andrew_matiga said:
@erikl.
However, I still cant explain how it provides hysteresis. Is it ok if you can explain it to me please?
@andrew: Your Schmitt-Trigger owns 2 concurrent gain loops for each input.
Hereafter, their signal paths together with their corresponding phase conditions (+) & (-) are shown (always related to the outputs, i.e. drains of the transistors). The 1st line represents the main loop, the second line is the loop which adds additional gain (actually not a common feedback scheme, but it works sort like a positive feedback, because it adds positive gain via a different path) :
VIN+(+) (M1 M4)(-) (M9 M10)(+) (M8 Vout)(-)
VIN+(+) (M1 M4)(-) (M6 M2 M3)(+) (M7 Vout)(-)
VIN-(+) (M2 M3)(-) (M7 Vout)(+)
VIN-(+) (M2 M3)(-) (M5 M1 M4)(+) (M9 M10)(-) (M8 Vout)(+)
This should give us the following info:
1. The input signal names should be inverted, because it's usual to relate their names to the output phase condition.
2. The 2 IO-paths have different lengths and number of phase inversions (3|3 resp. 2|4). This creates a certain asymmetry.
3. The gain values - as always - depend on the respective W/L ratios. So if you change the gain ratios
equally within the 2 concurrent (but gain-added) paths, you change the overall gain, and, by this, the switching speed.
4. Some hysteresis could only be achieved (if ever), if the two individual IO-path gain ratios are different, which creates additional asymmetry. But I can't explain exactly, why. All the 4 gain paths should result in an overall gain Vout/VIN(diff); they just have different IO-delays. May be these delay differences can create some hysteresis. Rely on your sim. results!
I must admit that your Schmitt works a bit differently than I thought after first sight! ;-)
Cheers, erikl
Thanks for your thanks points!