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https://designers-guide.org/forum/YaBB.pl Design >> Analog Design >> question in simulating amp https://designers-guide.org/forum/YaBB.pl?num=1147370163 Message started by glacieryy on May 11th, 2006, 10:56am |
Title: question in simulating amp Post by glacieryy on May 11th, 2006, 10:56am Hi all, I have a problem on how to simulate the frequency respoonse of amp in a SC integrator? When doing this simulation,should I include the CMFB block?The CMFB block is implemented by SC curcuit. Thanks in advance. Regards glacier |
Title: Re: question in simulating amp Post by sheldon on May 12th, 2006, 7:02pm Glacier, It would be best to include the CMFB network in the simulation. To include the CMFB network, you might try two approaches: 1) Use Spectre's analysis dependent switches to force the dc operating point with common-mode feedback active and the ac analysis with the common-mode feedback disabled. 2) Use SpectreRF's sampled pac analysis. Sample the frequency response when the amplifier is in the normal mode of operation. Best Regards, Sheldon |
Title: Re: question in simulating amp Post by glacieryy on May 12th, 2006, 9:12pm Hi Sheldon, Thanks for your reply. But may I ask a simple question?I am afraid that I do not understand the first way you have told me.Could you give me something in detail? Thanks a lot. Best wishes. Glacier |
Title: Re: question in simulating amp Post by ywguo on May 15th, 2006, 7:12pm Glaicer, I am not familiar SpectreRF. But I have a simple method. Make a CMFB macro model using R, C, and controlled voltage source, although it is not very accurate. .SUBCKT CMFB_G7 P1 P1D P1DB P2 P2D P2DB CBIAS CMC CMO VDD VON VOP VSS R1 CMC CMO1 200E3 R0 CMO2 CMC 200E3 V1 CMO 0 1.65 E1 CMO1 0 VOL='V(cbias)-(V(cmo)-V(VOP))' max=3.3 min=0 E2 CMO2 0 VOL='V(cbias)-(V(cmo)-V(VON))' max=3.3 min=0 C2 VON CMC 125E-15 C0 VOP CMC 125E-15 * END OF SUBCIRCUIT DEFINITION. .ENDS CMFB_G7 where VOP and VON are the differential output of an opamp, CMO is the bias for common mode voltage, CBIAS is the system bias for tail current, CMC is tied to the tail transistor in the opamp. Best regards, Yawei |
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