A Design Of DCO With 73.1% Frequency Tuning Range Based On Switched Transformer

A LC-DCO (digital-controlled-oscillator) with ultra wide FTR (frequency tuning range) is implemented in SMIC 55nm technology in this paper. A switched transformer is used to implement a wide tuning range through dividing the range into two band, which improves the tuning range to 73.1% with a constant gain. And a LDO (low dropout regulator) is designed to supply a constant power to the DCO. The post-layout simulation results indicate that a 2.30-4.95GHz tuning range is obtained. The coarse tuning gain is constant with 50MHz/LSB. The phase noise is about -126.64dBc/Hz and -113.65dBc/Hz at 1MHz frequency offset respectively with the output frequency of 2.30GHz and 4.95GHz. With a 0.6V power supply, the current consumption is from 5.14mA to 7.92mA as the varies of frequency.