Schmitt trigger circuit with adjustable trip point voltages

US6870413B1 · kind B1 · utility

Assignee

• Altera Corporation · US

Inventors

• Tzung-Chin Chang · San Jose, US
• Chiakang Sung · Milpitas, US
• Khai Nguyen · San Jose, US
• Joseph Huang · معلمی نژاد, US
• Bonnie I. Wang · Cupertino, US
• Yan Chong · San Jose, US
• Xiaobao Wang · Santa Clara, US
• Philip Pan · Fremont, US
• Gopinath Rangan · Milpitas, US
• In Whan Kim · San Jose, US

Key dates

• Filing date: Dec 14, 2001
• Grant date: Mar 22, 2005
• Expiry date: Dec 14, 2021

Classification

• Technology area (CPC H): Electricity
• CPC primary: H03K3/3565
• WIPO field: Basic communication processes
• WIPO sector: Electrical engineering

Abstract

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.