Architecture with I/O and signal conditioning provisions

Paul Boughton

The MicroTCA (µTCA) open-standard architecture provides a dense, high-speed, managed technology with built-in high availability options.  

The newer µTCA.4 sub-specification adds functionality in the provision of µRTMs for signal conditioning and I/O. This makes it attractive for I/O-intensive applications and those requiring mixed-signal capabilities in a single chassis.

A µTCA.4 chassis platform can include the following characteristics:

* High reliability chassis with full redundancy of power, cooling and MCH.
* Up to 12 AMC slots, each supporting µRTM.
* Capability to accept, filter and process many sensor inputs at high data rates.
* Precision clock and trigger generation and distribution.
* Compatible with an extensive range of processing and I/O AMCs (since a µTCA.4 chassis is also compatible with standard µTCA.0 AMCs).

One example is the 8U MicroTCA.4 chassis design from VadaTech. Designed for High-Energy Physics and other applications that require rear I/O, the chassis platform offers full redundancy, including dual fan trays, dual MicroTCA Carrier Hub (MCH) slots, and quad Power Module (PM) slots.

In an 8U size, you can fit 12 double-wide AMC (Advanced Mezzanine Cards) modules in the mid-size as well as the 12 µRTMs in the 19-in rack. See Fig. 1 which shows the chassis, µRTM, MCH, and PM. The MCH includes full platform management capability, ensuring all payload AMCs and µRTMs are completely compatible before completing system bring-up.

Early entrants to the µTCA.4 chassis market were designed for development use only, and that can show in the way a chassis is designed and manufactured. In contrast, later products such as the VadaTech VT81x series are production-ready chassis, as shown by their attention to detail.  

For example, utilising an aluminium construction provides a much lighter result while maintaining a strong, reliable frame, and aluminium is a preferred material for some particle physics experiments. For better cable management, cable ducts can be integrated within the chassis frame (often below the card cage) to protect and route the cables to the rear of the chassis.

The fan trays are arranged with sixteen 2-in fans each above and below the card cage in a push-pull configuration. The smaller, powerful fans ensure each slot gets optimal airflow, avoiding hot spots.  Insertion/extraction of the fan trays is considered as well.   

By installing Teflon strips where the fan trays are plugged, they can slide in and out much more smoothly and easily. It is also advisable to utilize shrouded blind-mate connectors for both the male and female ends of the plugs, which prevent damage and ease guided insertion.  

In addition, the backplane design takes into account the target applications – where precision timing is important – so the clock traces are laid out to give equal track length from MCH to each AMC slot, easing latency equalisation.

In a µTCA.4 chassis platform, as on other MicroTCA platforms, the radial I2C bus (IPMI) is routed to each AMC for monitoring/control for each module.  A pluggable Telco alarm can be incorporated as well as a JTAG Switch Module (JSM) which provides JTAG access to each AMC slot – suitable for FPGA code development.

An advantage of the MicroTCA architecture is the ability to utilize multiple fabrics with defined port allocations.  Mixed-fabric configurations are supported, either through the Extended Options region or by use of dual MCHs. All of this results in a modular product that offers a great deal of flexibility in both capability and price/performance.

Although MicroTCA.4 was first developed for the high-energy physics community, the architecture is suitable for all types of applications where its bandwidth, management/control, I/O, and large ecosystem is an advantage.  The AMC/µRTM division was specifically designed to support the combination of off-the-shelf standard processing elements (AMCs) with custom signal conditioning (RTMs), an attractive approach in many industries.