Rail-to-Rail nMOS Amplifier With Auxiliary Input Switching
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Solution Overview
Problem
Existing signal buffers for analog front ends face challenges in achieving rail-to-rail operation with low power consumption and minimal die area, while also dealing with limited voltage range and increased complexity due to the use of p-MOS or n-MOS transistors.
Innovation Solution
The proposed amplifier assembly includes a first and second input circuit with auxiliary control transistor elements connected in parallel to the control transistor elements, along with a load circuit. This configuration enhances linearity, reduces input voltage offset, and allows for rail-to-rail operation with low power consumption and minimal die area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a combination of p-MOS and n-MOS transistors is used as input stage for rail-to-rail operation, then the voltage range is improved, but the quiescent current and die area increase
Solution Approach 1:
The input stage is segmented into two separate input circuits, each handling a specific voltage range (first input circuit for lower voltage range, second input circuit for higher voltage range). This segmentation allows each circuit to be optimized independently, reducing the overall complexity and area compared to a full rail-to-rail implementation while maintaining extended voltage range capability.
Solution Approach 2:
The circuit dynamically switches between the first and second input circuits based on the input voltage level. The auxiliary control transistor elements enable automatic switching between circuits, allowing the amplifier to adapt its configuration to the current operating conditions, thus achieving rail-to-rail operation with optimized area and power consumption.
2Adaptability or versatility
If constant transconductance gm circuit and folded cascade load stage are used, then rail-to-rail operation is achieved, but the quiescent current and circuit complexity increase
Solution Approach 1:
The patent extracts and removes the constant transconductance gm circuit and folded cascade load stage from the design. Instead, it uses a simpler load circuit configuration that achieves rail-to-rail operation through the auxiliary control transistor elements in the input circuits, thereby reducing circuit complexity while maintaining the desired voltage range.
Solution Approach 2:
Rather than using complex constant transconductance circuits to achieve rail-to-rail operation, the patent inverts the approach by using voltage-controlled transistor switching to directly enable rail-to-rail input range with a simpler load circuit, thus achieving the same goal with reduced complexity.
3Measurement precision
If auxiliary control transistor elements are added to improve linearity, then the accuracy is improved, but the die area increases
Solution Approach 1:
The auxiliary control transistor elements serve multiple functions simultaneously: they improve linearity by compensating for transistor non-linearities, enable automatic switching between input circuits based on voltage level, and extend the input voltage range. This multi-functionality achieves high accuracy without proportionally increasing die area, as the same transistors perform multiple critical functions.
Data Source
AI summary
An amplifier assembly suitable for use as a rail-to-rail amplifier is provided. The amplifier assembly includes: a first input circuit connected to a first signal input node for a first input level range; a second input circuit connected to a second signal input node for a second input level range; a load circuit coupled to the first input circuit, the second input circuit and an output node of the amplifier assembly, wherein the first input circuit includes a first auxiliary control transistor element, and a first control transistor element. The first signal input node is coupled to a control terminal of the first control transistor element and a control terminal of the first auxiliary control transistor element. A path connected in parallel to the first control transistor element includes the first auxiliary control transistor element.