The nice thing about ZERO IF is that it immediately converts RF signals to baseband and then uses optimized amplifiers to support only the bandwidth required. This conserves power and enables very low power solutions. This is seen in cell phones, Bluetooth and other consumer technology where power conservation is key. However ZERO IF doesn’t do a good job at arbitrary wide bandwidths because excess BW is required to fulfill that need. BW costs money and power dissipation to support. Our analysis shows that right now ZERO IF can support ~200 MHz and still be about 2x as efficient as direct RF sampling. As occupied BW goes beyond 200 MHz, direct RF becomes more efficient and in current technology the cross over is somewhere around 400 MHz. So if you have to support 400 MHz of BW or more, then I’d go with direct RF. Of course these numbers are always moving as both process technology and design architectures evolve. See my article “Where ZERO IF wins” published in the last year or so for a few more details.
