Complex IF Mixer Imbalance Correction for Higher Image Rejection
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Solution Overview
Problem
Existing receiver architectures suffer from gain and phase imbalances in RF mixers, leading to image-rejection ratio (IRR) limitations, which cause interference between frequency carriers, especially when carriers have different bandwidths, resulting in performance degradation.
Innovation Solution
A complex intermediate frequency mixer with quadrature phase local oscillator signals and gain adjusting components is used to down-convert signals to baseband, allowing for compensation of gain and phase imbalances, reducing power consumption and improving performance by correcting imbalances at baseband frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional RF quadrature mixer is used for frequency translation, then the device complexity is low, but gain and phase imbalances occur leading to poor image-rejection ratio (30-40 dB)
Solution Approach 1:
The mixer is divided into multiple parallel paths (first-phase path and second-phase path), each with separate mixers and gain adjusting components. This segmentation allows independent control of gain and phase for each path, enabling precise imbalance compensation while maintaining modular structure
Solution Approach 2:
Gain adjusting components are introduced in advance to pre-compensate for gain and phase imbalances before the mixing operation. This preliminary adjustment ensures that the imbalances are corrected proactively rather than requiring complex post-processing
2Reliability
If the image-rejection ratio is improved by adding correction components, then the performance increases, but the device complexity increases due to additional gain adjusting components and summing units
Solution Approach 1:
The gain adjusting components serve multiple functions: they adjust the amplitude of individual mixer outputs and compensate for both gain and phase imbalances simultaneously. The summing units also perform multiple roles by combining signals and enabling differential operation, reducing the need for separate compensation circuits
3Adaptability or versatility
If gain and phase imbalances are not compensated, then the device complexity remains low, but carriers with different bandwidths interfere with each other due to limited IRR
Solution Approach 1:
The patent implements a feedback mechanism where the output signals from multiple mixers are summed and fed back through gain adjusting components. This closed-loop approach allows continuous compensation of gain and phase imbalances, ensuring high image-rejection ratio across different carrier bandwidths and preventing carrier interference
Data Source
AI summary
A complex intermediate frequency mixer (IFM) for frequency translating a received complex intermediate frequency, IF, signal, wherein the received complex IF signal comprises at least two frequency bands located at upper-side and lower-side of 0 Hz, is provided. The complex intermediate frequency mixer comprises a first, second, third and fourth mixer (M1, M2, M3, M4). The complex intermediate frequency mixer further comprises a first, second, third and fourth gain adjusting component (α1, α2, δ2, δ1), connected to a first, second, third and fourth mixer output (M1-out, M2-out, M3-out, M4-out), respectively. Moreover, a first summing unit (S1), connected to a first gain output (α1-out), a fourth gain output (δ1-out) and a third mixer output (M3-out) negated, and second summing unit (S2), connected to the second gain output (α2-out), the third gain output (δ2-out) and the fourth mixer output (M4-out), are configured to output a first baseband complex signal of the received complex IF signal.