Digitizers -Fundamentals - National Instrumentsindia.ni.com/sites/default/files/Oscilloscope Fundamentals.pdf · • Digital Trigger Types ... Memory Usage = Bit Resolution * Sample

Digitizers - Fundamentals

Chinmay Anand Misra

High-Speed Digitizers

Chinmay Anand Misra

Certified LabVIEW Developer

Staff Applications Engineer

Agenda

Introduction

DAQ and Digitizers

Programming High Speed Digitizers

NI Digitizers FamilyNI Digitizers Family

Digitizers – Additional Features (OSP, Flex Resolution, etc.)

Advanced Topics (TDC, RIS, etc.)


Digitizer - Introduction

• Also known as oscilloscopes

• Observe continuously varying signal voltages

over time


ApplicationsCable Fault Testing

• Using a DMM to measure a line voltage, and triggering a digitizer to examine the waveform when the RMS power drops below a given threshold.

Video Signal Analysis

• Capturing video signals with a frame grabber, and triggering a digitizer to check the quality of the scan lines.

Communication Protocol TestingCommunication Protocol Testing

• Checking communication protocols with a protocol analyzer, and triggering a digitizer to check the signal quality of the line when the protocol analyzer detects an error.

Disk Drive Testing, Ultrasonic Material Testing,Switching Power Supplies Testing,…….


Compared to DAQ, Digitizers Have…

• Higher sampling rates

• Deeper onboard memory

• Faster rearm times

• More accurate timestamps vs.• More accurate timestamps

• Programmed with NI-Scope

• No counters, AO or DIO

• No terminal blocks

• Fewer input channels


vs.

SMIO (611x, 6120) High Speed Digitizers

80kS/s to 10MS/s 20 to 1000 MS/s

10 to 16 bits 8 to 24 bits

2 or 4 AI and 2 AO Channels 1, 2 or 8 AI Channels

16MB to 32 MB onboard mem 1MB to 512MB onboard mem

DAQ vs. Digitizers


16MB to 32 MB onboard mem 1MB to 512MB onboard mem

$3595 to $4995 $900 to $14000

5105 5114 5922 5122 5124 5152 5153 5154

Form Factor PCI/PXI PCI/PXI PCI/PXIPCI/PXI/

PXIePCI/PXI PCI/PXI PCI/PXI PCI/PXI

Resolution (bits) 12 8 16-24 14 12 8 8 8

Sample Rate

(MS/s)60 250 0.5-15 100 200 2000 2000 2000

Bandwidth

(MHz)60 125 6 100 150 300 500 1000

NI Digitizers Product Line

(MHz)

Input

Impedance50Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω/1MΩ 50Ω 50Ω

Max Range

(Vpp)6/30 10/40 10 10/20 10/20 10 5 5

# Channels 8 2 2 2 2 2 2 2

Cost$4800-

$9600

$3000-

$6500

$7900-

$12100

$6500-

$14000

$7500-

$13500

$5500-

$10000

$7000-

$12000

$9000-

$14000

SMC-based device

5102 5112 5132 5133 5142 5620 5621 5622

Form Factor PCI PCI/PXI USB USB PCI/PXI PXI PXI PXIe

Resolution

(bits)8 8 8 8 14 14 14 16

Sample Rate

(MS/s)20 100 50 100 100 64 64 150

Bandwidth

(MHz)15 100 50 50 100 0.01-36 36

3-250

162.5-212.5

NI Digitizers Product Line

(MHz) 162.5-212.5

Input

Impedance1MΩ 50Ω/1MΩ 1MΩ 1MΩ 50Ω/1MΩ 50Ω 50Ω 50Ω

Max Range

(Vpp)10 50 40 40 10/20 2 2 2.8

# Channels 2 2 2 2 2 1 1 1

Cost $1600$3100-

$4700

$900-

$1200

$1200-

$1500

$8800-

$13500

$3700-

$5700n/a

$8000-

$11000

SMC-based device Legacy device

NI-Scope and LabVIEW• Driver for all high-speed digitizers

• Requires NI-DAQ, NI-VISA, and NI-IVI

• LabVIEW, CVI, Visual C++, Visual Basic, .NET and Microsoft C

• Available for Windows, Linux, and PharLap Operating Systems

• Includes the Scope Soft Front Panel

• IVI compliant


• IVI compliant

• Located in Measurement I/O

Measurements• Over 50 built-in measurements in NI-Scope!

