US 5,920,111 AGranted

CMOS OP-AMP circuit using BJT as input stage

AssigneeTaiwan Semiconductor Manufacturing Company, Ltd.

InventorsShyh-Chyi Wong, Mong-Song Liang

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Abstract

An accumulated-base bipolar junction transistor and an application of said transistor is described. A base region of an accumulated-base bipolar junction is formed by the implantation and then the diffusion of a first dopant material into the semiconductor substrate. A base contact region is a rectangular ring of a second dopant type that is implanted and annealed into the base region. The base contact region is to form a low resistance path from the base region to external circuitry. A collector region is formed by the implantation and annealing of third dopant into the base region in the form of a rectangular ring within the base contact region and a first distance from the base contact region. An emitter region is a rectangular form implanted and annealed of the third dopant within the collector region and a second distance from the collector region. An insulating material such as silicon dioxide is deposited upon the surface of said accumulated-base transistor with openings in the insulating material in the base contact region, the collector region, and the emitter region to allow contact with external circuitry. A layer of polycrystalline silicon is deposited over the insulating material in the area between the collector region and the emitter region to form a base accumulator means. The base accumulator means is coupled to the emitter and to external circuitry. When a voltage supply is coupled to the emitter and the base accumulator means, a charge is accumulated at an interface of the base region and the insulating material between the collector region and the emitter region. The charge will improve the conductivity of the base region and the transconductance of the accumulated-base transistor.

An operational amplifier circuit to create an inverted difference signal and a noninverted difference signal that are each the difference between a first signal and a second signal, coupled between a first and second power supply line comprising:

a) a biasing current source to provide a constant current having a first terminal connected to the first power supply line, and a second terminal;
b) a first accumulated base transistor comprising a base coupled to an inverting input terminal having the first signal, an emitter coupled to the second terminal of the biasing current source, a collector coupled to an inverted output terminal, and a base accumulation means connected to said emitter, such that a voltage presented to the inverting input terminal by the first signal that has a polarity with respect to said emitter so as to develop a charge of majority carriers at an interface of the base between the emitter and the collector thus increasing a parameter of said transistor that is the conductivity, wherein the increase in the conductivity of the base of said first accumulated base transistor will increase the transconductivity of said first accumulated base transistor;
c) a second accumulated base transistor comprising a base coupled to a a noninverting terminal having the second signal, an emitter coupled to the second terminal of the biasing current source, a collector coupled to a noninverted output terminal, and a base accumulation means operably coupled to said emitter, such that a voltage presented to the input terminal by the second signal has a polarity with respect to said emitter so as to develop a charge of majority carriers at an interface of the base between the emitter and the collector thus increasing a parameter of said transistor that is the conductivity, wherein the increase in the conductivity of the base of said second accumulated base transistor will increase the transconductivity of said second accumulated base transistor;
d) a first active load connected between the collector of the first accumulated base transistor and the second power supply line to develop said inverted difference signal;
and
e) a second active load connected between the collector of the second accumulated base transistor and the second power supply line to develop said noninverted difference signal.

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Abstract

Claims1