (Q2) by .DELTA.V, and hence, a base-emitter voltage of the transistor (Q2) stays unchanged. Thus, Miller effect is prevented and an input capacitance is reduced.

REFERENCES:
patent: 4703285 (1987-10-01), Woo
patent: 4885548 (1989-12-01), Wakimoto et al.

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