Ultrasonic Sensor Pixel Capacitance Modulation for Leakage Control
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Solution Overview
Problem
Ultrasonic sensors face challenges in maintaining signal integrity due to signal leakage during the hold phase, which limits the duration of signal storage and increases power consumption when multiple transmission phases are used to mitigate this issue.
Innovation Solution
The capacitance of the transistor's capacitive element is electrically modulated by coupling at least one of the drain or source to electric ground during the hold phase, increasing the RC time constant and reducing signal leakage without degrading gain, allowing for a longer hold time with a single transmit phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the hold phase duration is extended to improve signal storage, then signal leakage increases and degrades measurement precision
Solution Approach 1:
The patent applies dynamics by making the capacitance value time-dependent during the hold phase. The capacitance is dynamically adjusted in multiple stages: initially set to a first value to capture the signal, then switched to a second (higher) value to extend storage duration, and finally reset to the first value before reading. This dynamic adjustment allows the system to maintain signal integrity over extended periods by adapting the capacitance to different phases of signal storage.
Solution Approach 2:
The patent directly implements parameter changes by modifying the capacitance parameter of the holding circuit during operation. By changing the capacitance value from a first value to a second value (where the second value is greater than the first), the system extends the RC time constant and thereby extends the hold phase duration without proportionally increasing signal leakage. This parameter modification resolves the contradiction between storage duration and signal integrity.
2Measurement precision
If multiple transmission phases are used to reduce signal leakage, then power consumption increases
Solution Approach 1:
The patent changes the capacitance parameter during the hold phase to achieve better signal storage without requiring multiple transmission phases. By increasing the capacitance value after signal capture, the system extends the hold phase duration and reduces signal leakage within a single transmission phase, thereby avoiding the additional power consumption that would result from multiple transmission phases.
Solution Approach 2:
The patent enables continuous signal storage throughout the hold phase by maintaining an extended RC time constant through increased capacitance. This continuous effective signal retention eliminates the need for intermittent multiple transmission phases, allowing the system to achieve the same signal leakage reduction with a single continuous transmission phase, thus reducing power consumption.
3Duration of action of moving object
If capacitance is increased to extend hold time, then signal leakage increases
Solution Approach 1:
The patent applies dynamics by implementing time-dependent capacitance adjustment. The capacitance is not statically increased throughout the entire hold phase but is dynamically modified in stages: initially at a first value, then switched to a second (higher) value for the majority of the hold phase to extend storage time, and finally reset before the read phase. This dynamic approach allows extended hold time while minimizing signal leakage by optimizing capacitance timing.
Solution Approach 2:
The patent applies preliminary action by setting the capacitance to an optimized value before the signal decay becomes problematic. The capacitance is adjusted to a higher value during the hold phase to proactively extend the RC time constant and maintain signal integrity throughout the extended hold period, preventing signal leakage rather than reacting to it.
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 extended signal storage with reduced leakage and power savings by allowing a single transmit phase for large-area sensors, avoiding signal artifacts and gain degradation.
Implementation Method 1
coupling at least one of the drain or the source of the transistor, respectively, to an electric ground during a hold phase of the ultrasonic sensor... to store the sensor signal in a capacitive element of the transistor
Implementation Method 2
a piezoelectric device may be used to convert the ultrasonic reflection to an electric signal to be sensed by a receiver circuit
Data Source
AI summary
Certain aspects of the present disclosure provide apparatus and techniques for capacitance modulation to mitigate pixel leakage in ultrasonic sensors. For example, certain aspects are directed to an ultrasonic sensor including a column line, a pixel having a transistor coupled to the column line, a pixel control circuit coupled to a drain the transistor of the pixel. The ultrasonic sensor may also include a column control circuit coupled to a source of the transistor, wherein at least one of the pixel control circuit or the column control circuit is configured to couple at least one of the drain or the source of the transistor, respectively, to an electric ground during a hold phase of the ultrasonic sensor, and a receiver circuit coupled to the column line.