Precise control of VCE in close to saturation conditions
AssigneeNortel Networks Limited
InventorStepan Iliasevitch
Life of this patent
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Abstract
A pull-down circuit uses an npn transistor operating at close to saturation and the collector/emitter voltage is used as the pull-down voltage. To keep this within strict limits the npn transistor is connected in circuit with other transistors and resistors as well as a current source that generates a current proportional to absolute temperature. By selecting the values of the resistors and transistor parameters the collector/emitter voltage may be kept stable within a small range over wide temperature variation.
Claims18
A circuit comprising first and second bipolar junction transistors each having a base, an emitter and a collector, at least two resistors, a voltage drop device and a current source arranged to generate a current iPTAT which is proportional to absolute temperature, wherein:
- the bases of the first and second transistors are connected together;
- the first resistor is connected across the base/emitter junction of the second transistor;
- the second resistor is connected across the base/collector junction of the first transistor;
- the current source is connected across the base/emitter junction of the first transistor;
- the emitters of the first and second transistors are both connected to a biasing voltage terminal;
- the collector of the first transistor is connected directly or indirectly to an input terminal;
- the voltage drop device is connected between the input terminal and the collector of the second transistor;
- and
- the values of at least the first and second resistors are selected to provide a predetermined variation with temperature of the voltage VCE across the collector/emitter of the second transistor.
Dependencies are inferred from the claim text.