Two-Stage Operational Amplifier for Low Noise and Wide Output Swing

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Solution Overview

Problem

Operational amplifiers face challenges in achieving high bandwidth and high gain while minimizing noise and power consumption, particularly in applications like high-speed analog-to-digital converters.

Innovation Solution

The development of a low noise operational amplifier with wide output swing, featuring a two-stage architecture with a current-biased inverter amplifier at the input stage and a capacitively-biased inverter amplifier at the output stage, utilizing PMOS and NMOS transistors as drivers to enhance transconductance and reduce noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If high bandwidth and high gain are achieved in operational amplifiers, then signal amplification performance is improved, but noise increases and power consumption increases

Engineering Contradiction:

ImprovebandwidthVSAvoidnoise

Core Design Contradiction:

SpeedVSObject-generated harmful factors

Solution Approach 1:

The operational amplifier is divided into two distinct stages: a first amplifier stage with a current-biased inverter amplifier and a second amplifier stage with a capacitively-biased inverter amplifier. This segmentation allows each stage to be optimized for different functions - the first stage for high gain with low noise, and the second stage for bandwidth enhancement, thereby achieving high bandwidth and gain without excessive noise

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different biasing methods are applied to different stages of the amplifier. The current-biased inverter amplifier in the first stage provides high transconductance and low noise, while the capacitively-biased inverter amplifier in the second stage provides wide output swing and high bandwidth. This local differentiation of quality allows simultaneous optimization of noise performance and bandwidth

Inventive Principle:

Principle #3Local quality

2Speed

If high bandwidth and high gain are achieved in operational amplifiers, then signal amplification performance is improved, but power consumption increases

Engineering Contradiction:

ImprovebandwidthVSAvoidcurrent consumption

Core Design Contradiction:

SpeedVSUse of energy by moving object

Solution Approach 1:

The two-stage architecture segments the amplification function, allowing the first stage to operate at lower current for high gain while the second stage operates at higher current for bandwidth, optimizing the overall power-bandwidth tradeoff

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses different biasing parameters (current biasing in the first stage, capacitive biasing in the second stage) to achieve high bandwidth and gain without proportionally increasing power consumption, as capacitive biasing can provide frequency compensation and bandwidth enhancement without continuous high current draw

Inventive Principle:

Principle #35Parameter changes

3Object-generated harmful factors

If noise is reduced in operational amplifiers, then signal quality is improved, but bandwidth and gain may be limited

Engineering Contradiction:

ImprovenoiseVSAvoidbandwidth

Core Design Contradiction:

Object-generated harmful factorsVSSpeed

Solution Approach 1:

By segmenting the amplifier into two stages with different optimization goals, the first stage can be dedicated to low-noise high-gain amplification while the second stage handles bandwidth requirements, allowing noise reduction without sacrificing bandwidth

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The current-biased inverter amplifier in the first stage is specifically optimized for low noise with high transconductance, while the capacitively-biased inverter amplifier in the second stage is optimized for wide bandwidth, allowing each local region to excel at its specific function

Inventive Principle:

Principle #3Local quality

4Object-generated harmful factors

If a two-stage amplifier architecture is used with current-biased and capacitively-biased inverters, then noise is reduced and bandwidth is increased, but device complexity increases

Engineering Contradiction:

ImprovenoiseVSAvoidamplifier architecture complexity

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

The amplifier is segmented into two functional stages with distinct biasing approaches, which systematically addresses noise and bandwidth requirements separately, making the complexity manageable through functional decomposition

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Both stages use inverter amplifier topologies with different biasing methods, allowing a universal inverter structure to serve multiple functions (noise reduction in first stage, bandwidth extension in second stage), reducing the need for entirely different circuit topologies

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS20250047251A1Operational amplifier with low noise and wide output swing

Publication Date: 2025.02.06 STMICROELECTRONICS INT NV

AI summary

Various examples in accordance with the present disclosure provide an operational amplifier with low noise and wide output swing.