A 975-to-1960MHz fast-locking fractional-N synthesizer with adaptive bandwidth control and 4/4.5 prescaler for digital TV tuners

There is a high demand for high-performance tuners to meet the digital video broadcasting-terrestrial (DVB-T) standard. Often the DVB-T tuners employ a double-conversion zero-IF (DZIF) architecture that demands a wideband fractional-N synthesizer as the first local oscillator (LO 1 ) to cover the frequency range of 975 to 1960MHz. This LO1 needs to meet a stringent phase-noise requirement with an adequate target phase noise of −87dBc/Hz at a 10kHz offset and integrated rms phase error less than 1° [1]. Because of the very wide frequency range, the variation of loop bandwidth may affect the phase-noise performance and loop stability.