Medical Application Case Study - Data Acquisition Spectroscopy

Medical Applications

Kinetics of Preotein Dynamics

Customer Case

The customer is measuring kinetics of protein dynamics with a time scale of between a few nanoseconds and about a hundred milliseconds. The customer's two response signals occur after a few-nanosecond-pulse excitation that repeats at a rate of 1-10Hz. This requires a bandwidth from DC to a few hundred MHz, sampling speed of about 1-2GS/s, and processing time for one acquisition that is less than 1-0.1secs. An analog signal of about 10-30mV comes from a Photo-Multiplier Tube (PMT) or a photo-diode with a trans-impedance pre-amplifier.

The customer is currently using a couple of Tektronix scopes (TDS754A and TDS420A, with 50K and 60K points of memory, respectively) to effectively cover the whole capture time range. The sampling rate usually corresponds to 0.5ns/point, i.e. 2GS/s. The Tektronix scopes are able to keep up with a 1Hz pulse repetition rate without missing triggers. The customer wants to move to a higher performance embedded solution that is capable of keeping up with the 10Hz repetition rate.

GaGe Case Solution

The CompuScope 82G is able to sample at the required 2GS/s in single-channel mode. Models are available with 2, 4 or 8 Megasamples of acquisition memory, more than enough to fulfill the requirement.

Previously, the customer achieved repetitive signal averaging using the built-in signal averaging functions in his TDS oscilloscopes. The disadvantage of this set-up was that occasionally a strong, randomly occurring surge pulse would occur, compromising the integrity of the averaged signal. By contrast, the CS82G data are transferred to host PC memory for numerical averaging. This allows "intelligent averaging", wherein surge signals may be identified and rejected before being summed into the averaging buffer. Therefore, only signals that improve the signal-to-noise ratio are processed. The CS82G's ability to reject data before processing proved to be a powerful feature for the customer's application.

As an example of the achievable rate of repetitive captures, we consider the acquisition of 50,000 Samples on two channels at 2 GS/s using two CS82G's in a Master/Slave configuration. The current PCI bus transfer speed for the CS82G is over 3 MB per second. Consequently, the download time to PC RAM for 2 x 50,000 one Byte Samples would be:

PCI transfer time = 100,000 B / 3 MB/s = 33 milliseconds

The 25 msec capture time and the short trigger re-arm time are insignificant compared to this transfer time. Consequently, a signal repetition frequency of about 30 Hz (> 1/33 ms) can be achieved by the CS82G hardware.

GaGe Case Recommended Products

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