PLL Charge Pump Using Same-Polarity Transistors for Noise Control
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Solution Overview
Problem
Existing charge pumps in phase-locked loops face challenges in matching the dynamic behavior of transistors of different polarities, leading to transient errors and noise propagation, especially when performing DAC compensation for fractional-N division architectures.
Innovation Solution
A charge pump design with two current paths using transistors of the same polarity, such as PMOS transistors, and a capacitive element that alternates between connecting to current paths and a reference voltage to discharge electrical charges, ensuring balanced current flow and reducing transient errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If transistors of different polarities are used in the charge pump, then the charge pump can generate both up and down currents, but the transient responses of the transistors do not match, causing transient errors and noise propagation
Solution Approach 1:
The patent uses transistors of the same polarity (all PMOS or all NMOS) in both the first and second current paths. This homogeneity ensures that the transistors have identical electrical characteristics and transient responses, eliminating the mismatch problem that occurs when different polarity transistors are used. The charge pump can still generate both up and down currents by controlling which current path is active, while maintaining reliable transient response matching through the use of identical transistor types.
2Measurement precision
If a small reference frequency is used for fine frequency resolution, then the frequency resolution is improved, but the loop filter bandwidth must be narrowed to remove sidebands, which increases transition time and reduces noise suppression
Solution Approach 1:
The patent implements a feedback mechanism where the charge pump monitors the phase difference between the reference signal and the divided output signal, and dynamically adjusts the current paths to compensate for phase errors. This feedback control allows the system to maintain accurate frequency locking even with small reference frequencies, reducing the need for narrow loop filter bandwidths and thereby preserving both noise suppression and transition speed performance.
Solution Approach 2:
The patent dynamically changes the operational parameters of the charge pump by switching between different current paths based on the phase error signal. By adjusting which current path is active and modifying the current magnitudes, the system can adapt to different operating conditions, allowing fine frequency resolution to be achieved without sacrificing noise suppression capability or transition speed.
3Measurement precision
If fractional-N division is used to achieve lower reference frequencies, then the frequency resolution is improved, but the modulation of the division ratio causes huge transient voltages at the VCO input
Solution Approach 1:
The patent segments the current generation function into two separate current paths: one dedicated to generating up currents and another for down currents. Each path has its own current source and control mechanism. This segmentation allows independent optimization and control of each current path, enabling the charge pump to handle the transient voltage issues caused by fractional-N division by carefully managing the switching and current modulation in each path separately, thereby reducing the harmful transient effects at the VCO input.
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 design improves the matching of transient responses between transistors, reducing noise and enhancing the dynamic range, allowing for more precise control of current flow and improved performance in phase-locked loops, particularly in fractional-N division scenarios.
Implementation Method 1
a capacitive element having first and second capacitive plates and a switching arrangement arranged such that, during a first time period, the first and second capacitive plates are each in communication with a respective one of the current paths, whereby a current output by the first current path causes an electrical charge to be formed on the first capacitive plate and a current output by the second current path causes an electrical charge to be formed on the second capacitive plate, and during a second time period, the first and second capacitive plates are connected to a reference voltage and the output node respectively, the electrical charge formed on the first and second capacitive plates during the first time period thereby being discharged to form a current at the output node
Data Source
AI summary
A charge pump circuit causes a current to flow either into or out of another circuit in dependence on a current output by first and second current paths, each including a current source and a current control device having two switched nodes, and a control node arranged to control a current flow between the first and second switched nodes. The charge pump further includes a capacitive element and a switching arrangement arranged such that, during a first time period, the capacitive element is in communication with a respective one of the current paths, whereby a current output by the first current path causes an electrical charge to be formed on a first capacitive plate and a current output by the second current path causes an electrical charge to be formed on a second capacitive plate, and during a second time period, the electrical charge formed on the first and second capacitive plates during the first time period is discharged to form a current at an output node.