Amplifiers – With semiconductor amplifying device – Including push-pull amplifier
Patent
1998-09-02
2000-08-15
Mottola, Steven J.
Amplifiers
With semiconductor amplifying device
Including push-pull amplifier
330292, H03F 326
Patent
active
061042447
ABSTRACT:
A rail-to-rail output circuit synthesizes a constant product output characteristic by replicating the current through a pull-up transistor and utilizing a translinear loop to drive a complementary pull-down transistor responsive to the replicated current. A smaller replication transistor shares a common V.sub.BE with the pull-up transistor so as to generate a scaled replication current that is proportional to the current through the pull-up transistor. The replication transistor is coupled to the base of the pull-down transistor through a bias circuit that forms a fast translinear loop with the pull-down transistor. An emitter follower transistor sevoes the loop so that the product of the currents through the pull-up and pull-down transistors is proportional to the square of a bias current. To reduce the turn-off time of the pull-down transistor, a second replication transistor is be connected with its base-emitter junction sharing the V.sub.BE of the pull-up transistor and its collector coupled to the base of the pull-down transistor through a current mirror, thereby providing a deliberate path for discharging current from the base of the pull-down transistor as it turns off. A current limit circuit provides smooth and accurate current limiting by generating sense currents that replicate the currents through the pull-up and pull-down transistors, summing the sense currents with accurate reference currents, and diverting the bias current to the translinear loop or the tail current to a transconductance input stage responsive to the difference between the sense currents and the reference currents.
REFERENCES:
patent: 5412344 (1995-05-01), Franck
patent: 5869989 (1999-02-01), Furuya et al.
Gray, Paul R. and Meyer, Robert G.; Analysis and Design of Analog Integrated Circuits; Berkely, CA; (1993) pp. 378-403.
Gilbert, Barrie; Translinear Circuits: An Historical Overview; Boston, MA; 1996; pp. 95-118.
Solomon, James; The Monolithic Op Amp: A Tutorial Study; IEEE Journal of Solid-State Circuits, vol. SC-9, (1974) pp. 314-332.
Gilbert, Barrie; A New Wide-Band Amplifier Technique; IEEE Journal of Solid-State Circuits, vol. SC-9, No. 4 (1968) pp. 353-365.
Analog Devices Inc.
Mottola Steven J.
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