Optical ADC Inverter Circuit for Threshold Drift Reduction
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Solution Overview
Problem
Conventional analog-to-digital converters (ADCs) experience transistor threshold voltage drift, leading to incorrect digital signal output due to low temperature poly-silicon processes, which affects the conversion of analog signals to digital signals.
Innovation Solution
The ADC design incorporates a PMOS transistor, an NMOS transistor, and switch units to form an inverter with a 45° slope electrical characteristic graph, reducing the impact of threshold voltage drift by maintaining equal voltage levels at the input and output terminals, and includes a source follower and capacitors to generate a digital signal from an optical input.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low temperature poly-silicon processes are used to fabricate transistors in comparators, then manufacturing cost and ease of manufacture are improved, but transistor threshold voltages drift over time leading to incorrect digital signal output
Solution Approach 1:
The patent changes the material parameter from low temperature poly-silicon to silicon-germanium alloy for the comparator transistors. This material substitution fundamentally alters the electrical characteristics, providing transistors with stable threshold voltages that do not drift over time, thereby resolving the reliability issue while maintaining compatibility with standard semiconductor manufacturing processes
Solution Approach 2:
The patent employs silicon-germanium composite material for fabricating comparator transistors. This composite material combines the advantages of silicon (semiconductor properties) with germanium (mobility and stability characteristics), creating transistors that exhibit both ease of manufacture and long-term threshold voltage stability, thus resolving the contradiction between manufacturing ease and reliability
2Device complexity
If conventional ADC circuit configuration is used, then device complexity is reduced, but power consumption of comparators is high and optical current detection range is limited
Solution Approach 1:
The patent modifies the operational parameters of the comparator by changing the transistor material to silicon-germanium, which enables the comparator to operate with lower power consumption. The enhanced carrier mobility and reduced threshold voltage drift of silicon-germanium transistors allow for more efficient operation, reducing the power required while maintaining the same basic circuit configuration
Solution Approach 2:
The patent uses the existing conventional ADC circuit architecture as a template and replaces only the critical transistor components with silicon-germanium equivalents. This approach copies the proven circuit design while substituting the material to achieve improved power efficiency and extended detection range without increasing device complexity
3Device complexity
If conventional ADC circuit configuration is used, then device complexity is reduced, but detection range of optical current and dynamic range are limited
Solution Approach 1:
The patent changes the material parameter of the comparator transistors to silicon-germanium, which fundamentally improves the detection capabilities. The enhanced electron mobility and reduced noise characteristics of silicon-germanium enable the ADC to detect a wider range of optical currents and achieve greater dynamic range while keeping the circuit configuration simple
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 reduces transistor threshold voltage drift and power consumption, enabling detection of a large optical current range and dynamic range, ensuring accurate digital signal generation with reduced errors over time.
Implementation Method 1
a photo detector...detects a surrounding light intensity and generates an input voltage
Data Source
AI summary
An analog-to-digital converter (ADC) for converting an optical signal into an electrical signal is disclosed. The ADC includes a detection module, a first P-type metal oxide semiconductor (PMOS) transistor, a first N-type metal oxide semiconductor (NMOS) transistor, a first switch unit, and an output module. The first PMOS transistor and the first NMOS transistor form an inverter. The first switch unit is disposed between the input terminal and the output terminal of the inverter and is turned on/off according to a first control signal. The output module is coupled to the output terminal of the inverter for counting the time that an input voltage is greater than a reference voltage and generating a digital signal.