Ultrasonic Sensor Circuit Noise Reduction via Bias Voltage Control
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Solution Overview
Problem
Existing fingerprint sensor arrays on large-dimension display panels face challenges with circuit noises and variations in reference signals, affecting the stable collection of ultrasonic sensing signals, particularly in TFT-based pixel circuits.
Innovation Solution
A sensor circuit is designed with a piezoelectric device and a biasing-and-sampling sub-circuit that sets different bias voltages for transmission and reception periods, using AC excitation signals and control signals to isolate and output DC voltage components from ultrasonic echo signals, thereby reducing noise and reference signal variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If each sensor unit is coupled with a respective pixel circuit to independently convert ultrasonic signal to electrical signal, then fingerprint mapping capability is achieved, but circuit noises and variations in reference signals affect signal stability
Solution Approach 1:
The patent combines the transmission electrode and receiving electrode into a single piezoelectric device, merging the transmission and reception functions. This integration reduces the number of separate circuits needed and minimizes circuit noise by eliminating additional coupling points between separate transmission and reception circuits.
Solution Approach 2:
The patent extracts and separately processes the DC voltage component from the ultrasonic echo signal through dedicated sampling circuits. By isolating the DC component that contains fingerprint information from the AC noise components, the circuit achieves better signal stability while maintaining detection accuracy.
2Power
If piezoelectric device uses AC excitation signal for ultrasonic transmission, then ultrasonic signal generation is achieved, but isolation of DC voltage component from circuit-reference voltages becomes difficult
Solution Approach 1:
The patent applies preliminary action by setting different bias voltages for the receiving electrode during transmission period versus reception period. During the transmission period, the bias voltage is configured to optimize ultrasonic signal generation, while during reception, it is adjusted to maximize the DC voltage component from echo signals, thereby separating the detection function from circuit reference voltages.
Solution Approach 2:
The patent implements periodic action through time-division multiplexing where the piezoelectric device alternates between transmission mode and reception mode. Control signals periodically switch the bias voltage configuration to match the operational phase, enabling clear separation of DC voltage component detection from AC excitation signals through rhythmic sampling synchronized with the ultrasonic pulse sequence.
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 effectively minimizes noise and reference signal variations, enabling accurate detection and display of fingerprint images by isolating the ultrasonic echo signal from circuit-reference voltages, resulting in improved signal quality and stability across the sensor array.
Implementation Method 1
the piezoelectric device PED is configured to transmit an ultrasonic signal upon applying an exciting pulse signal Vtx to the transmitting electrode Tx
Implementation Method 2
to generate a voltage signal at the receiving electrode upon receiving an ultrasonic echo signal based on the ultrasonic signal it initially transmitted
Data Source
Figure 1~2
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AI summary
A circuit for generating and detecting ultrasonic sensing signals comprising a piezoelectric device, a biasing-and-sampling sub-circuit (10), a signal-collecting sub-circuit (20) and an output sub-circuit (30) is provided. The piezoelectric device having a transmitting electrode and a receiving electrode is coupled to the biasing-and-sampling sub-circuit (10) configured to set different bias voltages to the receiving electrode. The piezoelectric device is configured to transmit an ultrasonic signal upon applying an exciting pulse signal to the transmitting electrode and alternatively to generate a voltage signal at the receiving electrode upon receiving an echo signal based on the ultrasonic signal. The signal-collecting sub-circuit (20) is coupled to the receiving electrode to determine a first sampling voltage based on the voltage signal at the receiving electrode in a first sampling period and a second sampling voltage based on the voltage signal at the receiving electrode in a second sampling period. The output sub-circuit (30) is coupled to the signal-collecting sub-circuit (20) for outputting the first sampling voltage and the second sampling voltage at a same time.