(19)
(11) EP 0 731 403 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
23.07.1997 Bulletin 1997/30

(43) Date of publication A2:
11.09.1996 Bulletin 1996/37

(21) Application number: 96301270.3

(22) Date of filing: 26.02.1996
(51) International Patent Classification (IPC)6G05F 3/26
(84) Designated Contracting States:
DE FR GB IT

(30) Priority: 08.03.1995 US 399079

(71) Applicant: SGS-THOMSON MICROELECTRONICS, INC.
Carrollton Texas 75006-5039 (US)

(72) Inventor:
  • McClure, David
    Carrollton, Texas 75006 (US)

(74) Representative: Palmer, Roger et al
PAGE, WHITE & FARRER 54 Doughty Street
London WC1N 2LS
London WC1N 2LS (GB)

   


(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.







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