Programmable Variable Resistor for DAC Output Voltage Matching
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Solution Overview
Problem
In digital-to-analog converters, especially those in audio products, mismatches in resistor values can lead to incorrect output voltages due to differences in internal resistors.
Innovation Solution
A variable resistor is designed using a main resistor, non-volatile memory cell switches, and redundancy resistors, allowing for adjustment of resistance values by programming the switches to turn on or off, thereby correcting output voltage mismatches in digital-to-analog converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fixed-value resistors are used in digital-to-analog converters, then the circuit structure is simple, but the output voltage accuracy deteriorates due to resistor value mismatches
Solution Approach 1:
The patent transforms fixed resistors into variable resistors by incorporating switches (implemented as non-volatile memory cells) that can dynamically adjust the resistance value. This allows the resistor value to be changed after fabrication to compensate for mismatches, resolving the contradiction between simple structure and accurate output voltage.
Solution Approach 2:
The patent changes the resistance parameter of the resistors from fixed to variable by adding switch elements. The resistance value can be adjusted by programming the non-volatile memory cells, enabling correction of output voltage mismatches while maintaining a relatively simple circuit structure based on standard CMOS processes.
2Measurement precision
If resistor values are adjusted to correct mismatches, then output voltage accuracy improves, but the device complexity increases due to additional components
Solution Approach 1:
The non-volatile memory cells serve dual functions: they act as switches for adjusting resistor values and also store the calibration data. This multi-functionality reduces the need for additional components, allowing accurate output voltage correction without proportionally increasing device complexity.
Solution Approach 2:
The patent merges the switch function and memory function into a single non-volatile memory cell structure. This combination eliminates the need for separate switch and memory components, reducing overall device complexity while enabling resistor value adjustment for accurate output voltage.
3Ease of manufacture
If standard CMOS processes are used for fabrication, then manufacturing ease is high, but resistor value precision deteriorates due to process variations
Solution Approach 1:
The patent performs preliminary calibration by measuring the actual resistor values and programming the non-volatile memory cells with compensation data before the product is put into service. This preliminary action corrects for process variations in standard CMOS fabrication, achieving precise resistor values despite manufacturing tolerances.
Solution Approach 2:
The patent implements a feedback mechanism where the actual resistor values are measured, the discrepancies are calculated, and compensation is applied by programming the non-volatile memory cells. This feedback loop corrects the resistor value mismatches caused by process variations while maintaining ease of manufacture using standard CMOS processes.
Data Source
AI summary
A variable resistor and a digital-to-analog converter are provided. The variable resistor includes a main resistor, a plurality of switches, and a plurality of redundancy resistors. The switches are respectively constituted by a plurality of non-volatile memory cells. The switches are coupled to the main resistor. The redundancy resistors are respectively coupled to the main resistor through the switches.