Scaled Replica Oscillator Loop for Accurate ILO Frequency Tracking
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Solution Overview
Problem
Achieving low jitter and accurate frequency tracking across process, voltage, and temperature (PVT) variations in injection locked oscillators (ILOs) is challenging due to changes in free-running frequency, which affects the performance of high-frequency low noise multi-phase clocks used in wireline and wireless systems.
Innovation Solution
A frequency tracking loop (FTL) apparatus is introduced, comprising a main oscillator and a replica oscillator, where the replica oscillator operates at a lower frequency to reduce power consumption and is calibrated to have an oscillator gain exactly scaled with respect to the main oscillator, using a digital calibration algorithm to compensate for gain and offset errors, thereby reducing spurious tones and improving locking frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a replica oscillator is used for frequency tracking in an injection locked oscillator, then frequency tracking accuracy is improved, but spurious tones are generated and locking frequency range is reduced
Solution Approach 1:
The patent uses a replica oscillator that copies the frequency characteristics of the main ILO oscillator to enable frequency tracking. The replica oscillator is designed to have matched frequency and gain characteristics, allowing it to accurately track PVT variations while operating independently to minimize spurious tone generation in the main signal path
Solution Approach 2:
The patent introduces an intermediary frequency detector and control mechanism that monitors the replica oscillator's frequency and uses feedback to adjust the main ILO oscillator's control voltage. This intermediary system enables indirect frequency tracking without directly coupling the replica oscillator to the main signal path, thereby reducing spurious tone generation
2Ease of operation
If the replica oscillator operates at the same frequency as the main oscillator, then frequency tracking is simplified, but power consumption increases
Solution Approach 1:
The patent changes the operating frequency parameter of the replica oscillator from matching the main oscillator frequency to operating at a lower frequency. The replica oscillator is designed with frequency-scaling circuitry that maintains matched frequency characteristics through control voltage adjustments, enabling power savings while preserving tracking accuracy
Solution Approach 2:
The patent implements dynamic frequency scaling where the replica oscillator's operating frequency can be adaptively adjusted based on operating conditions. The system dynamically changes the replica oscillator frequency to optimize the trade-off between tracking accuracy and power consumption, using control logic that monitors PVT variations and adjusts the replica frequency accordingly
3Device complexity
If the replica oscillator gain is not exactly scaled with respect to the main oscillator, then circuit complexity is reduced, but frequency tracking accuracy deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where the frequency detector continuously monitors the replica oscillator's output frequency and feeds this information back to the control voltage generator. The control voltage is dynamically adjusted based on the frequency error signal, ensuring that the replica oscillator gain remains exactly scaled with respect to the main oscillator despite PVT variations, thereby maintaining high tracking accuracy without requiring complex hardwired gain scaling circuits
Data Source
AI summary
An accurate replica oscillator-based frequency tracking loop (FTL) is provided. The replica oscillator used in the FTL can be at a lower frequency and therefore can consume much lower power compared to a main oscillator, such as an injection locked oscillator (ILO). The proposed FTL accurately sets the free running frequency of an ILO across process, voltage and temperature (PVT). Techniques are also provided to compensate the gain and offset error between the replica oscillator and the ILO.