Supply Selection Circuit With Nonlinear Hysteresis for LDO Switching
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Solution Overview
Problem
Existing low-dropout (LDO) regulators face a tradeoff between minimum supply voltage and frequent switching (supply hopping) due to the use of resistive dividers and large hysteresis in decision comparators, which limits efficiency and introduces noise.
Innovation Solution
Implementing a non-linear transfer characteristic using current sources, diodes, and transistors to provide voltage reference signals to the decision comparator, reducing hysteresis and minimizing supply hopping by clamping the voltage reference signals, allowing for a smaller hysteresis without increasing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If large hysteresis is used in the decision comparator to avoid frequent switching, then supply hopping is reduced, but the minimum supply voltage increases
Solution Approach 1:
The patent changes the functional characteristic of the voltage reference signal generation from linear to non-linear. By using a non-linear transfer characteristic in the voltage reference signal generation circuit, the hysteresis width becomes variable rather than fixed, allowing the system to maintain stability while operating at lower minimum supply voltages.
Solution Approach 2:
The patent introduces dynamic adjustment of the hysteresis width based on operating conditions. The non-linear transfer characteristic causes the hysteresis width to automatically adjust according to the supply voltage level, providing larger hysteresis at low voltages to prevent switching and smaller hysteresis at high voltages to enable efficient operation.
2Device complexity
If resistive dividers are used to provide voltage reference signals, then the circuit is simple, but noise increases and supply hopping occurs frequently
Solution Approach 1:
The patent transforms the voltage reference signal generation from a linear resistive divider approach to a non-linear approach using current sources and transistors. This non-linear transfer characteristic clamps the voltage reference signals, reducing noise and preventing frequent supply hopping while maintaining circuit simplicity.
3Use of energy by moving object
If the hysteresis width is reduced to enable lower minimum supply voltage, then efficiency improves, but noise and supply hopping increase
Solution Approach 1:
The patent implements dynamic hysteresis width adjustment through the non-linear transfer characteristic. The hysteresis width automatically adapts to operating conditions, being larger when supply voltage is low to prevent switching and noise, and smaller when supply voltage is high to allow efficient operation, thus resolving the trade-off between efficiency and noise.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables a lower minimum supply voltage while reducing noise and supply hopping, ensuring stable operation and efficient switching between voltage supplies.
Implementation Method 1
A non-linear transfer characteristic is provided from a supply voltage to a voltage reference signal provided to an input of a decision comparator. The non-linear transfer characteristic may include a diode that clamps the voltage reference signal.
Implementation Method 2
The first transistor is configured to transfer a first voltage from the first voltage supply terminal to the first input of the comparator.
Data Source
AI summary
In an example, a method includes enabling a first voltage supply and a second voltage supply. The method also includes selecting, with a decision comparator, a selected voltage supply from either the first voltage supply or the second voltage supply based on which of the first voltage supply or the second voltage supply ramps up first. The method includes monitoring the selected voltage supply with the decision comparator. The method also includes, responsive to a voltage from the selected voltage supply dropping below a dropout voltage level of a low dropout regulator, switching to an other voltage supply with the decision comparator.