SLYT821 January   2022 AFE0064 , AFE1256 , AFE2256 , AFE3256 , DDC112 , DDC1128 , DDC114 , DDC118 , DDC232 , DDC264 , DDC316

 

  1. 1Introduction
  2. 2DDC
  3. 3X-ray AFE ROICs
  4. 4Final comparison
  5. 55
  6. 6Conclusion
  7. 7Related Websites
  8. 8Important Notice

4 Final comparison

Table 4-1 summarizes the differences between the two device families.

Table 4-1 Differences between the DDC and AFE families
DDC Family AFE Family
Number of channels 2, 4, 8, 16, 32, 64, 128, 256 64, 256
Current direction Into the device Into or out of the device
Bipolar signal integration No Yes
Input DC voltage 0 V Non-zero (1.68 V for the AFE0064)
Package TQFP, small-outline IC, BGA TQFP, COF
Full-scale charge range 12.5 pC to 350 pC, 1 nC ≅0.5 pC to >10 pC
Maximum full-scale current 3 µA 0.5 µA
Input referred noise (charge) 0.2 fCrms (1,250 electrons) <0.096 fCrms (600 electrons)
Input referred noise (current) 0.5 fArms (at 1 SPS) <96 fArms (at 1 ms)
Maximum sampling rate ≅5 kSPS >50 kSPS
Maximum integration time 1 s 1 ms

Assume that you want to measure all of the charge produced within 100 ms by each of the 64 photodiodes in an array. Also assume that the maximum current is 1.2 nA. In this case, the maximum charge is 1.2 nA × 100 ms = 120 pC, which the DDC264 could handle in range 3 (150-pC full scale) in a single integration.

Looking at Figure 4-1 and assuming a 24-pF parasitic detector capacitance, you would expect the noise to be about 0.9 fCrms.

GUID-1BFC80B8-5537-4535-9356-5FC0F8C0B3B3-low.png Figure 4-1 Noise vs Csensor