| A Phase-locked Loops (PLL) - based frequency synthesizer (FS) with a frequency range of 135 MHz to 700 MHz is presented. By taking advantage of multiple-phase signals from a ring-VCO (voltage-controlled oscillator) and synthesizing the clock through digital circuitry, the frequency range is boosted from 271 MHz ∼ 548 MHz to 135 MHz ∼ 700 MHz and the frequency switching is instant with coarse resolution.;Moreover, by employing Delta-Sigma fractional-N technique, the proposed frequency synthesizer is capable of generating arbitrary-frequency and low-jitter clocks compared to Flying-Adder architecture. In addition, the fabricated FS has the ability to adjust clock duty cycle, which is widely used in applications such as time-interleaved ADCs (analog to digital converters), switched-capacitor circuits, and DC-DC converters.;Finally, to address the significance of phase noise and wide frequency operation, this work presents the design of a wideband and low-phase noise frequency synthesizer based on LC VCO with digitally switched capacitor array. |
