differential ring oscillator problem

[ppat2006]

what is the output of single stage cmos differential ring oscillator square wave or sine wave? i have attached my circuit diagram .plz suggest me W & L values of each transistor.

how to control the frequency with the bottommost nmos transistor?i am simulating it in mentor graphics but it is showing wrong output.

if anybody has any readymade working diagram then plz attach it

 

[Milad-D]

You should charge Q2 and Q4 up side down. You have connected them wrong.

When the loop gain is much higher than 1, the output wave will be square wave, otherwise you will get sine wave. In this circuit pmos transistor have behn used as a resistor. Therefore the gain of each stage is ~sqrt((w/k)p/(w/l)n). This gain should be made big enough, to get square wave.

The differential swing of each stage is about 2Iss*(on resustance of pmos). The dominant pole of each stage is 1/(Rp*Cout). To the first order Rp is independent of current. Therefore, for tuning, it is better to connect the gate of both pmos transistors to a control voltage ,vb and by changing this voltage you can change the frequency. The disadvantage of this circuit is that as you change the vb, the ouput swing will change. There are better circuits for this purpose. You can find bunch of circuits in chapter 14 of analog book of razavi.

 

[ppat2006]

thanks a lot. u told me to change Q2 and Q4 upside down.plz make the necesarry chnages and also give w and l values of each transistor and send me the file. i want to do further phase noise analysis.

i will also chk analog book by razavi. but these books dont specify W and L values and i dont understand how to give W & L values for each transistor.

waiting for ur reply.