MOSFET Body-Bias Circuit for Wider Low-Voltage Input Range
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Solution Overview
Problem
MOSFET-based amplifiers face limitations in input voltage range due to threshold voltage constraints, where input signals below the threshold voltage result in insufficient drain current, preventing proper operation, and existing solutions often require special MOSFET types or circuit arrangements that are not always available or effective.
Innovation Solution
The proposed solution involves a circuit that dynamically adjusts the body terminal polarization of MOSFETs based on the input voltage level, using a control circuit to lower the threshold voltage when necessary, allowing the amplifier to operate within a wider input voltage range without requiring special MOSFET types or components, and can be integrated into existing CMOS technology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the input voltage is below the threshold voltage of the MOSFET, then the amplifier can process lower input signals, but the drain current becomes insufficient and the operating point cannot be properly set
Solution Approach 1:
The patent dynamically changes the threshold voltage parameter of the MOSFET by applying a body-source voltage through a control circuit. When the input voltage drops below the threshold voltage, the control circuit activates to apply a body effect that lowers the threshold voltage, enabling the MOSFET to conduct sufficient drain current at lower input voltages and thus expanding the input voltage range while maintaining reliable operation
Solution Approach 2:
The control circuit continuously monitors the input voltage level and provides feedback control over the body-source voltage applied to the MOSFET. When the input voltage falls below the threshold voltage, the feedback mechanism triggers the body effect to reduce the threshold voltage, ensuring the drain current remains sufficient for proper operating point establishment
2Adaptability or versatility
If special MOSFET types (natural, depletion) are used to extend input voltage range, then the amplifier can process lower input signals, but the availability and manufacturability are compromised
Solution Approach 1:
The patent employs standard, readily available MOSFET types and uses a control circuit to make the MOSFET self-adjust its threshold voltage through the body effect. This approach eliminates the need for specialized MOSFET types (natural or depletion mode) that are difficult to manufacture and source, while still achieving the capability to process lower input signals by dynamically modifying the threshold voltage through the accessible body terminal
Solution Approach 2:
Instead of relying on special MOSFET types with fixed threshold characteristics, the patent changes the threshold voltage parameter dynamically using the body effect in standard MOSFETs. This allows the use of commonly available MOSFET devices while achieving extended input voltage range by controlling the threshold voltage through the body-source voltage applied by the control circuit
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
This approach effectively widens the input voltage range of MOSFET-based amplifier circuits, enabling them to process lower input signals by reducing the threshold voltage through body effect modulation, thus maintaining normal operation without increasing current consumption or affecting the signal path.
Implementation Method 1
One or more embodiments may rely on the body effect applied on an input MOSFET for lowering its threshold voltage
Data Source
AI summary
A MOSFET has a current conduction path between source and drain terminals. A gate terminal of the MOSFET receives an input signal to facilitate current conduction in the current conduction path as a result of a gate-to-source voltage reaching a threshold voltage. A body terminal of the MOSFET is coupled to body voltage control circuitry that is sensitive to the voltage at the gate terminal of the MOSFET. The body voltage control circuitry responds to a reduction in the voltage at the gate terminal of the MOSFET by increasing the body voltage of the MOSFET at the body terminal of the MOSFET. As a result, there is reduction in the threshold voltage. The circuit configuration is applicable to amplifier circuits, comparator circuits and current mirror circuits.