Platforms

Supply Modulation Platform

Supply modulation platform

Supply modulation techniques employing buck converters based on pulse width modulation are known to present low pass frequency response characteristics. Envelope tracking in polar transmission systems using buck converters suffers from the inherent limited bandwidth of the supply modulation. Two major distortion mechanisms arise when buck converters are used to modulate the supply voltage. The first distortion mechanism is associated with the signal distortion introduced by the low pass filter characteristics of the converter and the second mechanism is originated from the ripple distortion introduced by the pulse width modulator (PWM). Increasing the bandwidth of buck regulators allows better tracking of the envelope but introduces higher PWM ripple distortion levels at the power amplifier supply voltage.

The determination of the optimum bandwidth of the buck regulator applied to polar transmitters generally requires an optimization of the output spectrum either to the transmission mask or to the adjacent and alternate channels power ratio (ACPR). For instance, output spectrum is optimized for the transmission mask and the ACPR in EDGE and WCDMA respectively.

The supply modulation platform comprises of

1. The RS2010 power management supply modulator
2. A commercially available power amplifier
3. The adaptive power efficiency improvement unit

The RS2010, representing the power section of the complete supply modulation solution, converts the broadband envelope signal into the power amplifier supply voltage variations. The composite output spectrum is present at the output of the power amplifier. The digital section of the supply modulation platform carries out the adaptive power efficiency control, signal pre-conditioning and reduction of non-linear distortions introduced by the power amplifier.