Passive Bootstrapped Charge Pump for NMOS Regulator Noise Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional charge pump techniques in low dropout (LDO) regulators result in higher output noise due to ripple leakage, require additional power and capacitors, and struggle with high load currents, leading to overcharging or discharging issues, especially when the servo amplifier needs to be wideband and operate at high frequencies.
Innovation Solution
A passive bootstrapped charge pump design that uses a first capacitor coupled to the gate of a pass transistor and a second capacitor charged in a first clock phase, which then charges the first capacitor in a second clock phase, eliminating the need for additional amplifiers and capacitors, and reducing ripple by utilizing the output capacitance for bootstrapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional charge pump technique is used to boost the gate voltage of the pass transistor, then the gate voltage can be enhanced higher than the output voltage, but the output noise increases due to ripple leak from the switching circuit
Solution Approach 1:
The invention extracts the charge pumping function from an active servo amplifier and implements it passively using capacitors and switches. The first capacitor C1 is charged to VOUT plus VGS through the switch network, and then this charged capacitor directly boosts the gate voltage without requiring continuous active control, thereby eliminating the ripple leakage that causes output noise.
Solution Approach 2:
The charge pump circuit uses itself to generate the required gate voltage. The capacitors C1 and C2 along with the switches form a self-contained charge transfer mechanism that automatically charges C1 to the required voltage level and transfers it to the gate node without external intervention or additional power consumption during operation.
2Stability of the object's composition
If a servo amplifier with additional charge pump is used to maintain the gate voltage, then the gate voltage can be maintained, but additional power is consumed due to quiescent current
Solution Approach 1:
The passive charge pump circuit eliminates the need for a powered servo amplifier by using capacitors and switches that transfer charge autonomously. The circuit charges capacitor C1 to the required voltage and transfers it to the gate node without continuous power consumption, achieving voltage stability through passive charge transfer rather than active regulation.
Solution Approach 2:
The charge pump operates in periodic phases: during the first phase, capacitor C2 charges capacitor C1 to VOUT plus VGS through the switch network; during the second phase, the charged capacitor C1 is connected to the gate node to maintain the required voltage. This periodic charge transfer eliminates the need for continuous power consumption while maintaining gate voltage stability.
3Speed
If a wideband servo amplifier is used to handle sudden load changes, then the response speed is improved, but additional power is required
Solution Approach 1:
The circuit pre-charges capacitor C1 to the required voltage level (VOUT plus VGS) before it is needed at the gate node. When load changes occur, the pre-charged capacitor can immediately supply the required gate voltage without waiting for amplifier response, achieving fast transient response without requiring a wideband powered amplifier.
4Quantity of substance
If additional capacitors are used in the charge pump circuit, then the charge storage capacity is increased, but the circuit area increases
Solution Approach 1:
Capacitor C2 serves multiple functions: it acts as the charge transfer capacitor that charges C1 to the required voltage, and it also functions as the output capacitor that supplies charge during load transients. This multi-functionality increases charge storage capacity without proportionally increasing circuit area, as one capacitor performs multiple roles in the charge pump mechanism.
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 solution significantly reduces output noise, saves power and area by eliminating the need for additional amplifiers and capacitors, and improves transient response and startup time by efficiently managing charge transfer between capacitors.
Implementation Method 1
a first capacitor (C1) coupled to the output and to a gate of a pass transistor; a second capacitor (C2) charged to an output voltage
Data Source
AI summary
A charge pump in a low dropout (LDO) regulator includes a first capacitor coupled to an output of an amplifier and to a gate of a pass transistor. A first plurality of switches is operable to couple a second capacitor between an output of the LDO regulator and to a ground in a first clock phase, such that the second capacitor charges to an output voltage. A second plurality of switches is operable to couple the second capacitor in parallel to the first capacitor in a second clock phase such that the second capacitor charges the first capacitor.