A 20Hz TTL waveform is applied to the circuit... 3. The attempt at a solution - I'm working an activity for my lab tomorrow (not actually due for any points, just to help us get an understanding of the lab), but I'm not really sure what it means when it says a "20 Hz TTL waveform". Can somebody explain this to me? I know that TTL usually means Transistor-Transistor Logic, but what does it mean in reference to a wave form. I should also note that I'm trying to simulate the circuit in Pspice capture.