I am trying to convert an input sine wave to a square wave. The sine wave is centered at 2.5V and has an amplitude of 200mV, with a frequency of 100kHz.
I am looking for a hysteresis of 100mV centered around 2.5V. (ie. 50mV below and 50mV above 2.5V)
I am trying to achieve something like the following , where both waves are centered about 2.5V:
To do so I looked through Design with Operational Amplifiers and Analog ICs, and I thought that I could work with a VTC offsetting single-supply inverting Schmitt trigger.
I then calculated the resistance values according to my parameters.
VTH = 2.55V VTL = 2.45V VCC = 5V
Where I get:
R1 = R2 = 1kΩ
R3 = 1kΩ
R4 = 50kΩ
R5 = 100Ω
Testing this on proteus:
yields undesired results:
I was expecting the hysteresis of 100mV and not 200mV.
On closer inspection,
VTL is 2.4Vand
VTH is 2.6V. This can be remedied by increasing R4 while keeping R3 constant. I would like to know why my initial calculations were incorrect.
Any suggestions on what I may be doing wrong would be appreciated.