Differential Non-Linearity

These spectra were created with a 2" Sodium Iodide detector and a radioactive source, Na22. Data acquisition used a CMC100 USB Camac  crate controller and the EZCAMAC program on a Windows box. The gate width was 400 nS for all spectra. The spectra shown are just part of the total spectrum.  The data were collected at a 5 KHz trigger rate for several hours. The the minimum count in the dip between the photopeak and the escape is about 20k-30k, so the expected rms is less than 1% in this slowly changing region. The count at the escape peak is about 100k.

The first spectrum used a LeCroy 2249w Camac ADC. This uses a Wilkinson type converter with a 20 MHz clock. It has a dead time of about 110 microseconds and 11 bits of resolution. The DNL is very good, esentially undetectable.


The second spectrum used a LeCroy 4300b 11 bit Fera ADC.  Readout was by Camac, not Fera. This is also a Wilkenson but with an effective 400MHz clock, achieved by interpolating a slower clock. The interpolation (the same technique is used in the MTD133 tdc chip) results in substatial DNL in the time measurement, which shows up in the adc value. The dead time is only about 14 microseconds (including Camac readout).  This was the fastest adc available when it was introduced in the mid eighties.

The third spectrum used the CMC081, a modern replacement (and upgrade) for the 4300b.  It uses a successive approximation adc, and a sliding scale. The  resolution is 12 bits, and the dead time is the same as the 4300b (in 4300b emulation mode). The DNL is undetectable. This adc is dual range (15 bit dynamic range), and has a dead time less than 4 microseconds in 4 channel mode.

The last spectrum is taken with the CMC080 12 bit triple range adc (18 bit dynamic range). This is a wilkenson, using an MTD135 to measure the rundown time. It also uses a sliding scale in the time domain to remove the MTD135 DNL (which is comparable to the DNL in the 4300b). The dead time can be as short as 4 microseconds.
Note the complete absence of DNL in the spectrum.