Frequency synthesizer for on-chip testing and automated tuning

This paper presents a compact, phase-locked loop (PLL) based, frequency synthesizer suitable for built-in testing and automatic tuning applications operating in the 100 MHz frequency range. Key features of this design include a differential charge pump with common mode feedback (CMFB) and a voltage controlled oscillator (VCO) based on a pseudo-differential OTA with a linear transconductance control and tuning invariant output resistance. Experimental results from an integrated prototype fabricated using standard 0.35 μm CMOS technology are presented. The measured HD3 of the output signal is better than -39 dB over 80% of the tuning range: 40-160 MHz. The circuit occupies a silicon area of 200×1000 μm² and operates from a 3.3 V power supply.