Transformer-Coupled Active Mixer Downconverter for High Isolation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Radio frequency down converters face challenges with low dynamic range, high power consumption, and poor local oscillator port to radio frequency port isolation, which are not effectively addressed by current commutating Gilbert cell mixers.
Innovation Solution
An active mixer-based microwave down converter is designed with a transformer magnetically coupling a low noise amplifier to the mixer, and two biasing circuits with transistors operating in the saturation region and filters to reduce noise, improving biasing and isolating the LNA and mixer domains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional down converter designs are used, then dynamic range is improved, but power consumption increases and isolation between LO and RF ports deteriorates
Solution Approach 1:
The down converter is divided into functionally independent segments: LNA stage, mixer stage, and biasing circuits. Each segment is optimized independently for its specific function, allowing dynamic range enhancement in the LNA while controlling power consumption in the mixer through separate biasing networks.
Solution Approach 2:
Independent biasing circuits act as intermediaries between the power supply and the mixer transistors. These biasing circuits provide precise current control to the mixer while isolating the RF and LO ports, thereby achieving good isolation without compromising dynamic range and reducing overall power consumption.
2Measurement precision
If traditional down converter designs are used, then dynamic range is improved, but isolation between LO and RF ports deteriorates
Solution Approach 1:
The isolation problem is addressed by segmenting the biasing functions into separate circuits for the mixer stage. This segmentation allows independent optimization of isolation performance without affecting the dynamic range characteristics of the LNA and mixer stages.
Solution Approach 2:
Independent biasing circuits serve as intermediary networks between the power supply and mixer transistors. These biasing circuits provide current control while blocking unwanted signal coupling between LO and RF ports, thereby achieving high isolation without compromising dynamic range.
3Speed
If commutating Gilbert cell mixers are used, then switching speed is improved, but noise increases
Solution Approach 1:
Independent biasing circuits are introduced as intermediary networks between the power supply and the mixer transistors. These biasing circuits provide stable current sources that reduce noise while maintaining the fast switching characteristics of the Gilbert cell mixer structure.
Solution Approach 2:
The biasing circuits enable independent control of transistor operating parameters (current, voltage) to optimize the trade-off between switching speed and noise performance. By adjusting bias conditions, the mixer maintains high switching speed while operating in a lower noise regime.
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 achieves a high dynamic range while reducing power consumption and enhancing isolation between the LNA and mixer, improving signal-to-noise ratio and maintaining signal bandwidth.
Implementation Method 1
The transformer includes a primary winding and a secondary winding. The primary winding is coupled to receive the amplifier output signal... The secondary winding is coupled to the mixer...
Implementation Method 2
Each biasing circuit includes a transistor biased to operate in the saturation region as a current source and a filter to reduce the noise of the transistor acting as a current source.
Data Source
AI summary
A down converter, including first and second biasing circuits, mixer, and transformer coupled to receive amplifier output signal. The first and second biasing circuits each include a biasing transistor and a first and second node, respectively. Mixer includes first and second transistors coupled to first node and third and fourth transistors coupled to second node. The second and fourth transistors are coupled to a third node. The first and third transistors are coupled to a fourth node. Mixer also includes a first resistor coupled to the fourth node and a supply voltage node and a second resistor coupled to the third node and a supply voltage node. Transformer includes a primary winding coupled to receive the amplifier output signal and to a supply voltage and a secondary winding coupled to mixer and first biasing circuit at first node and coupled to mixer and second biasing circuit at second node.