RF Transceiver DAC Image Calibration for Transmit QEC
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Solution Overview
Problem
Existing radio transceivers face challenges in effectively reducing undesired image signal components due to gain and phase mismatches in in-phase and quadrature signals, which interfere with the transmit signal and hinder accurate quadrature error correction.
Innovation Solution
A calibration subsystem for RF transceivers employs a tunable filter and DAC tuning to isolate and attenuate undesired sideband DAC images, allowing the QEC algorithm to precisely correct I/Q imbalances without affecting the desired signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If quadrature error correction is performed using standard methods, then I/Q imbalances are corrected, but undesired DAC image signals alias coherently and interfere with the correction process
Solution Approach 1:
The patent extracts and isolates the harmful DAC image signals from the observation channel by identifying their specific frequency locations. A tunable filter is applied to separate these image signals from the desired transmit signal, allowing the QEC algorithm to process only the clean signal components and ignore the aliased images.
Solution Approach 2:
The patent introduces an intermediary filtering stage between the ADC observation channel and the QEC algorithm. This filter acts as a mediator that removes the harmful DAC image components before they can interfere with the QEC process, while preserving the integrity of the desired signal for correction.
2Productivity
If the observation ADC samples at a rate related by a rational fraction to the DAC sampling rate, then aliasing occurs, but this aliasing causes coherent addition of image signals that reduce QEC effectiveness
Solution Approach 1:
The patent converts the harmful aliasing effect into a beneficial separation mechanism. By deliberately sampling at a rational fraction rate relationship, the DAC image signals alias to specific, predictable frequency locations. The tunable filter then exploits this predictable aliasing behavior to isolate and remove only the image components while preserving the desired signal.
3Object-generated harmful factors
If sideband filtering is applied to reduce undesired images, then image rejection improves, but the filter must be precisely tuned to avoid affecting the desired signal
Solution Approach 1:
The patent employs a tunable filter whose center frequency can be dynamically adjusted based on the specific rational fraction sampling rate relationship in use. This dynamic tuning capability allows the filter to adapt to different operating conditions and precisely target the aliased image frequencies without requiring fixed, overly selective filter designs.
Data Source
AI summary
A method of operating a radio frequency (RF) transceiver includes transmitting a narrowband calibration signal using a transmit channel of the RF transceiver, wherein a transmitted output signal includes a sideband of the calibration signal and a sideband of a digital-to-analog converter (DAC) image signal produced by DAC circuitry of the transmit channel; sampling the transmitted output signal using an analog-to-digital converter (ADC) circuit; filtering the transmitted output signal sampled by the ADC circuit to reduce power of the sideband of the calibration signal; attenuating DAC signals produced by the DAC circuitry to reduce power of the sideband of the DAC image signal; restoring the power of the sideband of the calibration signal sampled by the ADC circuit; and performing quadrature error correction (QEC) using the output of the ADC circuit.