Amplifiers – With semiconductor amplifying device – Including differential amplifier
Patent
1993-02-17
1994-08-02
Sikes, William L.
Amplifiers
With semiconductor amplifying device
Including differential amplifier
330258, 330261, H03F 318
Patent
active
053349482
ABSTRACT:
A CMOS constant gain operational amplifier (20) has two differential input circuits (22, 24), each having a current source (40, 40A) and a compensation circuit (45, 45A). Each compensation circuit (45, 45A) dynamically tracks the common mode input voltage relative to a respective supply voltage and generates a respective tracking voltage that is used to modulate the current source of the respective differential input circuit. By modulating the current sources in accordance with the common mode input voltage, the input circuits are maintained in their saturation mode of operation over almost the entire rail-to-rail voltage range of the operational amplifier. The amplification stage circuit (27) also includes a dynamic bias adjustment circuit (95) that adjusts the bias of pull-down transistors (88, 90, 92, 94) in the presence of high speed input signal transients so as to keep the pull-down transistors in the amplification stage circuit in their normal, saturation mode of operation. As a result, the operational amplifier maintains virtually constant open loop gain throughout its entire operating range.
REFERENCES:
patent: 4458212 (1984-07-01), Beehmer et al.
patent: 5059921 (1991-10-01), Vyne et al.
patent: 5130580 (1992-07-01), Min et al.
"A Rail-To-Rail Input/Output CMOS Power Amplifier"; Matthijs D. Pardoen et al.; IEEE 1989 Custom Integrated Circuits Conference; pp. 25.5.1-25.5.4.
"CMOS Low-Voltage Operational Amplifiers With Constant-Gm Rail-to-Rail Input Stage"; R. Hogervorst et al.; Reprint from Proceedings of the 1992 IEEE International Symposium on Circuits and Systems; San Diego, Calif.; May 10-13, 1992; pp. 2876-2879.
Fong Edison
Nguyen Nghiem
Abraham Fetsum
National Semiconductor Corporation
Sikes William L.
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