PLL Phase Frequency Detector Switching Supply for Better Linearity
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Solution Overview
Problem
Phase frequency detectors in phase locked loops exhibit non-linearity and DC offset issues due to dynamic and static errors, affecting noise and spur performance in mobile RF transceivers.
Innovation Solution
A phase frequency detector is designed with a switching supply that isolates the power supply to the reference and feedback paths using a reference capacitor and a feedback capacitor, selectively coupled via switches, to maintain a constant time difference between clock edges and improve linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional power supply is used for the phase frequency detector, then the circuit is simple, but non-linearity and DC offset occur due to supply coupling between reference and feedback paths
Solution Approach 1:
The power supply circuit is segmented into separate domains: a reference domain with a reference capacitor and reference switch, and a feedback domain with a feedback capacitor and feedback switch. This segmentation isolates the reference and feedback paths from each other, preventing supply coupling and improving linearity by eliminating the interaction between the two signal paths.
Solution Approach 2:
Capacitors are introduced as intermediary energy storage elements between the power supply and the reference/feedback paths. These capacitors act as local energy reservoirs that decouple the paths from the main power supply, reducing noise and preventing supply coupling effects that cause non-linearity and DC offset.
2Measurement precision
If separate power supply paths are used for reference and feedback domains, then linearity is improved, but device complexity increases
Solution Approach 1:
The reference and feedback domains are merged at the power supply input stage, where both domains share a common power supply source. This merging approach reduces the overall complexity compared to having completely independent power supplies, while still achieving isolation at the critical capacitor levels to maintain linearity.
Data Source
AI summary
A phase frequency detector (PFD) isolates supply (e.g., voltage supply) to a reference path and a feedback path of a phase locked loop (PLL) such that the power supply to the reference path is independent of the power supply to the feedback path. This isolation improves linearity. In one instance, the PFD includes a supply voltage, one or more switches, a reference capacitor and a feedback capacitor. The reference capacitor is selectively coupled to the supply voltage via the one or more switches and the feedback capacitor is selectively coupled to the supply voltage via the one or more switches.