Frequency Estimation Circuit Using TDC Phase Samples for Agile Measurement
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Solution Overview
Problem
Existing digital frequency measurement techniques face a trade-off between resolution and measurement time, leading to slow measurement speeds and potential inaccuracies due to environmental frequency drift, especially in agile frequency applications.
Innovation Solution
The integration of a time-to-digital converter (TDC) with a cycle counter to provide an optimal fractional frequency estimate, enhancing measurement precision and speed by using phase samples and resolving aliasing ambiguities, allowing for more precise and agile frequency estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a digital cycle counter is used for frequency measurement, then measurement resolution can be improved, but measurement time increases significantly
Solution Approach 1:
The frequency measurement is segmented into two parts: integer frequency measurement using a cycle counter and fractional frequency measurement using a TDC. The cycle counter measures the integer part of the frequency by counting complete cycles, while the TDC measures the fractional part by measuring phase differences. This segmentation allows each component to operate efficiently within its optimized range, achieving high overall resolution without requiring extremely long measurement times.
Solution Approach 2:
A time-to-digital converter (TDC) is introduced as an intermediary device to measure the fractional frequency component. The TDC converts time/phase differences into digital values, serving as a bridge between the analog phase information and the digital frequency measurement. This intermediary enables precise measurement of the fractional part that the cycle counter alone cannot capture, thereby improving overall measurement resolution without proportionally increasing measurement time.
2Measurement precision
If measurement time is extended to improve resolution, then frequency precision improves, but environmental frequency drift causes inaccuracies
Solution Approach 1:
By segmenting the measurement into integer and fractional components, the system can achieve high precision quickly without requiring long measurement times that would expose the system to environmental drift. The fractional measurement through TDC provides the necessary precision in a short time window, reducing the impact of frequency drift during measurement.
Solution Approach 2:
The system performs preliminary frequency estimation using the fractional measurement capability of the TDC to quickly establish an initial accurate frequency value. This preliminary action provides a head start on achieving precise measurement before environmental conditions can significantly alter the frequency being measured, thereby maintaining reliability under drift conditions.
3Productivity
If a standard cycle counter is used, then device complexity remains low, but measurement agility and speed are limited
Solution Approach 1:
A time-to-digital converter (TDC) is introduced as an intermediary device to measure the fractional frequency component. The TDC converts time/phase differences into digital values, serving as a bridge between the analog phase information and the digital frequency measurement. This intermediary enables precise measurement of the fractional part that the cycle counter alone cannot capture, thereby improving overall measurement resolution without proportionally increasing measurement time.
Solution Approach 2:
The combined measurement system serves multiple functions: it performs both integer and fractional frequency measurement, provides high-speed agile measurements, and maintains compatibility with existing cycle counter infrastructure. The TDC can operate in conjunction with the cycle counter to provide enhanced functionality while the cycle counter continues to handle the integer measurement task, creating a multi-functional measurement system.
Data Source
AI summary
An apparatus for generating a frequency estimate of an output signal includes a reference signal generator configured to generate a reference clock signal. The apparatus includes frequency estimation circuitry configured to generate a cycle count based frequency estimation of the output signal based on the reference clock signal and a clock cycle count of the output signal. The frequency estimation circuitry further generates a fractional frequency estimation of the output signal based on the reference clock signal and a plurality of time-to-digital conversion phase samples of the output signal. The frequency estimation circuitry further generates the frequency estimate of the output signal using the cycle count based frequency estimation within a range and a frequency error determined from the fractional frequency estimation. The plurality of time-to-digital conversion phase samples and the cycle count based frequency estimation use a same number of reference clock cycles of the reference clock signal.