PLL Tuning Control With Elevator Voltage for Reduced Frequency Transients
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Phase-locked loops (PLLs) in temperature-controlled oscillators experience near-instantaneous frequency transients during phase locking, which can disrupt downstream systems like amplitude-and-phase noise-degeneration circuitry, particularly in sapphire oscillators, and reduce the ability to maintain phase lock under external disturbances.
Innovation Solution
A PLL design that reduces the magnitude of frequency transients by limiting the PLL filter output voltage swing relative to the tuning voltage range and uses an elevator voltage with a controlled slew rate to access the full oscillator tuning range, ensuring effective capture and phase lock maintenance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the PLL filter output voltage swing is limited relative to the tuning voltage range, then frequency transients are reduced, but the capture range and ability to maintain phase lock are reduced
Solution Approach 1:
The tuning voltage is segmented into two independent components: a PLL filter output voltage that provides fine frequency adjustment with limited swing, and an elevator voltage that provides coarse frequency adjustment with full range. This segmentation allows the fine control portion to remain small (reducing transients) while the coarse control portion handles the full tuning range (maintaining capture range and lock stability).
Solution Approach 2:
The elevator voltage acts as an intermediary that bridges the gap between the limited PLL filter output range and the full oscillator tuning range. By controlling the elevator voltage to have a limited slew rate, it mediates the frequency transition process, preventing direct large-swing transients while still enabling full capture range through the combined effect of both voltage components.
2Speed
If the filter bandwidth is increased to improve dynamic performance, then the PLL responds faster to frequency changes, but the capture range is reduced
Solution Approach 1:
The frequency control function is segmented between the filter-bandwidth-limited PLL filter output (providing fast dynamic response) and the elevator voltage (providing broad capture range). This allows the filter to be optimized for fast response without sacrificing capture range, as the elevator voltage compensates for the limited filter output swing during capture.
3Loss of time
If the oscillator frequency varies rapidly during startup, then the oscillator reaches operating temperature faster, but downstream systems cannot track the frequency changes
Solution Approach 1:
The elevator voltage with limited slew rate acts as an intermediary that smooths the frequency transition during oscillator startup. It allows the oscillator frequency to change rapidly (reducing startup time) while the elevator voltage's controlled rate of change prevents excessive transients that would disrupt downstream systems.
Data Source
AI summary
A phased locked loop (PLL) having a filter output voltage that is limited to a fraction of the voltage range accepted by the tuning port of a voltage-controlled oscillator (VCO) under control and a control system responsive to the filter output voltage and for summing the filter output voltage with an elevator voltage and applying the summed voltage to the VCO tuning port.