The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Measurements >> Other Measurements >> Measure Equivalent Input Voltage and Current Noise of Op Amps
https://designers-guide.org/forum/YaBB.pl?num=1551337485

Message started by ZY He on Feb 27^th, 2019, 11:04pm

Title: Measure Equivalent Input Voltage and Current Noise of Op Amps
Post by ZY He on Feb 27^th, 2019, 11:04pm

Hello,

Recently i learn a few about the noise model about operational amplifier. And here i have some questions about how to understand the measure of equivalent input voltage noise and equivalent input current noise of an operational amplifiers in Noise analysis in Virtuoso ADE.

I want to know:
1. what is the noise model of an amplifier in ADE simulation
2. how they define the equivalent input voltage noise and equivalent input current noise
3. is there any relationship between equivalent input VOLTAGE noise and equivalent input CURRENT noise

Are there any helpful documents about it?
Please help me!! Thank you very much. ;D

Title: Re: Measure Equivalent Input Voltage and Current Noise of Op Amps
Post by Andrew Beckett on Mar 1^st, 2019, 1:01am

Attempting to answer your questions:

[olist]

I'm not sure what you mean by "noise model of an amplifier"? An amplifier doesn't have a noise model - unless you're talking about a Verilog-A model of an amplifier, in which case that would depend on the specific noise contributions added within the Verilog-A model (if any).

Who is "they" in your question? The noise analysis works by computing the total output referred noise - this is computed by computing the noise at each noise source in each device source, and then multiplying that by the transfer function from that noise source to the output, and summing up the noise powers at the output. Then for equivalent input noise calculations, the analysis computes the transfer function from the input to the output, and then divides the total output noise by that transfer function.

The difference is which transfer function is used between the input and output. If you specify a voltage at input, it's the transfer function from that input voltage to the specified output; if you specify a current, it's the transfer function from that current source to the specified output. The output noise is the same either way - it's just the denominator to compute the input referred noise that changes.
[/olist]

Regards,

Andrew

Title: Re: Measure Equivalent Input Voltage and Current Noise of Op Amps
Post by ZY He on Mar 1^st, 2019, 10:59pm

Thank you Andrew.

1. The reason why i mention the noise model of an Op Amp is in some case, i will assume there are a series noise voltage source 'Vn' and a shunt noise current source 'In' for each input port of an Op Amp.
I just thought that Noise Analysis will calculate these two noise sources as equivalent input voltage and current noise source.

2. 'they' is noise analysis in ADE. But now i know how the noise analysis works.

3. now i have another question. If there is a noiseless voltage source Vs with an source resistance Rs as the input source of an Op Amp, how should i define the noise caused by the input source Vs & Rs.

Should i consider equivalent input current source Ien multiply by Rs?

Title: Re: Measure Equivalent Input Voltage and Current Noise of Op Amps
Post by Andrew Beckett on Mar 2^nd, 2019, 6:55am

I have no idea what you mean by your new question. It doesn't make any sense to me, so I've no idea how to answer it.

For example, if the voltage source is noiseless, it won't cause any noise. The source resistance Rs would generate thermal noise (unless you've explicitly turned off noise for that resistor). Beyond that I don't really understand what you're getting at with your questions.

Regards,

Andrew.