Wide-bandwidth fully integrated Cartesian feedback transmitter

In this paper the potential of Cartesian feedback for wide-bandwidth operation is explored. The detrimental effect of the loop delay on the achievable bandwidth is discussed and several circuit arrangements are proposed, which can be exploited to overcome such limitation. The design and measured performance of the first fully integrated Cartesian feedback transmitter are presented. A novel phase shifter with full control range allows stable operation by compensating the phase shift due to the RF chain. The circuit achieves a linearization bandwidth as high as 60 MHz. An intermodulation improvement of up to 24 dB is observed as the device is tested by means of a wideband code-division multiple access 5-MHz-bandwidth modulated input signal.