3) The authors explain that " the impedance match at the input and output of an amplifier must be reasonably good " and hence apply matching between every two stages. It was against this backdrop that analog designers became interested in RF systems. Having dealt with the mass production of fairly complex bipolar and CMOS circuits-albeit operating at lower frequencies-they were trained to aim for a high yield and tackle PVT issues by on-chip techniques such as bandgap references, current mirrors, differential operation, etc. They furthermore relied on SPICE for simulations. Facing the low quality of spiral FIGURE 16: Siemens' 1994 direct-conversion transceiver [42]. inductors in silicon processes, analog designers also wondered whether (a) (b) (c) (d) FIGURE 17: (a) A CMOS mixer from 1993 [43], (b) an inverter-based LNA from 1996 [44], (c) a MESFET LNA from 1993 [45], and (d) a CMOS LNA from 1996 [46]. (Parts of diagrams omitted for clarity.) 70 SUMMER 2023 IEEE SOLID-STATE CIRCUITS MAGAZINE