Programmable Schmitt Triggers Are Digitally Controlled

March 18, 2002
The circuit in Figure 1 is a single-supply version of a programmable Schmitt trigger, or a comparator with hysteresis. A comparator, A1, and a digitally programmable potentiometer (DPP1) are used for the...

The circuit in Figure 1 is a single-supply version of a programmable Schmitt trigger, or a comparator with hysteresis. A comparator, A1, and a digitally programmable potentiometer (DPP1) are used for the function. The lower (VLL) and upper (VUL) limits of the hysteresis characteristic are a function of the relative setting of the potentiometer's wiper, given as:

VLL = (1 − p) 2.5 V

and

VUL = 2.5 V + (p) 2.5 V

where p is a dimensionless number from 0 to 1, representing the potentiometer wiper's position from one end of the pot (0) to the other end (1).

The characteristic's lower limit can be programmed from 0 to 2.5 V, while the upper limit can be programmed from 2.5 to 5 V. The circuit's transfer characteristic (VO versus VS) illustrates the hysteresis curve, and the lower and upper limits (Fig. 2). These limits are complementary, meaning that their values sum to 5 V. So, they're not in-dependently programmable.

By adding steering diodes D1 and D2, plus a second potentiometer, the lower and upper limits of the characteristic can be independently programmed (Fig. 3). For this circuit:

VLL = (1 − p2) 2.5 V

and

VUL = 2.5 V + (p1) 2.5 V.

The CAT5114 32-tap DPPs let the lower limit be programmed from 0 to 2.5 V in 81-mV increments. The upper limit can be independently programmed from 2.5 to 5 V with the same resolution.

Sponsored Recommendations

Board-Mount DC/DC Converters in Medical Applications

March 27, 2024
AC/DC or board-mount DC/DC converters provide power for medical devices. This article explains why isolation might be needed and which safety standards apply.

Use Rugged Multiband Antennas to Solve the Mobile Connectivity Challenge

March 27, 2024
Selecting and using antennas for mobile applications requires attention to electrical, mechanical, and environmental characteristics: TE modules can help.

Out-of-the-box Cellular and Wi-Fi connectivity with AWS IoT ExpressLink

March 27, 2024
This demo shows how to enroll LTE-M and Wi-Fi evaluation boards with AWS IoT Core, set up a Connected Health Solution as well as AWS AT commands and AWS IoT ExpressLink security...

How to Quickly Leverage Bluetooth AoA and AoD for Indoor Logistics Tracking

March 27, 2024
Real-time asset tracking is an important aspect of Industry 4.0. Various technologies are available for deploying Real-Time Location.

Comments

To join the conversation, and become an exclusive member of Electronic Design, create an account today!