Clock Generator Filtering to Reduce PLL Ripple and Spur Signals
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Traditional phase-locked loop circuits face challenges in generating a pulse wave current signal due to the response time of the charge pump, leading to high frequency components that require complex multi-pole low pass filters, which increase circuit area and design difficulty, and result in ripple signals in the control signal for the voltage-controlled oscillator.
Innovation Solution
A clock generating circuit with a phase detector, a first filtering device, a charge pump, and a second filtering device, where the first filtering device filters the detection result from the phase detector to generate a control signal, and the second filtering device further filters this signal to produce a lower frequency control signal for the controllable oscillator, reducing the complexity of the low pass filter and minimizing ripple signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the charge pump generates a pulse wave current signal to match the phase signal format, then the current signal format matches the phase signals, but the control signal contains ripple signals and requires complex multi-pole low pass filters
Solution Approach 1:
The patent converts the harmful ripple signals generated by the charge pump into a beneficial design feature by intentionally designing the current adjusting circuit to generate a triangular wave current signal instead of a pulse wave. This triangular wave format inherently reduces high frequency components, thereby reducing ripple signals in the control signal without requiring complex multi-pole low pass filters, thus converting the potential harm into a benefit
Solution Approach 2:
The patent changes the waveform parameter of the current signal from a pulse wave to a triangular wave. This parameter change fundamentally alters the frequency spectrum characteristics, reducing high frequency components and thereby reducing the complexity of the low pass filter required to eliminate ripple signals while maintaining adequate current signal format matching
2Manufacturing precision
If the current signal is adjusted to have a pulse wave format, then the current signal matches the phase signal format, but the circuit area increases due to the current adjusting circuit
Solution Approach 1:
The patent changes the waveform parameter from pulse wave to triangular wave, which maintains adequate format matching with phase signals while significantly reducing the complexity and area of the current adjusting circuit. The triangular wave generation requires simpler circuitry compared to pulse wave generation, thereby reducing the overall circuit area
3Manufacturing precision
If the charge pump operates at high speed to generate pulse wave current signal, then the current signal format matches, but the overall cost and complexity of the clock generating circuit increases
Solution Approach 1:
The patent changes the waveform parameter to triangular wave, which reduces the speed requirements for the charge pump and current adjusting circuit. This parameter change allows the circuit to operate at lower speeds while maintaining adequate signal format matching, thereby reducing overall circuit complexity and cost without sacrificing performance
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
The proposed solution reduces the design complexity of the low pass filter, decreases the circuit area, and significantly minimizes ripple signals in the control signal, improving the spur signals of the output clock and reducing the need for high-speed charge pumps, thus lowering the overall cost and complexity of the clock generating circuit.
Implementation Method 1
The first filtering device is used for filtering the detection result
Implementation Method 2
The second filtering device is used for filtering the control signal
Data Source
AI summary
A clock generating circuit includes a phase detector for detecting a phase difference between a first clock and a second clock to generate a detecting result associated with the phase difference, a first filtering device for filtering the detecting result, a charge pump for generating a control signal according to the filtered detecting result, a second filtering device for filtering the control signal, and a controllable oscillator for generating an output clock according to the filtered control signal, wherein the output clock is utilized to generate the second clock.