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always@smart
Joined: 08 Feb 2002
Posts: 308
Helped: 7
Location: ASIA
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 02 Dec 2004 4:44 plot CMRR graph of OPA |
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Hi all,
can anyone here suggest me a test method that can plot the OPA's CMRR in frequency response?
thanks so much in advance
regards,
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Fom
Joined: 10 Mar 2004
Posts: 758
Helped: 56
Location: Taiwan
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| 02 Dec 2004 8:11 Re: plot CMRR graph of OPA |
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| What kind of simulator do you use? For Cadence you can run parametric AC analysis with common mode DC source at input.
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Amuro
Joined: 15 Mar 2002
Posts: 293
Helped: 3
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| 02 Dec 2004 9:24 plot CMRR graph of OPA |
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| There is a simulation technique for ploting CMRR vs. Freq. by SPICE in P. Allen's CMOS Analog Circtuit Design. You can look from that.
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gevy
Joined: 17 Nov 2004
Posts: 377
Helped: 41
Location: Russia
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| 03 Dec 2004 9:08 Re: plot CMRR graph of OPA |
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You should necessarily make real voltage offset and mismatch of transistors of the input cascade, when will simulate the CMRR.
If it to not make, the result of simulation will be much better, than in silicon.
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always@smart
Joined: 08 Feb 2002
Posts: 308
Helped: 7
Location: ASIA
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| 05 Dec 2004 5:15 Re: plot CMRR graph of OPA |
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hi ,
thanks for ur reply.
i'm using hspice and i still don get from ur answer that how can i actually configure the OPamp in order to ge the CMRR vs Freq?
hmm...maybe u can show me in netlist or a diagram.
thanks in advance.
regards
smart
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devrimaksin
Joined: 13 Oct 2004
Posts: 93
Helped: 9
Location: Dallas, Texas, USA
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| 05 Dec 2004 5:50 plot CMRR graph of OPA |
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you have to connect both input to the same AC source and run AC simulation
This will give you common mode voltage gain
then you have to simulate differential gain (regular AC simulation to extract small signal gain) and the ratio of these two will give you CMRR
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always@smart
Joined: 08 Feb 2002
Posts: 308
Helped: 7
Location: ASIA
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| 07 Dec 2004 8:56 Re: plot CMRR graph of OPA |
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| devrimaksin wrote: |
you have to connect both input to the same AC source and run AC simulation
This will give you common mode voltage gain
then you have to simulate differential gain (regular AC simulation to extract small signal gain) and the ratio of these two will give you CMRR |
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but how can i configure the OPAmp to plot the CMRR vs Freq? Has anyone here done it b4, pls give me a suggestion.
thanks in advance.
regards,
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xuel
Joined: 16 Nov 2004
Posts: 397
Helped: 11
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| 07 Dec 2004 10:37 Re: plot CMRR graph of OPA |
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| always(at)smart wrote: |
| devrimaksin wrote: |
you have to connect both input to the same AC source and run AC simulation
This will give you common mode voltage gain
then you have to simulate differential gain (regular AC simulation to extract small signal gain) and the ratio of these two will give you CMRR |
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but how can i configure the OPAmp to plot the CMRR vs Freq? Has anyone here done it b4, pls give me a suggestion.
thanks in advance.
regards, |
Devrimaksin has told you how to do it. The key is to use 2 opamps, one for Avc the other for Avd.
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always@smart
Joined: 08 Feb 2002
Posts: 308
Helped: 7
Location: ASIA
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| 07 Dec 2004 11:02 Re: plot CMRR graph of OPA |
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hmmm, ok, i get it..i will try it. thanks for ur suggestion.
regards,
smart
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