Recursive All-Digital LDO With Binary Search Controller
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Solution Overview
Problem
Digital Low Drop-Out (LDO) regulators face challenges in achieving rapid response times and stable operation at low input voltages due to limited dynamic range and large active area requirements, with existing solutions experiencing oscillatory behavior and inefficiencies in load regulation.
Innovation Solution
A recursive all-digital LDO (RLDO) with a binary weighted transistor array and proportional derivative compensation, utilizing a binary search controller and hysteretic PWM control to achieve stable and efficient voltage regulation, reducing quiescent power and area while extending the effective resolution of the digital voltage regulator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a digital LDO regulator uses a conventional linear search method with a binary weighted transistor array, then the device can achieve voltage regulation functionality, but the response time is slow (taking up to 2^N cycles for N-bit control) and the active area is large
Solution Approach 1:
The patent replaces the conventional linear search mechanical process with a binary search algorithm implemented through digital logic circuits. The search controller uses binary weighted transistor arrays and successive approximation techniques to achieve logarithmic search speed (N cycles instead of 2^N cycles), dramatically improving response time while reducing the active area required for the control logic.
2Adaptability or versatility
If the digital LDO regulator operates at low input voltages (0.5V), then the device can function in subthreshold power domains, but the dynamic range is limited and stability is compromised
Solution Approach 1:
The patent implements dynamic control mechanisms including a search controller that adapts its search strategy based on voltage conditions, and a proportional derivative (PD) compensator that dynamically adjusts compensation parameters. The system uses dynamic element matching and adaptive biasing to maintain stability across the low voltage range while preserving the ability to operate in subthreshold power domains.
3Measurement precision
If the digital LDO regulator uses a high-resolution transistor array to increase dynamic range, then the voltage regulation precision is improved, but the active area and power consumption increase
Solution Approach 1:
The patent segments the voltage regulation function into multiple stages: a coarse regulation stage using a binary weighted transistor array for fast convergence, and a fine regulation stage using a redundant least significant bit (LSB) transistor for precision adjustment. This segmentation allows high-resolution voltage control to be achieved without proportionally increasing the total active area, as the fine regulation uses a minimal additional transistor.
4Ease of manufacture
If the digital LDO regulator uses conventional control methods, then the implementation is straightforward, but the load regulation performance and efficiency are poor
Solution Approach 1:
The patent implements multiple feedback mechanisms: a main feedback loop using a PD compensator for stable voltage regulation, and a secondary feedback path through the search controller that continuously monitors output voltage and adjusts the transistor array configuration. This multi-layer feedback approach significantly improves load regulation performance while maintaining implementation feasibility through modular circuit architecture.
Data Source
AI summary
A low power voltage regulator includes a weighted transistor array having a plurality of transistor switches with a total conductance of G, corresponding to bits from a MSB to LSB. A transistor switch corresponding to the MSB has a conductance of G/2 and remaining bits have a consecutive descending conductance of G/2N to the LSB, and search time takes a low number of cycles by starting with the MSB. A redundant LSB transistor switch has the same G/2N conductance of the LSB. The redundant LSB is used to correct steady-state errors, and a proportional derivative controller compensates output voltage. The compensation in a method eliminates an output pole of the voltage regulator to provide a stable voltage regulator operation irrespective of load current, load capacitance, or sampling frequency. Voltage can be regulated via the additional LSB below the resolution limit via pulse width modulation.