The Polar Plus Advantage
GSM/EDGE/WCDMA and CDMA2000 employ complex modulation schemes that require RF power amplifiers to be extremely efficient and linear. To achieve the necessary performance, polar modulation is often employed. In polar modulation, the modulation is broken down into amplitude and phase components that are processed separately. Further down the transmit lineup, the AM and PM signals are recombined to form a fully modulated RF waveform.
Large-signal open-loop polar modulation requires a considerable amount of factory phasing and calibration, along with the use of predistortion techniques. Large signal closed-loop polar modulation draws comparatively high transmit current, is complex, and its saturated distortion degrades Error Vector Magnitude (EVM) and Adjacent Channel Power Ratio (ACPR) performance. In addition, the closedloop circuit is complex and comparatively large.
In contrast, Freescale's Polar Plus small-signal polar modulation approach requires less transmit current and little factory phasing and calibration, while delivering a good compromise between current consumption and manufacturability.
Polar Plus modulation performs modulation at the low-level driver stage where very linear gain and high dynamic range can easily be realized. There is no need for predistortion or control loops, factory modulator phasing, or predistortion terms that vary with the manufacturing process. Polar Plus is essentially a "dual-mode" technique that allows GSM and EDGE requirements to be satisfied by operating the amplifier in linear mode for 8PSK (EDGE) and saturated mode for GMSK (GSM). Time synchronization is also easier with Polar Plus for maintaining precise AM-to-PM time alignment, because it can be automatically calibrated in the transceiver.
In short, various polar modulation schemes can be used. However, Freescale's Polar Plus offers the best combination of low power consumption, simple design, shortest manufacturing test time, and highest manufacturing yields.