Tail-Current-Free Residue Amplifier for Low-Voltage Pipelined ADCs
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Solution Overview
Problem
Existing residue amplifiers in Analog-to-Digital Converters (ADCs) face challenges with offset errors and reduced output voltage swing when operating at low power supply voltages, particularly due to the presence of a tail current source, which limits their performance in high-speed and high-resolution applications.
Innovation Solution
A differential residue amplifier design without a tail current source, utilizing a p-channel and n-channel differential pair of transistors with cascode transistors and AC-coupled input networks to achieve a wide output voltage swing and high gain, while maintaining low power consumption and minimizing noise and distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tail current source is used in the residue amplifier, then the amplifier can operate with proper bias current, but the output voltage swing is reduced and offset errors increase
Solution Approach 1:
The patent removes the tail current source from the differential amplifier circuit. Instead of using a traditional tail current source connected to the sources of the differential pair transistors, the invention employs AC-coupled input networks that eliminate this component, thereby removing the constraint it imposed on output voltage swing and offset errors.
2Use of energy by moving object
If the amplifier operates at low power supply voltage, then power consumption is reduced, but output voltage swing and gain are compromised
Solution Approach 1:
The patent introduces AC-coupled input networks that operate in a different voltage domain, allowing the amplifier to achieve wide output voltage swing and high gain even when powered by low voltage supplies. The AC coupling enables signal levels to be shifted and amplified without being constrained by the low supply voltage headroom.
3Measurement precision
If multi-bit ADC architecture is used, then conversion precision is improved, but the complexity of residue amplifier design increases
Solution Approach 1:
The patent designs a universal differential amplifier architecture that can support multi-bit ADC operations. The AC-coupled input networks and elimination of tail current sources create a flexible amplifier that handles multiple bits of residue voltage while maintaining simplicity, avoiding the need for complex multi-stage amplification circuits.
Data Source
AI summary
A differential residue amplifier fits between Analog-to-Digital Converter (ADC) stages. Switched-Capacitor Common-Mode Feedback circuits determine voltage shifts. An AC-coupled input network uses switched capacitors to shift upward voltages of the differential inputs to the residue amplifier to apply to an upper pair of p-channel differential transistors with sources connected to the power supply. The AC-coupled input network also shifts downward in voltage the differential inputs to the residue amplifier to apply to a lower pair of n-channel differential transistors with grounded sources. The drains of the p-channel differential transistors connect to differential outputs through p-channel cascode transistors. N-channel cascode transistors connect the drains of the n-channel differential transistors to the differential outputs. The drains of differential transistors can be input to differential amplifiers to drive the gates of the cascode transistors for gain boosting. No tail current is used, allowing for wider output-voltage swings with low supply voltages.