Source-Degenerated Differential Amplifier for Process-Corner Gain Stability
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Solution Overview
Problem
Integrated circuit equalizer circuits and differential amplifiers face challenges in maintaining operating characteristics across process corners, particularly at high frequencies, due to variations in manufacturing processes.
Innovation Solution
Incorporating a source-side resistor circuit with transistors biased in a triode region, which includes a MOS transistor configuration that connects channel terminals to both source and bulk terminals, providing source degeneration and improving gain stability across process corners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional differential amplifiers are used in equalizer circuits, then the circuit can operate at high frequencies, but the operating characteristics vary across process corners
Solution Approach 1:
The patent changes the operating region parameter of the MOS transistors from saturation to triode region. By biasing the source-side resistor circuit transistors in the triode region, the resistance becomes less sensitive to process variations, thereby stabilizing the amplifier's operating characteristics across process corners while maintaining high-frequency operation capability
Solution Approach 2:
The patent introduces a source-side resistor circuit as an intermediary element between the input pair transistors and the rest of the amplifier circuit. This resistor circuit, implemented with MOS transistors in triode region, acts as a mediator that provides stable degeneration resistance to improve overall circuit stability across process variations
2Power
If source degeneration is applied to improve AC gain at high frequencies, then the gain at target frequencies improves, but the circuit becomes more sensitive to process variations
Solution Approach 1:
The patent changes the operating region parameter of the MOS transistors from saturation to triode region. By biasing the source-side resistor circuit transistors in the triode region, the resistance becomes less sensitive to process variations, thereby stabilizing the amplifier's operating characteristics across process corners while maintaining high-frequency operation capability
Solution Approach 2:
The patent introduces a source-side resistor circuit as an intermediary element between the input pair transistors and the rest of the amplifier circuit. This resistor circuit, implemented with MOS transistors in triode region, acts as a mediator that provides stable degeneration resistance to improve overall circuit stability across process variations
Data Source
AI summary
A differential amplifier includes an input pair of transistors with a source-side resistor circuit, having a transistor biased in a triode region, and a current source. The resistor circuit in combination with a capacitance, causes source degeneration in the amplifier. The source side resistor circuit includes a first MOS transistor having a first channel terminal connected to the source of a first transistor in the differential pair, and a second channel terminal connected to the bulk terminal, and a second MOS transistor having a first channel terminal connected to the source of a second transistor in the differential pair, and a second channel terminal connected to the bulk terminal. A bias circuit biases the first MOS transistor and the second MOS transistor in a triode region. The resistance of the source-side resistor circuit and the gain of the transistors in the differential amplifier can track across process corners.