adc dynamic range
Now I'm designing a superheterodyne receiver. Now I have some puzzles:
1 How to partition the dynamic range of 16-bit ADC? The AGC should guarantee the signals from demodulator for which part of the ADC dynamic range
2 When I calculate the level of the demodulated signal, there are four signal I-/I+ and Q-/Q+, how to calculator the rms level of the demodulated signal
To define the portion of the Dynamic Range of ADC where AGC is active you have to do an RF System analysis which has to include Interfere Levels (Blocking, Adjacent Channel, etc) and Fading Margin. All these parameters are dependent by the Specifications of the Network where your receiver is used.
To calculate Vrms of IQ signal you can measure the peak voltage of each (for e.g. I+ to ground, and Q+ to ground) and:
Vrms = Vpeak * 0.707
Depend also of some parameters as sensitivity, overall gain, phase noise. You have to attenction also the ADC type (pipeline or Sigma delta), how mani bits you want to use, sampling frequency and jitter. The ADC is the intermediate point from analog to digital worlds, so it is not so simple to analyze its dinamic range.
By
It's my first time to hear fading margin? What's it? Does it overcome the amplitude
variation due to fading?
What's the practical value of fading margin?
Thanks,
Ok，thanks . the design is so complex that where i can get a book or article which particularly declares on the design?
thanks!
Quizeng Gu
RF system design of tranceivers for wireless communications
Springer
Good text for RF system design; page 284 deals with this issue
see if the file attached can be useful for u. it explains graphically hw to find the dynamic range of an ADC.
Fade margin definition:
http://en.wikipedia.org/wiki/Fade_margin
By the definition of this website, it looks like we need to do an overdesign of
SNR to overcome the fading loss. I make a more detailed statement as following,
please help me check I am right or wrong.
Assume the SNR requirement of Baseband is 21dB to do the demodulation.
We need to design the SNR more than 21dB by fading margin(assume 6dB).
So the Signal to Noise level at input of ADC should be more than 27dB, right?
Everything is related to the Network specification requirements where the receiver is used. Usually these specs doesn?t specify fading performance at the limits of the receive dynamic range, but if they specify you have to increase the limits of SNR.
I can't open the website about fading margin.