Charge Pump Voltage Boosting for Fast Capacitive Load Charging
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Solution Overview
Problem
Charge pumps face long time constants when driving large capacitive loads, particularly in applications like CMOS imagers, due to the significant difference between the charge pump capacitance and load capacitance, leading to slow voltage increments and extended charging times.
Innovation Solution
Incorporating a differential amplifier with a gain greater than unity in the reference voltage circuit, allowing the capacitor to be charged to a higher voltage than the reference voltage, and using additional voltage boost circuits operating out of phase to apply voltage during both phases of the cycle, thereby reducing the time constant.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional charge pump uses a capacitor to generate boosted voltage by alternating between charging to VCC and applying to load, then the circuit structure is simple, but the time constant is long when driving large capacitive loads
Solution Approach 1:
The patent changes the voltage parameter by which the capacitor is charged. Instead of charging to VCC (0V reference), the capacitor is charged to a higher voltage VCHIG that is a multiple of VCC (e.g., 2VCC, 3VCC, or more). This parameter change allows the capacitor to deliver larger voltage swings to the load, reducing the number of cycles needed to charge large capacitive loads and thereby reducing the time constant while maintaining the basic charge pump structure
Solution Approach 2:
The patent introduces dynamic voltage adjustment through a voltage generator that dynamically determines VCHIG based on the ratio of load capacitance CL to pump capacitance CP. When CL/CP is large, VCHIG is increased to multiple times VCC to accelerate charging. This dynamic adaptation allows the system to optimize charging speed according to actual load conditions, resolving the time constant issue without permanently complicating the circuit structure
2Productivity
If the capacitor capacitance is increased to reduce time constant, then the charging speed improves, but the device size and complexity increase
Solution Approach 1:
Instead of changing the physical size of the capacitor CP, the patent changes the electrical parameter VCHIG (charging voltage). By charging the capacitor to a higher voltage that is a multiple of VCC, the system achieves faster charging of the load without increasing the physical capacitance value. This avoids increasing device size while improving productivity
Solution Approach 2:
The system dynamically adjusts VCHIG based on the load capacitance CL relative to pump capacitance CP. When CL is much larger than CP, VCHIG is increased to multiple times VCC to compensate for the small capacitance ratio and maintain fast charging speed. This dynamic parameter adjustment allows small capacitors to achieve the performance of larger capacitors without the associated size and complexity penalties
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 faster charging of capacitive loads by maintaining higher voltage levels on the capacitor, resulting in significantly reduced time constants and improved efficiency in generating target voltages.
Implementation Method 1
the capacitor 20 having a capacitance CC
Data Source
AI summary
A charge pump and method converts an input voltage to a boosted voltage having a magnitude or polarity that is different from that of the input voltage. The input voltage is adjusted so that it has a relatively large magnitude until the boosted voltage approaches a target voltage. Therefore, the charge pump and method can more quickly charge a capacitive load. The magnitude of the input voltage may be proportional to the difference between the magnitude of a reference voltage and the magnitude of the boosted voltage. The magnitude of the input voltage may alternatively be substantially equal to the magnitude of a supply voltage until the magnitude of the boosted voltage is within a predetermined range of the target voltage, at which point it may be proportional to the difference between the magnitude of a reference voltage and the magnitude of the boosted voltage.