okay, thanks everybody for coming I didn't expect this big of a crowd yes so a
little uh little context for this Kin Chan who is TLO ASIC design manager
established a mentorship thing with CSU and as part of that we gave a series of
talks and so the the the presentation is more geared toward that for for people
who don't have a lot of exposure to the technology you know I mean us in R&D we
work with it all the time but a lot of people you know they've seen an oscilloscope
they might not know how it works or they don't really know what's going on
inside so I was asked to do a presentation that kind of initially told
what an oscilloscope is, its main function what it's supposed to do and then
ultimately going a little bit deeper kind of what the front end functions are
yeah the front-end functions inside the oscilloscope that actually condition the
analog signal before we we digitize it and then also before we do things like
calculate the time for the time axis so basically what does an oscilloscope do?
Obviously it measures volt measures both voltage and time and displays that on an
axis as waveform of voltage versus time. now you'll see in a lot of times in our
applications everything we have other ways to display the signal but that's if
that's effectively what we acquire we acquire voltage and then we calculate
the time that that voltage you know the time relative to what that when that
voltage was acquired so this presentation is going to focus more on
the analog signal processing technology before the analog to digital converter
sees it and also before the time base and trigger circuitry sees it so first
question why would we want to do that? well obviously you look at a circuit board like
this if it's running you don't really know it's running
I mean if it's powered on or powered off other than the thing maybe getting hot
or if there are LEDs or something that light up it really doesn't look any
different when it's running versus when it's turned off so in order for a human
to actually figure out and interact with this thing to figure out what it is
you need some ability to figure out what's going on in all this circuitry
and that's what oscilloscope does. It allows you to see all the signals in a voltage versus time waveform. And in order to see what's going on - either
troubleshoot it verify it or just understand its performance you need some
ability to measure that and so together with an oscilloscope probe, we make
a ton of those, there's several different versions here you put that probe down on
a trace that seemingly is doing nothing and then that sends a voltage signal
back through its cable into the front of the oscilloscope and then you're presented on
the oscilloscope with a waveform and that waveform in general is displayed versus
time so let's see so basically this is the front end this is a picture of our
Infiniium S-series oscilloscope these go up to 8 GHz we have versions scope families that are
in the hundreds of megahertz tens of megahertz actually now hundreds of
megahertz tens of gigahertz and of course now we're broaching 100 gigahertz
realm this disco came out I think oh maybe a year and a half two years ago
and I was involved in designing the front end ASIC for the preamp assembly
so ultimately the main parts of an oscilloscope there's the analog channel inputs these
are the front end BNC s where the probe took up two or even a coax cable can
hook up to that and then there is a in this particular one this is called a MSO
which stands for mixed signal oscilloscope we also have 16 digital
channel inputs that those can be probed and displayed along with the analog
voltages and they're both correlated in time so it's a pretty powerful
diagnostic instrument to see what's going on on the PC board the main
controls are the analog channel vertical scaling this is where you set the size
of the signal that you see on the screen and also its position in terms of an offset
then there's a horizontal scaling that's how you set the time axis the horizontal
axis here we're measuring voltage in the amplitude versus time and so turning
that knob compresses the signal it basically displays more or less time
of that signal along the horizontal axis and then there's a trigger level
basically a trigger level is a voltage that is used as a reference and when
this waveform passes through that that that generates an edge that is used by
the time measurement circuitry to figure out exactly when that particular point
in the waveform you're trying to measure how that is going to be calculated
relative to the timing of the the system clocks and everything else so you can
stabili put that waveform on the screen and I'll talk a little bit more about
those blocks in a minute so for those who don't know effectively you know
haven't used an oscilloscope or how it actually works and what the display is actually
telling you again we display volts versus time and what you're presented is
with a graticule the graticule has volts on the vertical axis and time on the
horizontal axis and it's funny that most of the controls the hardware controls
that are on the front of the oscilloscope are actually there they give you the
basic oscilloscope functionality in terms of an analog control to control things like
the horizontal axis and the voltage axis there's a lot of other functionality in
the oscilloscope but most of that is access through soft keys or there's a couple
keys that are on the front of the scope that are kind of universal you can push
that to bring down another set of measurements so don't think for a minute
that just the the ability or the the the functionality of the oscilloscope is is limited
to what you control with the with the hardware knobs but most of that in order
to get up and running and display waveforms and move the waveforms around
that's what we present in terms of the hardware function the hardware knobs and
buttons so this this first set of buttons is the vertical what that's what
that's done doing is this little guy right here you can see it's got a bit a
little waveform in a big waveform that's pretty much setting the volts per
division scale so right now for instance you
see in a display it's set to one volt per division turning that changes that
scale and so now we've got such a wonderful tradition so what that says is
that every division here represents one volt for the input signal the other
major control to control the time axis is this horizontal guy you can see that
that one looks like the same size analog signal except for it's compressed in
time so what that does is control the horizontal divisions how many seconds or
milliseconds or microseconds now we're in picoseconds that each one of these
divisions is relative to the voltages on the screen so so let's assume we apply
to two volt peak-to-peak hundred Hertz sine wave and we've got the thing set to
one volt per division and one millisecond per division that's got a
ten millisecond period so the waveform on screen will look like something
that's basically 2 volts peak-to-peak if we want to magnify that signal or
effectively cover more of the screen we hit the volts per division change that
to a half a volt per division and it effectively makes the signal look like
it's bigger it's not really a bigger signal at the input
it's just provide it's just scaling the signal so the downstream ADC
can actually use more of its range so if we if we then move the
horizontal so we're actually displaying more time on the screen we went from 1
millisecond to 2 milliseconds per division and and now we've got 10
milliseconds so that's two periods of the screen so those are the two
functions in order to get a screen to get a waveform basically on the screen
and initially displayed like you want it to want it to appear those are the two
you would look at there's another one called Auto scale here you know if you
don't really know what your signal looks like you can push that button and
there's all kinds of signal processing to try to figure out to do initial
measurements of this waveform and kind of set this volts per division and time
per division settings for you so a lot of times when people are first you know
making a measurement they don't really know what they're trying to see they'll
push that button and at least bring a waveform hopefully stabili onto the
screen so it's it's a trigger level sets the volts per
division the time for division and maybe even the trigger mode I think whether
it's triggering on a rising or falling edge so there's a like I said there's a
lot of functionality that's handled in the digital sections of the oscilloscope and
and additional hardware that's downstream from the front end so what's
the trigger then the trigger like if it is a is that is the other main control
and that basically as you move that you'll see a level going up and down
what that is is it's basically providing the zero time reference for displaying
the signal so whenever whenever this waveform passes through that level then
that's going to be calculated by the system to put that at time zero and so
the you know the other thing well you might ask well what about when it fault
goes here there's some slope they're the simplest
trigger functions are available at the front panel and so one is the slope here
I've set the slope in this particular thing to be this positive edge guy right
here so only the positive edge is the one that generates effectively a trigger
signal and so you'll see that this guy over here is not at time zero this guy
is if we would hit that and do the the negative edge triggering then this would
jump over there and you'd have the the negative slope going through time zero
so when you want to change that trigger level if you move the trigger level up
for instance what it does is it effectively pushes the waveform to the
left because now it's finding this point is time zero