D&TT: Specifications

MeasureBoard3 Specification Summary

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The D&TT four channel waveform analysis PCBA, MeasureBoard3, is being developed to supercede the D&TT MeasureBoard2. It is an evolutionary upgrade, scheduled for release during the summer of 2005. The D&TT MeasureBoard3 (MB3) improves upon the original MeasureBoard 2 (MB2) by increasing the data sample rate on each of the four channels to 200 MSPS and by increasing the size of the FPGA logic in order to handle significantly more complex data pre-processing tasks. The Measureboard2 series will still be available for less demanding tasks.

Each MeasureBoard channel provides for 12-bit waveform capture, spectrum analysis and raw data pre-processing in real time. A large block of field programmable logic is available for additional functions. The second generation MeasureBoard instrumentation, MB2, has been used for magnetic head and tape media test systems based on a variety of tape transports, including those for cartridge, loop, reel-to-reel and pancake. Typical heads/media being tested include those for Tape drive families LTO 1 (100GB) through LTO 3 (400GB) and similar high end products.

In addition to this specification summary, a downloadable document containing a full technical description and specifications is also available in PDF format.
For more information, please go to the White Papers page.

Overall Test Range and Accuracy

Analog input stage	· Gain variable: -17 to +25 dB · Bandwidth: 20 kHz to 60 MHz
Analog to Digital Converter	· 12-bit resolution · 200 MSPS sample rate · 80 dB spurious-free dynamic range
Bandpass filter	· Passband ripple: < 0.05dB · Stopband attenuation: > 80 dB · Center frequency: tunable in steps, 0 to 100 MHz · Bandwidth: tunable in steps, 5 KHz to 40MHz,
Data Generator	· Variable length pattern generator. RAM-based, up to 1MB. The data pattern is downloaded though the PCI bus. One independent generator per channel.
Data Generator Clock	· Programmable, 25-700 MHz
Memory	· 64MB per channel
Data Preprocessing, real time	· Spectrum analysis · Peak detection · FIR Filter · True-RMS in real time · Sequential Bandpass · Drop-out analysis · Drop-in (extra-pulse) analysis · A FPGA is accessible for additional custom test algorithms.

Measurement Hardware

Each MeasureBoard3 provides the basic measurement hardware necessary to implement the four independent test channels, including:

Programmable input gain stage to allow the unit to work over a wide range of input amplitudes.
High speed (200MSPS), 12-bit ADC, designed for very high spectral purity to support spectral analysis in addition to standard waveform analysis.
Programmable serial data generator, with up to 1MB user defined pattern and data rate set by a low-jitter PLL-based clock.
Custom, reprogrammable DSP functions in field programmable gate arrays to perform real-time data pre-processing before uploading the data to a work-station.
Programmable Digital Bandpass filter for spectral analysis.
64MB of on-board memory per channel.

Input stage and Analog to Digital Converter

The input circuit consists of an analog differential receiver which expects a signal of about .5V P-P. It is followed by a variable gain amplifier, whose output feeds the ADC.

The ADC digitizes the input waveform at a sample rate of 200 MSPS. The output data stream from the ADC is fed to each of the independent modules, the Peak Detector / Scope, Bandpass / RMS, and Threshold Detector circuits (and any other custom algorithms, as required.) The ADC circuit uses a 12-bit ADC that is specially designed for high spectral purity,a necessity when performing spectral analysis.

When measuring an input signal that is bandwidth limited to less than one-half the Nyquist sampling rate of the ADC, the input signal waveform can be fully reconstructed using band-limited interpolation with no loss of information beyond the quantization error of the 12 bit ADC.

Data Generator

The write data generator provides a variable length ring buffer that is clocked by a variable rate clock. This allows the generation of arbitrary serial digital data streams at any selected data rate. The standard configuration allocates 1 MB of the 64MB of on-board DRAM for the data generator (with the remaining DRAM used for measurement data). The data generator clock rate ranges from 25 MHz to 700 MHz, so the maximum data pattern length is approximately 12 mS to 335 mS depending upon the data generator clock rate. There are independent data generator clocks for each channel. This permits running fully independent tests on each of the 8 channels.

Bandpass/RMS Circuit

The bandpass / RMS circuit can be setup to measure either the true-RMS amplitude of the full-bandwidth input signal, or the amplitude of the input signal after being bandpass filtered by the programmable digital bandpass filter. These are both real-time functions.

When measuring the true-RMS amplitude the algorithm in the FPGA squares the input signal amplitude and accumulates it into a 56-bit accumulator. The sample size is selected by setting the 28-bit sample count register. In the true-RMS mode the circuit can accumulate up to 3.3 seconds worth of data in a single measurement.

When measuring in the bandpass filter mode, the circuit first filters the input signal through the programmable digital filter (see above). As with the true-RMS measurement, the sample size is selected by setting the 28-bit sample count register. This allows setting the measurement duration as short as a few milliseconds or as long as several hundred seconds on each bandpass amplitude measurement.

To perform spectral analysis, the circuit measures specific spectral component amplitudes using the programmable bandpass filter.