PLL Charge Pump Attenuation Circuit for Lower In-Band Noise
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Solution Overview
Problem
Conventional charge pump circuits in phase locked loops generate undesirable in-band noise, limiting their effectiveness in producing wide band phase locked loops.
Innovation Solution
A circuit comprising a phase frequency detector, an attenuation circuit with capacitors and current sources, and a loop filter, which generates control signals to adjust the voltage controlled oscillator, reducing noise by increasing charge-pump current while preserving overall loop gain through capacitive division and reducing thermal noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a charge pump circuit is employed to produce wide band phase locked loops, then the frequency range is improved, but in-band noise increases
Solution Approach 1:
The charge pump current is segmented into multiple parallel current sources, each contributing a portion of the total current. This segmentation allows the system to achieve wide frequency range while distributing the noise generation across multiple lower-noise components rather than a single high-current source.
Solution Approach 2:
Multiple parallel charge pump current sources are merged to achieve the required total current level for wide frequency operation. The parallel combination maintains the benefits of individual lower-current sources while achieving the cumulative current needed for wideband operation, thereby reducing in-band noise.
2Reliability
If charge pump current is increased to improve loop gain, then loop gain is improved, but thermal noise increases
Solution Approach 1:
The high loop gain requirement is satisfied by segmenting the total current into multiple parallel current sources. Each source operates at a lower current level, generating less thermal noise individually, while their combined effect achieves the required total loop gain.
Solution Approach 2:
The patent changes the parameter configuration by using multiple parallel current sources instead of a single high-current source. This parameter change allows the system to achieve the same effective loop gain through multiple lower-current paths, thereby reducing thermal noise generation.
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 significantly reduces output noise by a factor of 1/A, minimizing in-band phase noise and thermal noise, enhancing the performance of phase locked loops.
Implementation Method 1
An attenuation circuit is coupled in series with the PFD and includes first and second current sources, and a loop filter coupled between a voltage controlled oscillator (VCO) control node and a ground node
Implementation Method 2
A an attenuation circuit is coupled in series with the PFD and includes first and second current sources
Data Source
AI summary
Disclosed herein is a circuit including a phase frequency detector (PFD) configured to compare phases of an input signal and a feedback signal, and to generate first and second control signals as a function of that comparison. An attenuation circuit includes a capacitor coupled in series between a node and a switching node, and is configured to charge the capacitor and disconnect the switching node from ground based on assertion of the first control signal, and discharge the capacitor and connect the switching node to ground based on assertion of the second control signal.