Cascade Amplifier Stage Layout for Low Distortion at High Output
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Solution Overview
Problem
Conventional amplifiers achieve low distortion only during predetermined input power but fail to maintain low distortion during high output operations, requiring large circuit sizes and mechanisms for distortion detection and adjustment.
Innovation Solution
The amplifier employs a cascade connection of first and second amplification circuits with specific capacitance characteristics, where the first amplification circuit has large gate-to-source and drain-to-source capacitance per unit gate width and small gate-to-drain capacitance, and the second amplification circuit has small gate-to-source and drain-to-source capacitance and large gate-to-drain capacitance, to maintain low distortion characteristics even at high output levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional amplifiers use distortion detection and adjustment mechanisms to achieve low distortion characteristics, then low distortion is achieved during predetermined input power, but the circuit size becomes large and low distortion cannot be maintained during high output operations
Solution Approach 1:
The invention changes the capacitance parameters of the amplification elements by selecting specific transistor types (e.g., HEMT vs. MOSFET) with different capacitance characteristics. The first amplification circuit uses transistors with larger gate-to-source and drain-to-source capacitance, while the second uses transistors with smaller gate-to-source capacitance but larger gate-to-drain capacitance. This parameter change allows the amplifier to maintain low distortion during high output operations without requiring complex distortion detection and adjustment mechanisms.
2Manufacturing precision
If conventional amplifiers use distortion detection and adjustment mechanisms, then low distortion is achieved during predetermined input power, but the mechanism complexity increases
Solution Approach 1:
The invention extracts and eliminates the distortion detection and adjustment mechanisms from the amplifier system. Instead of using active feedback control, the solution relies on the passive capacitance characteristics of the cascade-connected amplification circuits to inherently suppress distortion. This extraction of unnecessary mechanisms reduces system complexity while maintaining low distortion performance.
3Power
If conventional amplifiers operate in high output region with backoff amount equal to or less than 6 dB, then output power increases, but distortion characteristics deteriorate
Solution Approach 1:
The invention applies local quality by assigning different capacitance characteristics to different stages of the amplification circuit. The first amplification circuit (closer to input) uses transistors with larger gate-to-source and drain-to-source capacitance to provide linearization, while the second amplification circuit (closer to output) uses transistors with smaller gate-to-source capacitance to handle high output power. This localized optimization of capacitance properties enables the amplifier to maintain low distortion even when operating in the high output region with backoff amount equal to or less than 6 dB.
Data Source
AI summary
An amplifier includes: an input terminal; an output terminal; at least one first amplification circuit having a first amplification element; and at least one second amplification circuit having a second amplification element in which gate to source capacitance and drain to source capacitance per unit gate width are small relative to those of the first amplification element and in which gate to drain capacitance per unit gate width is large relative to that of the first amplification element, in an operation region where a backoff amount from a saturation output power point is less than or equal to 6 dB, in which the first amplification circuit and the second amplification circuit are cascade-connected in two or more stages between the input terminal and the output terminal, and an amplification circuit connected to the output terminal is one of the first amplification circuit and the second amplification circuit.