Adaptive Body Biasing in CMOS Input Pairs for Wider 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 adjusting threshold voltage based on input common mode voltage.
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 circuit to maintain proper device operation across the entire common mode input range without early turn-off.
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 circuit to maintain proper device operation across the entire common mode input range without early turn-off.
3Length of moving object
If adaptive body biasing is applied to extend operating range, then common mode voltage range is increased, 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 main input devices. These replica devices are used to generate the body bias voltage, copying the operating conditions of the main devices to create appropriate biasing. This copying approach allows the system to achieve adaptive biasing without directly complex control circuitry, as the replica devices naturally mirror the main devices' behavior.
Solution Approach 2:
The patent introduces body bias circuits as intermediary elements between the power supply and the device bodies. These intermediary circuits generate and regulate the body bias voltage based on the operating conditions, acting as a mediator that simplifies the overall control architecture. The body bias circuits translate operating conditions into appropriate body voltages, reducing the complexity of direct device control.
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 extends the operating range of CMOS devices by optimizing threshold voltage at both high and low common mode voltages, minimizing the negative impact of body effect and maintaining small signal source-body voltage without affecting gain.
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.