AM-EWOD Array Element Circuitry for High Sensitivity
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Solution Overview
Problem
Conventional AM-EWOD devices lack sufficient sensitivity to detect small capacitance variations, making it difficult to reliably detect oil filling, air bubbles, and other conditions associated with small capacitance changes, such as contamination and cell gap height measurement.
Innovation Solution
The implementation of enhanced array element circuitry with a pre-charging effect that turns on the sensor readout transistor during the sensing phase, allowing for increased sensitivity by amplifying small capacitance changes into higher output currents, thereby improving the detection of conditions like oil filling and air bubbles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional AM-EWOD array element circuitry is used, then the device structure is simple and easy to manufacture, but the sensitivity to detect small capacitance variations is insufficient
Solution Approach 1:
The patent applies preliminary action by pre-charging the sensor readout transistor to a specific voltage state before the actual sensing operation. This pre-charging phase prepares the transistor to be in an optimal conduction state, enabling it to amplify small capacitance changes more effectively. The pre-charge voltage is applied through a dedicated pre-charge line that sets up the initial conditions for high-sensitivity detection without requiring permanent circuit modifications.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the voltage parameters of the sensor readout transistor during different phases of operation. During the pre-charge phase, a specific voltage is applied to put the transistor in saturation or linear region for optimal amplification. During sensing, the voltage parameters are maintained or adjusted to maximize the output current response to small capacitance variations. This dynamic parameter adjustment enables high sensitivity without permanently increasing circuit complexity.
2Measurement precision
If the sensor readout transistor is kept off during sensing, then power consumption is reduced, but small capacitance changes cannot be amplified into sufficient output current
Solution Approach 1:
The patent implements periodic action by cycling the sensor readout transistor between off-state and pre-charged on-state in a controlled sequence. During normal operation, the transistor remains off to minimize power consumption. Before sensing, it is periodically pre-charged to the appropriate voltage state, activated for the brief sensing duration, then returned to off-state. This periodic activation pattern enables high-sensitivity detection only when needed while maintaining low average power consumption throughout the measurement cycle.
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 configuration enhances the sensitivity of impedance sensing circuitry, enabling reliable detection of small capacitance variations, improving the accuracy of oil filling, air bubble detection, and other conditions, and facilitating electronic measurement of the cell gap height.
Implementation Method 1
enhanced the sensitivity to small capacitances by applying a pre-charging effect to turn on the sensor readout transistor in an array element being sensed prior to sensing
Implementation Method 2
Electrowetting on dielectric (EWOD) is a well-known technique for manipulating droplets of fluid by application of an electric field
Implementation Method 3
a pre-charging effect is applied whereby a pre-charging voltage is applied to a gate of the sensor readout transistor to turn on the sensor readout transistor during a sensing phase
Data Source
Figure 1~2
Figure 3~4B
Figure 5
AI summary
An AM-EWOD device includes a plurality of array elements arranged in an array of rows and columns, each of the array elements including array element circuitry, an element electrode, and a reference electrode. The array element circuitry includes actuation circuitry configured to apply actuation voltages to the element and/or reference electrodes for actuating the array element, and impedance sensor circuitry configured to sense impedance at the array element electrode to determine a droplet or device property at the array element, the impedance sensor circuitry comprising a sensor capacitor and a sensor readout transistor that outputs an output current for sensing. The sensor capacitor is electrically connected to a gate of the sensor readout transistor such that during a sensing phase a voltage perturbation is coupled through the sensor capacitor (and possibly other circuit elements) to the gate of the sensor readout transistor. The impedance sensor circuitry further comprises a pre-charging element that operates to turn on the sensor readout transistor during the sensing phase in combination with coupling of the voltage perturbation, thereby increasing the effect of the voltage perturbation on the output current.