wireless debug techniques

8/20/2019 Wireless Debug Techniques

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Prior to class:

ı

Verify each scope has the latest firmware (and the same firmware) and K0ı Verify each scope has at least 2 passive probes (Active probes will not be used

for this particular class)

ı Verify each scope has a demo board, USB cable for power to demo board,

SMA-BNC connector doe demo board, Demo Board Case

ı Verify each scope has at least one MSO cable set (should have two, only one

will be used for this class). Connect MSO cable set 0-7. Ensure all of the flying

leads are connected properly and numbered.

ı Connect each demo board to the USB connector on the scope. Connect

RFOUT to channel 4 of the scope.

ı Load “FAST_Wireless_Debug_fhop.dlf ” into the \Documents and Settings\All

Users\Documents\Rohde-Schwarz\RTO\SaveSets\ directory (This is the default

folder when the RTO opens a file) This file is out on the RSA Cloud

ı Lay out 2 passive probes.

9/9/2013 FAST: Advanced Triggering 1


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Instructor:

Hands-on Class: Embedded

Wireless Debug Techniques


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Agenda

In this workshop we’ll be learning ı The challenges of debugging embedded systems

ı Frequency domain analysis and FFT basics

ı Time gating : The key to unraveling the mysterious correlation between time

and frequency.

ı

Triggering considerations and Triggering on Serial Busesı Oscilloscope Familiarization

ı Hands On Example: Debug of noise issue on digitally-controlled attenuator

chain

ı Hands On Example: Measurement and Triggering of a frequency hopping signal

and VCO settling time.



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Agenda




and frequency.

ı

Triggering considerations and Triggering on Serial Busesı Oscilloscope Familiarization


chain





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Complex Embedded Systems

D/A

D/A

DSP

Micro controller

IQ modulator

Digital signals

Analog signals

RF signals

Oscillator

Flash

I/O


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The Challenge of Debugging Embedded Systems

ı

Baseband digital, RF and analog signals are interdependent Feedback control of RF by microcontroller

Low speed serial busses

Critical timing relationships

Interference between RF and digital signals

EMI related issues and interference problems


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Agenda



ı Time gating: The key to unraveling the mysterious correlation between time and

frequency.

ı Triggering considerations and Triggering on Serial Buses

ı Oscilloscope Familiarization


chain





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Using an FFT for Spectrum Analysis

Different techniques exist for viewing multiple domains on a single

instrument

Performing an FFT (Fast Fourier Transform) on a captured analog

waveform enjoys the following benefits:

ı Every analog channel is also an RF channel

ı Inherent synchronization between time and frequencyı Wide frequency band capture

ı Time gating can be used to locate causal effects

The quality and speed of measurement relies on

ı

A good input system Dynamic Range with clean ADC and low noiseı HW based processing for fast FFT updates even with deep memory

ı “Spectrum Analyzer Like” setup hiding complexity of acquisition setup


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Fourier Transform Concept

Any real waveform can be producedby adding sine waves


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Spectrum Analyzer

ı Spectrum is measured by sweeping the local oscillator across the band of

interest

Very low noise due to IF gain and filtering

Sweep can be fast over narrow span Real time operation possible using FFT after IF filter


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Spectrum Measurement is a Function of TimeGlitches

time

f 1 f 2 f 3 f 4 f 5 f 6 f 7

Measurement frequency


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FFT: Instantaneous Spectrum

f 1 f 2 f 3 f 4 f 5 f 6 f 7

f 1 f 2 f 3 f 4 f 5 f 6 f 7

f 1 f 2 f 3 f 4 f 5 f 6 f 7

t i m e

f 2 f 3 f 4 f 5 f 6 f 7f 1


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Frequency Domain Analysis

FFT Basics

ı NFFT Number of consecutive samples (acquired in

time domain), power of 2 (e.g. 1024)

ı ∆ f FFT Frequency resolution (RBW)