• Measurements are done in software by the driver.

• Scalar measurements including:

• Array measurements including:

• Frequency

• Rise/fall time

• Peak to peak voltage

• Period

• RMS voltage

• Max/min voltage

• Array measurements including:

• FFT Amplitude Spectrum

• Waveform math → Add, Subtract, Multiply, Divide

• Time and Voltage Histograms

• Can combine processing steps before final measurement (eg- filter

signal before returning RMS voltage)


LabVIEW RT Support

Supported Devices

• NI 5105

• NI 5114

• NI 5122

• NI 5124

NOTE: No legacy devices are

supported

• NI 5124

• NI 5142

• NI 515x

• NI 5922

• Any Digitizer with SMC


Scope Soft Front Panel

• Get started quickly

• Mimics look & feel of boxed scope

• Save waveforms

• Save configuration• Save configuration

• Simulation

• Multiple SFP Launches

• View time domain, freq. domain, or XY plot (CH0 vs CH1)

• View measurements


• Introduced in NI-SCOPE 2.7

• Allows quick and simple

configuration of an

acquisition

NI-Scope Express VI

• Provides access to most of

the functionality of the

digitizer


Programming Flow

1. Initialize session

2. Configure acquisition

3. Acquire/read data3. Acquire/read data

4. Include error information

5. Close session


Initialize

• Initialize opens a session to the instrument

• Initialize with options allows more custom

configuration


Vertical Parameters

Range Full Scale (peak to peak) voltage range

Vertical Offset Middle of the input range

Coupling Rejects or accepts the DC signal component

AC - rejects any DC component

DC - passes all frequencies including DC


DC - passes all frequencies including DC

Probe Attenuation Scales the acquired data

Channel Enabled Allows a channel to acquire data

Advanced Vertical Parameters

Input Impedance 50 Ω or 1 MΩ impedance for channel

Max Input Frequency Cutoff frequency of the analog input filter


Horizontal Parameters

Number of Records Number of records to acquire

Sample Rate Frequency at which digitized samples are acquired

Enforce Realtime Allows random interleaved sampling

Min Record Length Samples to store for each record

Reference Position Pretrigger versus posttrigger points specified in


Reference Position Pretrigger versus posttrigger points specified in

percentage

• Immediate

• Software

• Edge

• Digital

Trigger Types


• Digital

• Hysteresis

• Window

• Video (NI 5114, 5142 & 5122/5124 only)

Immediate Trigger

• The digitizer does not wait for a trigger of any kind


Software Trigger

• Triggers on a Software call

• Not supported on the 5102


Edge Trigger

• Trigger when a signal crosses a specified level with a specified slope

• Source can be a channel or the external trigger input


Digital Trigger

• Trigger on either a rising or falling edge of a digital signal

• Source can be a RTSI line, PFI line, or the PXI Star trigger


Hysteresis Trigger

• Positive slope • Negative slope



Window Trigger

• Entering window • Leaving window



Trigger Holdoff

• After a trigger is received, the digitizer will wait for a specified amount of time before starting the next record


Trigger Delay• Digitizer waits a specified amount of time after a trigger to start

post trigger acquisition

– Only on the NI 5105, 5112, 5114, 5122, 5124, 5142,. 5152 and 5922

– Not supported with Random Interleaved Sampling (Discussed Later)


Initiate Acquisition

• Commits settings to hardware

• Starts the acquisition (starts taking pretrigger

samples)


Fetch

• Retrieves the data from the board’s memory– Timeout - how long to wait for data

