adc for zero if

Dear All:

IfI use Zero IF or Low IF in my RF-structure ,Does I need two ADC in the Baseband . Thanks

Hi

If you use low IF, you will need only one ADC.
If you use zero IF, and your modulation scheme is like an FSK which signal spectrum is not symmetric around carrier, you should use two ADCs and I/Q downconversion.


Regards

Deare Circuit_seller :
If the modulator is 64-QAM , The Low-IF nad Zero-IF , is the same . Low-iF need one ADC // Zero-IF using two ADC . And Why ? I know using low-if oe Zero-IF need I/Q . Why need I/Q ? Thanks

Hi

Some modulated signals such as FSK have not symmetry around center frequency that is if we downconvert it to baseband without using I/Q downconversion upper half of the spectrum and lower part of it will be aliased(folded).

Regards

Dear Circuit_seller :

If I work on 64-QAM usig Zero-IF , like DVB-T , DVB-H , DO I need two ADC ,Thanks . Dou have any reference doc for this ? Thanks

Hi

I know two useful refrences about direct-conversion architecture.
1- Behzad Razavi's "Design Considerations for Direct-Conversion. Receivers".
2- Behzad Razavi's "RF Micro Electronics"

If you want to implement a 64QAM receiver, i recommend you to use other receiver architectures such as superhetrodyne or digital IF receiver.
Two implement an Direct-convesion receiver you have some problems. one big problem is output DC offset of the mixer.
Another problem is the phase differences between LOs and carrier frequency which corrupt signal content aroound DC.

Regards