An 18-mW 1.175–2-GHz Frequency Synthesizer With Constant Bandwidth for DVB-T Tuners

A fully integrated 1.175-2-GHz differentially tuned frequency synthesizer aimed for digital video broadcasting-terrestrial tuners is implemented in a 0.18-mum CMOS process. To maintain phase-noise optimization and loop stability over the entire output frequency range, techniques of constant loop bandwidth are proposed. The voltage-controlled oscillator gain K _VCO and band step f _res are both maintained by simultaneously adjusting the sizes of switched capacitors and varactors. Charge pump current I _CP is programmed to compensate the variation of the division ratio N . The measured results show an in-band phase noise of -97.6 dBc/Hz at a 10-kHz offset and an integrated phase error of 0.63 ^deg from 100 Hz to 10 MHz. The measured variations of K _VCO and f _res are less than 12.5% and 4.5%, respectively. The variations of the measured phase noise at 10-kHz and 1-MHz frequency offsets are less than 1 dB. The measured 3-dB closed-loop bandwidth is 110 kHz and the variation is less than 9%. The chip draws 10-mA current from a 1.8-V supply while occupying a 2.2-mm² die area.

I. Introduction

The digital video broadcasting-terrestrial (DVB-T) standard has ushered in a new era in TV entertainment. Often the DVB-T tuners employ a double-conversion zero-IF (DZIF) architecture, which demands the use of a wideband frequency synthesizer as the first local oscillator (LO) to cover the 48–862-MHz-wide frequency range and a fractional- frequency synthesizer as the second LO to support several channel bandwidths (6/7/8 MHz) [1], [2].