SSB Modulator Feedback Calibration for Spur Suppression
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Solution Overview
Problem
Single Sideband (SSB) modulators experience degradation over time due to aging and environmental factors, leading to suboptimal suppression of unwanted signal components and local oscillator bleed-through, which affects the efficiency of communication networks.
Innovation Solution
The integration of an IF sampling receiver and a feedback control loop allows for dynamic and automatic adjustment of modulation parameters, such as phase shift and common mode voltage, to optimize the power levels of sidebands and reduce unwanted signal components, using a local RF processor to continuously monitor and adjust the signal parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a calibration procedure is performed to optimize amplitude, phase and common mode voltage settings, then sideband suppression and LO rejection are improved, but the system requires manual intervention and external equipment, and performance degrades over time due to aging and temperature effects
Solution Approach 1:
The patent implements an automatic calibration system that uses the output signal itself as a reference for feedback. The system measures the actual sideband power levels and LO leakage, then automatically adjusts the I/Q modulator parameters (amplitude, phase, common mode voltage) to optimize suppression. This closed-loop feedback mechanism eliminates the need for manual calibration with external equipment and maintains optimal performance despite aging and temperature variations.
Solution Approach 2:
The system performs self-calibration by using its own output signal as the measurement reference. The automatic calibration routine measures the modulator's own performance characteristics and adjusts its parameters without requiring external test equipment or manual intervention. This self-service capability enables the system to maintain optimal sideband suppression and LO rejection automatically over time.
2Measurement precision
If manual calibration is performed with external equipment, then initial sideband suppression is improved, but the system cannot adapt to changes caused by aging, temperature, and drift
Solution Approach 1:
The automatic calibration system continuously monitors the modulator's output and uses feedback to detect changes in sideband power levels and LO leakage caused by aging, temperature, or drift. The system automatically adjusts calibration parameters in response to these changes, maintaining optimal suppression performance without requiring external equipment or manual recalibration.
3Object-generated harmful factors
If high Q filter is used to ensure specification compliance, then unwanted signal components are reduced, but device complexity and potential signal distortion increase
Solution Approach 1:
The patent converts the potentially harmful unwanted signal components into useful calibration information. By measuring the actual sideband power levels and LO leakage, the system uses these signals to automatically adjust calibration parameters, thereby eliminating the need for complex high-Q filters while maintaining specification compliance through active parameter optimization.
Data Source
AI summary
An IF receiver receives a tapped portion of a modulated communication signal. A processor, local with respect to the IF receiver, receives an interrupt from a main processor instructing it to evaluate the power levels of desired and undesired components of the communication signal. The interrupt may be sent for a variety of reasons, such as according to a predetermined schedule, or in response to changes in a communication network, such as new equipment installation and temperature changes. The local processor instructs the IF receiver to tune it's LO so that the evaluation range of the receiver and feedback loop to parameter-adjustable components includes the frequency, or frequencies, of a specified signal component. The local processor evaluates the power level of the specified signal component. Based on the evaluation, the local processor instructs parameter-adjustable signal processing components to alter parameters to optimize characteristics of the communication signal for transmission.