Design and Implementation of a Wideband Digital Interpolating Phase Modulator RF Front-End

Abstract

<p>This paper describes implementation details of a digital-intensive phase modulator architecture that does not require a frequency synthesizer to cover a wide carrier frequency range. The phase modulator operation is based on toggling the output accurately during the sample period to generate the phase-modulated signal. The toggling instants within the sample period are calculated by DSP solvers that utilize linear interpolation. The interpolation effectively multiplies the phase signal sample rate by the modulator phase resolution, which enables wider signal bandwidth and a completely digital method of defining the transmitter carrier frequency. The phase modulator concept is verified by implementing it as a part of an outphasing transmitter in 28 nm CMOS. With a constant sample rate of 1.5 GHz and without any predistortion, the transmitter achieves better than -28 dBc ACLR with 100 MHz aggregated LTE downlink signal between 0.8-2.0 GHz carrier frequency.</p>