PLL Charge Pump Self-Bias Circuit for Matched Current Control
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Solution Overview
Problem
In charge pumps used in PLL circuits, it is challenging to adjust the current due to the difficulty in matching the characteristics of N-type and P-type channels formed by different ion injection or diffusion processes, leading to variations in current flow.
Innovation Solution
The charge pump design includes a switch circuit that switches between a first current source and a second current source, both formed by N-type depletion mode MOS transistors, to stabilize current flow and adjust it based on signals from the phase frequency detector, using a self-bias circuit configuration to ensure consistent current supply and draw.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If different conduction-type MOS transistors (N-type and P-type) are used for current source and current drawing in the charge pump, then the charge pump can function properly with both current supply and current drawing capabilities, but the characteristics of the channels cannot be made the same due to different ion injection or diffusion processes, leading to difficulty in adjusting the current flowing through the charge pump
Solution Approach 1:
The patent uses the same conduction-type MOS transistors (either both N-type or both P-type) for both the current source and current drawing operations in the charge pump. This homogeneous approach ensures that both transistors undergo the same ion injection or diffusion process, resulting in identical channel characteristics. Consequently, the current flowing through the charge pump can be precisely adjusted and predicted, resolving the manufacturing precision issue while maintaining full charge pump functionality.
2Reliability
If N-type and P-type channels are formed by different ion injection or diffusion processes, then both current supply and current drawing functions can be implemented, but it becomes extremely difficult to make the channels have the same characteristics
Solution Approach 1:
The patent employs homogeneous MOS transistors of the same conduction type for both current source and current drawing functions. This eliminates the need for different ion injection or diffusion processes, simplifying the manufacturing process while ensuring consistent channel characteristics. The reliability of current flow is improved because both transistors exhibit identical electrical properties, and the device complexity is reduced by using a single-type transistor design throughout the charge pump circuit.
3Ease of operation
If conduction-type MOS transistors with different characteristics are used in the current source, then the charge pump can operate with both supply and draw functions, but the current flowing through the charge pump becomes difficult to adjust
Solution Approach 1:
The patent uses MOS transistors of the same conduction type for both current supply and current drawing operations. This homogeneous configuration ensures that both transistors have identical characteristics due to undergoing the same manufacturing process (same ion injection or diffusion). As a result, the current flowing through the charge pump becomes easily adjustable and predictable, directly improving ease of operation while maintaining high manufacturing precision.
Data Source
AI summary
A charge pump includes: a switch circuit that switches a current source conducted to an output node based on a signal from a phase frequency detector included in a PLL circuit; a first current source that is the current source provided between a high potential node and the switch circuit, and supplies a current to the output node by a first conduction-type depletion mode MOS transistor forming a self-bias circuit; and a second current source that is the current source provided between a low potential node and the switch circuit, and draws the current from the output node by the first conduction-type depletion mode MOS transistor forming the self-bias circuit.