Fractional-Cycle Frequency Estimation for Fast Calibration
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Solution Overview
Problem
Conventional frequency estimation methods face a trade-off between speed and accuracy, as the accuracy is inversely proportional to the measurement time period, limiting the speed of calibration and resulting in significant errors in frequency estimation.
Innovation Solution
A frequency estimator that counts an integer number of full cycles and measures a fraction of a cycle during a predetermined measurement time period, utilizing a synchronizer, counter, Time-to-Digital Converters (TDC), and a processor to determine the estimated frequency, improving resolution and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a counter is used to count integer cycles for frequency estimation, then the measurement can be performed with simple hardware, but the accuracy is limited and inversely proportional to the measurement time period
Solution Approach 1:
The frequency measurement is segmented into two independent parts: an integer counter for full cycles and a TDC for fractional cycles. This segmentation allows each component to optimize for its specific function, with the counter handling the integer portion and the TDC capturing the fractional portion, thereby improving overall measurement accuracy without extending the measurement time period.
Solution Approach 2:
The invention adds a temporal dimension to the measurement by capturing the fractional cycle information through the TDC. Instead of only measuring complete cycles over time, the system now measures both the integer count and the fractional remainder within the same measurement window, effectively adding a new dimension of precision to the frequency estimation.
2Measurement precision
If the measurement time period is extended to improve accuracy, then the frequency estimation becomes more precise, but the calibration speed decreases
Solution Approach 1:
By segmenting the measurement into integer and fractional components, the system achieves high accuracy without requiring extended measurement times. The TDC captures the fractional cycle information instantaneously, allowing the calibration to complete quickly while maintaining high precision.
Solution Approach 2:
The invention replaces the traditional mechanical counting approach with a hybrid system that uses a TDC to measure fractional cycles. This substitution enables the system to achieve high measurement precision without the need for prolonged measurement periods, thereby maintaining fast calibration speed.
3Measurement precision
If only integer cycle counting is used, then the device complexity remains low, but the frequency estimation error remains significant (2 MHz)
Solution Approach 1:
The measurement system is segmented into two independent components: a simple integer counter and a fractional TDC. This segmentation allows the system to achieve high accuracy (reducing error from 2 MHz to 10 kHz) while keeping each component relatively simple and manageable.
Solution Approach 2:
The TDC measurement of fractional cycles is nested within the overall frequency measurement process that already includes the integer counter. This nested structure allows the fractional measurement to complement the integer counting without requiring a complete redesign of the measurement system, thereby limiting the increase in device complexity.
Data Source
AI summary
A frequency estimator for estimating a frequency, including a counter configured to count an integer number of full clock cycles during a measurement time window; a Time-to-Digital Converter (TDC) configured to measure a fraction of a clock cycle during the measurement time window; and a processor configured to determine the estimated frequency based on the counted number of full clock cycles and the measured fraction of the clock cycle.