PLL Filter With Variable Resistance for Constant Damping Ratio
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Solution Overview
Problem
Conventional phase-locked loop (PLL) circuits experience variability in damping ratio due to fabrication process variations and operational changes, affecting stability and transient response.
Innovation Solution
Incorporating a variable resistive element in the low pass filter, where the resistance is modulated by the charge pump current, using a MOS transistor biased in the linear region to maintain a constant damping ratio independent of process and operational variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional low pass filter with fixed resistor is used in the PLL circuit, then the circuit structure is simple, but the damping ratio varies widely due to fabrication process variations and operational voltage/temperature changes
Solution Approach 1:
The patent applies the Dynamics principle by replacing the fixed resistor with a variable resistance element whose resistance can be dynamically adjusted. The resistance is modulated by a control signal derived from the charge pump current, allowing the low pass filter to adapt its damping characteristics in real-time to compensate for process variations and environmental changes, thereby maintaining a constant damping ratio.
Solution Approach 2:
The patent implements Feedback by using the charge pump current as a reference to generate a control signal that modulates the resistance of the variable resistance element. This feedback mechanism ensures that the damping ratio remains constant by automatically adjusting the resistance in response to changes in charge pump current, compensating for fabrication variations and operational conditions.
2Reliability
If the resistance in the low pass filter is made variable to compensate for process variations, then the damping ratio stability is improved, but the circuit complexity increases
Solution Approach 1:
The patent uses an intermediary approach by introducing a control signal as a mediator between the charge pump current and the variable resistance element. This control signal, generated through a straightforward relationship with the charge pump current, simplifies the control mechanism while achieving the desired damping ratio stability, thus limiting the increase in circuit complexity.
3Speed
If the resistance is modulated by charge pump current to maintain constant damping ratio, then the transient response is improved, but the sensitivity to operational voltage variations increases
Solution Approach 1:
The patent applies Parameter changes by modulating the resistance parameter of the low pass filter based on the charge pump current. This dynamic adjustment of the resistance parameter enables the circuit to maintain optimal transient response characteristics across different operating conditions. The charge pump current serves as a reference that automatically compensates for voltage variations, reducing the harmful effects of voltage sensitivity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures a stable and consistent damping ratio, enhancing the PLL circuit's stability and transient response by decoupling the damping ratio from resistance and charge pump current variations.
Implementation Method 1
using a MOS transistor biased in the linear region to maintain a constant damping ratio independent of process and operational variations
Data Source
AI summary
A filter circuit in a phase-locked loop circuit includes a capacitor coupled between a control voltage node and a first node; and a variable resistive element coupled between the first node and a ground potential. The variable resistive element has a resistance value modulated by a current proportional to the charge pump current of the charge pump. In one embodiment, the variable resistive element is a MOS transistor biased in the linear region and having a drain-to-source resistance modulated by the current proportional to the charge pump current.