Things to consider while selecting a Digitizer

Transcription

1 Things to consider while selecting a Digitizer Chinmay Anand Misra Certified LabVIEW Developer Staff Applications Engineer

2 Things to Consider Specifications Ecosystem

3 Agenda Top 10 things to consider while selecting a digitizer Bandwidth Sampling Rate Sampling Modes Specification Resolution and Dynamic Range Triggering Onboard Memory Channel Density Synchronization Ecosystem Mixed Signal capability Software Analysis Capability

4 Bandwidth Frequency range of an input signal that can pass through the analog front end Frequency at which a sinusoidal input signal is attenuated to 70.7 percent of its amplitude

5 Bandwidth Use a digitizer with bandwidth at least two times the highest frequency component in the signal

6 Bandwidth Bandwidth can be approximated by rise time of the signal Rise Time -time taken to transition from 10 to 90 percent of signal amplitude

7 Bandwidth Form Factor PCI/PXI PCI/PXI PCI/PXI PCI/PXI/ PXIe PCI/PXI PCI/PXI PCI/PXI PCI/PXI Resolution (bits) SampleRate (MS/s) Bandwidth (MHz) Input Impedance Max Range (Vpp) Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω 50Ω 6/30 10/ /20 10/ # Channels Cost $4800- $9600 $3000- $6500 $7900- $12100 $6500- $14000 $7500- $13500 $5500- $10000 $7000- $12000 $9000- $14000

8 Sampling Rate The rate at which the analog-to-digital converter (ADC) digitizes the incoming signal

9 Sampling Rate NyquistTheorem -Sample rate needs to be at least twice as fast as the highest frequency component in the signal Sampling at just twice the highest frequency component is not enough to accurately reproduce time-domain signals

10 Sampling Rate Digitizer s sample rate should be at least three to four times the digitizer s bandwidth

11 Sampling Rate Form Factor PCI/PXI PCI/PXI PCI/PXI PCI/PXI/ PXIe PCI/PXI PCI/PXI PCI/PXI PCI/PXI Resolution (bits) SampleRate (MS/s) Bandwidth (MHz) Input Impedance Max Range (Vpp) Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω 50Ω 6/30 10/ /20 10/ # Channels Cost $4800- $9600 $3000- $6500 $7900- $12100 $6500- $14000 $7500- $13500 $5500- $10000 $7000- $12000 $9000- $14000

12 Sampling Modes Real-time sample rate describes the clock rate of the ADC and indicates the maximum rate an incoming signal can be acquired in a singleshot acquisition Equivalent-time sampling is a method of reconstructing a signal based on a series of triggered waveforms that are each acquired in single-shot mode

13 RIS Bin 1 Bin 2 Bin 3

14 Sampling Modes Digitize r Model Chann els Real-Time Sample Rate Equivalent- Time Sample Rate Bandwidth Resolutio n NI GS/s 20 GS/s 300 MHz 8 Bits NI MS/s 5 GS/s 125 MHz 8 Bits NI MS/s 4 GS/s 150 MHz 12 Bits NI MS/s 2 GS/s 100 MHz 14 Bits NI MS/s 60 MHz 12 Bits NI ks/s to 15 MS/s 6 MHz 16 to 24 Bits User- Defined

15 Resolution and Dynamic Range Number of bits returned by the ADC is the digitizer s resolution

16 Resolution and Dynamic Range Dynamic range is a ratio of the maximum signal and minimum signal that can measured at a single time Expressed in decibels Dynamic Range (db) = 20 x log (Maximum Voltage / Minimum Voltage) The ability of the digitizer to measure small signals in the presence of large ones

17 Resolution and Dynamic Range One of the reasons for using a high-resolution digitizer is to measure small signals Why not just use a lower resolution instrument and a smaller range to zoom in on the signal to measure small voltages?

18 Resolution and Dynamic Range Form Factor PCI/PXI PCI/PXI PCI/PXI Resolution (bits) SampleRate (MS/s) Bandwidth (MHz) Input Impedance Max Range (Vpp) PCI/PXI/ PXIe PCI/PXI PCI/PXI PCI/PXI PCI/PXI Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω 50Ω 6/30 10/ /20 10/ # Channels Cost $4800- $9600 $3000- $6500 $7900- $12100 $6500- $14000 $7500- $13500 $5500- $10000 $7000- $12000 $9000- $14000

19 Triggering Trigger is an event Digitizer s triggering capability allows you to isolate this event and capture the signal before and after the event Most digitizers and oscilloscopes include analog edge, digital, and software triggering Window, hysteresis, and video triggering featured on theni 5122,NI 5124andNI 5114

