DAC and ADC architecture in SDRs What are the DAC and ADC architectures in SDRs for inphase and quadrature phase channels?

Do we have separate ADC and DAC for each channel or there is some clever way that they are  multiplexed to reduce area. 

Usually in diagrams one DAC and one ADC is shown. But then I wonder how the inphase and quadrature phase information will be separated. Would appreciate if we can get a architectural diagram with an explanation
To add here are two diagrams showing common transceiver architectures: (1) a super-heterodyne where the down-conversion is done first to an IF frequency and then to baseband and (2) a zero-IF receiver where RF is translated directly to baseband. Note in both architectures it is arbitrary (technical / technology choice) where the ADC/DAC boundary is as either approaches could be done with baseband, IF or direct RF sampling to the extent technology allows. Ultimately, at baseband we desire a complex IQ signal to support most modern modulations which require asymmetrical spectrums about the RF carrier for maximum spectral efficiency (and hence a complex baseband signal with I and Q components). We can separate into I and Q in the analog using quadrature local oscillators and then use a dual ADC/DAC, or we can use a single ADC/DAC and then separate into I and Q digitally using a quadrature NCO. 

The transmit and receive architectures need not match (Can use a ZIF transmitter and Super-het receiver for example). 





For high efficiency with a digital IF/RF approach, quadrature sampling can be implemented at a $f_s/4$ IF frequency with a single ADC datapath interleaving the I and Q channels as as follows:

Channel I: 1 0 -1 0 1 0 -1 0

Channel Q: 0 1 0 -1 0 1 0 -1

This concept is further illustrated in the figure below. Sampling at Fs/4:



A subsequent phase rotator would be required to remove carrier offsets, or the ADC clock itself can be in the carrier tracking loop.

Placing the digital IF at $F_s/4$ or $N F_s \pm F_s/4$ also has the advantage of simplifying ADC anti-alias filter design as the images will all be equidistant.