Resistive Feedback Amplifier Biasing at Reduced Supply Voltage
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Solution Overview
Problem
Capacitively fed back amplifiers in integrated semiconductor circuits face challenges with resistor implementation due to large area requirements and parasitic capacitances, and existing solutions require a supply voltage of at least two threshold voltages of MOSFET transistors.
Innovation Solution
An electronic device with a single-transistor amplifier configuration using a diode-coupled second transistor in the feedback path, where the first input transistor and diode-coupled second transistor are of opposite doping types, allowing for a defined resistive path and reduced supply voltage requirements, and optionally using capacitors to bias the amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resistor is used to define the DC bias point in a capacitively fed back amplifier, then the DC operating point is properly established, but the area occupied is large and parasitic capacitances increase
Solution Approach 1:
The patent changes the physical implementation of the resistive feedback path from a dedicated resistor to the on-resistance of a transistor operated in the triode region. This parameter change allows the same electrical function (providing a resistive path for DC bias) to be achieved with much smaller area and different parasitic characteristics, directly resolving the contradiction between DC stability and area occupation.
2Reliability
If a resistor is used to define the DC bias point in a capacitively fed back amplifier, then the DC operating point is properly established, but parasitic capacitances increase
Solution Approach 1:
The patent changes the physical implementation from a resistor to a transistor in triode region, which fundamentally alters the parasitic capacitance profile. The transistor's on-resistance provides the necessary DC path while its parasitic capacitances are different in magnitude and characteristics compared to a discrete resistor, thereby reducing the harmful parasitic effects while maintaining DC stability.
3Reliability
If existing amplifier solutions are used, then the amplifier can operate, but the supply voltage must be at least two threshold voltages of MOSFET transistors
Solution Approach 1:
The patent changes the operating region of the input transistor from saturation to triode region, and uses a capacitor in parallel with the transistor to provide AC feedback while maintaining DC bias through the transistor's on-resistance. This parameter change in operating mode allows the amplifier to function with a supply voltage lower than two threshold voltages, directly resolving the contradiction between operational reliability and energy consumption.
Data Source
AI summary
An electronic device comprising an amplifier having at least a first input transistor of a first doping type. A first transistor is coupled with a channel as a feedback path between an output of the amplifier and a control gate of the first input transistor forming an input of the amplifier. A diode-coupled second transistor is coupled with a channel between a first current source and the output of the amplifier wherein a control gate of the first transistor is coupled between the first current source and the diode-coupled second transistor and the first transistor is of a second doping type which is opposite to the first doping type of the first input transistor of the amplifier.