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Choosing a modular waveform digitizer

05 Mar 2014  | Arthur Pini, Greg Tate, Oliver Rovini

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A digitizer is an electronic acquisition device that acquires analogue waveforms, processes them through analogue-to-digital converters (ADCs) and sends the digitized sample to a buffer, which allows them to be saved before being processed by a computer. Digitizers date from the 1950's and 1960's when the need to rapidly acquire, store, and process multiple channels of data became evident. Today's modular digitizers share a common historical architecture augmented by new high speed serial data transmission standards such as PCI-express (PCIe) and its cousin, PXIe.

Figure 1 shows an example. These digitizers offer two or four channels with sample rates of 500MSamples/s with 16 bits of resolution. A PCIe x8 Gen2 interface supports transfer rates of up to 3.4GB/s.

Figure 1: Examples of a modern digitizer family, the Spectrum M4i series digitizer platform including both the 2 and 4 channel versions built on a PCI Express x8 Gen2 interface which supports transfer rates of up to 3.4 GB/s.

Digitizers or oscilloscopes?
Digitizers share many attributes with digital oscilloscopes. You may ask: "Which instrument is best suited to my measurement application?"

Will you be troubleshooting a circuit, device, or process or making measurements that may require analysis and processing?
The digitizer is the better tool if you will be measuring, analysing or processing data, particularly in a production environment. The intimate tie-in of the digitizer and computer makes them useful where large amounts of data are to be processed. On the other hand, troubleshooting requires the interactive viewing capability of the oscilloscope.
Do you need multiple channels in a small form factor with minimal power?
This is the forte of modular digitizers: multiple channels per card and multiple cards per system all fully synchronised. Modular instruments can extend the number of analogue or digital channels and analogue and pattern waveform generation capabilities.

Do you need high measurement throughput?
This is another area where you can use modular digitizers. Multi-lane PCIe based modular digitizers can stream data at speeds of up to 3.4 GB/s, which provide data processing within the computer.

Will the data acquired be processed by either commercial or custom analysis software?
The high throughput and large buffer memories make digitizers a great source for integrating a measurement system with processing software.

Do you need to keep the cost of ownership low?
Digitizers offer the lowest cost per acquisition channel, with ease of use, speed of integration, and reliability.

Digitizer terms
Selecting a digitizer requires matching the application needs to the digitizer specifications. The table contains a glossary of common digitizer specifications and terms.

Table: A glossary of digitizer related terms.

Selecting a digitizer
Selecting a digitizer requires that you match the application waveforms to the key digitizer specifications. This section provides some common rules of thumb to aid in the selection of a digitizer.

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