Cross-Coupled OCMFB Capacitors for Faster Dynamic Residue Amplifiers
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Solution Overview
Problem
Switched capacitor common-mode feedback in dynamic residue amplifiers results in reduced efficiency due to a large differential load, requiring higher power and longer amplification times to overcome this load, which affects the amplifier's performance.
Innovation Solution
The implementation of a cross-coupled amplifier structure that reuses current from the feedback path to boost differential gain, utilizing cross-coupled switched output common-mode feedback capacitors to reduce area, power consumption, and parasitic losses, while improving speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If switched capacitor common-mode feedback is used in dynamic residue amplifiers, then linear performance is improved and parasitic poles are eliminated, but power efficiency deteriorates due to large differential load requiring higher power consumption
Solution Approach 1:
The patent combines the common-mode feedback function with the differential signal path by cross-coupling the feedback capacitors to the differential inputs. This merging allows the feedback capacitors to serve dual purposes: maintaining common-mode voltage while boosting differential gain, thereby improving power efficiency without sacrificing linear performance
2Reliability
If switched capacitor common-mode feedback is used in dynamic residue amplifiers, then common-mode control is improved, but amplification time increases due to large differential load
Solution Approach 1:
The feedback capacitors are cross-coupled to the differential inputs, merging the common-mode feedback path with the differential amplification path. This allows the same capacitors to accelerate differential signal settling while maintaining common-mode control, thereby reducing amplification time without compromising common-mode performance
3Reliability
If traditional OCMFB structure is used, then common-mode feedback is provided, but area consumption increases due to additional feedback components
Solution Approach 1:
The feedback capacitors are designed to perform multiple functions: providing common-mode feedback, boosting differential gain through cross-coupling, and reducing parasitic losses. This multi-functionality eliminates the need for separate components, thereby maintaining reliable common-mode feedback while reducing overall circuit area
Solution Approach 2:
The patent merges the common-mode feedback function with the differential gain boosting function by cross-coupling the feedback capacitors. This consolidation of functions into existing components reduces the need for additional area-consuming elements while maintaining effective common-mode feedback
4Stability of the object's composition
If switched capacitor common-mode feedback is used, then common-mode stability is improved, but parasitic losses increase due to additional load capacitance
Solution Approach 1:
The patent converts the harmful effect of feedback capacitance (which normally causes parasitic losses when connected to ground) into a beneficial effect by cross-coupling it to the differential inputs. The same capacitance that would cause losses now provides differential gain boosting and pole zero cancellation, thereby maintaining common-mode stability while reducing parasitic losses
Data Source
AI summary
Cross-coupling of switched-capacitor output common-mode feedback capacitors in dynamic residue amplifiers is provided via a cross-coupled amplifier, comprising: a current source connected to a first node; a feedback capacitor connected to the first node and a second node; a feedback resistor connected between the second node and ground; an amplifier having an input connected to the second node; a gain transistor having: a drain connected to the first node; a source connected to ground; and a gate connected to an output of the amplifier; and a load capacitor connected to the first node and ground.