PLL Feedback Circuit for Consistent Fractional Divider Phase
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Solution Overview
Problem
In phase-locked loop circuits, the variability in the pattern of the division ratio control signal from a ΔΣ modulator leads to differing phases of output signals across multiple circuits with the same configuration, causing malfunctions in communication apparatuses.
Innovation Solution
A phase-locked loop circuit design incorporating a division ratio control circuit, first and second phase detection circuits, and a shift circuit that generates a negative feedback signal to synchronize the division ratio control signal, ensuring consistent phase output across identical circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a ΔΣ modulator is used to implement fractional division by randomly modulating the division ratio, then frequency control precision is improved, but phase consistency deteriorates because the pattern of the division ratio control signal varies even with the same input signal
Solution Approach 1:
The invention introduces a feedback mechanism where the actual pattern of the division ratio control signal is detected and fed back to the ΔΣ modulator. This feedback loop allows the system to correct deviations in the control signal pattern, ensuring that multiple phase-locked loop circuits produce consistent phase outputs even when using random modulation for fractional division.
Solution Approach 2:
The invention changes the parameter being controlled by the ΔΣ modulator from directly controlling the division ratio to controlling a correction signal that adjusts the division ratio control pattern. By modifying what parameter is being modulated, the system maintains frequency precision while achieving phase consistency across multiple circuits.
2Adaptability or versatility
If the pattern of the division ratio control signal is controlled by adding a signal corresponding to phase control amount to the input signal of the ΔΣ modulator, then phase control capability is improved, but phase consistency across multiple circuits deteriorates because different patterns are output for the same input signal
Solution Approach 1:
The invention uses feedback to detect the actual division ratio control signal pattern and provides correction signals to the ΔΣ modulator. This ensures that even when phase control signals are added to provide adaptability, the output patterns remain consistent across multiple circuits by compensating for any variations.
Solution Approach 2:
The invention performs preliminary detection of the division ratio control signal pattern and prepares correction signals in advance. By detecting and correcting the pattern before it causes phase inconsistency, the system maintains both phase control capability and phase consistency across multiple circuits.
Data Source
AI summary
A phase-locked loop circuit includes: a division ratio control circuit controlling a division ratio of an output signal of a variable frequency divider on the basis of an addition signal of a negative feedback signal and a division ratio setting signal indicating the division ratio, in synchronization with a divided signal output from the variable frequency divider; a first phase detection circuit calculating a first phase detection signal indicating a phase of an output signal of a signal output circuit; a second phase detection circuit calculating a second phase detection signal indicating a phase of the output signal of a case where it is assumed that the division ratio control circuit controls the division ratio of the output signal of the variable frequency divider in synchronization with the reference signal; and a shift circuit generating a negative feedback signal from a difference between the first phase detection signal and the second phase detection signal, and outputting an addition signal of the generated negative feedback signal and the division ratio setting signal to the division ratio control circuit.