Amplifiers – With semiconductor amplifying device – Including differential amplifier
Patent
1989-12-08
1991-04-23
Mullins, James B.
Amplifiers
With semiconductor amplifying device
Including differential amplifier
330259, 330260, H03F 345
Patent
active
050103032
ABSTRACT:
Integrated circuit amplifier (10) implements unity voltage gain and its current gain is determined by the ratio of integrated circuit resistors (R1, R2). Amplifier input stage (Q1, Q2, Q4-Q7) has a pair of transistors (Q4, Q5) connected as a differential amplifier. An output transistor (Q13) connected to the collector of one (Q4) of the differential transistors amplifies the differential signal from the input stage and provides an output signal (at terminal 22). Current mirror circuitry (Q12, Q9) develops a current mirror signal (at 24) corresponding to current drawn through the output transistor (Q13). A load balancing circuit (Q8, Q3, R8) includes a transistor (Q3) having an input terminal directly connected to and loading the collector of another one (Q5) of the differential transistors. This configuration results in equal impedance and current loading for each of the collectors of the differential transistors (Q4, Q5). This minimizes any offset variation for the differential signal at the collector of one of the transistors (Q4) as a function of the conduction of the output stage tansistor (Q13). This results in a more accurate true differential amplification by the differential input stage resulting in the amplifier current gain being a more direct function of just the ratio of the integrated circuit resistors.
REFERENCES:
patent: 4574221 (1986-03-01), Hess
patent: 4780625 (1988-10-01), Zobel
Motorola Schematic 12/15/87 for SC74589P ISC-BPA.
Melamed Phillip H.
Motorola Inc.
Mullins James B.
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