Two-Stage Charge Pump for Mobile Display Driver ICs
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Solution Overview
Problem
Display driver integrated circuits (DDIs) for mobile thin film transistor (TFT) liquid crystal displays (LCDs) face increased power consumption due to switching losses from higher switching frequencies needed to boost voltages, as there are limitations in the size of flying capacitors, leading to inefficiencies in voltage conversion.
Innovation Solution
A charge pump with a charge pumping unit that boosts voltages in a controlled manner using a middle voltage, generated by specific control signals, to minimize power consumption and enhance current driving capability, while preventing inverse currents through step-by-step pumping and discharging operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the switching frequency of the charge pump is increased to provide the required current, then the current driving capability is improved, but the switching losses increase leading to higher power consumption
Solution Approach 1:
The voltage boosting process is segmented into multiple stages using a two-stage charge pump architecture. The first charge pump boosts the input voltage to an intermediate voltage, and the second charge pump further boosts it to the final high voltage. This segmentation allows each stage to operate at lower switching frequencies while achieving the same overall voltage multiplication, thereby reducing switching losses while maintaining current driving capability.
Solution Approach 2:
An intermediate voltage stage is introduced as a mediator between the input voltage and the final high voltage output. The first charge pump generates this intermediate voltage, which serves as the input for the second charge pump. This intermediary approach enables gradual voltage escalation, reducing the switching frequency requirements and associated losses compared to a single-stage direct boosting approach.
2Loss of energy
If the size of flying capacitors is increased to reduce switching frequency, then the power consumption is reduced, but the DDI size increases violating size constraints
Solution Approach 1:
The total capacitance requirement is segmented across two charge pump stages. Each stage uses smaller flying capacitors that operate at reduced switching frequencies, achieving the same overall power transfer capability without requiring large capacitors in a single stage. This segmentation allows the DDI to maintain compact size while reducing power consumption.
Solution Approach 2:
The two-stage charge pump operates with periodic switching patterns, where the first charge pump switches during one phase and the second charge pump switches during another phase. This periodic operation allows smaller capacitors to achieve the required energy transfer by utilizing the time-domain separation of switching events, reducing both capacitor size and power consumption within the DDI.
3Device complexity
If a single-stage charge pump is used to boost voltage directly, then the device complexity is reduced, but the switching losses increase due to higher switching frequencies
Solution Approach 1:
The charge pump is divided into two independent but connected stages, with each stage having its own flying capacitors and switching network. This segmentation increases device complexity slightly but dramatically reduces switching losses by allowing each stage to operate at lower frequencies. The modular structure maintains manageable complexity while achieving superior efficiency.
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
The solution reduces unnecessary power consumption and improves efficiency by stabilizing voltage levels and minimizing charge loss caused by parasitic capacitances, thereby enhancing the charge pump's performance and reducing the time required for voltage stabilization.
Implementation Method 1
a charge pump including a charge pumping unit configured to boost a first voltage in response to a clock signal, the first voltage being boosted to a second voltage having a voltage level higher than the first voltage by a middle voltage
Data Source
AI summary
Disclosed is a charge pump and a method of controlling the charge pump. The charge pump including a charge pumping unit to boost a first voltage in response to a clock signal, the first voltage being boosted to a second voltage having a voltage level higher than the first voltage by a middle voltage, the middle voltage being generated in response to a first control signal, the first control signal being enabled during a time period in which the clock signal and a second control signal are disabled. The charge pumping unit boosts the second voltage to a third voltage, the third voltage being a voltage level higher than an input voltage by the first voltage, the input voltage being generated in response to the second control signal. The charge pump includes a first transfer unit to output the third voltage in response to the second control signal.