Tunable Filter Alignment Using Internal Noise Reference
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Solution Overview
Problem
Tunable filters in spectrum analyzers, such as YIG tuned filters, experience tuning inaccuracies due to non-linear frequency-versus-tuning-current responses and variations with temperature and age, leading to calibration errors and increased costs associated with frequent calibration.
Innovation Solution
A method involving an internal noise source and memory device to align the tuning response of the tunable filter by measuring gain alignment parameters at multiple frequencies and storing them in an alignment table for correction during measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration methods are used with external signal generators, then initial calibration accuracy can be achieved, but frequent recalibration is required due to tuning drift with temperature and age
Solution Approach 1:
The patent performs alignment measurements at multiple frequencies during manufacturing to establish baseline tuning response characteristics before the instrument is deployed. This preliminary characterization of the tunable filter's behavior across its operating range enables the system to compensate for future drift without requiring external calibration equipment, thereby reducing recurring calibration time and cost while maintaining measurement precision
Solution Approach 2:
The patent creates an internal alignment table that stores the tunable filter's original tuning response characteristics as a reference model. During operation, the system compares actual tuning behavior against this stored copy to detect and correct drift, eliminating the need for repeated external calibration while preserving measurement accuracy
2Ease of manufacture
If alignment measurements are performed at only one frequency, then the alignment process is simple and quick, but tuning inaccuracies at other frequencies are not compensated
Solution Approach 1:
The patent divides the frequency range into multiple discrete alignment frequencies and performs separate alignment measurements at each point. By segmenting the frequency spectrum and characterizing the tunable filter's behavior at each segment, the system achieves comprehensive coverage of the operating range, ensuring accurate tuning compensation across all frequencies while maintaining a systematic and manageable alignment process
Data Source
AI summary
A method is provided for aligning a measurement instrument that includes a tunable filter. The method includes: (i) applying an output signal of an internal noise source of the measurement instrument to the input of the tunable filter, (ii) applying a control signal to the tunable filter to tune the tunable filter to a selected alignment frequency, (iii) measuring a value for a gain alignment parameter of the tunable filter while the output signal of the internal noise source is applied to the input of the tunable filter and the control signal is applied to the tunable filter, (iv) storing the measured gain alignment parameter value in an alignment table in the memory device, and (v) repeating steps (ii) through (iv) for a plurality of selected alignment frequencies in an operating frequency range of the tunable filter.