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BANDWIDTH ENHANCEMENT OF SINGLE-SHOT DATA ACQUISITION SYSTEMS
BY DECONVOLUTION OF SYSTEM RESPONSE
John F. Aurand, Paul1 E. Patterson, Charles A. Frost
Sandia National Laboratories / High-Power ElectromagneticsDepartment
MS 1153, PO Box 5800 / Albuquerque, NM 87185-1153
Abstract SCD-5000 to a host personal computer, and then
deconvolution processing. The FlT spectrum of the
Procedures have been developed [ 11 for enhancing the
acquired signal is divided by the system transfer
effective bandwidth of single-shot measurement
function, and then an inverse FFT is used to compute
systems. One procedure characterizes the transfer
the compensated timedomain input signal. If
function of the measurement system hardware, and
necessary, any one of several lowpass filtering
the other is a software compensation technique to
algorithms may then used to reduce the deconvolution
deconvolve this transfer function from the acquired
data. The example shown employs a Tektronix
SCD-5000 Transient Digitizer, with a -3 dB
bandwidth improvement of 4.5 times, to over 15 GHz.
System Characterization
noise.
2-10
h
3 -20
0 0 ...._ ....
~ .......
_.__.__._,.._._.__...,~..........~........
.... ^...... . ......~.....................
Each of the components of a single-shot data .t
acquisition system (coaxial cabling, delay line, and
waveform recorder) is band-limited, and thus
degrades the acquired waveform. The measurement -50
system hardware is modeled as a cascaded
frequencydomain transfer function, and if mismatch 0 5 10 I5 20
S parameters are assumed negligible, then the transfer Frequency (GHz)
function can be formed as the ratio of the input and -
Fig. 1 Raw Hardware and Compensated Transfer
output signal spectra. Step timedomain excitation is Functions of SCD-5000 Measurement System
used to characterize the entire system as one network,
permitting simple and rapid evaluation of the Considering the difficulties associated with
measurement hardware. deconvolution of noisy data, these procedures have
The excitation step pulse is generated with a yielded stable, low-noise results. This success is due
Picosecond Pulse Labs 4015B pulse Generator (9 V, to careful consideration of many signal processing
15 ps), and it is measured with two systems: the details and fundamental hardware parameters.
single-shot SCD-5000system, and a wider-bandwidth Conclusions
sampling system consisting of a Tektronix CSA-803
sampling oscilloscope with 20-GHz SD-26 Sampling Bandwidthenhancement techmques have been
Head. This sampled waveform is taken as the input developed for single-shot data acquisition systems.
excitation pulse, and the transfer function of the The transfer function of the system hardware is
single-shot system is then formed as the ratio of the characterized using step timedomain excitation, and
FFT spectra of these two waveforms. robust data compensation algorithms implement
frequencydomain deconvolution of that transfer
For the example system, the hardware had a -3 dB function from the acquired data. These techniques are
bandwidth of 3.2 GHz (and a step-response risetime of most applicable to data acquisition systems with
109 ps), and an effective bandwidth after waveform recorders which have signifcant
deconvolution of 15.2 GHz (and a risetime of 23 ps). oversampling rates and well-behaved frequency
These transfer functions are shown in Fig. 1 below. rolloff.
Data ComDensation Reference
Once the transfer function of the single-shot system U1 P.E. Patterson, J.F. Aurand, C.A. Frost, 15-GHz
hardware has been characterized, then subsequent Bandwidth Enhancement of Transient Digitizers
compensation of desired data is performed by In a Portable Data Acauisition System, Sandia
post-processing. This s o h a r e performs data National Labs Technical Report, SAND93-2280,
acquisition over an IEEE-488 (GPIB) bus f o the
rm Feb. 1994.
282