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ADC: Analog-to-Digital Converter, converting analog signals into digital signals for processing by digital devices.
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DAC: Digital-to-Analog Converter, converting digital signals into analog signals for external interfaces.
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Layout Requirements:
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Avoid placing the power module near the front-end analog input.
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Keep the power to load path short to reduce transmission noise coupling.
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Place high-frequency decoupling capacitors close to the chip power pins.
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Compact layout for the input front stage.
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Use a “1” shaped layout, avoiding U-shaped and L-shaped layouts.
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Implement π attenuation and π filtering layout functions.
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For multiple identical circuit structures, use a symmetrical layout; ensure consistent trace lengths.
Consistency and phase alignment.
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Increase the layout spacing between multiple channels.
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Add shielding cavities or shielding walls.
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Wiring Requirements:
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Minimize loop power splitting.
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In addition to considering that the analog power layout should not be close to the front-end input, the transmission path should be as short as possible, with minimal loops to reduce power noise introduction.
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Control attenuation of the shortest analog front stage traces.
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Minimize wiring length.
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Control reference impedance in layers, increase wiring width.
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Use rounded corners and gradual transitions in traces.
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Use layer 2 for cutouts and layer 3 for grounding under the analog area.
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Impedance Continuity Control – Pad Layer Treatment
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Device pads are the most significant factor for impedance discontinuity in the wiring link; layer isolation can reduce the impedance changes caused by variations in pad and trace width.
Use layer 2 for cutouts and layer 3 for grounding under the analog area.
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Shielding Ground Treatment
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The size of the shielding ground hole spacing determines the amount of EMC radiation leakage; the smaller the distance, the better.
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Smaller shielding ground hole distances help reduce interference isolation for digital-to-analog and multiple analog front stages, especially when the distance is ≤ λ/20.
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Analog grounding helps reduce interference, but if the distance is too small, it may increase signal loss; grounding distance should be ≥ 1.5W width.
Cover the analog area with shielding ground and create λ/20 shielding ground holes around the analog traces.
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Multiple Isolation Treatment
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All power and ground planes need to use separation grooves to cut off the noise coupling loops from multiple AD inputs, reducing coupling paths between multiple channels.
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Digital and Analog Common Ground Treatment
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The common ground bridge does not provide a signal return path, only serves as an equipotential short circuit.
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The width of the bridge should not be too wide, recommended around 60 mils.
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Use 20-30 mils for isolation grooves.
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It is recommended to place it near the ADC chip, but not directly under the chip.
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Ferrite Bead Bridge Grounding
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The common ground bridge does not provide a signal return path, only serves as an equipotential short circuit.
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For multiple ADCs, it is best to have one pair share a common bridge.
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Analog Area Plane Treatment
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All layers in the analog area must be completely isolated, and all layers in the analog area should be grounded.
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Digital signal wiring is prohibited from entering this area.
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Power supply for the analog area should use signal layers for copper or traces.
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