DCO and TDC Frequency Characterization for Stable PLL Clocks
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Solution Overview
Problem
Phase locked loops (PLLs) face performance degradation due to shifts in the characteristics of digitally controlled oscillators (DCOs) and time to digital converters (TDCs) caused by process, voltage, and temperature variations, leading to noise and frequency distortions.
Innovation Solution
A system comprising a finite state machine (FSM) and a frequency measurement circuit (FMC) is used to characterize and calibrate DCOs and TDCs, compensating for PVT variations by adjusting gain and delay to maintain a constant overall gain, thereby mitigating frequency shifts and improving dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If DCO and TDC components are used in PLLs to generate high frequency clocks, then clock frequency and functionality are improved, but performance stability deteriorates due to PVT variations causing frequency shifts and noise
Solution Approach 1:
The patent performs frequency domain calibration and characterization of DCO and TDC components before actual PLL operation. By pre-measuring and storing the frequency responses and characteristics of these components under various PVT conditions, the system can compensate for their performance variations during operation, thereby maintaining clock stability despite environmental changes
Solution Approach 2:
The patent implements a feedback mechanism where the calibrated characteristics of DCO and TDC are used to adjust and optimize PLL performance in real-time. The system uses the pre-characterized frequency domain data to generate compensation signals that counteract the effects of PVT variations, ensuring stable clock output frequency and reducing noise
2Adaptability or versatility
If DCO gain is increased to improve frequency control range, then frequency tuning capability is improved, but noise and distortion increase due to component variations
Solution Approach 1:
The patent changes the operating parameters of DCO by applying calibration signals across different frequency ranges and measuring the actual frequency responses. Based on these measurements, the system adjusts DCO gain parameters to optimize the trade-off between frequency tuning capability and noise generation, ensuring minimal distortion across the entire tuning range
3Measurement precision
If TDC resolution is increased to improve time measurement precision, then time measurement capability is improved, but dynamic range is reduced due to quantization effects
Solution Approach 1:
The patent addresses the TDC resolution-dynamic range trade-off by moving from time domain analysis to frequency domain characterization. By measuring TDC performance in the frequency domain and analyzing its transfer function, the system can optimize TDC parameters to achieve both high resolution and wide dynamic range, as frequency domain measurements provide insight into the overall transfer characteristics rather than just single-point timing accuracy
Data Source
AI summary
A system for assigning a characterization and calibrating a parameter is disclosed. The system includes a frequency measurement circuit and a finite state machine. The frequency measurement circuit is configured to measure frequencies of an oscillatory signal and to generate a measurement signal including measured frequencies. The finite state machine is configured to control measurements by the frequency measurement circuit, to assign a characterization to a parameter based on the measurement signal, and to generate a calibration signal based on the characterized parameter.