Feedforward LDO Noise Rejection for Clock Jitter Control
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Solution Overview
Problem
Low drop-out regulator circuits in computer systems are affected by power supply noise, leading to undesirable jitter in clock signals due to the coupling of time-varying signals, which compromises their performance and noise rejection.
Innovation Solution
A switch device coupled between the input and regulated power supply nodes, with a control circuit that generates a feedback signal and injects a noise cancellation current based on the noise present on the input power supply node, to improve power supply rejection and maintain a desired voltage level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a low drop-out regulator circuit is used to generate regulated voltage, then power supply voltage levels can be efficiently regulated with low power consumption, but power supply noise couples into the regulated output causing jitter in clock signals
Solution Approach 1:
The patent samples the noise signal from the input power supply node and uses it to generate a noise cancellation current that is injected into the control node. This converts the harmful noise into a useful signal that actively cancels its own effect on the regulated output, thereby eliminating jitter in clock signals while maintaining low power consumption operation
Solution Approach 2:
The patent implements a feedforward noise rejection mechanism where the noise signal is sampled from the input power supply node and fed forward through a noise rejection circuit. This feedback loop allows the control circuit to dynamically adjust the noise cancellation current based on the actual noise conditions, improving power supply rejection ratio without increasing power consumption
2Object-affected harmful factors
If noise cancellation current is injected into the control node, then power supply rejection is improved and noise on regulated node is reduced, but circuit complexity increases
Solution Approach 1:
The patent introduces a noise rejection circuit as an intermediary component between the input power supply node and the control node. This circuit samples the noise signal and generates a noise cancellation current that acts as a mediator to counteract the harmful noise effects, thereby reducing noise on the regulated node while adding only moderate circuit complexity through the use of dedicated noise rejection circuitry
Data Source
AI summary
A voltage regulator circuit included in a computer system may include a switch device coupled between an input power supply node and a regulated power supply node. The switch device may change a value of a supply current flowing from the input power supply node and the regulated power supply node to regulate a voltage level of the regulated power supply node. A noise cancelation current may be feed forward onto a control terminal of the switch device to cancel noise on the regulated power supply node resulting from noise present on the input power supply node.