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(11) | EP 0 731 403 A3 |
(12) | EUROPEAN PATENT APPLICATION |
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(54) | Constant current source |
(57) A current source for generating a current that is relatively stable over variations
in the power supply voltage and temperature, and over variations in process parameters
is disclosed. The current source includes a bias circuit, for producing a compensating
bias voltage, and a current mirror. The bias circuit utilizes a voltage divider to
generate a divided voltage based on the power supply value. The divided voltage is
applied to the gate of a modulating transistor (biased in saturation) in a first current
mirror, which controls a current applied to a linear load device. The voltage across
the load device determines the bias voltage, which is in turn applied to the gate
of a transistor in the reference leg of a second current mirror. The bias voltage
controls the current in the reference leg of the second current mirror, and an output
leg mirrors the second reference current to produce a stable output current. |