Amplifiers – With semiconductor amplifying device – Including differential amplifier
Patent
1998-04-28
1999-12-07
Lee, Benny
Amplifiers
With semiconductor amplifying device
Including differential amplifier
330253, H03F 345
Patent
active
05999052&
ABSTRACT:
An integrated circuit differential amplifier with a digitally controllable gain. In a preferred embodiment, the differential amplifier employs first and second transconductance (gm) amplifiers and a digital to analog converter (DAC). The first gm amplifier converts a differential input voltage into a differential output current and the second gm amplifier converts the differential output current into a differential output voltage. A digital input code is applied to the DAC to generate an analog output voltage that is applied to one of the gm amplifiers to control its transconductance to thereby control the gain of the differential amplifier. The second gm amplifier employs a pair of low impedance feedback paths between input/output terminals of opposite polarity. The gain of the differential amplifier is thus a function of the ratio of the transconductance of the first gm amplifier to that of the second gm amplifier. Preferably, the same circuit topology is employed for both gm amplifiers, leading to a process- and operating temperature-insensitive differential amplifier gain. Additional gm amplifiers may be connected in parallel with the first gm amplifier to enhance gain. The load resistance presented by the second gm amplifier is preferably kept low to afford high speed operation.
REFERENCES:
patent: 5301072 (1994-04-01), Wilson
patent: 5410729 (1995-04-01), Kumagai et al.
patent: 5451901 (1995-09-01), Welland
patent: 5576976 (1996-11-01), White
patent: 5684653 (1997-11-01), Knowles
patent: 5855268 (1999-01-01), Zoladz
Choe Henry
Lee Benny
Lucent Technologies - Inc.
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