nd RFIC. have been explained in the JESD chapter before. In all cases, the interface is an analog one with associated reduction in pin count. An IF-based interface is commonly used in the handset world, where the associated pin- count reduction (only a single pair of wires is needed to be routed between baseband chipset and RF subsystem) is key. For the same reason, such IF interfaces can route (modulated) digital control and DC power between the baseband chipset and the RF subsystem. In a base station the pin-count argument is not very relevant, but cost reduction associ- ated with re-use from a handset solution can be worthwhile. Note that the IF interface is pro- prietary to each vendor, SO expect the baseband and RF solutions to have to be provided by a single party. In the case of a baseband I/Q interface, the RF subsystem can, if needed, be custom built for any desired band, bandwidth and other requirements. Integrated analog-only RFICs are available from multiple vendors including Analog Devices, Maxim and Texas Instruments at different price and performance targets. Sub 6 GHz front end module After modulation, the system needs to amplify the RF signal before it goes to the antenna. The Front-End Module (FEM, Fig. 4-24) includes transmitter, receiver, and controller com- ponents into a single subsystem that can be designed to the target use-case or bought as a premade subsystem. Given the wide range of RF bands that the final product may need to support (as we noted in Chapter 1, there is a plethora of RF options in 5G), modularity of the RF front-end can reduce design overhead by moving to a "plug and play" system where new RF bands are enabled by swapping out the FEM. 166 Open Radio Access Network (O-RAN) Systems Architecture and Design Note that MIMO systems implement multiple of these paths in parallel, one for each antenna. To reduce cost/size and simplify design in massive MIMO systems, some vendors offer multiantenna FEMs. FEMs may be available from traditional RF device vendors in the form of a com