Active PLL Loop Filter With Small Capacitor for Low Phase Noise
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Solution Overview
Problem
Conventional phase locked loops (PLLs) face challenges in reducing phase noise due to large stabilizing capacitors, which occupy significant die space when integrated or require additional components and pins when located off-chip, complicating design and increasing costs.
Innovation Solution
The implementation of an active loop filter in the PLL, incorporating a smaller stabilizing capacitor and an operational amplifier, along with a main and auxiliary charge pump, allows for reduced phase noise while maintaining a compact design by using an active low-pass filter to filter high-frequency components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large stabilizing capacitor is used in the loop filter, then PLL phase noise is reduced, but die space is significantly increased
Solution Approach 1:
The patent changes the fundamental parameter of the loop filter from passive to active by introducing an operational amplifier. This allows the use of a much smaller stabilizing capacitor (reducing die space) while maintaining the same phase noise performance through the active filtering capability of the op-amp, which provides gain and improved noise filtering without requiring large capacitance values.
2Reliability
If a large stabilizing capacitor is used in the loop filter, then PLL phase noise is reduced, but device complexity is increased
Solution Approach 1:
By transitioning from a passive loop filter to an active loop filter using an operational amplifier, the patent achieves superior phase noise performance with a more compact and manageable component configuration. The active filter provides enhanced filtering capability that allows for reduced component count and smaller capacitor values while improving overall PLL performance.
3Reliability
If a large stabilizing capacitor is used in the loop filter, then PLL phase noise is reduced, but manufacturing cost is increased
Solution Approach 1:
The active loop filter configuration using an operational amplifier enables the use of smaller, more cost-effective capacitor components. This reduces the bill of materials cost and simplifies manufacturing, as smaller capacitors are generally less expensive and require less board space, while the op-amp provides the necessary filtering function that would otherwise require large passive components.
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 configuration achieves low phase noise in PLL outputs, enabling efficient integration and reducing manufacturing costs by minimizing the size and number of components required, while maintaining accurate frequency tracking.
Implementation Method 1
The implementation of an active loop filter in the PLL, incorporating a smaller stabilizing capacitor and an operational amplifier, along with a main and auxiliary charge pump, allows for reduced phase noise while maintaining a compact design by using an active low-pass filter to filter high-frequency components.
Implementation Method 2
The implementation of an active loop filter in the PLL, incorporating a smaller stabilizing capacitor and an operational amplifier, along with a main and auxiliary charge pump, allows for reduced phase noise while maintaining a compact design
Implementation Method 3
Phase locked loops (PLLs) can be used in electronic circuits to generate high frequency signals that are multiples of lower frequency reference signals
Data Source
AI summary
A disclosed exemplary embodiment is a phase locked loop comprising a main charge pump driven by a phase error signal, and providing a first input to a loop filter. An auxiliary charge pump driven by the phase error signal feeds a second input of the loop filter. The loop filter can be an active loop filter comprising an operational amplifier and a feedback RC network. The first input of the active loop filter can be an inverting input of the operational amplifier and the second input can be a non-inverting input of the operational amplifier. An on-chip stabilizing capacitor fed by the auxiliary charge pump and coupled to the second input of the loop filter is significantly smaller than the conventional stabilizing capacitors. The loop filter outputs a regulating voltage for regulating the oscillation frequency of a voltage controlled oscillator in the phase locked loop.