Increased sensitivity option enhances digitisers

3rd April 2017
Posted By : Mick Elliott
Increased sensitivity option enhances digitisers

Looking to increase the sensitivity and therefore absolute resolution for low amplitude signals in the ±40 mV up to ±0.5 V range Spectrum has announced an option (M4i.22xx-ir40m) for high-speed 22xx series of digitiser products.  The current products are optimised to acquire, store and analyse signals in the ±200 mV up to ±2.5 V range.

Oliver Rovini, Spectrum's CTO, said, "The modular way that we design and build our products means that we can provide this front-end option very easily as a new daughter board within the 22xx range.  Matching the digitiser's range to the signal under test is important as it ensures maximum dynamic range as well as better measurement accuracy and resolution.  For example, if a signal only covers half of a digitiser's selected full scale range then only half of the digitiser's available analogue-to-digital converter (ADC) resolution can used.  Smaller, or lower level, signals will use even less of the ADC's capabilities and further reduce the digitiser's overall signal-to-noise performance.  This new option lets users select more sensitive, full scale ranges so that, even for low amplitude signals, the ADC's complete dynamic range is available."

He used the example of a 10-bit digitiser with a lowest 50Ω range at ±0.5V full scale input range that has to acquire a signal with an amplitude of around 50mV. 

The 10-bit ADC offers 1024 (210) levels of resolution each of about 1 mV (1V/1024). 

The signal would therefore only cover about 50 levels of the 10-bit ADC's available range.  Spectrum's 22xx series digitisers use 8-bit ADCs that give 256 (28) levels of resolution. 

So, by using this new low range option, the digitiser becomes more sensitive with around 0. mV (80mV/256) of resolution capturing the 50 mV signal with around three times more resolution than the more expensive 10-bit unit.

For extremely low amplitude signals, the 22xx series digitisers can also be used with Spectrum's high bandwidth (up to 2GHz) external SPA series amplifiers.

These free-standing units offer additional x10 (20dB) or x100 (40dB) gain making it possible to capture and analyse signals that go down into the low mV ranges.

The 22xx series digitisers come in a variety of popular form factors including PCIe, PXIe and LXI. 

Models are available with sampling rates of 1.25, 2.5 and 5 GS/s and bandwidths of 500 MHz or 1.5GHz (700MHz with low input range option).

Versions with one, two and four channels are available for units in the PCIe and PXIe formats, while the larger LXI-based instruments offer models that have from 2 to 24 fully synchronous channels.

All Spectrum digitisers are designed so that each channel features its own ADC, large acquisition memory (1GSample/channel) and independent, front-end, signal conditioning circuitry. 

The ADCs are clocked synchronously to ensure inter-channel timing measurements can be made with the best possible accuracy as well as maintaining a constant phase relationship. 

The combination of fast sampling rate, wide bandwidth and long acquisition memory enables the digitisers to capture long, complex, high frequency signals. 

It also makes it possible to characterise and measure fast events that go down into the nano- and sub-nanosecond timing ranges.

The digitisers come with all the tools necessary to capture, digitise and analyse electronic signals.  The products are fully programmable and come with drivers that allow users to write their own control programs with a variety of popular programming languages, including C++, Visual Basic, VB.NET, C#, J#, Delphi, IVI, Java and Python code. Third party software support is also provided for LabVIEW, LabWindows and MATLAB.

If users do not want to write their own programs, Spectrum offers SBench 6 -- an easy-to-use, graphical user interface.  

The 22xx series digitiser products, together with the new M4i.22xx-ir40m front-end option, are available for immediate delivery. 

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