A Wide-Band CMOS LC VCO With Linearized Coarse Tuning Characteristics

A pseudo-exponential capacitor bank structure is proposed to implement a wide-band CMOS LC voltage-controlled oscillator (VCO) with linearized coarse tuning characteristics. An octave bandwidth VCO employing the proposed 6-bit pseudo-exponential capacitor bank structure has been realized in 0.18-mum CMOS. Compared to a conventional VCO employing a binary weighted capacitor bank, the proposed VCO has considerably reduced the variations of the VCO gain (
K

_VCO
) and the frequency step per a capacitor bank code (
f

_step
/code) by 2.7 and 2.1 times, respectively, across the tuning range of 924-1850 MHz. Measurement results have also shown that the VCO provides the phase noise of - 127.1 dBc/Hz at 1-MHz offset for 1.752-GHz output frequency while dissipating 6 mA from a 1.8-V supply.