An Integer Frequency Synthesizer for Satellite TV Tuners

A frequency synthesizer has been design for analog TV tuner.The output frequency of the local oscillator covers 1.3 GHz to 2.7 GHz.The reference frequency can be set as 62.5 kHz or 31.25 kHz.The loop filter is a 3-stage active filter, and the loop bandwidth is 1 kHz.The output current of charge pump can be set as 50 μA or 250 μA.Differential feed-back structure is adopted in voltage-controlled oscillator (VCO) and the phase noise is less than-75 dBc/Hz at 10 kHz away from the central frequency.The structure of the divider is pulse-swallow and 15 control bits are used to set the divider ratio.There are two flip-flops and one logic gate when go through the P counter, which can reduce the phase noise rising from the cascade asynchronous dividers.Mismatch of current both in charging and discharging will deteriorate the reference spur performance.The paper will take the overshoot of current in charge pump into account and measures will be taken to reduce it.The chip is implemented in 0.18 μm RFCMOS technology, the area of which is 1.3 mm*1.5 mm.