MOS Operational Amplifier Current-Mirror Gain Boosting at Low Voltage
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Solution Overview
Problem
Conventional MOS amplifier circuits face performance issues such as impaired speed and high power consumption due to parasitic capacitance and asymmetric operation, particularly when operating at lower power supply voltages, which complicates the stabilization of closed-loop systems and limits rail-to-rail output capability.
Innovation Solution
The design incorporates a dual-section gain boosting stage with P-channel and N-channel transistors, utilizing current mirrors and Miller compensation capacitors to enhance frequency response and reduce current consumption, allowing for rail-to-rail voltage outputs with lower power supply voltages, while minimizing parasitic capacitance and circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional MOS amplifier circuits use multiple gain stages to achieve high gain, then the gain increases, but the system stability deteriorates due to multiple frequency poles and requires additional compensation circuitry
Solution Approach 1:
The patent combines multiple gain stages into a single gain stage that achieves high gain through a cascode configuration with current mirrors. This merging eliminates the need for multiple separate stages while maintaining high gain and improving stability by reducing the number of frequency poles in the system.
Solution Approach 2:
The gain stage is segmented into specific functional blocks (input differential pair, cascode transistors, current mirrors) that work together to achieve high gain in a single stage. This segmentation allows each component to be optimized for its specific function while contributing to the overall high gain without requiring multiple cascaded stages.
2Speed
If conventional amplifiers use passive circuitry such as Miller compensation capacitors to push non-dominant poles to higher frequencies, then the frequency response improves, but the circuit area and power consumption increase
Solution Approach 1:
The patent changes the architectural parameters of the amplifier by using a cascode configuration with current mirrors instead of traditional Miller compensation. This parameter change achieves high frequency response and pushes non-dominant poles to higher frequencies without requiring large compensation capacitors, thereby reducing circuit area.
Solution Approach 2:
The patent substitutes passive Miller compensation capacitors with an active cascode current mirror configuration. This substitution achieves the same frequency compensation effect through active circuit elements rather than large passive capacitors, reducing both area and power consumption.
3Use of energy by moving object
If conventional amplifiers operate at lower power supply voltages to reduce power consumption, then the power consumption decreases, but the voltage span for rail-to-rail operation is reduced
Solution Approach 1:
The patent employs dynamic biasing and a symmetrical dual-section gain boosting configuration that adapts to different voltage conditions. This allows the amplifier to maintain rail-to-rail output capability across a wide voltage range while operating efficiently at lower supply voltages, dynamically adjusting its operation to preserve both low power consumption and full voltage span.
Solution Approach 2:
The patent uses asymmetrical transistor sizing and configuration in the dual-section gain boosting stage to optimize performance for rail-to-rail operation at lower voltages. By carefully designing the asymmetry in the P-channel and N-channel sections, the circuit achieves full voltage span while maintaining low power consumption.
4Power
If conventional amplifiers use multiple gain stages to achieve high gain, then the gain increases, but the power consumption increases due to additional circuitry
Solution Approach 1:
The patent merges multiple gain stages into a single high-gain stage using cascode and current mirror configurations. This consolidation achieves the same or higher gain while reducing the number of active devices and interconnections, thereby lowering total power consumption.
Solution Approach 2:
The current mirrors in the patent serve multiple functions simultaneously: they provide gain multiplication, bias current generation, and impedance transformation. This multi-functionality eliminates the need for separate circuits for each function, reducing overall power consumption while maintaining high gain.
Data Source
AI summary
An amplifier has an input stage coupled to a current mirror for providing a first control signal. A gain boosting stage has first and second sections, each having first and second inputs and an output. The first input of the first section is coupled to the input stage. The second input of the first section is a first node between a source and a drain of a first pair of series-coupled transistors. The first input of the second section is coupled to the current mirror. The second input of the second section is a second node between a source and a drain of a second pair of series-coupled transistors. A pre-driver stage has inputs coupled to the input stage and the gain boosting stage. The pre-driver stage provides inputs to the gain boosting stage and receives outputs from the gain boosting stage prior to coupling to an output stage.