Bootstrapped MOS Feedback Resistor for Wide-Swing Amplifiers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In proximity communication systems, detecting small signals across capacitively coupled interfaces is challenging due to input offset and the need for precise biasing to achieve adequate gain, especially in advanced fabrication processes where transistor mismatch effects are significant, and existing feedback resistors fail to maintain high resistance over a wide range of signal voltages.
Innovation Solution
An active feedback resistor with a MOS pass-gate and bootstrapping transistors, where the gate bias voltages are modulated based on the voltage levels across the resistor, maintaining transistors in the subthreshold region for consistent resistance, and using coupling capacitors to ensure operation over the full signal range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional feedback resistors are used in proximity communication sense amplifiers, then the amplifier can provide gain, but the resistance cannot be maintained at high levels over a wide signal voltage range, leading to instability and erroneous spikes
Solution Approach 1:
The patent implements dynamic biasing of the feedback resistor using bootstrapping transistors that adjust the gate-source voltage of pass-gate transistors based on the instantaneous signal voltage. This dynamic adjustment maintains consistent resistance characteristics across the full signal voltage range, preventing instability and erroneous spikes that occur with conventional fixed-bias resistors
Solution Approach 2:
The invention changes the biasing parameters of the feedback resistor dynamically. By modulating the gate voltage of pass-gate transistors through bootstrapping capacitors and transistors, the resistor operates with optimized parameters across different signal levels, maintaining high resistance consistency where conventional resistors would vary significantly
2Area of stationary object
If the feedback resistor uses simple pass-gate transistors, then the circuit area is minimized, but the resistance varies significantly with voltage, causing instability
Solution Approach 1:
The patent introduces bootstrapping transistors and capacitors as intermediary elements between the simple pass-gate transistors and the signal path. These intermediaries dynamically adjust the bias conditions of the pass-gate transistors, maintaining stable resistance characteristics while preserving the compact area benefits of simple pass-gate implementations
Solution Approach 2:
The bootstrapping mechanism implements local feedback by sensing the voltage across the feedback resistor and using it to adjust the gate voltage of the pass-gate transistors through coupling capacitors. This feedback loop ensures that the resistor maintains consistent characteristics despite voltage variations, achieving reliability without increasing area significantly
3Productivity
If advanced fabrication processes are used to improve integration, then transistor mismatch effects increase, but offset cancellation becomes more critical for robust communication
Solution Approach 1:
The feedback amplifier circuit performs self-correction by using its own output signal to bias the feedback resistor through the bootstrapping mechanism. This self-biasing approach automatically compensates for transistor mismatch effects without requiring external offset cancellation circuits, maintaining measurement precision while benefiting from advanced fabrication integration density
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The active feedback resistor provides reliable high resistance across a wide signal range, reducing instability and erroneous spikes, and requires minimal silicon real estate with low parasitic capacitance, enabling robust signal amplification in proximity communication systems.
Implementation Method 1
a coupling capacitor coupled between the gate of the pass-gate transistor and the output node
Implementation Method 2
a bootstrapping MOS transistor coupled between the gate of the pass-gate transistor and a bias voltage
Data Source
AI summary
An active resistor and its use in a negative feedback amplifier allow wide voltage swings on the input and output signals. One embodiment includes parallel pass-gate MOS transistors of opposite conductivity types connected between the input and output nodes. Bootstrapping transistors are connected between the gates of the pass-gate transistors and respective bias voltages. Coupling capacitors are connected between the gates and the output node. Additional coupling capacitors may be connected between the gates and the input node to make the resistor symmetric. In other embodiments, only one pass-gate transistor is used.