(19)
(11) EP 0 443 238 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
08.01.1992 Bulletin 1992/02

(43) Date of publication A2:
28.08.1991 Bulletin 1991/35

(21) Application number: 90309885.3

(22) Date of filing: 10.09.1990
(51) International Patent Classification (IPC)5: G05F 3/26
(84) Designated Contracting States:
DE FR GB IT NL

(30) Priority: 20.02.1990 US 482319

(71) Applicant: PRECISION MONOLITHICS INC.
Santa Clara California 95052 (US)

(72) Inventor:
  • Smith, Douglas S.
    Scotts Valley, California 95006 (US)

(74) Representative: Crawford, Andrew Birkby et al
A.A. THORNTON & CO. Northumberland House 303-306 High Holborn
London WC1V 7LE
London WC1V 7LE (GB)


(56) References cited: : 
   
       


    (54) Precision switched current source


    (57) A precision switched current source uses two transistors, preferably bipolar devices, with one transistor (Q1) establishing a reference current and the second transistor (Q2) connected to provide an output current which proportionately mirrors the reference current. A voltage controlled switch, preferably a field effect transistor (FET) (T1), is connected between the bases of the two bipolar transistors (Q1, Q2), and is switched to open and close that connection. The mirrored output current is thus switched on and off, under the control of the FET switch (T1). A second switch (T2) may be provided and operated inverse to the first FET switch (T1) to discharge the base of the output bipolar transistor (Q2) when that transistor is off.






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