The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Sep. 13, 1994
Filed:
Mar. 31, 1993
Baoson Nguyen, Plano, TX (US);
Texas Instruments Incorporated, Dallas, TX (US);
Abstract
A current switch (30) includes a switching transistor (Q1) having a collector electrode for coupling to a first voltage source (Vcc), an emitter electrode, and a base electrode for receiving a control signal (V.sub.IN1). Switching transistor (Q1) is responsive to the control signal (V.sub.IN1) to turn on to produce a collector current (I.sub.CQ1). A bias circuit (26) is coupled to the emitter electrode of the switching transistor (Q1) for causing the collector current (I.sub.CQ1) of the switching transistor (Q1) to have a predetermined value. The bias circuit includes first and second transistors (Q3 and Q4) having base electrodes coupled in common. The first transistor (Q3) has a collector electrode coupled to the emitter electrode of the switching transistor (Q1) and an emitter electrode for coupling to a second voltage source (Vss). The second transistor has a collector electrode for coupling to a current source (24) and an emitter electrode for coupling to the second voltage source (Vss). A third transistor (Q6) has a collector electrode coupled to the emitter electrode of the switching transistor (Q1), a emitter electrode coupled to the base electrode of the first transistor (Q3), and a control electrode coupled to the collector electrode of the second transistor (Q4). The third transistor (Q6) reduces the dependance of the collector current (I.sub.CQ1) on the .beta. of the switching transistor (Q1) to make the collector current (I.sub.CQ1) less sensitive to process variations.