United States Patent  [ii] Patent Number: 5,298,800
Dunlop et al.  Date of Patent: Mar. 29,1994
 DIGITALLY CONTROLLED ELEMENT SIZING
 Inventors: Alfred E. Dunlop, Murray Hill, N.J.; Thaddeus J. Gabara, North Whitehall Township, Lehigh County, Pa.; Scott C. Knauer, Mountainside, N.J.
 Assignee: AT&T Bell Laboratories, Murray Hill, N.J.
 Appl. No.: 970,415
 Filed: Nov. 2,1992
Related U.S. Application Data
 Division of Ser. No. 724,560, Jim. 28, 1991, Pat. No. 5,194,765.
 Int. C1.5 H03K 3/01; H01S 3/30
 U.S. CI 307/270; 307/475;
307/443; 307/311; 250/551; 250/205  Field of Search 307/570, 270, 443, 475,
307/311; 250/205, 214 DC, 551, 552
 References Cited
U.S. PATENT DOCUMENTS
3,770,966 11/1973 Sagawa et al 307/311
4,310,754 1/1982 Check, Jr 250/551
4,592,057 5/1986 Comerford 250/205
4,598,198 7/1986 Fayfield 307/311
4,730,114 3/1988 Portmann 307/311
4,855,623 8/1989 Flaherty -307/270
5,095,231 3/1992 Sartori et al 307/270
5,134,311 7/1992 Biber et al 307/270
5,170,073 12/1992 Hahn et al 307/270
Sensor Circuit, Patent Abstracts of Japan, Publication
No. JP-59051303, publication date Mar. 24, 1984, Egu-
chi Osamu et al. Translation: Abstract only.
Conf. Proc. Military Microwaves '88 5-7/7/88 London
(GB); P. G. A. Jones: "Digitally Controlled MMIC
Attenuators-Techniques and Applications"pp. 217-222.
IEEE Journal of Solid-State Circuits, vol. 23, No. 2,
Apr. 1988, "A Self-Terminating Low-Voltage Swing
CMOS Output Driver", Thomas F. Knight, Jr., pp.
Primary Examiner—Edward P. Westin
Assistant Examiner—Richard Roseen
Attorney, Agent, or Firm—Henry T. Brendzel;
Christopher N. Malvone
Effective control of impedance values in integrated circuit applications is achieved with an integrated circuit transistor whose size is digitally controlled. The digitally controlled size is achieved, for example, with a parallel interconnection of MOS transistors. In one application, the digitally controlled transistor serves as a controlled impedance connected to an output terminal of an integrated circuit. In that application, a number of transistors are enabled with control signals, and the collection of enabled transistors is responsive to the input signal that normally is applied to a conventional transistor. In another application, where the digitally controlled transistor serves as a controlled impedance at the input of a circuit, only the control signals that enable transistors and thereby determine the effective developed impedance are employed. In still another application, the digital control of the transistor's size is employed to control the speed or power consumption of the effective transistor. Such control is exercised to erase the manufacturing variability of the integrated circuit. Alternatively, such control is exercised as part of a feedback control of the operational characteristics of the entire circuit. In the feedback control application, the digital signals that control the transistor's size are obtained from an assessment of the circuit's operation. In the manufacturing variability control application, the digital signals that control the transistor's size are obtained from a measure of the integrated circuit's parameters relative to a reference element.
4 Claims, 6 Drawing Sheets