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Design >> Analog Design >> Noise Analyzes for fully differential amplifiers
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Message started by mateenfl on Sep 15^th, 2003, 2:26am

Title: Noise Analyzes for fully differential amplifiers
Post by mateenfl on Sep 15^th, 2003, 2:26am

Hello all,

I am interested in measuring the input referred noise for the fully differential amplifiers.

1> In Cadence, there is a noise analzes window, and a small section on output noise. I selected the voltage option from the drop down box.

It asks to specify two nodes for noise measurement. Which nodes should I specify there (and why)

a>Should I specify the two outputs of fully differential amplifier or

b> should I choose one of the outputs of my differential amplifier and other as ground

2.> Is there a special circuit setup for measuring the noise. (I would like some link on it)

Kind Regards,
Faisal Mateen

Title: Re: Noise Analyzes for fully differential amplifie
Post by Mighty Mouse on Sep 15^th, 2003, 11:36am

You measure the differential output noise by specifying the two output nodes to the noise analysis (if you specify one as ground, you would be measuring the single ended noise, not the differential noise).

To measure the input referred noise, you must also specify the input source.

An alternative approach, that is more powerful, is described in a paper called "A test bench for differential circuits" that you can find at http://www.designers-guide.com/Analysis.

- MM -

Title: Testbench for fully differential amplifiers
Post by mateenfl on Sep 16^th, 2003, 12:16pm

Hello,

Thanks for the reply. I am facing a problem related to the testbench (that you indicated out on this website)

I do not have an ideal balun in analog library (0.18u UMC, cadence). I tried using ideal transformer in the analog library but it does not has the veriloga/hdla models as well.

So how can I implement the balun required for this testbench.

Kind Regards,
Faisal Mateen

Title: Re: Noise Analyzes for fully differential amplifie
Post by Mighty Mouse on Sep 16^th, 2003, 6:10pm

In the more recent versions of Artist, the ideal balun is available from analogLib (ideal_balun). If you cannot find it, you can build one using ideal transformers (xfmr from analog lib) as shown in Figure 4 of the paper.

- MM -

Title: Re: Noise Analyzes for fully differential amplifie
Post by Andrew Beckett on Sep 22^nd, 2003, 10:05pm

And there's also a behavioural model of a balun in rfLib
(which has been there for many releases).

I believe ideal_balun was added to analogLib in an
MSR of IC50 (it's certainly there in IC50 MSR3).

Andrew.