Low Dropout Voltage Regulator Noise Reduction via RC Filtering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional low dropout (LDO) voltage regulators face challenges in reducing noise, particularly due to large resistances in the voltage divider and the error amplifier, which complicates the provision of efficient, low-noise voltage regulation, especially as electronic circuits become more susceptible to high-frequency noise.
Innovation Solution
The proposed LDO voltage regulator incorporates a scaling amplifier, a reference MOSFET device, an RC network for filtering, and an output buffer to reduce noise, with the RC network filtering the scaled bandgap voltage and the output buffer recovering the regulated voltage output, while using a clamping PMOS device to extend the input voltage supply range and maintain regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a low pass filter is interposed between the bandgap reference voltage and the inverting input of the error amplifier to reduce noise, then high frequency noise is reduced, but the noise produced by large resistances in the voltage divider and the error amplifier is not addressed
Solution Approach 1:
The patent extracts the noise sources (voltage divider and error amplifier) from the traditional feedback path and places them in a separate noise filtering path. The voltage divider is repositioned to feed directly into a noise filter, bypassing the error amplifier's inverting input, thereby isolating the noise-generating components from the main regulation loop while maintaining their voltage division function.
Solution Approach 2:
A dedicated noise filter is introduced as an intermediary component between the voltage divider and the feedback path. This noise filter specifically targets and attenuates the noise generated by the large resistance values in the voltage divider and error amplifier, while allowing the main regulation signal to pass through the error amplifier unchanged.
2Productivity
If large resistance values are used in the internal voltage divider to provide efficient voltage regulation, then voltage regulation efficiency is improved, but a large amount of noise is contributed to the system
Solution Approach 1:
The patent segments the feedback path into two separate paths: a main regulation path through the error amplifier and a noise filtering path through the dedicated noise filter. This segmentation allows the voltage divider to maintain its high resistance values for efficiency while the noise filter separately handles the noise attenuation, preventing the noise from entering the main regulation loop.
Solution Approach 2:
The noise filter serves as an intermediary that specifically addresses the noise problem caused by large resistance values. It is positioned to receive the divided voltage from the voltage divider and provide a cleaned version to the feedback path, thereby enabling the use of large resistance values without the associated noise penalty.
3Reliability
If the error amplifier compares the bandgap reference with feedback voltage to control the pass transistor, then voltage regulation is achieved, but noise from the error amplifier is added to the system
Solution Approach 1:
The patent extracts the noise-generating comparison function from the main feedback path by repositioning the voltage divider output to feed a dedicated noise filter instead of directly entering the error amplifier's inverting input. This extraction separates the noise generation point from the noise propagation path, allowing the error amplifier to focus solely on regulation while the noise filter handles noise attenuation.
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 configuration achieves a very low noise, unity gain regulated output by pre-filtering noise sources and maintaining efficient voltage regulation across varying load currents and input voltages, with a low output spectral noise density below 20 nV/rtHz for frequencies above 10 KHz.
Implementation Method 1
an RC network for filtering the reduced level of the scaled Vbg and outputting a filtered voltage
Implementation Method 2
a reference MOSFET device for reducing the scaled Vbg by a voltage Vgs formed across gate and source nodes of the reference MOSFET device
Data Source
AI summary
A low dropout (LDO) voltage regulator includes a scaling amplifier for receiving a bandgap voltage, Vbg, and outputting a scaled Vbg. A reference MOSFET device is included for reducing the scaled Vbg by a first voltage Vgs formed across gate and source nodes of the reference MOSFET device. This forms a reduced level of the scaled Vbg. An RC network filters the reduced level of the scaled Vbg and outputs a filtered voltage. An output buffer is included for receiving and increasing the filtered voltage by a second voltage Vgs in order to recover the scaled Vbg. The scaled Vbg is used as the desired regulated voltage output. The second voltage Vgs, which is produced by the output buffer, is equal to the first voltage Vgs, which is produced by the reference MOSFET device.