PLL Secondary Control Loop for VCO Noise and Temperature Drift
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Solution Overview
Problem
Phase-locked loop (PLL) systems face challenges due to VCO power supply noise and extreme temperature variations, which cause phase jitter and frequency shifts that exceed the control loop's compensation capacity, especially in applications requiring direct connections to noisy supplies and extreme temperature ranges.
Innovation Solution
A secondary control subsystem is introduced, connected to the primary control subsystem, which includes an analog-to-digital converter and a digital-to-analog converter to generate a secondary control signal that independently adjusts the VCO, providing additional compensation capacity and maintaining the primary control signal at its design value, thereby addressing frequency and phase changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a direct connection is made between the VCO and noisy power supply bump, then the VCO can be easily powered, but the PLL becomes exposed to noise-induced jitter
Solution Approach 1:
A noise filter circuit is introduced as an intermediary component between the noisy power supply bump and the VCO. This filter circuit removes noise from the power supply voltage before it reaches the VCO, thereby eliminating the harmful noise-induced jitter while maintaining the direct power connection architecture for ease of manufacture
2Device complexity
If the control loop voltage range is limited, then the circuit design is simplified, but the compensation capacity for extreme temperature variations is insufficient
Solution Approach 1:
The temperature compensation function is segmented into two independent parts: the primary control loop that handles routine phase adjustments with limited voltage range, and a secondary control subsystem that specifically handles extreme temperature compensation. This segmentation allows each subsystem to be optimized independently - the primary loop remains simple while the secondary loop provides extended temperature adaptability
3Reliability
If a secondary control subsystem is added, then the compensation capacity for frequency shifts is improved, but the device complexity increases
Solution Approach 1:
An intermediary transfer function is introduced that couples the primary and secondary control subsystems. This transfer function acts as a mediator that allows the secondary subsystem to compensate for frequency shifts beyond the primary loop's voltage range without requiring complete redesign of the control architecture. The intermediary function enables coordinated operation between the two subsystems, improving reliability while managing complexity through functional coupling rather than structural duplication
Data Source
AI summary
The phase-lock loop (PLL) can include a variable frequency oscillator adjustable to control the phase of the output signal; a primary control subsystem including a phase detector and a connection between the output signal and the phase detector, the phase detector generating a primary control signal to adjust the variable frequency oscillator; and a secondary control subsystem having an analog-to-digital converter and a digital-to-analog converter connected in series to receive the primary control signal and generate a secondary control signal also connected to independently adjust the variable frequency oscillator.