X-Ray Sensor Readout Circuit Using Correlated Triple Sampling
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Solution Overview
Problem
In common readout circuits for light sensors, thin-film transistors can cause unstable transistor characteristics, leading to error-prone signal sensing and underutilization of the analog-to-digital converter's decoding range.
Innovation Solution
A processing circuit with an amplifier and sampling circuit that employs correlated triple sampling (CTS) to accurately read out the sensing voltage of an X-ray sensor by obtaining and processing voltages in different sampling periods, effectively compensating for transistor variations and background noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If thin-film transistors are used in the readout circuit, then the circuit can be manufactured with standard TFT processes, but the transistor characteristics become unstable due to process errors
Solution Approach 1:
The patent implements feedback by measuring the actual transistor characteristics (threshold voltage, mobility) through the sensing circuit and using these measurements to compensate for process variations. The system continuously monitors and adjusts for TFT parameter drift, transforming the unstable TFT characteristics into reliable sensor readings through closed-loop compensation.
Solution Approach 2:
The patent changes the operating parameters of the TFTs by applying different voltages during sensing operations and compensating for parameter variations. By dynamically adjusting voltage levels and timing parameters, the system adapts to TFT characteristic changes caused by process errors, maintaining stable sensor performance across manufacturing variations.
2Device complexity
If standard sensing methods are used, then the readout circuit is simple, but the sensing signals are prone to errors and the ADC decoding range cannot be fully utilized
Solution Approach 1:
The patent segments the sensing operation into multiple distinct phases: reset phase, sampling phase, and compensation phase. Each phase captures specific voltage components separately, allowing the system to isolate and eliminate error sources (such as offset voltages and noise) while preserving the actual sensor signal. This temporal segmentation enables precise signal extraction without requiring complex circuit topologies.
Solution Approach 2:
The patent performs preliminary actions by capturing reference voltages and compensation signals before the actual sensing measurement. The reset voltage and background noise levels are measured in advance and stored for subsequent subtraction from the sensor signal, effectively pre-compensating for systematic errors and expanding the usable ADC range.
3Measurement precision
If multiple sampling operations are performed to compensate for variations, then the measurement precision improves, but the readout time increases
Solution Approach 1:
The patent employs periodic action by structuring the sensing operation as a repeating sequence of reset, sample, and compensate phases that occur at optimized intervals. This periodic methodology allows the system to efficiently capture multiple voltage samples in a rhythmic fashion, maximizing the use of available time while maintaining high measurement precision through systematic error cancellation.
Data Source
AI summary
The disclosure provides a processing circuit adapted to read out a sensing voltage of an X-ray sensor and a signal processing method of a sampling circuit. The processing circuit includes an amplifier and the sampling circuit. An inverting input terminal of the amplifier is coupled to the X-ray sensor. The sampling circuit is coupled to an output terminal of the amplifier. The sampling circuit obtains a first voltage, a second voltage, and a sampling voltage of the X-ray sensor in different periods. The sampling voltage is between the first voltage and the second voltage. In the readout period, the sampling circuit subtracts the second voltage from the sampling voltage to obtain a third voltage, subtracts the second voltage from the first voltage to obtain a fourth voltage, and divides the third voltage by the fourth voltage to read out the sensing voltage of the X-ray sensor.