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# what is the standard unit of parameters for calculation of SNR(signal to noise ratio)

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#### dotronghop

##### Newbie level 4
Hi,
I have these equations with some parameters:
**broken link removed**

The problem is I don't know the standard unit of these parameters. I don't know if I have to change the background light current from microampere to ampere, or change the fixed capacitance from pF/cm2 into pF/m2, or things like that. Can you give me the answer? Thanks.

Did the equations come with the list at right? The list specifies the units you wondered about.

We have to trust that the designer of the equation used a micro unit in one place, then divided by a micro unit somewhere else, in order to maintain unity.

Test the equation with values that should come out to a reasonable answer. Does it seem to be off by 10^6, or 10^-6? Then you know you need to look closer at the units multipliers.

Did the equations come with the list at right? The list specifies the units you wondered about.

We have to trust that the designer of the equation used a micro unit in one place, then divided by a micro unit somewhere else, in order to maintain unity.

Test the equation with values that should come out to a reasonable answer. Does it seem to be off by 10^6, or 10^-6? Then you know you need to look closer at the units multipliers.
There are many combinations of these units. The correct result come only when all the units are correct. So, it seems that I have to try by myself. Thank you very much!

The SNR, or signal-to-noise ratio is an engineering expression used in communication.
Your formulas refer to infrared communication where noise contributions differ from those of thermal noise utilized in radio and microwave communication.
SNR is expressed in dB while the signal and noise is measured in watts.

In digital communication it became useful to replace SNR with Eb/No, bit energy related to noise energy. Communication quality is then measured by BER, bit error rate. Mutual relationship between BER and SNR or BER and Eb/No is not linear and differs for different modulation methods and coding.

The SNR was established in 1920s for what we now name "analog communication", Eb/No in the 1960s when digital communication entered.

dotronghop

### dotronghop

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@jiripolivka : thank you very much!

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