huber
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GO BEARS!
Posts: 45
Los Angeles
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When the delay cells in ring oscillators are hard switched then you are basically just charging a capacitor w/ the tail current (slew rate limit). Noise of the tail is very important here, because the tail current directly modulates the delay. I agree w/ Vivek that you should only see tail noise from a diffamp if the circuit is unballanced. The unballance can come from asymmetry in the circuit topology or from an asymmetric operating point (this is what's happening in ring oscillator delay cells). -Dan
PS- a good paper that explains noise in ring oscillators: Abidi, A.A.; Samadian, S., Phase noise in inverter-based & differential CMOS ring oscillators Custom Integrated Circuits Conference, 2005. Proceedings of the IEEE 2005 , vol., no.pp. 457- 460, 18-21 Sept. 2005
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