Differential Current Conveyor Circuit for RF Load Isolation
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Solution Overview
Problem
Current direct conversion receivers in cellular communications devices face challenges in achieving low input impedance, high output impedance, and high bandwidth while maintaining low power dissipation, especially in current conveyor circuits used for RF signal processing.
Innovation Solution
The implementation of a current conveyor circuit with cascode structures and cross-coupled transistors, coupled with channel filters and variable gain amplifiers, to create a differential current conveyor with low input impedance and high output impedance, enhancing signal processing and isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional current conveyor circuits are used in direct conversion receivers, then signal processing functions are performed, but input impedance is high and output impedance is low which causes poor load isolation
Solution Approach 1:
The patent inverts the conventional current conveyor impedance characteristics by swapping the input and output impedance roles. The first current conveyor is configured with low input impedance and high output impedance, while the second current conveyor has high input impedance and low output impedance. This inversion resolves the load isolation problem by ensuring proper impedance matching and isolation between stages.
Solution Approach 2:
The patent employs asymmetric configuration of the two current conveyors with opposite impedance characteristics. The first current conveyor uses a specific transistor arrangement to achieve low input and high output impedance, while the second current conveyor uses a mirrored arrangement to achieve high input and low output impedance. This asymmetric design enables both good load isolation and proper signal transmission.
2Speed
If bandwidth is increased in current conveyor circuits, then signal processing capability is improved, but power dissipation increases
Solution Approach 1:
The patent divides the current conveyor function into two separate current conveyors with specialized roles. The first current conveyor handles the input stage with optimized bandwidth characteristics, while the second current conveyor handles the output stage. This segmentation allows each stage to be optimized for bandwidth with minimal power consumption, rather than requiring the entire circuit to operate at high power for high bandwidth.
Solution Approach 2:
The patent changes the operating parameters of the current conveyors by using opposite impedance configurations. The first current conveyor operates with low input impedance and high output impedance, while the second operates with high input impedance and low output impedance. This parameter change enables bandwidth optimization in each stage without requiring excessive power dissipation across the entire circuit.
Data Source
AI summary
A system includes a first variable gain amplifier configured to receive an input signal and a first down-mixer coupled to the first variable gain amplifier. Also, the system includes a first current conveyor coupled to the first down mixer, where the first current conveyor includes a first cascode and a second cascode coupled to the first cascode. Additionally, the system includes a first channel filter coupled to the first current conveyor and a second variable gain amplifier coupled to the first channel filter.