Hysteresis
The system is designed to propose two bipolar references per signal. At its core, it is articulated with two comparators and two bipolar references set by DAC. Given the intrinsic nature of the comparator, when the input signal is close to the reference, noise can cause an unwanted transition which leads to an erratic output. The use of two voltage levels, hysteresis, avoids the mentioned problem at the condition to be bigger than the noise. Comparators often incorporate internal hysteresis. But a bigger hysteresis level might be required. To increase the hysteresis a feedback is used as external hysteresis.
A picture of the solution used is joined.
Simulation
With Excel:
- Vref = N5V0
- R = 2000Ohm
- Rf = 100000Ohm
- V0a = P7V0
- V0b = 0V
- Vtha = N2V406
- Vthb = N2V475
- Hysteresis = 69 mV (rounded)
With Pspice: hysteresis is 67mV.
With DAC that sets N5V0 and R=2kOhm and Rf=100kOhm and V0a which is P7V0, the hysteresis calculated and simulated is the same. The difference comes from the rounded values in the Excel.