PLL VCO Free-Running Voltage Circuit for Stable Unlock Frequency
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Solution Overview
Problem
Adjusting the constant free-running frequency of a voltage controlled oscillator (VCO) in a Phase-Locked Loop (PLL) is complicated due to the lack of a constant-current injection, unlike current controlled oscillators, which makes it harder to maintain a stable frequency when the PLL is not in a locked state.
Innovation Solution
A buffered voltage signal is provided to the VCO, using a configuration with differential amplifiers and pass transistors to ensure a constant free-running voltage, allowing the VCO to maintain a stable frequency by selecting between a control signal and a constant signal based on their voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a simple constant-current injection branch is used in a current controlled oscillator, then the free-running frequency is easily maintained, but the same approach cannot be applied to voltage controlled oscillators due to lack of constant-current injection capability
Solution Approach 1:
The patent replaces the current-based control mechanism with a voltage-based control mechanism. Specifically, it substitutes the constant-current injection branch (used in CCOs) with a constant-voltage injection branch in VCOs. The buffered voltage component generates a constant free-running voltage signal that can be injected into the VCO, enabling the same free-running frequency maintenance functionality to work with voltage-controlled oscillators instead of being limited to current-controlled oscillators.
2Reliability
If the control-current Icont reaches zero in a current controlled oscillator, then the constant-current Iconst ensures the oscillator continues to deliver a free running frequency signal, but implementing the same in voltage controlled oscillators is complicated
Solution Approach 1:
The patent introduces a buffered voltage component as an intermediary element between the filter component and the voltage controlled oscillator. This buffered voltage component contains a constant voltage source that generates a free-running voltage signal. When the control voltage from the filter drops (analogous to control current reaching zero), the buffered voltage component maintains the VCO operation by providing its constant free-running voltage signal, ensuring continuous frequency delivery without requiring complex direct voltage control circuitry.
3Stability of the object's composition
If a buffered voltage component is added to provide constant free-running voltage to a VCO, then temperature and process independence is achieved, but the device complexity increases
Solution Approach 1:
The buffered voltage component is designed with dynamic switching capability using differential amplifiers and pass transistors. It can dynamically select between providing a constant free-running voltage signal or passing through the control voltage from the filter, depending on the operational state of the PLL. This dynamic behavior allows the component to adapt to different operating conditions (locked vs. unlocked state) while maintaining temperature and process independence, reducing the need for additional static complexity.
Data Source
AI summary
This disclosure relates to a Phase-Locked Loop (PLL) device and a method for providing a stable free-running voltage signal to a voltage controlled oscillator.