Stacked Poly Resistor Layout for High-Voltage Audio Linearity
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Solution Overview
Problem
Audio amplifiers face challenges with distorted audio due to substrate voltage dependencies and self-heating effects in semiconductor resistors, leading to non-linearity and harmonic distortion, especially at high voltage swings like 40V, which existing technologies fail to adequately address.
Innovation Solution
The use of stacked poly resistors on n-well and p-well polysilicon layers with shallow trench isolators, where resistors are biased to cancel voltage dependencies and thermally isolated to reduce self-heating, resulting in ultra-linear, high-voltage capable resistors with improved matching characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional semiconductor resistors are used in audio amplifiers, then the device complexity is low, but substrate voltage dependencies and self-heating effects cause non-linearity and harmonic distortion
Solution Approach 1:
The resistor is divided into multiple segments with different doping types (n-type and p-type) arranged in alternating layers. Each segment has opposite voltage dependency characteristics that cancel each other out, eliminating substrate voltage dependencies while maintaining overall resistor functionality.
Solution Approach 2:
The resistor uses composite semiconductor structures combining n-type and p-type doped regions with different electrical characteristics. This composite approach allows the opposing voltage dependencies of n-type and p-type segments to compensate for each other, achieving ultra-linear performance.
2Power
If high voltage swings (40V) are used in audio amplifiers, then the power output is improved, but self-heating effects increase causing resistance fluctuations and distortion
Solution Approach 1:
The high voltage resistor is segmented into multiple lower-voltage sections with alternating n-type and p-type doping. This segmentation distributes the voltage stress and heat generation across multiple segments, reducing self-heating effects in each individual segment while maintaining high overall power capability.
Solution Approach 2:
The resistor structure changes physical parameters including doping concentration, layer thickness, and material composition to optimize thermal performance. These parameter changes enable the resistor to handle high voltage swings while minimizing temperature rise and resistance fluctuations.
3Manufacturing precision
If simple resistor structures are used, then manufacturing is easier, but matching characteristics between resistors are poor leading to audio distortion
Solution Approach 1:
Matched resistor pairs are constructed using identical segmented structures with alternating n-type and p-type layers. This segmentation ensures that both resistors in a pair experience identical voltage dependencies and self-heating characteristics, improving matching precision for audio applications.
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 solution achieves a Total Harmonic Distortion (THD) of -100dB or better, significantly reducing noise and distortion, and maintains performance across high voltage swings while minimizing temperature effects and substrate noise.
Implementation Method 1
resistors are biased to cancel voltage dependencies
Implementation Method 2
thermally isolated to reduce self-heating
Data Source
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AI summary
Disclosed is a resistor which may be used in audio conversion for an ADC. The resistor comprises a first poly resistor (302) on an n-well (NWELL) with a first shallow trench isolator (STI) therebetween and a second poly resistor (304) on a p-well (PWELL) with a second shallow trench isolator (STI) therebetween. The poly resistor on n-well and the poly resistor on p-well are biased oppositely. The resistors on n-well and p-well may be in series with other n-well or p-well resistors respectively. Similarly, multiple poly resistors on n-well may be connected in series, parallel with multiple poly resistors on p-well.