(12) United States Patent
(10) Patent No.: US 8,026,740 B2
Hollis (45) Date of Patent: Sep. 27, 2011 (54) MULTI-LEVEL SIGNALING FOR LOW OTHER PUBLICATIONS POWER’ SHORT CHANNEL APPLICATIONS Farzan et al., “A CMOS 10-Gb/ s power-efficient 4-PAM transmitter,” _ _ _ _ IEEE Journal ofSolid-State Circuits, vol. 39, No. 3, pp. 529-532 (75) Inventor: Timothy M. Hollis, Mendian, ID (US) (Man 2004)‘ _ _ Farjad-Rad et al., “An equalization scheme for 10Gb/s 4-PAM sig(73) Assignee: MICFOH Technology, IIIC-, B0153, ID naling over long cables,” Center for Integrated System, Stanford (US) University, Mixed Signal Conference, Jul. 1997, Cancun, Mexico, 4 pages. ( * ) Notice: Sutbjetct. to any diiscilaimeé, the tiermdof §‘_';1-frijgllril-ifi(ac1r<:1itt,:r2 41-5-19A§1§\,/I-2PIf)<Z1';£Phasis pa en 15 ex en e or a Jus e un er Zerbe et al.,“1.6 Gb/s/pin 4-PAM signaling and circuits for a multiU~S~C~ 15403) by 740 day5~ drop bus,” Symposium on VLSI Circuits Digest of Technical Papers, vol. 10, No. 2, pp. 128-131 (2000). (21) App1_ NO; 12/053,265 Zerbe et al., “Equalization and Clock Recovery for a 2.5—10Gb/s 2-PAM/4-PAM/ backplane transceiver cell,” IEEE International . Solid-State Circuits Conference, ISSCC 2003 / Session 4 / Clock (22) Flledi Mar‘ 211 2008 Recovery and Backplane transceivers / Paper 4.6 (2003). (65) Prior Publication Data * Cited by examiner
Primary Examiner — Vibol Tan
(74) Attorney, Agent, or Firm — Knobbe, Martens, Olson &
Apparatus are disclosed, such as those involving a transmitter circuit that is configured to generate multi-level signals based on a plurality of data digits. One such transmitter circuit includes a signal output and an encoder configured to provide control signals based at least partially on the plurality of data digits. The transmitter circuit also includes a first set of switches configured to receive one or more of the control signals, and to selectively conduct a first or second voltage reference to the signal output. The transmitter circuit further includes first and second voltage drop circuits that provide third and fourth voltage references, respectively. The third and fourth voltage references have voltage levels between those of the first and second voltage references. The transmitter circuit also includes a second set of switches configured to receive one or more of the control signals, and selectively conduct the third or fourth voltage reference to the signal output.