Tuned Radio Frequency (TRF) receivers suffer from poor frequency stability, and poor selectivity, as even filters with a high Q factor have a wide bandwidth at radio frequencies. In Radios using this principle, all signal frequencies are converted typically to a constant lower frequency before detection. This constant frequency is called the Intermediate Frequency, or IF.
A zero-IF approach enables direct conversion of analog RF signals to a digital baseband format. This dramatically reduces component count and thus handset footprint and cost. Reducing the number of parts also simplifies the supply chain and manufacturing and hence improves yield.
For example, a traditional quad-mode heterodyne architecture for a CDMA phone uses an IF CDMA SAW filter, an IF FM surface-acoustic-wave (SAW) filter and an IF Global Positioning Satellite (GPS) SAW filter. A quad-mode zero-IF architecture would replace those components. It also would eliminate the need for an IF-to-baseband conversion circuit, an external IF switch, a receive IF voltage-controlled oscillator (VCO), a dual phase-locked-loop synthesizer, a transmit IF VCO, a transmit IF filter, electromagnetic interference shields and a multitude of resistors, capacitors and inductors as well as the board space required for all those components.