LDO Regulator Buffer Topology for Wide Bypass-Capacitance Stability
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Solution Overview
Problem
Low-dropout (LDO) voltage regulators face challenges in maintaining stability and high bandwidth while operating with a large range of bypass capacitors and reducing die-size, especially in response to load transients and varying load currents.
Innovation Solution
The voltage regulator design incorporates a buffer circuit with a pass device, such as a MOS transistor, that combines outer and inner feedback mechanisms to reduce output impedance and increase stability and bandwidth, eliminating the need for a Miller capacitor, thereby allowing operation with a wide range of output capacitors and reducing die-size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a Miller capacitor is used to stabilize the voltage regulator, then stability is improved, but die-size increases
Solution Approach 1:
The patent removes the Miller capacitor from the traditional voltage regulator architecture. By extracting this component, the die-size is reduced while stability is maintained through alternative compensation mechanisms involving the output capacitor and modified feedback network configuration.
Solution Approach 2:
The output capacitor serves multiple functions: it acts as both the bypass capacitor for load stabilization and as part of the frequency compensation mechanism. This multi-functionality eliminates the need for a separate Miller capacitor, reducing overall component count and die-size.
2Speed
If the bandwidth is increased to respond rapidly to load transients, then response speed is improved, but stability may deteriorate
Solution Approach 1:
The patent implements dynamic bandwidth control through the interaction between the output capacitor and the feedback network. The compensation pole and zero are dynamically positioned based on the output capacitor value, allowing the system to maintain optimal stability margins while achieving high bandwidth for rapid load transient response.
Solution Approach 2:
The patent changes the compensation strategy from fixed Miller capacitor values to a dynamic compensation scheme where the pole-zero locations are determined by the output capacitor and feedback network parameters. This allows bandwidth and stability to be optimized simultaneously across different operating conditions.
3Area of stationary object
If the die-size is reduced, then manufacturing cost is improved, but the range of stable operation with bypass capacitors may be limited
Solution Approach 1:
The output capacitor is designed to serve dual purposes: load stabilization and frequency compensation. This universal approach allows the voltage regulator to maintain stability across a wide range of output capacitor values (200nF to 100µF) without requiring additional compensation components that would increase die-size.
Solution Approach 2:
The patent employs a compensation scheme where the dominant pole and zero locations are determined by the output capacitor value and feedback network parameters. This parameter-based compensation approach enables the regulator to adapt to different capacitor values, providing stable operation across a broad range without increasing die-size.
Data Source
Figure 1a~1b
Figure 2
Figure 3a
AI summary
The present document relates to amplifiers, notably multi-stage amplifiers, such as linear regulators or linear voltage regulators (e.g. low-dropout regulators) configured to provide a constant output voltage subject to load transients. An amplifier (300) is described. The amplifier (300) comprises a first amplification stage (302) configured to provide an intermediate voltage, based on an outer feedback voltage (107) and based on a reference voltage (108). Furthermore, the amplifier (300) comprises an output stage (301) configured to provide a load current at an output voltage (305) based on the intermediate voltage (528). In addition, the amplifier (300) comprises an outer feedback circuit (104) configured to derive the outer feedback voltage (107) from the output voltage (305). The output stage (301) comprises a buffer (301) configured to provide a drive voltage based on the intermediate voltage (528) and based on an inner feedback voltage derived from the output voltage (305). The buffer (301) comprises a pass device (201) which is configured to provide the load current (527) at the output voltage (305) based on the drive voltage.