Amplifiers – With semiconductor amplifying device – Including differential amplifier
Patent
1996-12-19
1998-12-08
Mottola, Steven
Amplifiers
With semiconductor amplifying device
Including differential amplifier
330292, 330300, H03F 345, H03F 114
Patent
active
058476075
ABSTRACT:
A high speed fully differential operational amplifier with fast settling time for switched capacitor applications includes a high gain active cascode applied to the operational amplifier's input stage transistors to improve the gain, provide a higher output impedance, and thus, reduce the Miller feedback gate drain capacitance of the input stage devices. This improves the speed of the amplifier. A biasing technique is used to keep the active cascodes biased during transient overload so that settling will not be adversely affected during the recovery of the cascodes. A pair of transistors are used to feed forward a fraction of the tail current to "keep-alive" the cascode transistors. In other words, the fraction of the tail current that is fed to the source of the cascode transistors via the keep-alive transistors effectively biases the active cascodes sufficiently so that they do not turn off completely during slewing.
REFERENCES:
patent: 4714895 (1987-12-01), Nicollini et al.
patent: 5420539 (1995-05-01), Fensch
A 10-b 20 Msample / s Analog-to-Digital Converter, Stephen H. Lewis et al., IEEE Journal of Solid-State Circuits, vol. 27, No. 3, Mar. 1992, pp. 351-358.
A Fast-Settling CMOS Op Amp for SC Circuits with 90-dB DC Gain, Klaas Bult et al., IEEE Journal of Solid-State Circuits, vol. 25, No. 6, Dec. 1990, pp. 1379-1384.
A Fully Differential Sample-and-Hold Circuit for High-Speed Application, Germano Nicollini et al., IEEE Journal of Solid-State Circuits, vol. 24, No. 5, Oct. 1989, pp. 1461-1465.
A High-Swing, High-Impedance NOS Cascode Circuit, Eduard Sackinger et al., IEEE Journal of Solid-State Circuits, vol. 25, No. 1, Feb. 1990, pp. 289-298.
MOS Operational Amplifier Design--A Tutorial Overview, Paul R. Gray et al., IEEE Journal of Solid-State Circuits, vol. SC-17, No. 6, Dec. 1982, pp. 969-982.
Lewicki Laurence D.
Opris Ion E.
Mottola Steven
National Semiconductor Corporation
Santisi Steven M.
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