Amplifiers – With semiconductor amplifying device – Including differential amplifier
Patent
1993-07-30
1994-12-20
Mottola, Steven
Amplifiers
With semiconductor amplifying device
Including differential amplifier
330257, H03F 345
Patent
active
053748980
ABSTRACT:
A low power complementary gain control circuit adjusts the gain of an input signal with a gain control signal to provide a ground referenced output signal having low distortion. The gain control circuit includes an input stage having the topology of a current feedback amplifier input stage, which operates in conjunction with a complementary pair of gain control amplifiers and a complementary pair of current mirrors to control the amplitude of an input signal by means of a control signal applied to the gain control amplifiers. Each gain control amplifier comprises a pair of differentially connected transistors of the same conductivity type, the common emitters, the collectors, and the bases of the differentially connected transistors forming the current input, current outputs, and gain control inputs of the gain control amplifier. One current output of each gain control amplifier is connected to one of a pair of complementary current mirrors for coupling signal currents to a common gain node, and the other output is coupled to a corresponding voltage supply. A current signal generated by the input amplifier is coupled to the common emitters of the differentially connected transistor pairs and distributed between the corresponding current mirror and bias supply in accordance with control signals applied to the gain control inputs. The portion of the current signal directed to the complementary current mirrors is replicated at a common gain node, to provide an output current signal. The emitter areas of each complementary pair of differentially connected transistors are adjusted so that the errors due to non-zero R.sub.bb are symmetric about zero input current, and a transconductance resistor is connected between the inverting input of the input stage and ground to linearize large input currents.
REFERENCES:
patent: 4516081 (1985-05-01), Katakura
Elantec, Inc.
Mottola Steven
Novakoski Leo V.
Smith Albert C.
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