PLL Voltage-Controlled Oscillator With Split-Band Noise Filtering
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Solution Overview
Problem
Existing phase locked loops (PLLs) face challenges in generating a stable clock signal due to noise in the current and voltage signals, particularly in the middle frequency band where the pass bands of the PLL and voltage-current converter overlap, making it difficult to achieve loop stability and reduce current noise effectively.
Innovation Solution
A voltage-controlled oscillator is designed with a current source, narrow-band filter, voltage-current converter, and current-controlled oscillator, utilizing pMOS and nMOS transistors to output a stable clock signal by passing currents through different frequency bands, reducing noise through narrow-band and low-pass filters, and using a current mirror circuit to manage current ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a voltage-current converter is used to generate current in a PLL, then the clock signal can be generated, but noise in the middle frequency band increases due to overlapping pass bands
Solution Approach 1:
The patent segments the frequency response into distinct bands by introducing a narrow-band filter with a pass band that does not overlap with the VIC band. This separation divides the frequency spectrum into non-overlapping regions, allowing the voltage-current converter to operate in the VIC band while the narrow-band filter handles other frequency ranges, thereby eliminating noise in the middle frequency band.
Solution Approach 2:
The patent introduces a narrow-band filter as an intermediary component between the voltage-current converter and the current-controlled oscillator. This filter acts as a mediator that selectively passes only the necessary frequency components while blocking noise in the middle frequency band, thus resolving the contradiction between generating a stable clock signal and reducing current noise.
2Adaptability or versatility
If the pass band of the voltage-current converter overlaps with the pass band of the PLL, then current can be generated across a wide frequency range, but loop stability deteriorates due to noise amplification
Solution Approach 1:
The patent segments the frequency response into distinct bands by introducing a narrow-band filter with a pass band that does not overlap with the VIC band. This separation divides the frequency spectrum into non-overlapping regions, allowing the voltage-current converter to operate in the VIC band while the narrow-band filter handles other frequency ranges, thereby eliminating noise in the middle frequency band.
Solution Approach 2:
The patent applies local quality by giving different parts of the frequency spectrum different characteristics. The voltage-current converter provides current gain in the VIC band, while the narrow-band filter provides selective passing of frequencies outside the VIC band. This localized optimization allows wide frequency range coverage in the VIC band while maintaining loop stability by preventing noise amplification in other bands.
3Reliability
If noise filtering is applied to reduce current noise, then clock signal stability improves, but the complexity of the circuit increases
Solution Approach 1:
The patent introduces a narrow-band filter as an intermediary component between the voltage-current converter and the current-controlled oscillator. This filter acts as a mediator that selectively passes only the necessary frequency components while blocking noise in the middle frequency band, thus resolving the contradiction between generating a stable clock signal and reducing current noise.
Solution Approach 2:
The patent changes the frequency response parameters of the system by introducing a narrow-band filter with specific pass band characteristics. This parameter change allows the system to achieve noise filtering in the middle frequency band while maintaining proper operation in the VIC band, thus improving clock signal stability without requiring complex multi-stage filtering.
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 solution effectively reduces noise in the current and voltage signals, enabling the output of a stable clock signal by isolating high-frequency noise and maintaining VIC band pass characteristics, thus improving the stability of the clock generation in the phase locked loop.
Implementation Method 1
a first filter that passes a current in a first frequency band to reduce noise of the second current
Implementation Method 2
a second filter that passes a current in a second frequency band to reduce noise of the sixth current
Implementation Method 3
a current mirror circuit that outputs a fourth current corresponding to the first current, and a fifth current corresponding to the first current
Data Source
AI summary
According to one embodiment, a voltage-controlled oscillator includes a voltage-current conversion circuit and hold circuit that outputs a first current corresponding to a control voltage, a current addition circuit that outputs a second current corresponding to the first current, and a current subtraction circuit that outputs a third current corresponding to the first current. The voltage-controlled oscillator also includes a narrow-band low-pass filter that passes a current in a first frequency band to reduce noise of the second current, a voltage-current converter that outputs a sixth current corresponding to a fifth current obtained by subtracting the third current from a fourth current corresponding to the control voltage, and a low-pass filter that passes a current in a second frequency band to reduce noise of the sixth current. The second frequency band is different from the first frequency band. The voltage-controlled oscillator further includes a current-controlled oscillator that oscillates a clock signal in accordance with a combined current of the second current and the sixth current.