Quad-band GSM/GPRS/EDGE polar loop transmitter

Abstract

An enhanced data-rates for GSM evolution (EDGE) transmitter using a nonlinear GSM-type PA is presented. It is based on a novel polar loop architecture that employs separate feedback control of the amplitude and the phase of the output signal. With this approach, the problems with AM-to-PM as well as AM-to-AM of the nonlinear PA are essentially eliminated. In addition, this architecture allows for a large dynamic output power control range, as required by the GSM specification. The transmitter uses a standard I/Q interface and does not require the extraction of amplitude and phase modulation in the digital domain. The dual feedback loop ensures robust performance even under voltage-standing wave ratio variations without using an isolator. No external PA filtering is required to meet the transmitter noise in the receive band. The EDGE spectral mask is met with an rms error vector magnitude of <3% at 29 dBm at the antenna, corresponding to 2 dB above nominal maximum output power. There is no mode change between GMSK and EDGE, and the transmitter operates seamlessly in multislot Enhanced General Packet Radio Service. The polar modulation transmitter meets or exceeds the GSM-type approval requirements for both EDGE and GMSK in quad band (850/900/1800/1900 MHz).