Adaptive Body Biasing for Wider CMOS Input Common-Mode Range
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Solution Overview
Problem
CMOS circuits face early turn-off issues due to body effect, limiting their common mode input range, and existing solutions either sacrifice low or high common mode ranges, affecting device performance.
Innovation Solution
An adaptive body biasing method using replica devices with isolated well structures to independently control the body bias of NMOS and PMOS devices, matching intrinsic parameters, and utilizing body effect to adjust threshold voltage across varying common mode voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the body of NMOS input pair is connected to Ground to raise threshold voltage through body effect, then high common mode input range is achieved, but low common mode input range is sacrificed and NMOS devices turn off earlier
Solution Approach 1:
The patent applies dynamic body biasing by connecting the body of NMOS input pair to a dynamically adjustable voltage through a body bias circuit, rather than a fixed ground connection. This allows the body voltage to adapt based on the common mode input voltage level, preventing early turn-off while maintaining high common mode range. The body bias circuit dynamically adjusts the body-source voltage difference to optimize threshold voltage at different operating points.
Solution Approach 2:
The patent changes the body voltage parameter dynamically based on operating conditions. By using a body bias circuit that adjusts the body voltage according to the common mode input voltage, the threshold voltage is optimized for different ranges. This parameter change approach allows the system to maintain reliable device operation across the entire common mode input range while achieving both high and low common mode ranges.
2Length of moving object
If the body of PMOS input pair is connected to Supply to raise threshold voltage through body effect, then low common mode input range is achieved, but high common mode input range is sacrificed and PMOS devices turn off earlier
Solution Approach 1:
The patent applies dynamic body biasing to PMOS input pair by connecting the body to a dynamically adjustable voltage through a body bias circuit, rather than a fixed supply connection. This allows the body voltage to adapt based on the common mode input voltage level, preventing early turn-off while maintaining low common mode range. The body bias circuit dynamically adjusts the body-source voltage difference to optimize threshold voltage at different operating points.
Solution Approach 2:
The patent changes the body voltage parameter dynamically for PMOS devices based on operating conditions. By using a body bias circuit that adjusts the body voltage according to the common mode input voltage, the threshold voltage is optimized for different ranges. This parameter change approach allows the system to maintain reliable device operation across the entire common mode input range while achieving both low and high common mode ranges.
3Adaptability or versatility
If adaptive body biasing is applied to extend common mode operating range, then wider operating ranges are achieved, but device complexity increases due to isolated well structures and replica devices
Solution Approach 1:
The patent uses replica devices that replicate the electrical behavior of the input devices to generate appropriate body bias voltages. These replica devices are simpler to implement than full isolated well structures for each device, and they provide the necessary dynamic body biasing functionality. The copying approach reduces complexity by using simplified surrogate structures that capture the essential behavior needed for adaptive biasing.
Solution Approach 2:
The patent implements a universal body biasing approach where isolated well structures and replica devices serve multiple functions: they provide dynamic body biasing, replicate device behavior, and extend common mode operating range simultaneously. This multi-functionality reduces the need for separate complex circuits for each purpose, thereby managing overall device complexity while achieving wide operating ranges.
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
Enables wider operating ranges for NMOS and PMOS devices by minimizing threshold voltage increase at low common mode voltages and maximizing it at high common mode voltages, maintaining device gain and preventing early turn-off.
Implementation Method 1
the body effect is the change in threshold voltage of a transistor due to the voltage difference between the source and bulk (substrate) of the transistor device
Data Source
AI summary
In order to get the best of both high and low common mode ranges, an adaptive body biasing method using a pair of replica devices is implemented. Each replica device corresponds to a NMOS (or PMOS) device that constitutes the input pair used in a logic circuit or other type of integrated circuits. This configuration helps to increase the threshold voltage of the device, utilizing body effect, at high input common mode voltage, as desired for NMOS, and at low input common mode voltage, as desired for PMOS. At the same time, this configuration scales the threshold back to normal at low input common mode voltages, thereby countering the negative impact of body effect. In short, the body bias applied to the NMOS (or PMOS) device helps in adapting the threshold voltage to the operating condition.