Fully Differential Op-Amp Dynamic CMRI for Common-Mode Ripple
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Solution Overview
Problem
Fully-differential operational amplifiers suffer from common-mode variation issues that degrade performance, leading to reduced linearity and increased noise in applications like ADCs and DACs, with existing solutions either introducing additional noise or increasing power and area consumption.
Innovation Solution
A dynamic common-mode reference input (CMRI) signal is generated using a signal-dependent common-mode generator (SDCG) to maintain the common-mode component of the amplifier inputs independent of the input signals, reducing common-mode ripple and noise, while minimizing power consumption and area cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If two op-amps are used to maintain constant common-mode voltage, then common-mode variation is reduced, but noise increases by at least 3 dB
Solution Approach 1:
The patent introduces a dynamic common-mode reference input (CMRI) signal as an intermediary that mediates between the input signals and the op-amp operation. This CMRI signal is generated based on the actual input common-mode voltage and used to adjust the reference, thereby maintaining stability without requiring an additional op-amp that would introduce noise.
Solution Approach 2:
The patent transitions from a static common-mode reference voltage to a dynamic CMRI signal that adapts in real-time to input signal variations. This dynamic adjustment allows the system to maintain optimal performance without the noise penalty of additional amplifiers, as the reference automatically tracks input conditions.
2Stability of the object's composition
If two op-amps are used to maintain constant common-mode voltage, then common-mode variation is reduced, but power consumption and area increase
Solution Approach 1:
The patent implements a self-service mechanism where the dynamic CMRI generation block uses the existing op-amp's input signals to generate its own reference adjustment. This eliminates the need for additional power-consuming components while maintaining common-mode stability through intelligent signal processing of available resources.
3Stability of the object's composition
If a DAC with current sources is used to compensate common-mode variation, then common-mode stability is improved, but additional noise is introduced
Solution Approach 1:
The patent replaces the mechanical/electrical conversion approach of a DAC with a direct voltage generation approach. Instead of converting digital common-mode samples to analog voltages through a DAC (which introduces quantization and switching noise), the system directly generates the CMRI voltage through analog circuitry that processes the input signals, eliminating the noisy conversion stage.
Data Source
AI summary
A dynamic common reference input (CMRI) signal may be provided to an operational amplifier, or “op-amp,” in an amplifier system to reduce the common mode ripple of the fully-differential op-amp, while adding little or no noise in the amplifier system. The dynamic CMRI signal may be controlled such that a common-mode component of two amplifier input nodes of the operational amplifier is made approximately independent of two input signals received at two system input nodes of the amplifier system. An amplifier system with the dynamic CMRI may be used in class-D amplifiers, such as amplifiers for audio systems that generate output for headphones or speakers.