Part Number: ADS8556
Other Parts Discussed in Thread: REF6225, , DAC8734, PSIEVM
Hello!
We are designing a precision control system using one ADS8556 along with four multiplexers to achieve switching and acquisition of more than 20 analog signals, and two DAC8734 for single-ended output. The reference source is REF6225, which drives both the ADC and three DACs. The system focuses on the frequency range of 0.1Hz to 200Hz, with a target of 16-bit accuracy and a noise floor goal of 300µV.
Phenomenon:
When the ADC/DAC is not operating, the ripple on the REF6225 decoupling capacitors is <300µV (oscilloscope noise floor level), but there is a spike at 65kHz (analyzed by N9020).
After the ADC/DAC runs at full speed, the overall board ripple rises to about 1mV (at this time, the DAC is not driving the downstream amplifier).
The design references the TI PSIEVM, but understanding of return paths and ground plane segmentation may be insufficient.
Questions:
Please advise on the layout and routing for the ADC/DAC board, especially for ground plane segmentation and return path design.
The digital control signals for the multiplexers need to cross the analog signal area. How should this be handled to reduce coupling?
REF6225 provides the reference for one ADC and three DACs. How should the layout and routing be done to improve accuracy?
Test conditions:
Keysight MOSX4154, N2870A 1:1 probe (with ground spring), N9020 spectrum analyzer.
PCB layout diagrams, local routing screenshots, and test waveforms can be provided if needed.
Thank you for your guidance!
