Dual ADC Module With Isolation

This module captures two analog signals and converts them to digital form. It features both a non‑isolated ADC and an isolated sigma‑delta ADC, along with a rad‑hard power regulator. The design is suitable for space or industrial environments requiring reliable data acquisition.

Module Functions

The points below differentiate between the isolated and non‑isolated ADCs and the purpose of the radiation‑hardened regulator.

• Non‑isolated ADC – An ADC128S102 eight‑channel, 12‑bit converter handles signals referenced to the module’s ground. It interfaces over SPI and is powered from a 3.3 V regulator.
• Isolated ADC – The AMC1203 sigma‑delta converter digitises signals on an isolated ground. A separate +5 V supply powers its analog side through an SMA connector, maintaining galvanic isolation.
• Rad‑hard regulation – An ISL75051 regulator accepts +5 V and provides a radiation‑hardened 3.3 V rail for the non‑isolated circuitry.

How To Use The Module

This section describes how to connect power, inputs and outputs to the module while maintaining isolation.

• Power connections – Provide +5 V to the SMA connector labelled +5 V_ISO for the isolated ADC. Connect another +5 V supply to the pin header labelled +5 V to power the non‑isolated section and the regulator. The ISL75051 produces the 3.3 V rail for the non‑isolated ADC and digital logic.
• Analog inputs – Two SMA connectors accept the analog signals. The left connector is for the isolated channel; the right connector is for the non‑isolated channel. Because these ADCs operate at low sample rates, you can connect directly to low‑impedance sources without additional buffering.
• Digital interface – The I/O header exposes SPI pins for the non‑isolated ADC and digital outputs from the isolated ADC. Connect these to a microcontroller or FPGA for data capture.
• Grounding – Keep the isolated and non‑isolated grounds separate. The module uses split ground regions connected only through the transformer inside the AMC1203. Do not short these grounds externally or you will defeat the isolation.

Design Features

The design features listed here deal with isolation strategy, assumptions and PCB layout that ensure accurate and reliable measurements.

• Isolation strategy – The isolated ADC receives power through a separate SMA connector (+5 V_ISO). Its reference and digital grounds are isolated from the non‑isolated side.
• Assumptions and limitations – The design assumes that the SMA cables can supply the small current needed for the isolated side and that the +5 V on the pin header is properly regulated. If you use longer cables or higher current, add additional filtering or a local regulator.
• PCB layout – The board uses a four‑layer stack with an internal ground plane. The analog section is on one side, and the digital and regulator sections are on the other. A copper pour region is assigned as analog ground and separated from digital ground by clearance. Stitching vias connect the pour to the inner ground plane.
• Decoupling – Place decoupling capacitors near every power pin, and consider additional filtering for the isolated power input. Avoid routing digital lines near the analog inputs to minimize noise.

By following these guidelines, you can integrate this module into instrumentation systems requiring both isolated and non‑isolated analog inputs. Pay attention to grounding, power filtering and isolation to ensure accurate measurements.

The sigma‑delta ADC’s digital output can be filtered in your microcontroller to achieve higher resolution at lower bandwidths. For very high impedance sensors, consider adding buffer amplifiers at the inputs to avoid loading effects. In radiation‑prone environments, select screened versions of the AMC1203 and ADC128S102 to match the regulator’s rad‑hard performance. If you need simultaneous sampling, ensure that both ADCs are triggered appropriately and that the isolated side’s clock remains synchronised with the non‑isolated side.

Additional Resources

Read the full guide article on Altium Resources for a deep dive on this project. The video below shows the design approach and preparation for manufacturing of the Rev A release of this project, including the PCB layout justification and the approach to implementing the grounding strategy for galvanic isolation.