Folded Cascode Op-Amp Self-Biasing With Subthreshold MOS Drive
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Solution Overview
Problem
Conventional operational amplifiers require multiple external biasing voltages, leading to increased power consumption, larger fabrication areas, and susceptibility to noise and cross-talk, while also having limited signal-to-noise ratios and dynamic range.
Innovation Solution
The design incorporates a positive biasing circuit with a drive PMOS transistor and a negative biasing circuit with a drive NMOS transistor, both biased in the subthreshold region, along with an amplification circuit featuring PMOS and NMOS transistors and a resistive element that self-biases the gain-boosting stages, reducing the need for external biases and enhancing DC gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple external biasing voltages are used in conventional operational amplifiers, then the amplifier can achieve proper biasing and operation, but power consumption increases and fabrication area increases
Solution Approach 1:
The operational amplifier uses self-biasing circuits where the biasing voltages are generated internally by the amplifier itself rather than requiring external biasing voltage sources. The biasing circuitry is integrated within the amplifier, allowing it to autonomously establish the necessary bias conditions for proper operation.
2Reliability
If multiple external biasing voltages are used in conventional operational amplifiers, then the amplifier can achieve proper biasing and operation, but fabrication area increases
Solution Approach 1:
The biasing circuitry is merged with the amplification circuitry into a single integrated structure. The operational amplifier combines the biasing generation functions with the signal amplification functions in one unified circuit block, eliminating the need for separate external biasing voltage sources and reducing overall fabrication area.
3Reliability
If multiple external biasing voltages are used in conventional operational amplifiers, then the amplifier can achieve proper biasing and operation, but susceptibility to noise and cross-talk increases
Solution Approach 1:
The design extracts and eliminates the external biasing voltage sources from the operational amplifier system. By removing these external connections, the amplifier becomes less susceptible to noise and cross-talk that would otherwise be introduced through external biasing pathways, while maintaining proper biasing through internal generation.
4Productivity
If conventional operational amplifiers are designed with standard biasing, then they can achieve adequate operation, but signal-to-noise ratio is limited and dynamic range is reduced
Solution Approach 1:
The operational amplifier employs parameter changes in the biasing scheme, specifically using subthreshold biasing conditions and optimized current levels that improve the signal-to-noise ratio. By adjusting the biasing parameters to operate in specific regions, the amplifier achieves enhanced dynamic range and improved signal fidelity while maintaining proper operation.
Data Source
AI summary
A first embodiment is directed to a circuit including a positive biasing circuit with a drive PMOS for biasing in subthreshold, a negative biasing circuit with a drive NMOS for biasing in subthreshold, and an amplification circuit coupled to the biasing circuits. The amplification circuit includes a first stage with a first boosting stage, a second stage with a second boosting stage, and a resistive element coupled between the first and second stages. A second embodiment is directed to a folded cascode operational amplifier wherein a value of the resistive element is selected to place at least one of a drive MOS in subthreshold. A third embodiment is directed to an integrated circuit with a resistive area neighboring a first boosting area and a second boosting area, the resistive area including a resistive element directly connected to a drive PMOS and a drive NMOS.