A low power quadrature direct digital frequency synthesizer using non–linear resistor string DACs

Abstract

A quadrature direct digital frequency synthesizer (DDFS) was designed and implemented in a 1.2 µm CMOS process using two non-linear resistor string DACs. These DACs are used in place of the phase-to-amplitude ROM look-up tables and the linear DACs in a conventional quadrature DDFS to give a low power design. At 25 MHz clock frequency, the DDFS dissipates less than 4 mW at 3.3 V and has SFDR better than 55 dBc at low synthesized frequencies.