The best commercial alternative to the custom FADC design is manufactured by Acquiris which uses a very high quality 500 Msps or 1Gsps FADC IC manufactured by Thomson. The Acquiris DC265 is a CompactPCI card with 4 FADC channels with sampling rates of 500 Msps and an analog bandwidth of 150 MHz. For the quantity required for VERITAS Acquiris is quoting $1250 per channel. Acquiris also makes an 8 slot CompactPCI crate (CC108) which could be used. These cards have a very high speed data interface, the ability to read out a small amount of data at a specified boundary in RAM and most of the other essential features needed for the mode of operation required for VERITAS.
The Acquiris FADC is, however, more than twice as expensive as the custom combined FADC/CFD board; the price difference in custom and commercial electronics has been and remains to be one of the principle drivers for the custom development. If these commercial units were to be used, we would need to purchase separate fan-outs, commercial CFDs, fan-out cables, and singles rate scalers which would result in an even larger price difference. While the Acquiris boards appear to be the best commercial choice (especially for applications which require 1 Gsps) there are a number of disadvantages for their application to VERITAS. The lower channel density of 32 channels per crate (4 per board, 8 boards per crate) compared with 170 channels per VME crate requires more than 5 times as many (albeit 6U form factor) crates, CPUs and other hardware (such as reflective memory modules) compared with the custom units. These FADCs have no ability to extend the dynamic range above 8 bits or to latch the CFD hit pattern. While DMA from a single card is supported, currently these cards lack the ability to chain data transfers. This results in a significant amount of dead-time since the CPU has to do the readout sequencing, and the CPU latency will dominate the dead-time.