LDO Compensation Circuit for PLL Noise and Stability Tradeoffs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Prior-art low dropout regulators (LDOs) suffer from poor noise performance due to a low transconductance upper limit of the error amplifier, which compromises system stability and noise performance, especially in noise-sensitive applications like phase-locked loops.
Innovation Solution
The introduction of a second compensation circuit in the LDO, which includes a compensation resistor connected to the error amplifier and a transistor, allows for regulation of the dominant and secondary dominant poles, increasing the secondary dominant pole and reducing the gain-bandwidth product, thereby enhancing system stability and transconductance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the transconductance of the error amplifier is significantly increased to improve noise performance, then noise performance is improved, but system stability is compromised
Solution Approach 1:
The patent divides the compensation function into two separate circuits: a first compensation circuit with a nulling resistor and Miller compensation capacitor, and a second compensation circuit with a compensation resistor. This segmentation allows independent optimization of noise performance and stability, enabling the error amplifier to achieve high transconductance without compromising system stability.
Solution Approach 2:
The second compensation circuit acts as an intermediary element that mediates between the error amplifier's high transconductance requirement and the system stability requirement. By introducing this intermediate compensation stage, the patent enables the error amplifier to operate at high transconductance values while the second compensation circuit ensures system stability is maintained.
2Power
If the gain-bandwidth product of the error amplifier is increased to improve transconductance, then transconductance upper limit is increased, but the maximum value lower limit constraint is violated
Solution Approach 1:
The patent introduces dynamic pole regulation through the second compensation circuit, which can adjust the dominant and secondary dominant poles of the LDO. This dynamic adjustment allows the system to optimize the gain-bandwidth product and transconductance relationship, overcoming the fixed constraint of maximum value lower limit while achieving higher transconductance.
Data Source
AI summary
Embodiments of the present invention disclose a low dropout regulator and a phase-locked loop. The low dropout regulator includes: a reference voltage source, an error amplifier coupled to the reference voltage source, a regulating circuit, a load coupled to the regulating circuit, a first compensation circuit, and a second compensation circuit. The regulating circuit produces a regulating current under control of a control voltage from the error amplifier. The first compensation circuit is coupled between the error amplifier and the regulating circuit. The second compensation circuit is coupled between an input terminal and an output terminal of the regulating circuit.