Current-Source DAC Layout for Uniform Voltage and Low Distortion
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Solution Overview
Problem
Conventional D/A converters experience voltage drops and current errors due to irregular wiring lengths, leading to distortion in output analog signals, especially at low power source voltages where output resistance increases.
Innovation Solution
The D/A converter design includes current sources with equal-length current supply wirings and ground-side wirings to ensure uniform voltage distribution, reducing IR drops and minimizing current variations, thereby decreasing signal distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If wiring lengths from current supply point to each current source are different, then device complexity is reduced, but voltage uniformity deteriorates due to IR drops
Solution Approach 1:
The patent applies equipotentiality by designing current supply wirings and ground-side wirings to have equal lengths from the constant voltage source and ground terminal to each current source. This ensures that all current sources experience the same voltage drop, maintaining uniform voltage levels across the circuit despite the presence of wiring parasitic resistance.
Solution Approach 2:
The patent changes the wiring length parameter to be equal for all current supply paths and ground paths. By standardizing the wiring length parameter across different paths, the patent eliminates the variation in voltage drops that would otherwise occur due to different path lengths, thereby resolving the voltage uniformity issue.
2Volume of moving object
If power source voltage is reduced due to CMOS element miniaturization, then device size is reduced, but output resistance increases leading to higher current errors
Solution Approach 1:
The patent maintains equipotential conditions by ensuring equal wiring lengths, which compensates for the increased output resistance effect. Even at low power source voltages, the uniform voltage distribution ensures that current sources operate under consistent conditions, minimizing current errors despite the higher output resistance caused by miniaturization.
Solution Approach 2:
The patent converts the harmful effect of wiring parasitic resistance into a beneficial uniform voltage distribution. By designing equal-length wirings, the patent ensures that the IR drops occur uniformly across all paths, which actually helps maintain current accuracy by preventing differential voltage errors that would be more problematic at low power source voltages.
3Ease of manufacture
If wiring parasitic resistance is present, then ease of manufacture is improved, but signal distortion increases due to voltage drops
Solution Approach 1:
The patent applies equipotentiality by ensuring that all current supply wirings and ground-side wirings have equal lengths. This design approach maintains uniform voltage levels across all current sources despite the presence of wiring parasitic resistance, thereby preventing signal distortion while remaining easy to manufacture through standardized wiring patterns.
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 effectively suppresses signal distortion and improves precision by maintaining consistent output currents across current sources, even at low power source voltages, reducing the impact of IR drops and output resistance errors.
Implementation Method 1
a voltage supplied to the source of a P-type MOS transistor (or an N-type MOS transistor) as a current source decreases in the order of Vss1, Vss2, and Vss3 due to a voltage drop (or an IR drop) generated by a wiring parasitic resistance
Data Source
AI summary
A D/A converter includes a plurality of current sources configured to be on or off according to input digital data; a constant voltage source configured to apply a constant voltage to the current sources; current supply wirings provided between the constant voltage source and the respective current source, the current supply wirings respectively having equal length from the constant voltage source to the respective current source; ground-side wirings summing up output currents from the plurality of current sources; and output terminals connected to the ground-side wirings, the output terminals outputting analogue data corresponding to the input digital data.