Ding Yan
Newbie level 4
vco lc+q
Hi guys,
I got a little confused in determine the parameters in LC VCO. Normally, people make gmRtank>2. I don't have the accurate varactor model, so I assume the Q value is twice of the inductor. So, I my design, I make gmRinductor>3.
I got inductor's PI model from ASITIC and the Q value is something around 15 @ 5GHz. I do not think it is reliable because I didn't take the eddy current into consideration. So again, I assumed Qinductor is 10. Thus, I meet the following problem:
1. When I calculate the shunt resistance of the inductor, I use wLQ or Rs*Q*Q ? (the Rs is around 1.5 ohm), if I Q=15, wLQ=Rs*Q*Q. However, I assume Q can not reach such a high value. So what should I do?
2. Assume the Rinductor is 300 ohm, the gm should be greater than 0.01 according to gmRindctor>3. So, how can I determine the W/L of the NMOS? I use 1V supply. Can I just apply 1V voltage to the drain and gate terminals and evaluate the gm with 2Id/(Vgs-Vth) ? Please help. THX
Hi guys,
I got a little confused in determine the parameters in LC VCO. Normally, people make gmRtank>2. I don't have the accurate varactor model, so I assume the Q value is twice of the inductor. So, I my design, I make gmRinductor>3.
I got inductor's PI model from ASITIC and the Q value is something around 15 @ 5GHz. I do not think it is reliable because I didn't take the eddy current into consideration. So again, I assumed Qinductor is 10. Thus, I meet the following problem:
1. When I calculate the shunt resistance of the inductor, I use wLQ or Rs*Q*Q ? (the Rs is around 1.5 ohm), if I Q=15, wLQ=Rs*Q*Q. However, I assume Q can not reach such a high value. So what should I do?
2. Assume the Rinductor is 300 ohm, the gm should be greater than 0.01 according to gmRindctor>3. So, how can I determine the W/L of the NMOS? I use 1V supply. Can I just apply 1V voltage to the drain and gate terminals and evaluate the gm with 2Id/(Vgs-Vth) ? Please help. THX