20 Triggering Reference (Stop) Trigger Types NI 5112 NI 5114 NI 5122 NI 5124 NI 5922 Immediate, Analog Edge, Digital Edge, Hysteresis, Window, Software Immediate, Analog Edge, Digital Edge, Hysteresis, Window, Software, Video Immediate, Analog Edge, Digital Edge, Hysteresis, Window, Software, Video Immediate, Analog Edge, Digital Edge, Hysteresis, Window, Software, Video Immediate, Analog Edge, Digital Edge, Hysteresis, Window, Software Reference (Stop) Trigger Sources CH 0, CH 1, TRIG, PFI<1..2>, RTSI<0..6>, PXI STAR CH 0, CH 1, TRIG, PFI<0..1>, RTSI<0..7>, PXI STAR CH 0, CH 1, TRIG, PFI<0..1>, RTSI<0..7>, PXI STAR CH 0, CH 1, TRIG, PFI<0..1>, RTSI<0..7>, PXI STAR CH 0, CH 1, TRIG, PFI<0..1>, RTSI<0..7>, PXI STAR Trigger Coupling AC, DC AC, DC, LF Reject, HF AC, DC, LF Reject, HF AC, DC, LF Reject, HF DC (External TRIG Reject, AC + HF Reject, AC + HF Reject, AC + HF Input) Reject Reject Reject Trigger Coupling (Analog Input Channel) Trigger Holdoff AC, DC From trigger to first point of next record Same as input channel, HF Reject, LF Reject From trigger to trigger Same as input channel, HF Reject, LF Reject From trigger to trigger Same as input channel, HF Reject, LF Reject From trigger to trigger Same as input channel From trigger to trigger Trigger Delay Y Y Y Y Y External TRIG Input Impedance 1 MΩ, 50 Ω 1 MΩ 1 MΩ 1 MΩ 1 MΩ

21 Onboard Memory Digitizers can sample data at several GS/s Data is transferred from the digitizer to the PC for measurements and analysis Data transfer rate to the PC is limited by bandwidth of the connecting bus such as PCI, USB, GPIB

22 Onboard Memory Onboard memory enables digitizers to acquire the signals at the maximum rate, store it, and later fetch the data to the PC for processing More onboard memory lets you sample at a high sample rate for a longer period of time to capture more points

23 Onboard Memory Onboard memory not only increases acquisition time, but also provides frequencydomain benefits

24 Onboard Memory Digitizer Model Channels Real-Time Sample Rate Equivalent-Time Sample Rate Bandwidth Memory Options NI GS/s 20 GS/s 300 MHz 16 MB, 128 MB, 512 MB, 1 GB NI MS/s 5 GS/s 125 MHz 16 MB, 128 MB, 512 MB NI MS/s 4 GS/s 150 MHz 16 MB, 64 MB, 512 MB, 1 GB NI MS/s 2 GS/s 100 MHz 16 MB, 64 MB, 512 MB, 1 GB NI MS/s 60 MHz 16 MB, 128 MB, 512 MB NI ks/s to 15 MS/s 6 MHz 16 MB, 64 MB, 512 MB, 1 GB

25 Things to Consider Specifications Ecosystem

26 Channel Density Important factor in a digitizer purchasing decision is the number of channels on the instrument or the ability to add channels by synchronizing multiple instruments

27 Synchronization Automated test applications frequently involve multiple types of instruments such as digitizers, signal generators, digital waveform analyzers, digital waveform generators, and switches Most of the times these instruments need to be synchronized

28 Synchronization Inherent timing and synchronization capability of PXI and NI modular instruments allows you to synchronize all these types of instruments without the need for external cabling Synchronization and Memory Core (SMC) -the common architecture for all NI high-speed modular instruments

29 Mixed Signal Capability SMC enables PXI Platform and NI Modular Instruments to come together as a system capable of handling mixed signals PXI digitizer can be used with arbitrary waveform generators and digital waveform generator/analyzers to build a complete mixed-signal application with the benefits of both an oscilloscope and a logic analyzer

30 Software, Analysis Capability, and Customizability Boxed oscilloscope provides many of the standard functions Not enough to solve every application Modular digitizer leverages the PC architecture while letting you customize an application to your requirements

31 Software, Analysis Capability, and Customizability NI digitizers are all programmed using the free NI- SCOPE driver software More than 50 prewritten examples NI-SCOPE Soft Front Panel provides a familiar interface similar to an oscilloscope Same hardware can be programmed for both common and custom measurements Same driver can be used with LabWindows/CVI, Visual Basic, and.net

32 Thank you!