determine ADC bit and speed

[fanshuo]

Hi,
I am not very clear about the the relationship between the receiver data rate and ADC speed(sampling rate) and what receiver specification will determine the number of ADC bits.

Thanks a lot.

 

[pit1000]

Maybe these slides from PHILLIPS will help.

**broken link removed**

 

[fanshuo]

well, thanks pit1000
but I want a more detailed mathematical relationship

 

[A.Anand Srinivasan]

the sampling frequency of data (fs) ≥ 2(frequency of input signal) is the required condition and is called nyquist criteria....
the number of bits of ADC bits depends on the required resolution and speed of the receiver...

 

[fanshuo]

and what is the input signal frequency?It is the bandwidth or its center frequency?

so bits/second of ADC= data rate of the transceiver?

 

[svicent]

The Nyquist–Shannon sampling theorem states that

"Exact reconstruction of a continuous-time baseband signal from its samples is possible if the signal is bandlimited and the sampling frequency is greater than twice the signal bandwidth."

More information:

h**p://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem

 

[fanshuo]

I am confused,
then why those signal at several GHz carrier frequency but with several MHz bandwidth cannot be direct AD converted....

 

[A.Anand Srinivasan]

what i meant by input frequency is the maximum frequency of the signal.... that is what nyquist criteria means crudely....

 

[wilco]

Hi fanshuo:
It's not common to AD convert signals at several GHz because of the very difficult design issues related to circuits operating at such frequencies...
For that reason, it's easier to convert those signals down to baseband before using the ADC, where the important topic for its sample rate is the signal bandwidth (usually of several kHz or MHz)...
For the resolution, the start point is the required SNR in the ADC, using the well known expression SNR = 6.02*bits +1.76

 

[qqic]

in fact it is not easy to both get high speed and resolution