Charge Pump Array Circuit for Touch Sense Signal Generation
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Solution Overview
Problem
Conventional capacitive sensing driving circuits face challenges in distinguishing measured signals from noise due to low signal-to-noise ratio (SNR), particularly when operating with limited supply voltage, leading to increased noise and reduced sensitivity.
Innovation Solution
A circuit is designed to generate a programmable supply voltage with an amplitude greater than the available power supply voltage, utilizing a charge pump array and feedback circuits to maintain a target voltage, which includes a clock ripple reduction scheme and a comparator to adjust pump strength, thereby improving SNR and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional charge pump is used to boost voltage above supply voltage, then the signal amplitude increases and SNR improves, but the pump generates ripple noise that degrades measurement precision
Solution Approach 1:
The patent divides a single charge pump into multiple parallel charge pump stages (first charge pump stage, second charge pump stage, etc.), each contributing to the overall voltage boost. This segmentation allows the system to achieve the required signal amplitude while distributing the ripple generation across multiple stages, enabling noise filtering and reduction techniques to be more effective.
Solution Approach 2:
The patent introduces a capacitor connected in parallel with the load as an intermediary energy storage element. This capacitor smooths out the ripple noise generated by the charge pump stages, acting as a mediator between the charge pump output and the load, thereby reducing the harmful ripple effects while maintaining the voltage boost.
2Object-generated harmful factors
If a large reservoir capacitor is used to reduce ripple noise, then noise is reduced, but the capacitor cannot be implemented on-chip increasing device complexity and cost
Solution Approach 1:
Instead of using a single large reservoir capacitor, the patent segments the noise filtering function across multiple smaller capacitors distributed at different stages of the charge pump output path. This allows effective ripple noise reduction while keeping individual capacitor sizes small enough for on-chip integration.
Solution Approach 2:
The patent transitions from a single-point noise filtering solution (one large capacitor) to a distributed multi-point filtering approach across the temporal dimension of the charge pump operation cycles. Multiple capacitors are strategically placed at different stages, utilizing the time-domain characteristics of charge pump operation to achieve effective filtering with smaller components.
3Power
If the charge pump operates at high frequency to boost voltage, then voltage amplification is achieved, but electromagnetic interference increases
Solution Approach 1:
The patent segments the high-frequency charge pump operation into multiple parallel stages operating at the same frequency, which allows the electromagnetic interference to be distributed and reduced through constructive interference cancellation. The segmented approach maintains voltage amplification capability while mitigating EMI through the distributed nature of the stages.
Solution Approach 2:
The patent exploits the rhythmic nature of charge pump operation by introducing capacitors that charge and discharge in sync with the pump cycles. The capacitor charging during high-voltage phases and discharging during low-voltage phases converts the harmful EMI spikes into controlled current transitions, reducing overall electromagnetic interference while maintaining voltage boost functionality.
4Power
If a single charge pump stage is used, then device complexity is low, but the voltage boost is insufficient to achieve adequate signal amplitude
Solution Approach 1:
The patent segments the voltage boosting function across multiple parallel charge pump stages, each contributing a portion of the total voltage gain. This segmentation allows the system to achieve adequate signal amplitude for capacitive touch sensing while keeping each individual stage relatively simple, balancing performance with complexity.
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 enhances the signal-to-noise ratio, decreases power consumption, and reduces electromagnetic interference (EMI) by spreading current transitions across a broader time window, resulting in improved sensitivity and accuracy for capacitive touch sense arrays.
Implementation Method 1
A circuit is designed to generate a programmable supply voltage with an amplitude greater than the available power supply voltage, utilizing a charge pump array and feedback circuits to maintain a target voltage
Data Source
AI summary
A circuit for generating a voltage is disclosed. The voltage has an amplitude greater than an available power supply. The circuit includes a driver to supply the voltage on an output terminal to an electrode of a touch sense array. The circuit also includes a charge pump array coupled to the driver. The charge pump array includes an array of charge pumps to supply an input voltage to the driver. The circuit also includes a feedback circuit coupled to the charge pump array. The feedback circuit is configured to measure the input voltage and to select different combinations of the array of charge pumps to maintain the voltage on the output terminal.