Folded Cascode Amplifier Circuit for Low-Voltage PAM4 Linearity
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Solution Overview
Problem
Amplifier circuits in reception circuits face challenges in maintaining linearity and high-frequency signal amplification due to nonlinearity in transistors, especially when handling PAM4 signals, which requires higher power supply voltage and increased load resistance, but this can lead to output common voltage decrease and transistor shutdown.
Innovation Solution
The implementation of a folded cascode amplifier circuit with inductors connected between folded nodes and output nodes to achieve linearity and high-frequency signal amplification without increasing the power supply voltage, using P-channel and N-channel transistors with current sources and load resistors, and incorporating inductors to form parallel resonant circuits to separate parasitic capacitance and boost source voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the power supply voltage is increased to expand the linear gain region, then the linearity of the amplifier circuit is improved, but the power consumption increases and the miniaturization benefit is reduced
Solution Approach 1:
The patent changes the circuit topology from a conventional differential pair amplifier to a folded cascode amplifier configuration. This structural parameter change allows the circuit to achieve wide linear gain region with lower power supply voltage by folding the cascode structure and using current sources at both input and output nodes, fundamentally altering how the amplifier operates to resolve the contradiction between linearity and power consumption
2Power
If the load resistance is increased to widen the output voltage range, then the gain is improved, but the output common voltage decreases causing transistors to stop operating
Solution Approach 1:
The patent introduces a current source connected to the output node as an intermediary element. This current source acts as a mediator that maintains the output common voltage at an appropriate level, preventing the voltage from dropping too low when load resistance is increased. The current source ensures that transistors remain in their active region while still achieving high gain through the folded cascode structure
3Measurement precision
If the power supply voltage is increased to maintain linearity for PAM4 signals, then the reception accuracy is improved, but the circuit complexity and voltage requirements increase
Solution Approach 1:
The patent fundamentally changes the amplifier configuration to a folded cascode structure with specific current sources positioned at strategic nodes. This parameter change in circuit topology enables the amplifier to achieve the linearity required for accurate PAM4 signal reception while operating with lower power supply voltage, thus improving reception accuracy without increasing device complexity or voltage requirements
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 configuration enables linear gain characteristics up to higher frequencies, maintaining good reception accuracy for high-frequency signals while operating at lower voltages, effectively addressing the linearity and voltage challenges in amplifier circuits.
Implementation Method 1
incorporating inductors to form parallel resonant circuits to separate parasitic capacitance and boost source voltages
Data Source
AI summary
There are an amplifier circuit which includes a first current source that is connected to a power supply line to which a first electric potential is supplied, a differential input circuit that is connected between the first current source and a first node and configured to receive a differential input signal, a second current source that is connected between a power supply line to which a second electric potential is supplied and the first node, and a load circuit that is connected between a power supply line to which the first electric potential is supplied and a second node, and an inductor circuit is further connected between the first node and the second node. Thereby, the amplifier circuit achieves both lower voltage and linearity.