Switched-Capacitor Common-Mode Feedback for Charge Pump Noise Reduction
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Solution Overview
Problem
Existing phase-locked loops (PLLs) in wireless communication networks face challenges in accurately controlling common-mode noise and power consumption due to the use of continuous-time amplifier-based common-mode feedback circuits, which contribute noise to differential outputs and consume excessive power.
Innovation Solution
Implementing a switched-capacitor common-mode feedback (SC-CMFB) circuit within a fully differential charge pump, which replaces continuous-time CMFB, reduces noise and power consumption by using capacitors to adjust common-mode voltage based on reference signals and control inputs from phase-frequency detectors, ensuring actual common-mode voltage matches the desired level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If continuous-time amplifier-based common-mode feedback circuits are used, then common-mode voltage control is achieved, but noise is introduced to differential outputs and power consumption increases
Solution Approach 1:
The patent employs periodic switching action through switched-capacitor CMFB circuit that operates in discrete time intervals rather than continuous operation. The circuit periodically samples the common-mode voltage and adjusts capacitance values at specific moments, achieving control while minimizing continuous noise generation and power consumption associated with amplifier-based continuous feedback.
Solution Approach 2:
The patent changes the operating parameters by using variable capacitance values (C1, C2, C3, C4) that can be dynamically adjusted to control common-mode voltage. By modifying capacitance parameters rather than using continuous amplifier gain adjustment, the circuit achieves precise control with lower noise and power consumption.
2Object-generated harmful factors
If switched-capacitor common-mode feedback circuit is implemented, then noise and power consumption are reduced, but circuit complexity increases due to multiple capacitors and switches
Solution Approach 1:
The patent segments the common-mode feedback function into multiple discrete capacitive elements (C1, C2, C3, C4) and switching components that can be independently controlled. This segmentation allows the complex control function to be distributed across multiple simpler components, making the overall circuit more manageable and implementable despite the increased number of elements.
Solution Approach 2:
The patent uses a replica phase-frequency detector that copies the structure and functionality of the main PFD. This replica detector provides control signals for the switched-capacitor CMFB circuit, allowing the complex feedback control to be achieved through a simplified copied structure rather than requiring a fully complex original design.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The SC-CMFB circuit effectively reduces noise and power consumption while maintaining accurate common-mode voltage control, enhancing the performance and efficiency of PLLs in wireless communication networks.
Implementation Method 1
a switched-capacitor common-mode feedback (SC-CMFB) circuit coupled to the differential output nodes of the charge pump. The SC-CMFB circuit is configured to receive a reference common-mode voltage (Vcm) and to generate a common-mode feedback signal configured to bias the charge pump branches such that an actual Vcm of the differential signals equals the reference Vcm
Data Source
AI summary
Certain aspects of the present disclosure provide methods and apparatus for implementing a fully differential charge pump circuit that eliminates a source of noise and power consumption by using a low-noise switched-capacitor common-mode feedback (CMFB) circuit, rather than a continuous-time amplifier-based CMFB circuit. The fully differential charge pump circuit presented in this disclosure includes the switched-capacitor CMFB (SC-CMFB) unit connected to differential output nodes of the charge pump and provides a feedback signal to the charge pump to control a common-mode voltage of the differential signals based on a reference common-mode voltage. In certain aspects, a replica phase-frequency detector (PFD), a frequency divider, and a non-overlapping clock generator provides control signals for the SC-CMFB circuit.