LDO Compensation Circuit for Wideband PSRR Noise Rejection
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Solution Overview
Problem
Achieving a high power supply rejection ratio (PSRR) across a wide range of operating frequencies in low dropout (LDO) voltage regulators is challenging due to noise limitations at high frequencies, which existing technologies struggle to address effectively.
Innovation Solution
A low dropout voltage regulator design that includes a pass element, an error amplifier, a first compensation element, and a compensation circuit configured to control the trans-conductance of the first compensation element based on noise compensation criteria, utilizing parameters such as trans-conductance of the pass element, parasitic capacitance, and an additional capacitance to reduce noise across a wide frequency range, with features like memory cells and switches for current storage and injection to enhance noise compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional LDO regulator design is used, then the circuit structure is simple, but the PSRR degrades at high frequencies due to noise beyond the error amplifier bandwidth
Solution Approach 1:
The compensation function is segmented into multiple elements: a first compensation element (transistor) whose trans-conductance is controlled by a compensation circuit, and a second compensation element. This segmentation allows independent optimization of noise compensation and stability, resolving the contradiction between high-frequency PSRR and circuit complexity by distributing compensation functions across specialized components rather than using a single complex circuit
Solution Approach 2:
The trans-conductance of the first compensation element is made dynamically controllable through the compensation circuit, which adjusts it according to the noise compensation criterion involving pass element trans-conductance, parasitic capacitance, and compensation capacitance. This dynamic adjustment enables the circuit to maintain optimal noise compensation across varying operating conditions and frequencies, achieving high PSRR without requiring a statically complex circuit structure
2Reliability
If the error amplifier bandwidth is increased to reduce noise at high frequencies, then the PSRR improves, but the device complexity and bandwidth requirements increase
Solution Approach 1:
The first compensation element acts as an intermediary between the error amplifier and the output, providing noise compensation at high frequencies without requiring the error amplifier itself to have extended bandwidth. The compensation circuit mediates the control signal to adjust the compensation element's trans-conductance, effectively filtering high-frequency noise while keeping the error amplifier's bandwidth requirements unchanged
Solution Approach 2:
The noise compensation function is separated from the error amplifier's primary voltage regulation function. By introducing dedicated compensation elements controlled by a separate compensation circuit, the system achieves high-frequency noise rejection without increasing the error amplifier's bandwidth, thus resolving the contradiction between PSRR and bandwidth requirements
3Reliability
If a fixed trans-conductance compensation element is used, then the circuit is simpler, but noise compensation is ineffective across a wide frequency range
Solution Approach 1:
The compensation circuit dynamically controls the trans-conductance of the first compensation element based on a noise compensation criterion that considers pass element trans-conductance, parasitic capacitance, and compensation capacitance. This dynamic control enables effective noise compensation across a wide frequency range by adapting the compensation element's characteristics to varying operating conditions, justifying the added circuit complexity
Solution Approach 2:
The compensation circuit changes the trans-conductance parameter of the first compensation element according to the noise compensation criterion. By varying this key parameter in response to different operating conditions and frequencies, the system achieves broad-spectrum noise compensation, resolving the contradiction between wide frequency range effectiveness and circuit simplicity
Data Source
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AI summary
A low dropout voltage regulator (100) includes: a pass element (M0) connected between an input terminal (Vin) and an output terminal (Vout) of the low dropout voltage regulator; an error amplifier (OP0) driving a control terminal of the pass element (M0); a first compensation element (M6) connected to the output terminal (Vout) of the low dropout voltage regulator; and a compensation circuit (101) connected to a control terminal (A) of the first compensation element (M6), wherein the compensation circuit (101) is configured to control a trans-conductance (g m6 ) of the first compensation element (M6) in accordance with a noise compensation criterion.