Adaptive Biasing Input Stage With Current Mirrors for Low-Power GBW
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Solution Overview
Problem
Existing adaptive biasing amplifiers face challenges in achieving high gain bandwidth, minimizing area, and reducing operating voltage while maintaining high current efficiency, due to high static current dissipation and limited minimum operating voltage.
Innovation Solution
An adaptive biasing input stage is designed with a single static current source and fewer diode-connected MOSFETs, utilizing differential coupled amplifying and sensing field effect transistors with current mirrors to increase current efficiency and reduce area, and optimizing the area ratio of mirror transistors to maximize current flow based on differential inputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If numerous current mirrors and static current paths are used to increase biasing currents, then the biasing current increases, but the static current dissipation increases resulting in low current efficiency
Solution Approach 1:
The patent implements dynamic biasing where the biasing current is automatically adjusted based on the input signal amplitude. When the input signal is large, the biasing current increases to maintain linearity. When the input signal is small, the biasing current decreases to minimize static power consumption. This dynamic adaptation resolves the contradiction between needing high biasing current for performance and avoiding static current dissipation for efficiency.
Solution Approach 2:
The patent changes the biasing current parameter dynamically based on operating conditions. By using detection circuits to monitor input signal characteristics and adjusting the biasing current accordingly, the system transitions from a fixed high current state to a variable current state, achieving both high performance when needed and high efficiency when not needed.
2Device complexity
If diode-connected PMOSFETs are used as loads for input NMOSFETs, then the circuit is simplified, but the GBW (gain bandwidth) is reduced
Solution Approach 1:
The patent replaces static diode-connected PMOSFET loads with dynamic active loads that can adjust their impedance characteristics. The active loads use transistors operating in specific regions to provide the necessary gain and bandwidth while maintaining circuit simplicity. This dynamic loading approach resolves the contradiction between simplified structure and high GBW performance.
3Power
If multiple static current sources are used to provide biasing currents, then the biasing is improved, but the area occupied increases
Solution Approach 1:
The patent designs current sources that serve multiple functions simultaneously. A single current source structure provides biasing for multiple stages or transistors, reducing the total number of current sources needed. This multi-functional approach maintains proper biasing while minimizing the area occupied by biasing circuitry.
Solution Approach 2:
The patent combines multiple biasing functions into unified current source structures. By merging the functions of multiple separate current sources into a single integrated biasing network, the patent reduces area while maintaining the necessary biasing currents for various circuit stages.
Data Source
AI summary
An adaptive biasing input stage includes pairs of differentially coupled amplifying and sensing field effect transistors having gates with differential inputs applied thereon. In addition, a static current source is coupled to sources of the amplifying and sensing field effect transistors at a predetermined node. Also, current mirrors are coupled to the sensing field effect transistors for forming loop mechanisms for increasing the current through the predetermined node when the differential inputs have a non-zero difference.