D-SCOPE

Overview

This page contains the Waveform Recording Firmware packages of the NEW  27xx Open FPGA Digitizers.

Principle of Operation
The basic operating mode of a digitizer running Waveform Recording FW is essentially the same as a digital oscilloscope: the analog signal, after an input stage of signal conditioning mainly used to adapt the dynamic range, is sampled by a flash ADC, whose output, i.e. the stream of digital samples, is continuously read by an FPGA and stored in a circular memory buffer of a programmable size. At the arrival of the trigger, the buffer is frozen and made available for the readout while the acquisition can continue in a new buffer. However, there are few important differences between a digitizer and a commercial digital oscilloscope:

A. The digitizers allow for dead-timeless acquisition

In fact, unlike most oscilloscopes, they have the ability to accept two consecutive triggers very close to each other thanks to the multi buffer memory management: there is no dead time between an acquisition window and the next one.

It is even possible to accept two trigger for which the acquisition windows overlap. The dead‐timeless acquisition is a very important feature, especially in the case of events randomly distributed in time (in nuclear physics this is typically a Poissonian distribution), so that two of them, even at low rate, can occur at very short distance but you still want to capture both.

B. In the digitizers, all the channels are allowed to generate triggers independently
The individual trigger can be used locally by the channel that generated it (independent triggering) or can participate to the assertion of a global trigger for all the channels in the board, as well as to generate a pulse on the TRG‐OUT.

C. Scalability and synchronization of multi‐board systems
In most cases, the applications that require the use of several channels need to synchronize the acquisition across different digitizers. This is performed according to the following points:
Distribution of a common clock reference in order to have the same sampling clock on all the ADC channels. CAEN digitizers feature a programmable PLL able to generate the sampling clocks locked to an external clock input, whose distribution can be done in parallel from a common source, using a fan‐out, as well as through an in‐out daisy chain with the ability to use the first board as a clock master (VME models only).
Alignment of the time stamp associated with the triggers to allow off‐line reconstruction of the events read from different boards. This can be done by using an external signal as well as through an in‐out daisy chain.
Distribution of the triggers from channel to channel and from board to board, according to a certain trigger logic. Each card has different trigger sources: external TRG‐IN from the front panel, software trigger and channel self‐triggers. All these triggers can be combined in order to make coincidences, majorities, global triggers and other functions.

D. Fast data readout links
The new digitizers, compared to the previous ones, feature USB 3.0 and Ethernet ( 1/10 GbE) interfaces. These new connectors will increase the possible means to connect the digitizer to a computer, that together with the CONET optical link, now offer fast and ductile ways to operate the digitizer and download large amount of data from any detector to a computer at a speed around 280 MB/s, thus the VME-bus will not be used anymore for data transfer as the optimal rate is achievable using a direct connection.

All CAEN digitizers are equipped with their proper default firmware for waveform recording. WaveDump2 software is available to manage the acquisition. Data can be saved in real time for offline analysis.