Double-loop frequency synthesizer and phase noise analyzing method

The invention relates to a double-loop frequency synthesizer and a phase noise analyzing method. The double-loop frequency synthesizer comprises a crude regulation loop and a fine regulation loop, wherein the crude regulation loop comprises a frequency and phase discriminator, a charge pump, a filtration capacitor, a voltage-controlled oscillator and a programmable divider sequentially connected with each other; and the fine regulation loop comprises a frequency and phase discriminator, a charge pump, a loop filter, a voltage-controlled oscillator and a programmable divider sequentially connected with each other; and the frequency and phase discriminator, the voltage-controlled oscillator, the programmable divider and the crude regulation loop are shared. The phase noise analyzing method of the double-loop frequency synthesizer obtains the noise transfer function of each noise source in the double-loop frequency synthesizer by obtaining the transfer function of a crude regulation branch, a fine regulation branch and a common loop. The phase noise of the double-loop frequency synthesizer is lower than that of a single-loop frequency synthesizer under the same condition.