Folded Cascode Op-Amp Current Mirroring for Higher Slew Rate
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Solution Overview
Problem
Conventional folded cascode operational amplifiers increase power consumption to achieve high slew rates, which is not suitable for low power consumption in high-speed IC applications.
Innovation Solution
A folded cascode operational amplifier design that adjusts the width-to-length ratio of current sources and the bias current of the load current source to enhance slew rate without increasing power consumption, by using a mirroring current source with a current ratio greater than one and optimizing transistor configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the bias current value of the tail current source is increased to achieve a high slew rate, then the slew rate is improved, but the power consumption increases by multiple folds
Solution Approach 1:
The patent divides the current source into two separate current sources (first current source and second current source) with different width-to-length ratios. This segmentation allows each current source to contribute differently to the slew rate, enabling high slew rate performance without requiring a single high-current tail current source, thus reducing power consumption.
Solution Approach 2:
The patent applies different width-to-length ratios to different parts of the current source configuration. The first current source has a first width-to-length ratio while the second current source has a second width-to-length ratio that is different from the first. This local differentiation optimizes the current distribution to achieve high slew rate without proportionally increasing power consumption.
2Speed
If conventional folded cascode operational amplifiers use a single current source configuration, then the circuit structure is simple, but the slew rate is limited and cannot achieve high-speed performance without increasing power consumption
Solution Approach 1:
The patent segments the single current source into two distinct current sources (first current source and second current source) connected in series between the first voltage terminal and the second voltage terminal. This segmentation enables differentiated current contribution from each source, achieving high slew rate performance while maintaining reasonable circuit complexity through systematic design.
Solution Approach 2:
The combined configuration of the two current sources serves multiple functions: the first current source provides baseline current while the second current source provides additional current for high-speed operation. This multi-functional arrangement allows the circuit to achieve high slew rate without proportionally increasing overall power consumption or complexity.
Data Source
AI summary
A folded cascode operational amplifier is disclosed. The folded cascode operational amplifier includes a first current source, a second current source, and a first voltage terminal connected to the first current source and the second current source. The folded cascode operational amplifier also includes a first input-transistor connected to the first current source in series, and a second input-transistor connected to the second current source in series. Further, the folded cascode operational amplifier includes a tail current source connected to a connection point between the first input-transistor and the second input-transistor, a load current source, and a second voltage terminal connected to the tail current source and the load current source. The folded cascode operational amplifier also includes an output-transistor connected to the load current source, and an output-terminal arranged between the second current source and the second input-transistor and connected to the output-transistor. The second current source is a mirroring current source of the first current source, and a ratio of a current passing through the second current source to a current passing through the first current source is greater than one.