Ring oscillator
Hello,
I'm working on an assignment for my microelectronics course, which is to design ring oscillators with different number of inverters and compare their characteristics. Oscillators with 3 or more inverters work fine, but I can't seem to get a single inverter to oscillate of its own accord . Why is that? Is it just that the delay is too small for the inverter to 'notice'?
Also, I designed the inverter of which the oscillators are composed so that it has symmetric characteristics (i. e. equal low-high and high-low time delays as well as the output of 1/2 V_DD at input equal to 1/2 V_DD). However, when I measure the delays in oscillators they are different (e. g. 5 and 7 ps). I can't think of a reason for that either. Could someone please explain that as well?
I'm using Microwind 2 for the simulations.
TIA,
Greg