Passive Balanced Mixer Circuit With Balun-Free RF/IF Isolation
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Solution Overview
Problem
Existing FET-based mixer circuits for low-bandwidth applications face challenges in achieving high isolation and linearity without increasing complexity, particularly due to the need for baluns at LO, RF, and IF frequencies.
Innovation Solution
A FET-based mixer circuit constructed solely of passive components, eliminating the need for baluns by using a synchronized FET pair to generate in-phase IF signals and employing a diplexer filter to separate RF and IF components, ensuring isolation without additional complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If baluns are added at LO, RF, and IF frequencies to achieve high isolation and linearity, then performance is improved, but device complexity increases
Solution Approach 1:
The patent extracts the balun functionality from the mixer circuit by using separate balanced output circuits that are coupled to the mixer through isolation elements. This removes the need for integrated baluns at LO, RF, and IF frequencies while maintaining the isolation and linearity benefits, thereby reducing device complexity without sacrificing performance
Solution Approach 2:
The patent introduces isolation elements as intermediary components between the mixer and the balanced output circuits. These isolation elements mediate the signal transmission while providing the necessary isolation and impedance transformation, replacing the need for complex integrated balun structures
2Ease of manufacture
If passive mixer components are used to reduce complexity, then ease of manufacture is improved, but isolation between ports deteriorates
Solution Approach 1:
The patent employs a composite structure combining passive mixer components with separate balanced output circuits and isolation elements. This composite architecture maintains the manufacturing simplicity of passive components while adding isolation capabilities through the structured combination of multiple functional blocks
Data Source
AI summary
Systems, circuits, and methods for mixing signals are provided. An illustrative circuit may include mixer circuitry including multiple inputs and at least one output, where the multiple inputs are connected across a local oscillator. The circuit may further include a terminal Radio Frequency (RF) output circuitry that is isolated from the local oscillator, where the at least one output of the mixer circuitry is directly connected to an input of the terminal RF output circuitry. The circuit may further include terminal Intermediate Frequency (IF) output circuitry that is isolated from the local oscillator, where the at least one output of the mixer circuitry is directly connected to an input of the terminal IF output circuitry.