Common-Gate Differential Amplifier With Body-Source Cross Coupling
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Solution Overview
Problem
Conventional differential amplifiers face a trade-off between increased gain due to body effect and reduced breakdown voltage, as the body effect enhances gain but lowers the breakdown voltage, particularly in common gate amplifiers.
Innovation Solution
The implementation of body-source cross coupling in common gate differential amplifiers, where the bodies of the common gate amplifiers are cross-coupled to the sources of opposite common gate amplifiers, allowing the potential of the body to equal that of the source, thereby increasing gain while alleviating breakdown voltage reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the body effect is utilized to improve gain in common gate amplifiers, then the gain increases, but the breakdown voltage of the transistor is reduced
Solution Approach 1:
The patent applies body-source cross coupling where the body of one transistor is connected to the source of another transistor in the differential pair. This inversion of the conventional body connection (where body is tied to source of the same transistor) enables the body effect to enhance gain while the cross-coupling configuration prevents breakdown voltage reduction by distributing the voltage stress across different transistor pairs.
2Reliability
If bodies are tied to sources to remove body effect, then breakdown voltage is maintained, but gain enhancement from body effect is lost
Solution Approach 1:
Instead of tying each body to its own source (conventional approach), the patent inverts the connection by cross-coupling bodies to opposite sources in the differential pair. This allows the body effect to be harnessed for gain enhancement while the differential configuration and cross-coupling topology maintain adequate breakdown voltage characteristics.
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 enhances the gain of differential amplifiers in both AC and DC modes, particularly in low current conditions, and reduces the breakdown voltage drop, making it suitable for low-power analog and RF circuits.
Implementation Method 1
the body effect improves a gain of the common gate amplifier, but reduces a breakdown voltage of the transistor, because the potential of the body is lower than that of the source
Data Source
AI summary
Disclosed herein is a differential amplifier using body-source cross coupling. In a common gate differential amplifier in which common gate amplifiers are implemented in a differential structure, since the bodies of the common gate amplifiers are cross coupled to the sources of the opposite common gate amplifiers, it is possible to increase transconductance due to body effect to improve a gain. Since the potential of the body is equal to that of the source in a DC mode, a breakdown voltage reduction problem is alleviated.