What are the price defining differences between 46xx and 49xx series
On the first look when comparing PCIe digitizer M2i.465x series with M2i.491x series (the same for Ethernet/LXI digitizer DN2.465-xx and DN2.491-xx) one will only see the higher sampling rate of the 491x series and may wonder where the higher price of the 3 MS/s 465x series compared to the 10 MS/s 491x series comes from. This comparison will show the technical differences and advantages of the one product compared to the other.
Both product lines are state-of-the-art 16 bit digitizer with best performance and a high quality analog front-end. The families are available with different channel counts on different platforms:
|Type||465x 3 MS/s series||491x 10 MS/s series|
|PCIe 2 channels||M2i.4650-exp||n.a.|
|PCIe 4 channels||M2i.4651-exp||M2i.4911-exp|
|PCIe 8 channels||M2i.4652-exp||M2i.4912-exp|
|LXI/Ethernet 4 channels||DN2.465-04||DN2.491-04|
|LXI/Ethernet 8 channels||DN2.465-08||DN2.491-08|
|LXI/Ethernet 16 channels||DN2.465-16||DN2.491-16|
|PXI 2 channels||MX.4650||n.a.|
|PXI 4 channels||MX.4651||MX.4911|
Besides the obvious sampling rate difference there are some mayor technical differences between the two product lines that explain the price difference. In general the 491x series is more a general purpose 16 bit digitizer product while the 465x series is an outstanding high quality 16 bit digitizer with best dynamic performance. The following list shows the main differences and explains the advantages (marked in bold):
Sampling Rate + Bandwidth
465x Series: 3 MS/s maximum sampling rate with 1.5 MHz bandwidth
491x Series: 10 MS/s maximum sampling rate with 5 MHz bandwidth
The higher sampling rate gives a better time resolution and allows to acquire more samples per waveform. The higher bandwidth shows signals with higher frequeny parts in the acquisition but alos collects mor ehigh frequent noise. More information on sampling speed is found here.
Differential Input Configuration
465x Series: Each channel can be switched individually between single-ended and differential input allowing to easily mix single-ended and differential inputs and also giving the maximum number of synchronous differential inputs.
491x Series: The complete card can be switched between single-ended or differential input mode. When using differential inputs the number of available channels is divided by two (4912: 8 single-ended inputs or 4 differential inputs)
465x Series: 50 mV to 10 V
491x Series: 200 mV to 10 V
The two additional input ranges of the 465x series allow to directly acquire low voltage signals. The 50 mV input range gives 4 times the resolution for small voltage signals than the 200 mV. In the smallest available range the sensitivity (voltage per LSB) is 1.56 ?V for the 465x series and 6.25 ?V for the 491x series. Details on input ranges and sensitivity are found here and here.
SNR, THD and ENOB
465x Series: SNR=82.5 dB, THD=-90.1 dB, ENOB=13.3 LSB (10 kHz signal)
491x Series: SNR=74.5 dB, THD =-80.0 dB, ENOB=12.0 LSB (1 MHz signal)
Looking into the dynamic parametersone can see the signal quality difference between the two products. The effective number of bits (ENOB) show a great advantage for the 465x series cards. As long as the signal frequency is low and fits into the bandwidth and sampling rate of the 465x series this is a clear advantage.
A general introduction to all the terms is found here.
Zero Noise Level
465x Series: 3.0 LSB rms (? 500 mV) or 30 uV rms (< 500 mV)
491x Series: 4.0 LSB rms (? 500 mV) or 31 uV rms (< 500 mV)
The zero rms noise level is measured with open inputs and external 50 ? termination and shows the self generated noise floor of the digitizer.
465x Series: ?110 dB on all channels and input ranges
491x Series: ?58 dB to ?100 dB depending on input range and card type
The crosstalk shows how the adjacent channels influence each other and how much of the neighbour signal can be seen on the acquisition. The higher the value the less the neighbour signal is seen.