aaron_do wrote on Jul 1st, 2008, 12:44am:if i use an image-reject architecture, in theory i can completely cancel the image noise that appears in-band due to noise folding in a mixer.
No. you are misunderstanding. Even though you apply image rejection mixer such as combination of I/Q down mixer and complex BPF, holding noise from mixer itself can not be canceled.
aaron_do wrote on Jul 1st, 2008, 12:44am:However, in some receivers i've seen, image rejection is done in the digital domain. Just intuitively, since the signal is already digitized, the bit errors due to the noise in the signal are already there,
I can't understand why bit errors already exists there.
If quantized noise is enough small, there is no degradation in baseband BER.
aaron_do wrote on Jul 1st, 2008, 12:44am:so in theory the image noise cannot be canceled using digital domain image rejection. Is that right?
No, it is not correct.
Assume an architecture where I/Q-ADC after I/Q down mixer and digital complex BPF or complex Bandpass-Delta-Sigma-ADC. you can realize image rejection architecture.