RF Amplitude Control in an All-Digital PLL based Transmitter

Abstract — A fully-digital frequency synthesizer for RF wireless applications has recently been proposed. At its foundation lies a digitally-controlled oscillator that deliberately avoids any ana-log tuning controls. The conventional phase/frequency detector, charge pump and RC loop filter are replaced by a time-to-digital converter and a simple digital loop filter. When implemented in a digital deep-submicron CMOS process, the proposed architecture is more advantageous over conventional charge-pump-based PLL’s since it exploits signal processing capabilities of digital circuits and avoids relying on the fine voltage resolution of analog circuits. In this paper, we present new techniques for achieving amplitude control of the RF output. This approach has been incorporated in a Bluetooth radio realized in 130-nm CMOS. I