Variable Gain Amplifier Switching for Linearity at High Frequency
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Solution Overview
Problem
Conventional variable gain amplifier circuits face challenges in adjusting gain without reducing linearity, as adjusting transconductance decreases current and affects linearity, while signal bypassing introduces parasitic capacitance, limiting high-frequency operation.
Innovation Solution
A variable gain amplifier circuit design that achieves gain adjustment through the subtraction or addition of signals using a cascoded amplifier structure with gain switching circuits and switch sets, allowing for wide-range gain adjustment without changing the current through transistors, thus maintaining linearity and enabling high-frequency operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the gain is adjusted by adjusting transconductance, then the gain can be increased or varied, but the current flowing through the amplifier must be reduced which reduces the linearity of the amplifier
Solution Approach 1:
The amplifier is divided into multiple parallel signal paths (first amplifier path with first amplifier, second amplifier path with second amplifier). Each path has its own transistor operating at optimal current for linearity. The gain adjustment is achieved by selectively switching between these segmented paths rather than adjusting the current in a single path, thus maintaining linearity while providing gain variation.
2Reliability
If the gain is adjusted by way of signal bypassing, then the current flowing through the amplifier does not change and the linearity is maintained, but more signal bypass paths are needed for large gain range which generates extra parasitic capacitance making the amplifier unable to be operated at high frequency
Solution Approach 1:
The invention uses dynamic switching between fixed gain amplifier paths rather than static bypass paths. The switching circuit selectively connects the input signal to different amplifier paths based on the desired gain level. This dynamic approach achieves wide gain range adjustment without requiring multiple fixed bypass paths, thereby avoiding the accumulation of parasitic capacitance that would limit high-frequency operation.
3Adaptability or versatility
If more signal bypass paths are added for large gain range adjustment, then the gain range is increased, but extra parasitic capacitance is generated which prevents high frequency operation
Solution Approach 1:
The signal path is segmented into multiple parallel amplifier paths, each providing a specific gain level. By switching between these segmented paths, the system achieves wide gain range adjustment without accumulating parasitic capacitance from multiple bypass components. This segmentation approach maintains signal integrity at high frequencies while providing versatile gain control.
4Adaptability or versatility
If the current through transistors is changed for gain adjustment, then the gain can be varied, but the linearity of the amplifier is reduced
Solution Approach 1:
Multiple amplifier paths are provided, each with transistors operating at their optimal current levels for maximum linearity. The switching circuit enables a single amplifier system to provide multiple gain levels (first gain and second gain) without changing the operating current of any transistor. This multi-functional approach allows gain variability while maintaining optimal linearity across all gain settings.
Data Source
AI summary
A variable gain amplifier circuit is disclosed. The variable gain amplifier circuit includes a first transistor, a second transistor, a third transistor, a fourth transistor, a first gain switching circuit, and a second gain switching circuit. The first and the second transistors are respectively coupled to the first and the second nodes for receiving a differential input signal pair. The third transistor is coupled between the first node and a third node. The fourth transistor is coupled between the second node and a fourth node. The first gain switching circuit is coupled between the first node and the third node and further cross-coupled to the fourth node. The second gain switching circuit is coupled between the second node and the fourth node and further cross-coupled to the third node.