Transformer-Coupled RF Mixer Circuit for Low-Noise Linearity
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Solution Overview
Problem
Conventional RF mixers, such as the Gilbert cell mixer, suffer from noise issues, lower power gain, and impedance mismatch, leading to increased noise levels and limited power handling capabilities.
Innovation Solution
The proposed RF mixer apparatus employs a plurality of transformers and commutator cells, with each transformer having a primary and secondary connected in series, and commutator cells coupled to both local oscillator and intermediate frequency ports in parallel, along with an amplifier mechanism and filter mechanisms to provide impedance matching and variable gain, enabling improved power handling and linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a Gilbert cell mixer is used, then frequency conversion is achieved, but noise figure increases to eight to ten decibels and power gain decreases
Solution Approach 1:
The RF mixer is divided into multiple commutator cells (first, second, third, and fourth commutator cells) that are coupled in parallel. Each commutator cell is further divided into quadrants with transistors operating at different phases. This segmentation allows the noise from individual cells to be distributed and combined constructively, improving the overall noise figure while maintaining power gain through parallel operation.
Solution Approach 2:
Multiple commutator cells are combined in parallel configuration, where the outputs of individual cells are summed at the IF port. The transformers combine the signals from multiple cells constructively for the desired frequency component while combining noise from independent cells, which improves the signal-to-noise ratio. The amplifier mechanism also combines currents from multiple transformer secondaries to achieve higher power gain.
2Ease of operation
If the transconductor is loaded by low impedance of the quad core, then mixing is achieved, but impedance mismatch occurs
Solution Approach 1:
Transformers are introduced as intermediary components between the commutator cells and the amplifier mechanism. These transformers provide impedance transformation to match the low impedance of the commutator cell outputs to the higher impedance required by the amplifier input. The transformers act as mediators that enable proper power transfer and impedance matching without directly connecting the mismatched components.
Solution Approach 2:
The impedance parameters are transformed through the use of transformers with specific turns ratios. The transformers change the impedance level from the low impedance of the commutator cells to the optimal impedance for the amplifier, thereby improving both impedance matching and linearity. This parameter transformation allows the system to operate in the optimal impedance regime for both stages.
3Power
If DC level is increased to improve power handling, then power handling improves, but distortion increases
Solution Approach 1:
The total DC current is divided and distributed across multiple commutator cells operating in parallel. Each cell handles a portion of the total power, allowing the system to achieve high power handling capability without requiring any single transistor or cell to operate at excessively high DC levels. This distribution prevents individual components from entering distortion-prone operating regions.
Solution Approach 2:
The mixer employs dynamic switching of transistors between different operating states during each RF cycle, with transistors switching between cutoff and active regions. This dynamic operation allows the system to handle large input signals without sustained operation in the nonlinear region, thereby maintaining low distortion while achieving high power handling capability through the switching action.
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 enhances power handling, increases the input intercept point, and improves impedance matching, resulting in reduced noise figures and increased linearity, allowing the RF mixer to operate effectively with higher DC levels and larger input power without distortion.
Implementation Method 1
Each of the plurality of transformers includes a primary and a secondary
Implementation Method 2
an amplifier mechanism connected across the series connection of the primaries of the plurality of transformers
Data Source
AI summary
Embodiments of power efficient radio mixers are provided. A generalized impedance matched low-voltage active mixer circuit technique, which utilizes a plurality of commutator cells and transformers, is disclosed. The low voltage active mixer function is coupled to an impedance matched amplifier allowing for insertion of image rejection filtering between the amplifier and the mixing function. The commutator cells can be driven in parallel by common local oscillator (LO) and intermediate frequency (IF) ports combined in parallel to yield highly linear mixers. A multi-channel receiver with a common impedance matched radio frequency (RF) amplifier driving a plurality of commutator cells with multiple LOs and IFs is also disclosed.