Phase-locked loop frequency synthesizer and open-loop frequency coarse adjustment method

Abstract

The invention discloses a phase-locked loop frequency synthesizer. At an open loop frequency coarse tuning stage, fixed control voltage is provided to a voltage controlled oscillator; a frequency divider carries out frequency division on the output frequency of the voltage controlled oscillator, so that the feedback frequency Fdiv output by the frequency divider to a counter of an automatic frequency controller is obviously larger than the frequency Fref of a reference signal; the feedback frequency Fdiv is obviously larger than the frequency fed back to a phase detection discriminator by the frequency divider at a closed loop fine tuning stage. The invention also discloses a corresponding open loop frequency coarse tuning method. By the phase-locked loop frequency synthesizer and the open loop frequency coarse tuning method disclosed by the invention, the open loop digital coarse tuning method is greatly reduced.

Description

technical field [0001] The invention relates to the field of wireless communication, in particular to a phase-locked loop frequency synthesizer and an open-loop frequency rough adjustment method. Background technique [0002] The circuit diagram of a typical frequency synthesizer 100 based on a charge pump phase-locked loop is shown as figure 1 As shown, the frequency synthesizer 100 includes: a phase frequency detector (PFD) 102, a charge pump (CP) 103 (the phase frequency detector 102 and the charge pump 103 are integrated in one chip, and the chip can also include a internal low-pass loop filter (LPF), for optional use), low-pass loop filter (LPF) 104, voltage-controlled oscillator (VCO) 105, frequency divider (DIV) 106 and automatic frequency controller (AFC ) 107. In addition, a pre-frequency divider can also be set as required, and the reference signal can be frequency-divided by the pre-frequency divider. When the frequency synthesizer 100 is working, it first ente...

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Problems solved by technology

In order to achieve higher precision, the set counting time is often longer, so that the counting of the feedback frequency Fdiv is more obvious within the set counting time, which leads to a longer open-loop coarse adjustment time

[0004] Secondly, the logic control circuit of the automatic frequency controller 107 adopts the method of sequentially comparing the count difference, which also makes the search for the optimal value of the switched capacitor array control word for controlling the voltage controlled oscillator 105 very long.

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