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Signal to noise ratio. And dynamic range

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student14

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Hello

I want to know what is the difference between signal to noise ratio and dynamic range. Are they same?

How to find this using cadence?

My input range is from 4uV to 100mV for a gm-c filter. What should be the SNR and DR? How to calculate both in cadence?

I have tried using spectrum function using calculator but there is an option of SFDR not DR? What is this SFDR?
 

SNR and DR are very similar. For your specified input signal the Dynamic Range is 20*log(.1/4E-6). The SNR has nothing to do with your signal; that's a measurement of your system's performance. SFDR, which you would have found if you had bothered to do a search yourself, is the ratio of the maximum output to the highest spur in your output.
 

Thankyou for your reply. This input range which is specified above (4m to 100uV) is a general range used in biosignals. For my circuit I have applied a fixed 20mVpp signal and obtaining the results. For my circuit how can I find the DR. Do I have to vary my input signal from 20mVpp and check upto what input range my circuit is in saturation region? (the minimum and maximum range upto which my circuit is working properly)?



[\QUOTE] The SNR has nothing to do with your signal; that's a measurement of your system's performance.[\QUOTE]

If I am calculating noise then I think I can find SNR. i.e. if my noise is 400uVrms and input signal applied is 20mVpp. Then 20log(20m x sqrt 2/400u)

Am I right?
 
Last edited:

DR is the ratio of the maximum to minimum measurable signal. Your SNR calculation is wrong. You want to divide your pp value by sqrt2, not multiply.
 

Hi,

20mV pp = 10mV p = 7.07mV RMS (for sinewave)

for noise:
400uV RMS = 6 * 400uV pp (as a rule of thumb. In detail it depends on noise distribution)

Thus you get different SNR values when you calculate with RMS or PP.

Klaus
 

oh yes its 20m/sqrt2.

But still the question is for the DR. For my circuit do I have to first find the input range by changing the input values and check upto what input value my circuit is working properly. That input range will help in finding the DR. Is this the way of finding DR? or is there any function in cadence calculator to find DR?

Thanks
 

You're only doing half the measurement. By measuring the maximum input your circuit can accept all you've got is the maximum allowable input. To determine DR you also need to measure the MINIMUM detectable input.
 

Hi,

oh yes its 20m/sqrt2.
Click to expand...
Are you sure?
See post#5
IMHO it should be 20mV / (2 x sqrt(2))

Klaus
 

First I decrease ac signal for finding minimum input range then increase ac signal to find maximum input for which my ckt is working properly
 

Hello

I am confused in finding the dynamic range of a fully differential circuit.

DR = 20log * (Vin_max/Vin_min) dB.

How can I find this Vin_max and Vin_min?

Vin_max I think could be found by the maximum ac input signal applied at which the THD reaches -40 dB for a fully differential structure but for Vin_min what do I have to consider?
 

See post #2. And post #4. And post #7. The fact that it's differential has absolutely. Nothing to with it.
 

barry said:
See post #2. And post #4. And post #7. The fact that it's differential has absolutely. Nothing to with it.
Click to expand...

I have read all the above post which defines DR. But while simulation how can I find minimum signal. How to get that minimum signal? Maximum signal I have understood Its related to the non-linearity, while increasing the input signal the point where my Thd is detoriating I pick that signal as Vmax. What about minimum signal. Minimum signal I know is related to noise. How should I find this minimum signal voltage? How to find this DR in cadence?
 

Determine noise level, specify required SNR and you get minimal signal level.
 

My SNR should be at least 38 dB. Is the input referred noise the noise level? At 100mVpp I am getting 25uV/sqrtHz. Is 100mVpp minimum signal?
 

I still can't find the DR. DR =20log(vmax-vmin).
Vmax I have taken at the point where my tHD is degrading. But Vmin signal what to take? Is it the signal at which I am calculating noise. I have applied 100mVpp signal and got 25uV/sqrtHz. Is this 100mVpp the Vmin?

My SNR is 38 dB Im I. e. 38dB x 25uV/sqrtHz= Vmin?
 

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