| 摘要 |
A Schmitt trigger circuit has an adjustable hysteresis characteristic by providing a plurality of feedback circuits that differently affect at least one, and preferably both, of the circuit's upper trip point level and lower trip point level. The upper trip point level can be adjusted by selecting a desired feedback circuit from a first set of feedback circuits, and/or the lower trip point level can be adjusted by selecting a desired feedback circuit from a second set of feedback circuits. Feedback circuit selection is achieved by one or more control signals that may be programmable. The hysteresis characteristic can be adjusted to meet desired noise margin, delay, and input recognition criteria at different VCC levels. The Schmitt trigger circuit may be a CMOS Schmitt trigger with two input stage NMOS, two input stage PMOS transistors, a first set of NMOS feedback circuits, and a second set of PMOS feedback circuits.
|
