PMOS Differential Amplifier for Low-Voltage Wide Input Range
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Solution Overview
Problem
Conventional differential amplifiers face difficulties in low-voltage operation due to the requirement of a high power supply voltage, which limits their ability to maintain a wide in-phase input voltage range.
Innovation Solution
A differential amplifier design that includes PMOS transistors as part of the differential input circuit, with a PMOS transistor acting as a bias current source and limiting the back-gate voltage of other PMOS transistors, allowing for lower power supply voltage operation while maintaining a wide in-phase input voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a diode-connected NMOS transistor is used to limit the back-gate voltage of PMOS transistors, then the offset voltage is suppressed and the in-phase input voltage range is widened, but the power supply voltage must be higher than the sum of gate-source voltages, making low-voltage operation difficult
Solution Approach 1:
The patent changes the type of transistor used for back-gate voltage limitation from NMOS to PMOS. This parameter change allows the circuit to operate with lower power supply voltage because the PMOS transistor's gate-source voltage requirement is compatible with low-voltage operation, while still achieving the back-gate voltage limitation function to suppress offset voltage and widen the in-phase input voltage range.
2Adaptability or versatility
If a diode-connected NMOS transistor is used to limit the back-gate voltage, then the in-phase input voltage range is widened, but the circuit requires high power supply voltage operation
Solution Approach 1:
The patent changes the transistor type parameter from NMOS to PMOS for the voltage limitation function. This enables the circuit to achieve wide in-phase input voltage range adaptation while operating at low power supply voltages, as the PMOS transistor's electrical characteristics are suitable for low-voltage operation unlike the NMOS-based conventional design.
3Use of energy by moving object
If the power supply voltage is reduced for low-voltage operation, then energy consumption is reduced, but the ability to maintain a wide in-phase input voltage range is compromised
Solution Approach 1:
The patent employs parameter change by switching from NMOS to PMOS transistor for the back-gate voltage limitation. This enables the circuit to operate at low power supply voltages while preserving the wide in-phase input voltage range, because the PMOS transistor maintains the necessary voltage limitation function without requiring high voltage headroom.
Data Source
AI summary
A differential amplifier includes first and second MOS transistors of a first conductivity type which constitute a differential input circuit, a bias current source which supplies a bias current to the first and second MOS transistors, and a third MOS transistor of the first conductivity type provided between the bias current source and the first and second MOS transistors and constituted to limit a back-gate voltage of the first and second MOS transistors.