CMOS Amplifier Threshold Voltage Adjustment via Body Biasing
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Solution Overview
Problem
CMOS low voltage amplifiers face limitations in maintaining a high common mode rejection ratio over a wide range of common mode input voltages due to high threshold voltages of field effect transistors, which restrict the common mode input voltage range and degrade other circuit parameters.
Innovation Solution
A method and structure that adjust the threshold voltages of transistors by steering current through a resistance in response to input signals, varying the body region potential of semiconductor material, allowing for bi-directional body biasing to increase or decrease effective threshold voltages, thereby expanding the common mode input voltage range while maintaining a good common mode rejection ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high threshold voltage transistors are used in CMOS low voltage amplifiers, then manufacturing is easier and device reliability is improved, but the common mode input voltage range is restricted and common mode rejection ratio deteriorates
Solution Approach 1:
The patent applies body biasing techniques to dynamically adjust the threshold voltage of transistors based on the common mode input voltage level. By varying the body-to-source voltage (VBS), the threshold voltage can be modulated to extend the common mode input voltage range while maintaining proper amplifier operation. This dynamic adjustment resolves the contradiction between using fixed high threshold voltage devices and achieving wide voltage range adaptability.
Solution Approach 2:
The patent changes the electrical parameters of the transistor threshold voltage through body biasing. By applying different bias voltages to the body terminal, the threshold voltage parameter is adjusted to optimize performance across different common mode input voltage ranges. This parameter change enables the amplifier to maintain high common mode rejection ratio while operating over an extended voltage range.
2Stability of the object's composition
If high threshold voltage transistors are used, then device stability is improved, but common mode rejection ratio deteriorates over wide voltage ranges
Solution Approach 1:
The patent employs feedback mechanisms through body biasing circuits that sense the common mode input voltage and adjust the body bias accordingly. This feedback control maintains optimal threshold voltage settings that preserve both device stability and high common mode rejection ratio across varying operating conditions. The feedback loop ensures that stability and precision requirements are met simultaneously.
3Device complexity
If fixed threshold voltage transistors are used, then device complexity is reduced, but the ability to maintain optimal performance across voltage ranges is limited
Solution Approach 1:
The patent makes the transistor device multi-functional by adding body biasing capability. The same transistor structure can operate optimally across different common mode input voltage ranges by adjusting the body bias voltage. This universal approach allows a single device design to adapt to various operating conditions without requiring multiple specialized transistor types, thus managing complexity while enhancing versatility.
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 solution effectively increases the common mode input voltage range of CMOS operational amplifiers by dynamically adjusting transistor threshold voltages, ensuring optimal performance across a broader voltage range while maintaining a high common mode rejection ratio.
Implementation Method 1
A method and structure that adjust the threshold voltages of transistors by steering current through a resistance in response to input signals, varying the body region potential of semiconductor material
Data Source
AI summary
A method and circuit for changing a threshold voltage of a transistor. The circuit includes a sense circuit coupled to a switching transistor, a circuit transistor and to one terminal of a resistor. The other terminal of the resistor is connected to a body contact. The switching transistor directs current along one of two different paths in response to an input voltage sensed by the sense circuit. When the switching transistor directs a first current along one path, the first current is steered towards the resistor and flows through the resistor in one direction and when the switching transistor directs a second current along the other path, the second current is directed towards the resistor and flows through the resistor in the opposite direction from the first current. Steering the currents varies the potential of a body with respect to the potential at the source of the circuit transistor.