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USB modules tout simultaneous-channel data conversion, digital I/O

Posted: 09 Nov 2005 ?? ?Print Version ?Bookmark and Share

Keywords:dt9836? data-acquisition? data translation?

underscoring USB 2.0 ascendancy

These high-resolution DT9836 series data-acq products from Data Translation truly underscore the ascendancy of USB 2.0 (Universal Serial Bus) in the lab and on the factory floor. In many instances, it's now the networking scheme of choice for data acquisition and measurement applications.

With USB's inherent plug-and-play capability, it's also relatively easy to implement multi-module PC-hosted systems. The fact that high-speed USB, running at 480Mbps, can support simultaneous data capture on up to a dozen parallel A/D channels in these products, is testimony to USB's utility and efficiency.

In this USB application there are virtually no limits to simultaneous operation of all the sub-systems in a DT9836. What's more, these products are also USB v1.1 compatible. And, they're available in both board-level versions for embedding, or as a box-level implementation replete with I/O connectors.

2.5MHz-bandwidth channels
As the press statement notes, a DT9836 series device runs at up to 225kHz/channel, with each 2.5MHz-bandwidth input packing its own track-and-hold stage and analog-to-digital converter (ADC). That architecture eliminates timing errors (phase shift) between channels. As such, you can correlate simultaneous measurements of six or 12 analog inputs at the maximum rate of the sample clock.

The 1ns aperture uncertainty spec, found during a track-and-hold transition, virtually eliminates any phase-noise from channel-to-channel. You also get a maximum aperture delay of 35ns; that delay is the time that it takes an A/D to switch from track to hold mode). That aperture matching is within a tight 5ns. Across all track-and-hold circuits, it virtually eliminates channel-to-channel skew that you typically see with MUXed A/D inputs.

In operation, these systems accept bipolar input signals of 5V and 10V on high-impedance inputs. By configuring each analog input channel for the input range that you want, you can connect many types of transducers. That can simplify a measurement system and make it more versatile.

High performance ADCs
As for the ADCs, they tout INL (integral non-linearity) specs of 0.015 percent. DNL (differential non-linearity) is within 0.003 percent. Bias current is less than 1nA. These converters dish up an ENOB (effective number of bits) rating of 13.5-bits and a SFDR (spurious-free dynamic range) spec of a healthy 96dB.

On the output side, DT9836 Series devices include a pair of de-glitched analog outputs, and these operate simultaneously, too. Each output channel has its own digital-to-analog converter (DAC). These DACs generate outputs over 10V with 16-bit resolution. Settling time for a 10V step is 5?s, and settling time for a 100mV step is 2?s.

Simultaneous stimulus and response
With the output DACs updating at 500kS/s, you can update as you're acquiring input data. That means you can run a data-acq-and-control system with simultaneous stimulus and response. You can also update the 16 digital outputs with the analog outputs at the analog output rate.

Speaking of digital I/O, the DT9836s pack 16 input lines and 16 output lines; all are LVTTL-compatible (3.3V). Eight inputs can be used to sense interrupts on a change of state. In that kind of operation, you can read all the digital inputs simultaneously with the analog inputs at the A/D clock rate.

The digital input lines can also be clocked separately at up to 225kS/s. For digital output operations, you can update all the digital output lines with the analog output channels at the DAC output clock rate.

The DT9836 series modules also use independent clocks and triggers for the ADCs and DACs. This lets you trigger and clock analog outputs synchronously with, or independent of, analog inputs.

The A/D and DAC sub-systems also support the use of both an internal 36MHz clock (with a divider that makes it useful from 225kHz down to 0.00838Hz) and external clocks. The DAC clock ranges from 0.00838Hz to 500kHz. Triggers can be derived from software, an analog level, or an edge-sensitive external LVTTL input.

Rotating machinery
Data Translation's release notes mention the three quadrature decoders on-board. These permit simultaneous de-coding of three quadrature-encoded inputs. That can be used to gather relative or absolute position of a motor shaft, for example, or (by calculating the difference between samples) a shaft's rotational speed. The quadrature encoders also support X-Y positioning apps.

The quadrature inputs also pack noise filters, with selectable filter-clock frequency selection.

Software galore
Data Translation's press statement indicates the DT9836 Series ships with device drivers for Windows 2000 and Windows XP. These are called DT-Open Layers drivers. Significantly, almost all of the company's data-acq products, including the DT9836s, are compatible with the DT-Open Layers software standard.

So, if you have an application that was previously developed with the company's software, you can upgrade readily to this series. Little or no re-programming is likely needed. If, for example, you're currently using one of Data Translation's PCI plug-ins, upgrading to a USB-connected DT9836 series module involves little more that loading and configuring a new driver.

Canned applications
The notes also mention the ready-to-measure applications. Data Translation calls these Scope and Quick Data Acq. They let you take data almost immediately after set-up. you also get an eval version of DT MeasureFoundry, a test-and-measurement builder.

DT Measure Foundry, now in rev v4.0.7, is a visual software environment for creating test-and-measurement, control, and analysis applications. By dragging and dropping instrument-like components onto a worksheet, and then configuring so-called property pages, you develop your applications without any programming or wiring changes or switch settings.

These tools and software options, as well as the use of third party packages such as LabVIEW, let you program applications at many levels, from writing source code to using graphical environments.

- Alex Mendelsohn

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