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-mm
²
die area.