US 7,449,913 B1
Pre-driver having slew-rate and crowbar-current controls for a CMOS output buffer
Kenneth Wai Ming Hung, Pak Shek Kok (Hong Kong Special Administrative Region of the People's Republic of China, The)
Assigned to Smartech Worldwide Limited, Hong Kong (China)
Filed on Jun. 20, 2007, as Appl. No. 11/765,751.
Int. Cl. H03K 17/16 (2006.01); H03B 1/00 (2006.01)
U.S. Cl. 326—27  [326/26; 326/83; 327/108; 327/112; 327/170; 327/207] 20 Claims
OG exemplary drawing
 
1. An output buffer having slew-rate control and crossbar current control, comprising:
a pull-up PMOS transistor coupled to a high voltage supply terminal VDD and having a gate configured to receive a signal PUP;
a pull-down NMOS transistor arranged between and the pull-up PMOS transistor and a low-voltage supply terminal VSS, wherein the gate of the pull-down NMOS transistor is configured to receive a signal NDN;
a pull-up network coupled to the gate of the pull-up PMOS transistor, wherein the pull-up network comprises:
a first logic gate circuit having a threshold voltage VTHP for an input signal PPUP and configured to produce at least a portion of PUP;
a first Schmitt trigger circuit configured to receive PUP as an input and output a signal FPUP, wherein the first Schmitt trigger circuit has a switching threshold voltage VSTP for PUP; and
a second logic gate circuit having a threshold voltage substantially at VTHP for the input signal PPUP and configured to produce at least a portion of PUP, wherein the second logic circuit is enable controlled by the signal FPUP; and
a pull-down network coupled to the gate of the pull-down NMOS transistor, wherein the pull-down network comprises:
a third logic gate circuit having a threshold voltage VTHN for an input signal PNDN and configured to produce at least a portion of NDN;
a second Schmitt trigger circuit configured to receive NDN as an input and output a signal FNDN, wherein the second Schmitt trigger circuit has a switching threshold voltage VSTN for NDN; and
a fourth logic gate circuit having a threshold voltage substantially at VTHN and an output connected to the gate of the pull-down NMOS transistor, wherein the fourth logic circuit is enable controlled by the signal FNDN.