For most Ge detector applications, digital trapezoidal shaping provides Gaussian
equivalent resolution with half the processing time. Faster processing time means the
9660 provides significantly greater throughput than a traditional analog system with its
processing or shaping times set for equivalent resolution. When using small Ge detec-
tors which are optimized for high count rate performance, throughputs of 100 kcps can
be achieved. To achieve 100 kcps and higher throughput, the highest spectral peak
must not exceed 80% of full scale. For more information on count rate performance,
refer to Canberra’s Application Note “Performance of Digital Signal Processors for
Gamma Spectroscopy”. Please contact your sales representative to request a copy.
However, the settings which realize reduced processing time, high throughput and
equivalent resolution for Ge detectors may be a bit aggressive for some low energy ap-
plications. For these applications, which include LEGe, Si(Li) and X-ray detectors,
resolution will be equal to or better than that obtained with traditional analog systems
when the Rise Time and Flat Top filter parameters are optimized for resolution. For
this case, the trapezoidal rise time parameter is increased so that the processing time
and throughput are equivalent to Gaussian shaping.
Table B.1 lists the 9660 Rise Time and Flat Top settings which optimize performance
for high throughput/good resolution and optional setting for best resolution/lower
throughput when using Germanium Coaxial detectors.
Table B.1 Gaussian Shaping vs. Throughput and Resolution
Gaussian Shaping ( s)
Highest Throughput
1
Rise Time/Flat Top
Highest Resolution
2
Rise Time/Flat Top
0.5
µ
s
0.8
µ
s/0.2
µ
s
1.2
µ
s/0.2
µ
s
1.0
µ
s
1.2
µ
s/0.6
µ
s
2.8
µ
s/0.6
µ
s
2
µ
s
2.8
µ
s/0.6
µ
s
5.6
µ
s/0.6
µ
s
4
µ
s
5.6
µ
s/0.8
µ
s
12
µ
s/0.8
µ
s
6
µ
s
8.8
µ
s/1.2
µ
s
18.4
µ
s/1.2
µ
s
12
µ
s
16.8
µ
s/2.4
µ
s
28
µ
s/2.4
µ
s
Note 1: Optimized for high throughput, good or equivalent Gaussian shaping
resolution.
Note 2: Optimized for highest resolution, equivalent Gaussian shaping
processing time/throughput.
Appendix B - Performance Adjustments
64
Model 9660-9660A ICB Digital Signal Processor
