Pharmaceutical & medical Cases FWHM (ns) CH1/CH2 Mean
CH1=8 dB, CH2=7 dB 0.6543/0.6531 CH1=9 dB, CH2=7 dB 0.6656/0.6532 CH1=10 dB, CH2=7 dB 0.6549/0.6520 CH1=10 dB, CH2=0 dB 0.6708/0.6652 CH1=20 dB, CH2=0 dB 0.6722/0.6657
SD
0.0050/0.0028 0.0037/0.0024 0.0028/0.0024 0.0075/0.0044 0.0141/0.0056
SNR (dB) CH1/CH2 Mean
46.21/47.28 46.24/47.22 47.44/47.05 41.72/41.02 32.07/40.98
Table 2. Measured FWHM and SNR
Figure 5. Overlap of five test cases with either saturation or over attenuation.
Figure 6. Test cases with input attenuated by 10 dB and 20 dB.
The AD9082 ADC has an overload protection circuit, which will be activated if the amplitude of the input is higher than the upper limit. There is often a recovery tail at the falling phase of the pulse if the protection circuit is activated, resulting in a clipped peak at FS and a recovery tail. A shorter recovery tail is important for accurate time and hence mass measurement for TOF MS. Figure 5 showed the plot of five cases with either saturation (up to 6 dB) or attenuation. There was a recovery tail of <0.4 ns for 6 dB saturation, suggesting minimal recovery widening when the protection circuit was activated. To test ADC performance with weak input, we acquired the signal attenuated by 10 dB and 20 dB, as shown in Figure 6. The clean trace of the signal was at 10 per cent FS, or attenuated by 20 dB, suggesting minimal noise contributed by the ADC. For the ADC noise floor, CH1 was connected with 50 Ω terminator while CH2 remains at >90 per cent FS, as shown in Figure 7. We analysed the noise data by plotting the histogram and calculating its standard deviation, as shown in Figure 8. The standard deviation of this case was at 0.0025, suggesting an SNR of 52 dB at FS. To further quantify the accuracy of time measurement and noise performance, we segmented each pulse with the peak in the center of a 30 ns window. We then fitted each pulse with a Gaussian model to measure its FWHM. We used 12 ns data on each side, or 24 ns total, of the 30 ns window as the baseline for noise calculation. Figure 9 was the plot of the complete acquisition for the test case of input at 10 per cent FS and zoom-in of a single pulse with Gaussian fit and segmented baseline. Table 1 listed the mean and measured FWHM and calculated SNR. We measured the FWHM and SNR of all test cases with input attenuated from 1 dB to
20 dB. The results were summarised in Table 2. The results suggested accurate time measurement with consistent FWHM readout across various input amplitudes.
Figure 7. Noise floor measurement with CH1 connected with 50 Ω terminator.
DISCUSSION AND CONCLUSION With the establishment of MALDI TOF MS as standard care for bacterial identification in clinical microbiology laboratories and growing interest in proteomics for personalised medicine, the MALDI TOF MS is expected to continue its growth momentum in healthcare in the coming decades. There are also broad applications of TOF MS in biomedical and drug discovery research, food safety, and environmental surveillance because of its advantage for intact molecules with a wide range of molecular weights. With superior noise performance and sampling rate 3× to 6× faster than the ADCs in the current generation of TOF MS instruments, the low noise, high speed ADC is a critical part of next-generation high performance TOF MS instruments. The high sampling rate makes it possible to reduce the footprint of TOF MS instrument without sacrificing performance because it can reduce the length of the flight tube and hence the burden of the vacuum system. A smaller footprint is important for point-of-care applications and various field applications of TOF MS.
Figure 8. Histograms of noise floor (CH1, left) and FS signal (CH2, right) measurement.
There are limitations in our bench test of the AD9082, including limited availability of external attenuators for creating test cases with low amplitude input (such as 1 per cent FS, or 40 dB attenuation), impedance mismatch causing reflection in the data, and open space without shielding of electromagnetic interference. The reported SNR of the test cases was lower than its actual value because reflection in the baseline caused by impedance mismatch was not removed in the noise calculation. MxFE evaluation boards along with graphic user interface (GUI) software are available for more intensive test. Detailed instructions aided by live demonstration can facilitate setting up the customer evaluation system. Prototyping with MxFE samples is easy with guidance from an experienced application team.
The measured FWHM and SNR demonstrate superior time accuracy and noise performance of the MxFE ADCs. The up to 10 GSPS sampling rate of MxFE available on the market gives the flexibility to design next-generation TOF MS with better mass accuracy and mass resolution, higher sensitivity, and an even smaller footprint. In addition, MxFE ADCs are backed by power, clocking, and driver products to help ensure seamless systems integration and optimisation.
Figure 9. Pulse and baseline segmentation for FWHM and SNR measurement for the test case of input at 10% FS.
48 Analog Devices
www.analog.com January 2024 Instrumentation Monthly SD
0.275/0.363 0.408/0.439 0.587/0.273 0.556/0.248 0.468/0.203
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93
