Questions about receiver and relationship between AGC &

[abcyin]

Need help about receiver

In our lab, we are trying to design a DVB receiver, I am responsible for the variable gain amplifier, after which there is an ADC, I am thinking about the relationship between the AGC and ADC, Is there anybody can give me a hint about following questions:

1, How to determine the bits of the ADC required in the receiver?
2, The Dynamic Range(the signal range the ADC can deal with) and the SFDR of the ADC are not the same, and the SFDR should be larger than the DR when the ADC can operate in full bits. Is it right?
3, what is the relationship between the SFDRs of the VGA and ADC, that's to say should I determine the SFDR of the VGA by the ADC, or are they really related?

Thanks!

 

[flatulent]

Re: Need help about receiver

There are several things to consider.

1. For low level signals the analog gain should be high enough that the analog receiver noise dithers the ADC by two or so LSBs. Otherwise the SNR of low level signals is degraded by the quantization noise.

2. There should be enough bits that as the signal level is increased above the noise the ADC does not clip on signals high enough that the analog SNR meets the best case received signal SNR.

3. The analog AGC should have enough range so that as the signal level is increased to the specification maximum input value the ADC does not clip.

 

[Sal]

Need help about receiver

Hi

About the ADC, usually having the highest number of bis is desirable, but it is not always possible for the following reasons: 1) The available ADC are limited in number of bits, if you want higher resolutions you need arrangements of ADCs 2) The larger the number of bits in the ADC, the larger the processing capacity impossed to the processing units, understand it as higher memory requirements for buffering and the higher the number of processing data the slower the system becomes, this can be a disadvantage for real time applications.

As you are talking about a variable gain amplifier, you need a logic which control this gain, then thinking about an algorithm will be necessary.

cheers

Sal