Analog Frequency Conversion Feedback for Transmitter Spur Calibration
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Solution Overview
Problem
Direct upconversion transmitters face challenges in calibration due to analog imperfections, requiring expensive ideal receivers and time-consuming recursive algorithms to suppress spurs, and there is a need for a simpler method to determine and compensate device characteristics without such receivers.
Innovation Solution
An electrical device with analog conversion circuitry that feeds back a portion of its output signal as input, allowing for the double exposure to non-idealities, enabling the derivation of device characteristics and precompensation without an ideal receiver, using feedback circuitry and characterization blocks to determine and correct for errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an expensive ideal receiver is used to measure spurs, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The transmitter uses itself to measure its own spur characteristics by feeding back the RF output signal through the same frequency conversion circuitry, eliminating the need for an external ideal receiver. The system performs self-characterization by processing the feedback signal through the analog conversion circuitry and deriving spur parameters from the resulting baseband signal.
Solution Approach 2:
The frequency conversion circuitry serves dual purposes: it performs both the upconversion function and the downconversion measurement function. The same analog conversion circuitry used for signal generation is reused for characterizing spurs, making the measurement system universal and eliminating the need for separate specialized measurement equipment.
2Manufacturing precision
If a recursive trial-and-error algorithm is used to determine optimal baseband corrections, then manufacturing precision is improved, but loss of time increases
Solution Approach 1:
The system performs preliminary characterization by measuring the RF output signal and deriving spur parameters (amplitude, phase, frequency) before applying corrections. By obtaining complete characterisation data upfront through feedback measurement, the system can calculate optimal baseband corrections directly without requiring iterative trial-and-error adjustments, significantly reducing calibration time while maintaining precision.
3Measurement precision
If additional frequency conversion circuitry is added for measurement, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The measurement and correction functions are merged into the existing transmitter architecture. The feedback path combines the RF output signal with the baseband input signal, and the same analog conversion circuitry processes both transmission and measurement signals, eliminating the need for separate dedicated measurement circuitry and reducing overall device complexity.
Data Source
AI summary
An electrical device comprises analog conversion circuitry having an input and an output. The electrical device is essentially provided for converting a first input signal within a first frequency range applied to the input to a first output signal within a second frequency range different from the first frequency range at the output. The electrical device further comprises a signal adding means for adding at least a portion of the first output signal as second input signal to the first input signal. The analog conversion circuitry is also capable of converting the second input signal, which is within the second frequency range, back to the first frequency range. Additionally, a characteristic deriving means is provided for deriving at least one characteristic of the electrical device from the frequency converted second input signal, which appears at the output of the analog conversion circuitry.