PLL Charge Pump Control for Reference Signal Loss
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Solution Overview
Problem
Conventional PLL circuits continue to flow current to the charge pump circuit when the reference frequency signal is not input, leading to operational amplifier saturation and degradation in phase settling.
Innovation Solution
Incorporating a phase-difference-pulse stop unit that detects the non-input state of the reference pulse and prevents the phase difference pulse from being fed to the charge pump circuit, thereby stopping the current flow and preventing saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the reference frequency signal is not input to the PLL circuit, then the PLL circuit enters a non-input state, but current continues to flow to the charge pump circuit from the loop filter causing operational amplifier saturation
Solution Approach 1:
The patent applies preliminary action by detecting the non-input state of the reference frequency signal before current flow causes saturation. The detection unit identifies when the reference signal is absent, and the control unit preemptively stops current flow to the charge pump circuit, preventing operational amplifier saturation before it occurs.
Solution Approach 2:
The patent implements feedback by using a detection unit to monitor the reference frequency signal input state and feeding this information back to the control unit. The control unit adjusts the charge pump circuit operation based on this feedback, stopping current flow when the reference signal is absent and resuming it when the signal is present, thereby preventing saturation while maintaining normal operation.
2Reliability
If current continues to flow to the charge pump circuit during non-input state, then the loop filter operational amplifier saturates, but stopping current flow requires additional control mechanisms
Solution Approach 1:
The patent applies universality by designing the detection unit and control unit to serve multiple functions. The detection unit not only detects the non-input state but also provides control signals to stop current flow. The control unit manages both the charge pump circuit operation and the overall PLL circuit state, reducing the need for separate dedicated components for each function.
Solution Approach 2:
The patent implements self-service by enabling the PLL circuit to automatically detect its own input state and self-regulate current flow without external intervention. The detection unit monitors the reference signal, and the control unit automatically adjusts the charge pump circuit, allowing the system to manage itself and prevent saturation without additional complex external control mechanisms.
Data Source
AI summary
A PLL circuit according to the present invention includes a VCO that outputs an VCO signal having a frequency according to an input voltage, a loop filter that feeds a voltage according to an input current to the VCO, a phase comparator that outputs a phase difference pulse having a width according to a phase difference between a first input signal and a second input signal, a charge pump circuit that receives the phase difference pulse, and inputs the current to the loop filter, and a phase-difference-pulse stop unit that stops the input of the phase difference pulse to the charge pump circuit in a non-input state in which an REF signal (reference frequency signal) is not input. The first input signal is the REF signal itself or a signal obtained by dividing the frequency of the REF signal, and the second input signal is the VCO signal itself or a signal obtained by dividing the frequency of the VCO signal.