ı tint integration time

ı f s sample rate FFT

s FFT N

f t

f int

1

Integration time tint

NFFT samples input for FFT

FFT

Total bandwidth f s

NFFT filter output of FFT

FFT f ts


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FFT Implementation

Digital Down Conversionı

Conventional oscilloscopes Calculate FFT over entire acquisition

ı Improved method:

Calculate only FFT over span

of interest

f C = center frequency of FFT

=> FFT much faster & more flexible


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Agenda




frequency.




chain





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Time Gating

•Signal characteristics change over the acquisition interval

•Gating allows selection of specific time intervals for analysis


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Time GatingTg

g T f

1


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Time Gating – A key to debug

ı

Frequency spectrum isoften a function of time

Locking of a PLL

EMI caused by time

domain switching

ı Time gating allows the

user to select a specificportion of the waveform

for frequency domain

analysis

Window limits frequency

resolution


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Agenda




frequency.




chain





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20

Triggering

l Events of interest for debug can occur in any domainl Time Domain Analog (edge, runt, width, etc.)

l Time Domain Digital (pattern, serial bus)

l Frequency Domain (amplitude/frequency mask)


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21

Typical Analog Triggers

Glitchl typically narrow pulse, e.g. caused by cross-talk

Transition timel slow / fast edges, e.g. circuit instability / radiation of troublesome energy

Statel logical combination of various channels, e.g. troubleshooting parallel busses

Widthl defined pulse width, e.g. observing Inter-Symbol-Interference (ISI)

Runtl limited amplitude, e.g. meta-stable conditions in digital systems

Setup & Holdl timing relation between 2 channels, e.g. synchronous data interface

Windowl event that enters / exits a window , e.g. capture bus contentions

Time outl dead time, e.g. system errors by wrong dead time relations to other signals


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22

Time Domain Mask

l Draw a violation zone or zones

l Set for “stop on failure”


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NW4C Oscilloscope Training | Serial bus | 23

l Most Serial Bus Architectures rely on the concept of Abstraction Layers or

a Protocol Stack to transmit information fewer physical lines.

l Since an Oscilloscope captures the analog information (Physical Layer) itoften contains the root information for viewing protocol as well.

Protocol or Packet Triggering

Physical Layer

Data Link Layer

Network Layer

Transport Layer

Application Layer

Physical Layer

Data Link Layer

Network Layer

Transport Layer

Application Layer

Bit Stream

T

r a n s m i t D a t a

R

e c e i v e D a t a

Physical Link

Framing/Packets


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NW4C Oscilloscope Training | Serial bus | 24

Example: RS232/UART

Trigger Types:

• Start bit

• Frame start

• Packet start

• A specified symbol

• Parity errors, and breaks• Frame errors

• Stop errors

• A serial pattern at any or a specified position


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25

Frequency Domain Mask

l

Mask test on spectruml Set for “stop on failure”

Frequencymask

Gated FFT


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Agenda




frequency.




chain





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Oscilloscope Familiarization

ı Focused on operation of the RTO, assumes

basic knowledge of Oscilloscopes.

Ensure this is the latest version, as this is a

standard section of all Hands on FAST


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Interface Overview

09.09.2013 28

Signal Bar(Location to where

active waveforms and

results reside in icon

form. Can contain

both Signal icons and

result icon.)

Tool Bar(Quick access to commonly used functions)

Smart Grid(Flexible drag and drop

diagram / measurement

display)

Menu Bar( Complete Access to all

functionality)

Quick Start Guide


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Tool Bar

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Helpful Things to

know:Tool bar operates on a

“touch” basis (not drag and

drop). Simply touch the tool

you want to use and then thewaveform, result window, etc

Select can also act as

“unselect” for instance when

you are done drawing a

mask window

The toolbar can be

customized in the

DisplayToolbar menu

Everything in the tool bar is

available elsewhere in the

interface.

To configure a measurement

or select a differentmeasurement type, tap the

tool icon in the results

window that appears on

screen.

