Miscellaneous active electrical nonlinear devices – circuits – and – External effect – Temperature
Reexamination Certificate
2000-05-11
2001-12-11
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
External effect
Temperature
C327S378000
Reexamination Certificate
active
06329868
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to electronic circuits generally, and more particularly the invention relates to analog electronic circuits.
Analog circuits typically operate on linear or analog signals which represent real world phenomenon such as temperature, pressure, and sound and are continuously variable over a wide range of values. This is to be distinguished from digital signals which represent the “ones” and “zeros” of binary arithmetic.
In temperature sensor products, for example, a signal proportional to absolute temperature (PTAT) and a signal complimentary to absolute temperature (CTAT) are obtained and manipulated. The PTAT signal, or current, is generally developed by applying the voltage difference of two bipolar junctions (transistors or diodes) running at different current density across a resistor. The current through the bipolar junctions should be constant or exponential in temperature. The CTAT current is developed by applying the voltage from a single bipolar junction (transistor or diode) across a resistor.
The junction voltage of a bipolar diode or transistor, whose current is constant or an exponential function of temperature is almost linear in temperature. The non-linear portion of the temperature function is called the curvature. This negative linear temperature coefficient is useful in band gap references, temperature sensors and other products. In most cases, a strictly linear response with curvature canceled would be optimal.
The present invention is directed to canceling the curvature in the temperature function of a bipolar junction base-emitter voltage.
SUMMARY OF THE INVENTION
In accordance with the present invention, the curvature in the temperature function of a bipolar junction base emitter voltage is canceled by providing a circuit in which curvature is offset over an operating range.
More particularly, curvature for two quadrants (e.g. low temperature curvature and high temperature curvature) are combined to offset the non-linear portions of current versus temperature for the junction voltage. In one embodiment, one quadrant is provided by applying a first current source, PTAT−CTAT, through first and second serially connected diode connected transistors. A second current source, PTAT+&bgr;CTAT, is applied through a third transistor, with the voltage across the first and second serially connected transistors connected to the control electrode (e.g. base or gate) of the third transistor. The voltage of the emitter (source) of the third transistor is the control electrode voltage minus the base-emitter (gate-source) voltage, which is then applied across the base-emitter (gate-source) of a fourth transistor. The circuit output is the current through the fourth transistor.
The other quadrant is provided by a similar circuit but with the first current source being CTAT−PTAT. The output currents of the two quadrants are combined to provide the curvature offsets in current.
The circuit can be implemented with either the bipolar transistors, or MOSFET transistors operating in subthreshold conduction.
The invention and objects and feature thereof will be more readily apparent when the following detailed description and dependent claims when taken with the drawings.
REFERENCES:
patent: 4061959 (1977-12-01), Ahmed
patent: 4313082 (1982-01-01), Neidorff
Blakely , Sokoloff, Taylor & Zafman LLP
Callahan Timothy P.
Maxim Integrated Products Inc.
Nguyen Linh
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