Single-Pin ADC Reader Using Nonlinear Resistor Divider Coding
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Solution Overview
Problem
Existing methods for achieving 8-bit accuracy using a single pin of an integrated circuit require very accurate current sources and resistors, which are costly and limited by the accuracy of inexpensive resistors typically used, making it challenging to provide high-resolution analog-to-digital conversion within pin-limited packages.
Innovation Solution
The implementation of an 8-bit ADC reader using a resistor divider network with a non-linear step, where the ratio between resistors is selected to achieve high accuracy, combining a 5-bit ADC for least significant bits and a delta detect circuit for most significant bits, allowing for 8-bit accuracy using 1% accuracy resistors and a single pin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional ADC reader uses a resistor divider with linear steps to achieve high-resolution conversion, then the measurement precision improves, but the device complexity and cost increase due to requiring very accurate current sources and resistors
Solution Approach 1:
The patent divides the 8-bit ADC conversion into two segments: a 5-bit linear ADC for the least significant bits (LSB) and a 3-bit non-linear delta detect circuit for the most significant bits (MSB). This segmentation allows each segment to use simpler, less accurate components while achieving overall 8-bit accuracy when combined.
Solution Approach 2:
The patent applies different quality requirements to different parts of the conversion process. The LSB portion uses standard 1% accuracy resistors and a simple linear ADC, while the MSB portion uses a non-linear scaling approach that compensates for component inaccuracies. This local differentiation in quality requirements reduces overall system complexity and cost.
2Ease of manufacture
If inexpensive resistors with 1% accuracy are used in the resistor divider, then the ease of manufacture improves, but the measurement precision deteriorates due to limited resistor accuracy
Solution Approach 1:
The patent changes the parameter space by introducing non-linear scaling factors that map the inaccurate linear resistor divider ratios to the correct non-linear ADC code values. This allows inexpensive 1% resistors to achieve 8-bit accuracy through mathematical compensation rather than requiring expensive high-precision resistors.
Solution Approach 2:
The patent creates a mathematical model (lookup tables or calculation algorithms) that copies the ideal non-linear transfer characteristic into the digital domain, compensating for the linear inaccuracies of the physical resistor divider. This digital copy corrects the analog imperfections.
3Productivity
If a single pin is used for ADC input to reduce pin requirements, then the productivity improves, but the measurement precision worsens due to the need for very accurate current sources and resistors
Solution Approach 1:
The patent makes a single pin perform multiple functions: it serves as the input for the resistor divider network and also as the output for the ADC reading. The dual-use nature of the pin is enabled by the non-linear scaling approach that compensates for the limitations of single-pin operation.
Solution Approach 2:
The system uses the same single pin for both input and output operations, and the non-linear correction algorithm automatically compensates for the inaccuracies introduced by this constrained configuration, making the system self-correcting without requiring additional external components.
Data Source
AI summary
An integrated circuit has a single input pin for determining a value associated with a resistor divider. First circuitry determines a resistor ratio of the resistor divider through the single input pin. A first register stores a first group of bits representing the resistor ratio. The first group of bits represents the least significant bits of the value. Second circuitry determines an equivalent resistance of the resistor divider through the single input pin. A second register stores a second group of bits representing the equivalent resistance.