UNDO (see manual for things that cannot be revoked)

REDO

Tool Tip (Enables the tooltip display)

Show / Hide signal bar

Select / Unselect

Hardware zoom (Changes the Horiz & Vert) instrument settings

Zoom (Display with zoom diagram)

Coupled zoom (Creates a coupled zoom area and its related zoom diagram.)

Cursor (Displays vertical and horizontal cursors & performs a cursor measurement.)

Masks (Tap the icon and then tap the points that build the mask. Double-tap the last point to finish)

Vertical histogram

Horizontal histogram

Measurement

FFT

Search (Performs a search according to the settings in the "Search Setup" dialog box. )

Delete ( Removes zoom and histogram areas and their associated diagrams; measurement areas

and their associated results; and mask segments. The icon also switches off a waveform.)

Find level (Sets the trigger level to 50%.)

Quick Start Guide

A ti i l ill h


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Signal BarHelpful Things to

know:

If you need the complete

screen to see the diagrams,

you can alter the behavior of

the signalbar in the toolbar or

the DisplaySignal Bar

menu.

If more than 5 items are on

the signal bar . Clicking and

vertically dragging between

one of the signal icons willscroll through the signals.

Remember the UNDO button

if you don’t like something

that happened using the

signalbar.

Waveforms,

Measurements,

decode tables, (and

nearly anything) can be

dragged onto the

signal bar

Signal bar will highlight

when something is

ready to be dropped

onto it

Active signals will show

information about the

signal and be

displayed in the

SmartGrid.

Waveforms, are in“Minimized” state when

an icon of the actual

waveform appears in

the signal bar instead

of a waveform in the

SmartGrid.

This is achieved one of

two ways

1) A single click on the

top bar

2) Dragging a

waveform from the

Smartgrid onto the

signal bar.

Minimized waveforms

can be dragged back

onto the SmartGrid fordisplay.

Clicking the “X” from

the minimized state will

turn the signal off.

(Signal then needs to

be turned on from the

front panel or in menu

system.Quick Start Guide


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SmartGridHelpful Things to

know:You can always tap the

Icon from the toolbar and

then tap a waveform to turn itoff.

Measurements need to be

dragged from the numbers

not the top of the toolbar

To change the size of the

new diagram, drag its edge

to the new position.

SmartGrid can display up to

XX different waveforms,

result windows, tables, etc

When something is tabbed

(dragged onto placement 4),

it is now hidden from view in

a different tab. Select the

tab of the window you want

displayed on top.

SmartGr id posi t ion s

1 = Placement will be in existing diagram (overlay of signals),

creates floating icon for results.

2 = New diagram (Grid) on the left or right

3 = New diagram (Grid) above or below

4 = New tab (similar to a sheet in an Excel notebook)

5 = XY-diagram 6 = YX-diagram (only available in certain configurations)

Smart Grid works through

Drag and Drop. Two things

control what happens in the

Smart Grid

1, What you drag onto the

SmartGrid. Waveforms and

Results boxes will behave

slightly different.2. Where you drag it. See the

descriptions below.

Quick Start Guide


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Setting up a multiple channel measurementı Press “PRESET:

ı Connect CH1 to RARE_SIG on the demo board,

ı Connect CH2 to 10_MHZ_CLK

ı Toggle Demo Board DOWN button until 8 is displayed.

ı Press “AUTOSET”

ı Note that this is two signals overlayed

ı Have users adjust Vertical and Horizontal position and Scale here to line up two

measurements in one window like below. (~40ns/div, 1V/Div on each channel).

ı

Note the use of the colors to indicate the different waveform in focus. Math and Ref willalso display in alternate colors.

ı Also note that vertical controls all time bases.

09.09.2013 Quick Start Guide 32


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Similar Display Using Smart Grid

ı Press Autoset Again.

