Low Dropout Regulator Chopping Error Amplifier Noise Reduction
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Solution Overview
Problem
Low dropout regulators face challenges in minimizing noise, particularly flicker noise, as supply voltages decrease in deep submicron gate length CMOS technology, limiting the unity-gain frequency and increasing noise effects in analog, mixed signal, and RF circuits.
Innovation Solution
The implementation of a low noise, low dropout regulator using a chopping error amplifier to shift low-frequency noise to high frequencies, combined with a voltage buffer and a low pass filter to suppress noise, and a feedback network to provide feedback to the chopping error amplifier, effectively reducing output noise and improving settling time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional error amplifier design is used in deep submicron processes, then the regulator can operate at lower supply voltages, but flicker noise becomes dominant and output noise increases
Solution Approach 1:
The patent converts the harmful flicker noise by using a chopping mechanism that modulates the error amplifier's operation. The chopper switches the error amplifier on and off at a high frequency, transforming low-frequency flicker noise into high-frequency noise that can be filtered out by the low-pass filter, thereby converting a harmful effect into a manageable one
Solution Approach 2:
The patent introduces a chopper circuit as an intermediary between the error amplifier and the rest of the regulator. This chopper acts as a mediator that processes the error amplifier's output, modulating the signal and noise characteristics before they reach the control element, thus isolating the harmful flicker noise from the critical regulation path
2Loss of energy
If supply voltage amplitude decreases to accommodate deep submicron technology, then power consumption is reduced, but noise effects on circuit components increase
Solution Approach 1:
The low-pass filter converts the high-frequency chopped noise (which includes the transformed flicker noise) into a form that can be easily filtered out. By modulating the noise to high frequencies through chopping, the patent enables the low-pass filter to effectively remove it, turning the voltage reduction benefit into a working solution that maintains low power while suppressing noise effects
Solution Approach 2:
The patent changes the frequency parameter of the noise signal through the chopping mechanism. By modulating the error amplifier at a high frequency, the noise spectrum is shifted from low frequencies (where flicker noise is problematic) to high frequencies (where it can be filtered), thus changing the noise characteristics without changing the supply voltage level
3Speed
If unity-gain frequency is increased to improve regulator performance, then regulation speed is enhanced, but noise from error amplifier and feedback network becomes more significant
Solution Approach 1:
The chopping mechanism converts the error amplifier's noise into high-frequency components that can be filtered by the low-pass filter. This allows the error amplifier to operate at higher frequencies (improving unity-gain frequency) while the harmful noise is transformed and removed, preventing it from degrading the output signal
Data Source
AI summary
Low noise, low dropout regulators are described. An example low noise, low dropout regulator includes a chopping error amplifier to receive an input signal and a feedback signal and to output a modified signal having an undesired portion of the input signal shifted to a higher frequency and a regulator to receive the modified signal and to generate an output signal by filtering the undesired portion of the input signal from the modified signal.