PNP multiplier

Details PNP multiplier PNP multiplier

2001-11-08

2003-09-02

Fahmy, Wael (Department: 2814)

Miscellaneous active electrical nonlinear devices, circuits, and

Specific input to output function

C327S334000

Reexamination Certificate

active

06614284

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to emitter followers. In particular, the present invention relates to an apparatus and method that has a voltage gain and current gain that are comparable to a PNP emitter follower circuit that employs a PNP transistor with a large die area.
BACKGROUND OF THE INVENTION
An emitter follower is a single transistor circuit that is arranged in a common-collector configuration. The transistor in the emitter follower can be an NPN transistor or a PNP transistor. An emitter follower has a voltage gain from the base of the transistor to the emitter that is close to one. The emitter follower is often used to provide a high current output since the transistor has a high current gain. Additionally, the emitter follower has a high input impedance and a low output impedance. An emitter follower is useful for isolating or buffering a high-resistance source such that a low-resistance load does not excessively load down the source.
SUMMARY OF THE INVENTION
A method and apparatus are directed to emulating an emitter follower with a small PNP transistor that is arranged in a PNP multiplier configuration. The PNP multiplier includes a PNP emitter follower and a current mirror. The PNP follower is coupled between the input and the output. A current mirror is coupled to the collector of the PNP follower such that mirror produces a current that is a scaled version of the collector current from the PNP follower. The current mirror is arranged to scale the PNP collector current by a factor of N. The effective output current from the PNP multiplier circuit corresponds to &bgr;·I
IN
·(N+1), where &bgr; corresponds to the large signal forward gain of the PNP follower. By multiplying the output current by a scaling factor, the effective forward gain of the PNP transistor is increased while utilizing a small geometry PNP device.


REFERENCES:
patent: 6130549 (2000-10-01), Buck
patent: 6181202 (2001-01-01), Yamasaki
patent: 6291977 (2001-09-01), Iliasevitch
patent: 06189531 (1994-07-01), None
Adel S. Sedra and Kenneth C. Smith, Microelectronic Circuits 1998, Oxford University Press, Inc., 4thedition, pp 512-514.

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