ı Minimize both channels (tapping on the channel icon)

ı Move CH1 onto smart gridı Move Channel two around the screen and show the smart grid locations. Drop

it below CH1

ı Change Horizontal scaling to 20ns/div. Note the vertical scaling has not been

reduced, it is the auto set default ~500mV/div



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Using Toolbarı Start the same display as the smart Grid demo.

ı Discuss the Tap-Tap or Tap-Drag mentality of the tool bar.

ı

Have them execute a zoom on C21 to isolate the pulse.ı Point out the Mask Function, utilize this to draw a square mask in the zoomed window.

Note that it is a tap-tap (tap, tap tap), not a tap-drag. Also show the select tool and how

this “unselects”: the mask. They may notice an error coming across occasionally and

turning the mask red. This error is occuring 1/s and is very rare.

ı Show how to use the trash can to delete the mask, and then the zoom window. Note that

if a mistake is made you can press undo. Add back the zoom window undo. to



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Display Menuı Change demo board to “0.” (10, but the period indicated the 10).

ı Press Preset – note that only channel one is active now. We want this, but if they pressed

this and wanted channel 2 or any other channel to autoset, they need to turn it on first

(including MSO channels)

ı Press Autoset. Change horizontal scale to 20ns/div

ı Press the DISPLAY hard Key. Enable infinite persistence.

ı Show how to use the intensity knob. Pressing toggles different display and dialog

settings. Use the main control intensity to raise the intensity of the display to 100%

ı Shortly a runt pulse should appear.

ı Note the level of the runt pulse (good time to highlight the annotated grid).

ı They can remember or jot this down. For to set the trigger. (should be ~2.3V with clear

areas at 2.8V and 1.85V)


Can also highlight

dots mode and colortables the DISPLAY

menu.


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Trigger Menuı Keep the same configuration. Press PRESET and AUTOSCALE. Change horizontal scale

to 20ns/div

ı Press the TRIGGER hard key or show how to get their from the menu system.

ı Point out the source selection. If they had an MSO or other channel to trigger on, it can be

selected here.

ı Select trigger type “RUNT” from the flyout, but point out the other selections.

ı Set the upper and lower limits to the “white space” around the runt we saw in the display

exercise. (clear areas should be at ~2.8V and ~1.8V) – NOTE Scope will not appear

triggered, important lesson here!

ı Close the window, show the that the LEVELS knob when toggled can control both the top

and bottom runt levels. Still keep them at the same levels (~2.8V and ~1.8V)

ı Explain the trigger MODE and have them press the MODE button. Now the scope is

triggered.


Note that this error is

1/s. In Auto mode,the scope paints

screen captures in-

between trigger

events.


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Agenda




and frequency.




chain





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Hands on Lab

ı Hands On Example: Debug of noise issue on

digitally-controlled attenuator chain


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What are we going to look at

ı The 5 ATTEN bits show the digital signal that sources a digitally-controlled

attenuator chain that controls the signal strength at the RFOUT port.

ı The ATTEN bits form a 5-bit word which is 3dB per LSB.



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Our signal in the Frequency Domainı Connect RF out of the demo board to CH1 utilizing the SMA-BNC cable.

ı Set Demo board to demo #1 (LED=1)

ı Press PRESET..

ı Note that the RTO will default to 1MΩ setting. Explain this and show how to change into

the direct 50Ω path. Also note the diagram change in the dialog box.

ı Press AUTOSCALE (note that if Autoscale was done before the input path was altered, it

would not have scaled properly. )

ı Perform FFT on this signal (settings, 825MHz CF, 50MHz Span, 100KHz RBW). Discuss

the similarities of the settings here and what you’d find on a spec an.


Ch h di i ll d i l


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Change to the digitally attenuated signalı Toggle Demo board to demo #3 (LED=1)

ı Immediately you should start to see the signal amplitude raise and lower on screen.

ı Users may also see a glitch that appears on screen. We will change some settings to

make this more obvious.

ı Press the DISPLAY Hard Key and select “use color table” any are OK, I’ve chosen

spectrum these screen shots.

