Bandgap Voltage Reference Switching for High-PSR LDO Startup
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Solution Overview
Problem
Existing linear voltage regulators face challenges in achieving high power supply rejection (PSR) without the need for large filters or external components, and they often experience issues with voltage reference stability, overshoots, and inefficiencies in power management during startup and operation.
Innovation Solution
A voltage regulation loop comprising a bandgap voltage reference circuit, two linear voltage regulators, and a soft startup circuit, with a selector block that smoothly transitions between voltage references to prevent overshoots and ensure high PSR, allowing for independent regulation of power supplies without external components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a voltage reference selector and soft startup circuit are added to manage multiple voltage references, then voltage reference stability and PSR are improved, but device complexity increases
Solution Approach 1:
The patent implements dynamic switching between different voltage reference sources (Vref1 from first BGR, Vref2 from second BGR, or Vref3 from third BGR) based on operational conditions. The voltage reference selector dynamically chooses the appropriate reference source, and the soft startup circuit dynamically adjusts the startup sequence, allowing the system to adapt to different operating states and optimize performance while maintaining manageable complexity through conditional logic rather than fixed architecture
Solution Approach 2:
The patent divides the voltage reference generation function into multiple independent bandgap voltage reference circuits (first BGR, second BGR, third BGR), each capable of operating independently. This segmentation allows the system to select the most appropriate reference source for each operating condition, improving overall reliability and PSR while keeping each individual reference circuit relatively simple
2Stability of the object's composition
If two voltage references are switched simultaneously with power supply switching, then regulation continuity is improved, but the risk of voltage drops and output glitches increases
Solution Approach 1:
The soft startup circuit implements preliminary action by pre-charging capacitors and gradually enabling voltage references before full power switching occurs. The circuit prepares the voltage reference switching in advance of the power supply switching, ensuring that Vref1 or Vref2 is already stable and ready before the power transition, thereby preventing voltage drops and output glitches during the switching event
Solution Approach 2:
The soft startup circuit provides beforehand cushioning by using RC time constants and gradual charging mechanisms to smooth out the transitions. Capacitors are charged in advance through resistors, creating a cushioning effect that prevents sudden voltage changes when switching between voltage references and power supplies, thereby maintaining regulation continuity without causing glitches
3Productivity
If VDD power to the first voltage reference generator is not shut down after switching, then power management efficiency deteriorates, but quiescent power consumption increases
Solution Approach 1:
The patent implements discarding and recovering by shutting down the first voltage reference generator (Vref1 from first BGR) after its function is no longer needed following the switching to Vref2 or Vref3. The control circuit detects when Vref1 is no longer required and disables its power supply, eliminating unnecessary quiescent power consumption. This allows the system to recover power efficiency by discarding the functionality of the first BGR when operating in modes that use alternative voltage references
4Adaptability or versatility
If a single linear voltage regulator is designed with a large pass transistor to support all loads, then adaptability is improved, but PSR deteriorates
Solution Approach 1:
The patent segments the load support function by using multiple linear voltage regulators (first LDO, second LDO, third LDO) instead of a single regulator with a large pass transistor. Each regulator can be optimized with appropriately sized pass transistors for their specific load requirements, maintaining good PSR performance. The system achieves adaptability through the combination of multiple specialized regulators rather than one general-purpose regulator
Solution Approach 2:
The patent implements dynamic load distribution by enabling different combinations of voltage regulators and voltage references based on operating conditions. The system can dynamically activate or deactivate specific LDOs and BGRs to match the actual load requirements, allowing each active regulator to operate with an optimally sized pass transistor rather than requiring all regulators to support the maximum possible load
Data Source
AI summary
A voltage regulation loop includes a voltage reference generation block that includes a bandgap voltage reference circuit; a linear voltage regulator block that includes a first and second linear voltage regulators, wherein the first linear voltage regulator provides a first regulated power supply to the bandgap voltage reference circuit in the voltage reference generation block, and the second linear voltage regulator provides a second regulated power supply to a load; and a soft startup circuit connected between the voltage reference generation block and the linear voltage regulator block, wherein a selector functions with a control block to output a selected voltage reference to pass to the soft startup circuit, wherein the soft startup circuit smooths the selected voltage reference and produces a smoothed voltage reference to pass to the linear voltage regulator block to prevent overshoots at startup.