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Receivers are evolving and are increasingly using differential components. This evolution began at the ADC and is gradually moving up the signal chain. In the past, signal application issues and limited high performance differential RF building block availability lead to single-ended or partially differential signal chains. As discussed earlier, one example of a partial differential signal chain is the designer’s choice to omit a differential ADC driver and use single-ended devices up to a transformer to the ADC. While this offers a simple solution, the performance demands are simply pushed upstream. In addition to consuming higher power, single-ended driver amplifier solutions tend to have worse even-order distortion, CMRR and PSRR. The receiver signal chain shown here is an architecture commonly used for receivers with single-ended RF input and differential output. The dividing line between single-ended and differential operation seems to have settled at the mixer, with RF components such as the LNA still being offered as single-ended components. Most SAW filters and mixer cores are also natural differential circuits, but they are converted to single-ended due to application limitations. For years doubly balanced mixer topologies have been adopted for cellular applications due to their highly linear performance. Unfortunately, the traditional transformer networks used to couple the signals to the mixing core, to keep the system differential, consume considerable board space and add significant cost to the design.