ı Note that his visual of the broad band noise glitch is a direct function of the FFT

processing discussed earlier. This signal IS NOT visible on all instruments (even those

claiming to have a spectrum channel.

ı Also point out that the lowest setting of this attenuator block is ~75dbm, but we can still

see the smallest signal. (for those interested, it is actaully fully attenuated on demo

setting 2).


Th B d b d Glit h


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The Broad band Glitchı Let’s first take a look at the broadband glitch in the frequency domain.

ı Note that users have already seen the time domain mask, but that it also works

in the frequency domain.ı Have them draw a mask (tap, then tap, tap…).

ı Have them set up a “stop on violation”

ı They should catch a glitch.


Note: if the mask is drawn too close tothe noise floor, smaller glitches will be

caught. The material is based on the

big glitch (although you can do the

same with the small ones)

Th B d b d Glit h


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The Broad band Glitchı Have the users press the “HISTORY” button. By pressing History, we can see

the preceding acquisitions and spectrums displayed. (Although they don’t

contain the clue to this puzzle, YET). Move back to time 0ı With the time domain trace, we can see the burst of noise. Zoom in on this

noise.

ı Also have them set a marker measurement on the burst (use the cursor tool tip

and drag a window around the burst). The bursts will vary in time but might be

between 300ns and 550ns.


Wh t ld b i lit h?


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What could be causing our glitch?

ı An interim step to debug of this system might be to probe with a sniffer probe to

see if there is any broadband EMI that is coupling into our channel. (alsopossible with the RTO ) Let’s assume this was done, and nothing obvious

appeared.

ı In thinking about the design, we remember the digital attenuation chain is

controlled by a 5 bit signal.

ı The 5 bit value is the attenuation factor such at 00 is the least amount of

attenuation 0dbm) , and 1F is the largest amount (-93dbm, ~-75dbm realized)

ı Let’s use the logic channels to view these signals.


C ti d bli th l i h l


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Connecting and enabling the logic channels


Connect Logic ChannelsGND GND

Logic D0 ATT0

Logic D1 ATT1

Logic D2 ATT2

Logic D3 ATT3

Logic D4 ATT4

T i d i th l i h l


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Turning on and using the logic channels

ı Logic Channels are accessed from the ProtocolParallel buses

Configuration menu on the menu bar (Note that in future FW releases, theProtocol Menu will be updated to be Analysis.)

ı Turn on Channels D0-D4. Select “Show Bus. All other settings should be

default.

ı Close the window

ı The logic channels will not appear until “Run” is pushed again. Then they will

appear.


T i d i th l i h l


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Turning on and using the logic channelsı Press “Run” again.

ı Until the glitch is caught, you can see the digital bus appears as a counting value up

and/or down.

ı Wait until Glitch is captured.

ı Once the glitch is captured by the mask, have the users press the “HISTORY” button.

ı Go back in time using the history button and confirm the sequence leading up to the

glitch. It should be a counting pattern that is increasing or decreasing (either can be the

case) until the glitch occurs.


T i d i th l i h l


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Turning on and using the logic channelsı Return to the ‘0’ moment in time (when the glitch occurred).

ı Notice the ’00’ that appears on the digital bus.

ı This ’00’ is out of sequence is somewhat time aligned with the broadband glitch.

ı Use the markers to measure both the glitch duration in the analog waveform and in the

digital waveform (digital waveform should include the transition signals afterward as well).

(either move the markers that are still out there, or put a new set down with the market

toolbar icon.)

ı These two should be roughly the same duration. (Analog may be slightly longer)


T i d i th l i h l


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Turning on and using the logic channelsı Let’s clean up the display:

Minimize the analog waveform (tap the signal bar CH1 box) to make the digital signals

easier to see.

Turn off the cursors by tapping the green wrench and unchecking enable on both C1

(cursor1) and C2 (Cursor2). Also minimize the mask (don’t turn off).

