Hybrid Feedback Amplifier for Low Offset and High CMRR
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Solution Overview
Problem
Current feedback amplifiers exhibit faster slew rates and larger bandwidth but have poor DC performance characteristics, including high input offset voltage, high input bias current, and poor common-mode rejection ratio (CMRR), necessitating improved amplifiers with increased bandwidth, enhanced CMRR, and reduced input offset error.
Innovation Solution
The implementation of an amplifier that combines voltage and current feedback error correction, utilizing a voltage feedback circuit to control the voltage level of the input terminal based on a voltage feedback signal generated by replica transistors, which tracks the bias conditions of input transistors, thereby reducing input offset voltage and improving CMRR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If current feedback amplifier configuration is used, then output slew rate and bandwidth are improved, but DC performance characteristics deteriorate
Solution Approach 1:
The patent combines voltage feedback and current feedback configurations into a hybrid amplifier circuit. The input stage uses current feedback for high slew rate and bandwidth, while a voltage feedback path is added to correct DC errors. This merging allows the amplifier to achieve both fast transient response and accurate DC performance simultaneously.
Solution Approach 2:
The patent introduces an intermediary voltage feedback path that mediates between the current feedback input stage and the output. This voltage feedback path acts as a mediator to correct DC errors without interfering with the high-speed current feedback operation, thus resolving the contradiction between speed and DC accuracy.
2Speed
If current feedback amplifier configuration is used, then bandwidth is increased, but input offset voltage increases
Solution Approach 1:
The patent applies dual feedback mechanisms: current feedback for AC signal amplification and voltage feedback for DC error correction. The voltage feedback path specifically targets and corrects input offset voltage by comparing the voltage at the inverting input with the non-inverting input and adjusting accordingly, while the current feedback path maintains high bandwidth for AC signals.
3Speed
If current feedback amplifier configuration is used, then slew rate is improved, but common-mode rejection ratio deteriorates
Solution Approach 1:
The patent merges voltage feedback and current feedback paths, where the voltage feedback path provides common-mode rejection by maintaining equal voltages at both inputs, while the current feedback path preserves high slew rate performance. This combination allows simultaneous achievement of fast transient response and high common-mode rejection ratio.
Data Source
AI summary
Amplifiers with voltage and current feedback error correction are provided. In one embodiment, an amplifier includes a first input terminal, a second input terminal, an output terminal, a first stage, and a voltage feedback amplification circuit. The first stage can be used to generate first and second output currents, which can be used to control a voltage level of the output terminal. The first and second output currents can change in response to a current feedback signal and a differential input signal received between the first and second input terminals. The first stage can also generate a voltage feedback signal, which can be used by the voltage feedback amplification circuit to control a voltage level of the second input terminal based on a voltage level of the first input terminal.