Cross-Coupled Switched Capacitor Branches for Low-Power Sigma-Delta Feedback
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Solution Overview
Problem
Sigma-delta modulator circuits face challenges in reducing power consumption while maintaining speed and accuracy, particularly in applications like audio circuits and cellular telephones, where power efficiency is crucial.
Innovation Solution
The implementation of a feedback loop with plural switched capacitor branches, allowing charge to be transferred on each clock phase and relaxing charging requirements, reduces power consumption by not requiring full settling of capacitors during a single phase, thereby reducing the speed requirements of the operational amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If charge is provided to capacitors once each clock period in a standard switched capacitor sigma-delta modulator, then the circuit operates with simpler timing, but the speed is limited and input capacitors must be larger to maintain noise performance
Solution Approach 1:
The feedback loop is divided into multiple parallel branches (first branch, second branch, etc.), each with its own switched capacitor circuit. This segmentation allows charge to be provided to the integration capacitor through multiple paths simultaneously during different clock phases, effectively doubling the charge transfer rate and increasing circuit speed without requiring larger capacitors
2Speed
If cross-coupled summing junctions are used to provide charge on each clock phase, then circuit speed increases, but power consumption increases due to repeated charging operations
Solution Approach 1:
The switched capacitor circuits in parallel branches provide charge transfer during specific clock phases without requiring full settling of capacitors during each phase. This partial action approach maintains high speed charge transfer while reducing the total energy consumed per clock cycle compared to traditional cross-coupled designs that require complete charging operations
Solution Approach 2:
The circuit uses periodic clock phases to control the switching of capacitor branches, where different branches are activated during different phases (first phase, second phase). This periodic activation pattern allows efficient charge transfer while minimizing redundant charging operations, thereby reducing power consumption while maintaining high-speed operation
3Measurement precision
If full settling of capacitors is required during each phase, then accuracy is maintained, but the operational amplifier speed requirements increase and power consumption rises
Solution Approach 1:
The circuit achieves sufficient accuracy without requiring complete capacitor settling during each clock phase. The parallel branch structure with selective phase activation provides the necessary charge transfer precision through distributed charging across multiple branches, reducing the speed and power requirements of the operational amplifier while maintaining signal accuracy
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
This approach reduces power consumption in sigma-delta modulators by allowing charge transfer on each phase without full capacitor settling, enhancing power efficiency and maintaining circuit speed.
Implementation Method 1
During a first phase for the first branch, an input voltage is provided that causes charge to be placed onto a plate of the capacitor. An equivalent amount of charge is transferred to a summing node of the sigma-delta modulator.
Implementation Method 2
During the first phase, the charge is provided through a resistor to the capacitor in the first branch defining an RC circuit and corresponding RC time constant.
Data Source
AI summary
A cross-coupled switched capacitor circuit that has two branches. During a first phase for the first branch, an input voltage is provided that causes charge to move through a resistor and to be placed onto a plate of the capacitor within the branch. An equivalent amount of charge is transferred to an output node. The output node may be a summing node of a sigma-delta modulator. The summing node is one of the inputs to an operational amplifier that is part of the integrator of the sigma-delta modulator. The resistor and the capacitor in the first branch define an RC circuit and corresponding RC time constant. During the first phase, the capacitor does not reach a fully settled voltage for a desired resolution. During the second phase, the capacitor in the first branch of the circuit is set to a defined voltage. The defined voltage may be the settling voltage had the capacitor been allowed to settle during the first phase. The second branch of the switched capacitor feedback circuit operates similar to the first branch, but on opposite phases. By not requiring the voltage to settle during the first phase, power can be conserved, since the integrator of the sigma-delta modulator does not need to operate as fast with respect to movement of charge.