Move the “Bus” view in the zoom window by selecting it in the display window and using

the vertical position knob to move it up.

Scale the digital signals a bit (select them on screen and use the vertical scale and

position knobs to scale and move them)


T rning on and sing the logic channels


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Turning on and using the logic channelsı Notice that all of the signals are transitioning at slightly different times. (Below, bit 4 is

slow to rise from 01)

ı This difference in transition time causes a temporary (but long enough) state of ‘00’ on the

bus, which sets the attenuator chain briefly to -0bdm. This is the cause of the broad

band glitch we are seeing.

ı The fix would be to work on the digital circuit to clear up the timing issues. The Logic

channels would contine to be a valuable resource due to their timing resolution.


Agenda


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Agenda

In this workshop we’ll be learning

ı The challenges of debugging embedded systems



and frequency.




chain




Hands on Lab


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Hands on Lab

ı Hands On Example: Measurement and Triggering of a frequency

hopping signal and VCO settling time.

What will we be looking at?


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What will we be looking at?


Microcontroller

SPI Input Control

Signal

u1

x2

x1 * / *VCO

CPV

RFOUT

Connect to the Demo Board


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Connect to the Demo Board

ı RFOUT connects using SMA to BNC into CH4 of the Oscilloscope

ı Connect CH2 to the CPV Signal on the demo board

ı Toggle Demo Board to Demo ‘4’ ı Load FAST_Wireless_Debug_fhop.dlf (FILE hardkey ‘Open…’ )


Since we are using a config

file, it is important these

connects are exact.

Connect Logic Channels:

GND GNDLogic D0 SPI_CLK

Logic D1 SPI_DATA

Logic D2 PSI_CSL

Logic D3 UART/LIND0

D1

D2

D3

Initial View and Explanation


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Initial View and Explanationı The Explain to the users what they are looking at in the various windows that will appear

ı All of the windows are labeled, so utilize this

ı Note the signal bar is off by default. If they want it back simply tap the signalbar icon on

toolbar:


ı This is the “hop”

from 835MHz down

to 825MHz.

ı The two FFT’sindicate a “safe”

settle time for the

VCO. This could be

validated with the Rx

Device Spec.

ı See Speaker notes

for more info.

Changing the view


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Changing the viewı Either by selecting and dragging, or using the navigation knob after selection, move the

right gated FFT to approximately where the CPV label is located (during the overshoot of

the CPV)

ı IMPORTANT NOTE: The system is a little slower right now since there is a lot going on,

and the memory depth is set to 10Msa. This is a lot of data to process.

ı This measurement would allow us to understand more about the overshoot caused by the

CPV. We would then check with the specification for the Rx device of this signal and

understand if it can accept this much overshoot. We could filter or modify the CPV circuit

to improve if needed.


Triggering on another part of the hop


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Triggering on another part of the hopı There are 3 different SPI commands that control this VCO.

Tune 825MHz: (835->825) = SPI MOSI pattern: 14 80 14

Tune 815MHz: (825->815) = SPI MOSI pattern: 14 40 14

Tune 835MHz: (815->835) = SPI MOSI pattern: 14 C0 14

ı Have the user enter the other two values in the protocol trigger menu. You will see that

the tune to 815MHz is also well behaved, but the hop from 815MHz835MHz is pretty

wild. The zoom can be position on top of the voltage transition to see the impact here.

ı If time permits, you can also add a cursor to this window to measure the settle time.


Conclusion


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Conclusion

What we learned


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What we learned.

ı When digital signals are controlling analog or RF signals within a circuit, it is

important to think in both time and frequency.

ı Many triggering and mask techniques can be used.

We can start in the frequency domain with something we don’t like or didn’t

expect to see.

We can start in the time domain with something that is known like a serial

control signal.ı Using a “frequency gate” or “time gate” can allow us to “back into” the root

cause of a problem.

ı A fast updating FFT can be critical to capturing detailed and complex transitions

that occur during anomalous behavior.