RF Signal Generator Calibration for Spur and Image Suppression
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Solution Overview
Problem
Conventional RF signal generators face challenges in suppressing unwanted sideband images and spurious signals due to amplitude and phase imbalances in I/Q signal components, which are typically addressed using costly and power-intensive on-chip or off-chip calibration instrumentation, particularly at cryogenic temperatures.
Innovation Solution
A low-power and small-footprint calibration system that adjusts differential signal paths and local oscillator signals using digitally controllable current actuators and sensors to balance amplitudes and phases, correcting DC offsets and duty cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional on-chip or off-chip calibration instrumentation is used to detect and calibrate amplitude and phase imbalances, then measurement precision is improved, but device complexity and power consumption increase significantly
Solution Approach 1:
The patent extracts the essential calibration function from complex RF measurement instrumentation and implements it using simple DC voltage measurements. Instead of using sophisticated spectrum analyzers or vector network analyzers, the invention extracts baseband signal components and measures their DC voltages to determine amplitude and phase imbalances, thereby eliminating the need for complex calibration instrumentation.
Solution Approach 2:
The patent replaces complex RF measurement systems with simple voltage measurement circuits. Instead of using RF down-conversion receivers, spectrum analyzers, or other sophisticated electronic measurement equipment, the invention uses basic voltage probes and DC voltmeters to measure the baseband signal components, substituting mechanical/electronic complexity with simple electrical measurement.
2Measurement precision
If conventional RF measurement calibration systems are implemented, then measurement precision is improved, but power consumption increases significantly
Solution Approach 1:
The patent extracts the calibration measurement function from power-intensive RF measurement equipment and implements it using minimal-power DC voltage measurements. By extracting baseband signal components and measuring their DC voltages, the system achieves accurate amplitude and phase imbalance detection without requiring the significant power consumption of conventional RF spectrum analyzers or vector network analyzers.
3Device complexity
If single-ended baseband filter structures are used, then device complexity is reduced, but manufacturing precision deteriorates due to inherent amplitude imbalances
Solution Approach 1:
The patent implements a feedback mechanism where DC voltage measurements of the baseband signal components are used to detect amplitude imbalances between I and Q channels. These measurements provide feedback information that can be used to adjust and correct the imbalances, thereby maintaining manufacturing precision even when using simpler single-ended baseband filter structures.
Solution Approach 2:
The patent replaces complex differential filter structures with simpler single-ended filters and compensates for the resulting amplitude imbalances using electronic adjustment based on DC voltage measurements. This substitution approach maintains manufacturing precision through measurement and correction rather than relying on precise mechanical or electrical symmetry in the filter design.
4Reliability
If DC offset calibration is performed, then reliability is improved by suppressing LO leakage spurs, but device complexity increases
Solution Approach 1:
The patent extracts the DC offset calibration function from complex calibration systems and implements it using simple DC voltage measurements of the baseband signal components. By measuring the DC voltage levels and adjusting the offset accordingly, the system achieves effective LO leakage spur suppression without requiring sophisticated calibration circuitry.
Data Source
AI summary
A device comprises a radio frequency (RF) signal generator and a calibration system. The RF signal generator is configured to upconvert a baseband signal to an RF signal using first and second LO signals. The RF signal generator comprises first and second signal paths to process first and second differential signals. The calibration system comprises calibration control circuitry and actuator circuitry. In response to digital control signals generated by the calibration control circuitry, the actuator circuitry is configured to: inject currents into the first and second signal paths to adjust offsets of the first and second differential signals, and to balance amplitudes of the first and second differential signals; and adjust at least one of respective duty cycles of the first and second local oscillator signals, and a phase difference between the first and second local oscillator signals.