Voltage Regulator Noise Injection Path for High Frequency Rejection
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Solution Overview
Problem
Current on-chip voltage regulators in integrated circuits face challenges in effectively rejecting power supply noise, especially at higher frequencies, due to limited bandwidth and noise amplification issues, which hinder the regulation of power supply voltages down to required levels without external capacitors.
Innovation Solution
A noise injection path, utilizing a capacitor to inject in-phase noise into the gate of a pass transistor, ensures that source and gate voltages of the pass transistor vary at a common phase, canceling out noise and improving the power supply rejection ratio by actively engaging at frequencies above the closed loop bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional voltage regulator design is used, then the circuit is simple and stable, but the power supply rejection ratio deteriorates at high frequencies above the closed loop bandwidth
Solution Approach 1:
The regulator circuit is segmented into two independent noise rejection paths: one for low-frequency noise (handled by the conventional feedback loop) and one for high-frequency noise (handled by the noise injection path with capacitor Cinj). This segmentation allows each path to optimize for its specific frequency range without compromising the other.
Solution Approach 2:
A capacitor Cinj is introduced as an intermediary element that selectively couples power supply noise to the gate of the pass transistor at high frequencies. This intermediary enables the noise injection mechanism without disrupting the conventional feedback loop operation at lower frequencies.
2Reliability
If the closed loop bandwidth is increased to improve high frequency noise rejection, then the power supply rejection ratio improves, but the stability of the regulator deteriorates
Solution Approach 1:
The noise rejection function is segmented across two separate mechanisms: the conventional feedback loop maintains stability at lower frequencies, while the noise injection path through Cinj provides high-frequency rejection without requiring an increase in the closed loop bandwidth, thus avoiding stability issues.
Solution Approach 2:
The circuit parameters are changed by adding the capacitor Cinj that creates a frequency-dependent noise injection path. This parameter change enables high-frequency noise rejection through a different mechanism that does not rely on increasing the feedback loop bandwidth, thereby maintaining regulator stability.
3Reliability
If off-chip capacitors are used to improve power supply rejection, then the noise filtering improves, but the integration level and compactness deteriorate
Solution Approach 1:
The on-chip capacitor Cinj serves multiple functions: it acts as a noise injection element for high-frequency rejection, maintains the pass transistor in saturation region, and works within the existing on-chip regulator architecture. This multi-functionality eliminates the need for separate off-chip filtering components.
Solution Approach 2:
The regulator circuit provides its own high-frequency noise rejection capability through the on-chip capacitor Cinj and noise injection path, making it self-sufficient without requiring external capacitors or additional off-chip filtering components.
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 approach significantly enhances the power supply rejection ratio, achieving a peak improvement of about six decibels at 100 megahertz, effectively suppressing external power supply noise and maintaining stable output voltage regulation.
Implementation Method 1
providing a noise injection path for injecting external noise into the voltage regulator, where the noise injection path becomes active at the frequencies above the closed loop bandwidth
Data Source
AI summary
A method for reducing noise in an output of a voltage regulator at frequencies above a closed loop bandwidth, by providing a noise injection path for injecting external noise into the voltage regulator, where the noise injection path becomes active at the frequencies above the closed loop bandwidth, where the noise injection path reduces the noise in the output of the voltage regulator.