– NumSamples - how many samples to retrieve

• Scaled or binary data


Scaled or binary data– Scaled - applies a gain, offset and probe attenuation to the

retrieved data

– Binary - retrieves the data unformatted for faster transfer

rates

Fetch Versus Multi-Fetch

• Fetch– Single channel, single record acquisition in LabVIEW

– Single channel, multiple channel and/or multiple record in

non-LabVIEW environments

• Multi-Fetch– Multiple channel and/or multiple record acquisition

– LabVIEW only


Read

• Initiates and fetches data– timeout - how long to wait for data

– numSamples - how many samples to retrieve

• Scaled data onlyScaled data only

• Read and Multi-Read in LabVIEW


Reading vs. Fetching

• Fetch supports binary data

• Read is a blocking function – You cannot do other things in the thread while this

function waits for the data

– Initiate, Acquisition Status and Fetch for non-blocking

retrieval

• Fetch supports software triggering


Digitizers – Additional Features

• Onboard Signal Processing (OSP)

– 5142

– 5622

• Flexible Resolution• Flexible Resolution

– 5922

• USB

– 5132

– 5133


Onboard Signal Processing

• Equalization FIR Filter

• Digital Gain/Offset

• Digital Downconverter (DDC)

– Frequency Translation – Frequency Translation

– Filtering and Decimation

– Data Processing Mode Selection


Onboard Signal Processing


5922 Flex Resolution

• 16 to 24 bit Resolution

• 500 kS/s to 15 MS/s

• Anti-aliasing hardware filter

• Large dynamic range• Large dynamic range


USBUSB--513x513x

• Bus Powered!

• 2 ch, 50/100 MS/s

• 8-bit resolution

• 8 or 64 MB onboard memory• 8 or 64 MB onboard memory

• Analog and digital triggering

• 0.04 V – 40 V software selectable input range

• BNC connectivity with 1 MΩ input impedance

• 20 MHz noise filter


Advanced Topics

1. Timestamps

2. Random Interleaved Sampling (RIS)

3. Multiple Record Acquisition

4. Continuous Acquisition4. Continuous Acquisition

5. Onboard Memory


Time Stamps

• A free running clock and a counter is used to accurately record the time of an event

• A time is recorded for the first point in an acquisition and for the time between the first point and a triggerpoint and a trigger

• Allows you to correlate multiple records or even multiple acquisitions


Time to Digital Conversion (TDC)

• Measures the time between the trigger and

the sample clock


Random Interleaved Sampling (RIS)

• Uses TDC to effectively increase sample rate

• Must be periodic/repetitive signal

• Combines multiple waveforms


RIS

Bin 1 Bin 2 Bin 3


Multiple Record Acquisition

• A digitizer performs multiple acquisitions without reconfiguring

• NI-SCOPE stores each acquisition in separate memory records

• Hardware advances to the next record without software interaction

• Fast rearm time ≤ 100 µs

• Supported on all digitizers except NI 5102 and USB-513x.

• Software Timed workaround for NI 5132, 5133

– NI USB-5132/5133 Acquisition Benchmarks


Onboard Memory

• 100,000 records limitation

– With modification I32 size limitation

• Memory not shared across channels except 5105

• Depth of On Board Memory• Depth of On Board Memory


Memory Usage = Bit Resolution * Sample Rate * Acquisition Time * No. Records

Memory Usage = 12 bits * 10 MS/s * 50 ms * 10 Records

Memory Usage = 16 bits * 10 MS/s * 50 ms * 10 Records

Memory Usage = 80 MB

Continuous Acquisition

• “Fetch forever”

• Configuring a single triggered record and never sending the trigger

• Continuously fetching pre-triggered samples• Continuously fetching pre-triggered samples


Fetch Forever Block Diagram


Thank you!


Documents

Digitizers -Fundamentals - National Instrumentsindia.ni.com/sites/default/files/Oscilloscope Fundamentals.pdf · • Digital Trigger Types ... Memory Usage = Bit Resolution * Sample