BiCMOS circuit for controlling a bipolar current source

Details BiCMOS circuit for controlling a bipolar current source BiCMOS circuit for controlling a bipolar current source

1999-03-18

2001-09-11

JeanPierre, Peguy (Department: 2819)

Coded data generation or conversion

Analog to or from digital conversion

Digital to analog conversion

C326S110000, C307S402000, C327S530000

Reexamination Certificate

active

06288660

ABSTRACT:

TECHNICAL FIELD
This invention relates to a switch circuit, and more particularly to a BiCMOS circuit which allows a low voltage CMOS signal to control a bipolar current source or sink circuit.
BACKGROUND OF THE INVENTION
BiCMOS current switching circuits are known, in which a signal applied to a CMOS transistor determines a current through a bipolar transistor. For example, current steering digital-to-analog converters may include a plurality of bipolar devices, each bipolar device having a respective CMOS device associated with it, and with the total current drawn by the bipolar devices being determined by the inputs to the CMOS devices.
As an example of this, U.S. Pat. No. 5,548,288 describes a current cell and current switch for use in a current-steering digital-to-analog converter. In the circuit described therein, an output current is determined by the digital signal applied to the circuit inputs.
However, the circuit described therein has the disadvantage that it includes a relatively large number of components and hence that it uses a relatively large area in an integrated circuit.
SUMMARY OF THE INVENTION
The present invention provides a circuit which, in some embodiments, can be implemented using fewer components than at least some of the prior art circuits, and hence uses a smaller area in an integrated circuit.
More specifically, one embodiment of a first aspect of the invention provides a BiCMOS circuit which includes a first bipolar transistor which, in operation, draws a current. The collector of the first bipolar transistor is connected to a voltage source through a CMOS transistor, and to a circuit output through a second bipolar transistor. The output current drawn through the second bipolar transistor depends on whether the CMOS transistor is turned on or off by a control voltage applied thereto.
According to a second aspect of the invention, there is provided a digital-to-analog converter which includes a plurality of BiCMOS circuits in accordance with the first aspect of the invention. The respective first bipolar transistors thereof preferably form respective current mirror circuits with a further bipolar transistor, and draw respective currents which can be added to form a total output current which depends on the respective control voltages applied to the respective CMOS transistors.
According to a third aspect of the invention, there is provided a charge pump circuit which includes two BiCMOS circuits in accordance with the first aspect of the invention. A first circuit is configured as a current source, and a second is configured as a current sink. Controlling the inputs to the two circuits results in changes in the output current.


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