[R-390] Ramp Generators

[Barry]

I think that same scheme is used in HP's digital voltmeters (e.g. HP3456A, etc.) as part of the sampling circuit(?).  As I recall, the integrator cap has to be very high quality for it to work correctly.

Thanks,
Barry - N4BUQ

----- Original Message -----
> From: "David Wise" <David_Wise at Phoenix.com>
> To: "Barry" <n4buq at knology.net>, "Roy Morgan" <k1lky68 at gmail.com>
> Cc: r-390 at mailman.qth.net
> Sent: Friday, April 26, 2019 12:16:41 PM
> Subject: Re: Ramp Generators
> 
> The canonical Tektronix ramp generator is the "Miller Integrator" used in the
> sweep section of most of their old analog scopes.  Here, the constant
> current comes through a resistor.  It's constant because the voltage across
> the resistor is constant.  The voltage is (nearly) constant because it's the
> input voltage to a high-gain DC amplifier with feedback.  This is your
> generic "operational amplifier" circuit: the output will do whatever is
> necessary (and possible) to maintain the "virtual ground" at its input.  The
> resistor forms the low leg of the feedback network.  The cap, wired from amp
> output to input, forms the high leg.  With a constant current trickling into
> the low end of the cap, the amplifier has to elevate the high end at a
> constant rate to keep the low end from drooping.
> 
> Dave Wise
> Tektronix, 1980-1995
> ________________________________________
> From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> on behalf
> of Barry <n4buq at knology.net>
> Sent: Friday, April 26, 2019 9:09 AM
> To: Roy Morgan
> Cc: r-390 at mailman.qth.net
> Subject: Re: [R-390] OT: Ramp Generators
> 
> Hi Roy,
> 
> Ahh, okay.  That's a small detail I missed.  Indeed, the sample I was looking
> at states it's a steady current (through a transistor).  That makes sense to
> me now.
> 
> Thanks for the explanation.  My electronics world is back in order now.
> 
> Barry - N4BUQ
> 
> ----- Original Message -----
> > From: "Roy Morgan" <k1lky68 at gmail.com>
> > To: "Barry" <n4buq at knology.net>, r-390 at mailman.qth.net
> > Sent: Friday, April 26, 2019 10:55:16 AM
> > Subject: Re: [R-390] OT: Ramp Generators
> >
> > Barry,
> >
> > Some bits in reply - hopefully useful:
> >
> > The usual capacitor charging curve shown in texts and explanations assumes
> > (usually states) that the charging current comes through a fixed resistor
> > from a steady voltage source. We see the familiar exponential curve
> > approaching the source voltage as time goes on.
> >
> > BUT in ramp generators there is usually a constant CURRENT source. This
> > produces a linear voltage change with time on the cap.
> >
> > Tektronix produced a number of explanatory documents related to their
> > oscilloscopes, and I am sure one of them tells about time bases. I can send
> > more info on that later but in the meantime search for “tekwiki”:
> > W140.com/tekwiki/wiki ... main page, scroll way down to find “Concept
> > Series”.
> >
> > The Tektronix folks were/are masters at ramp generators.
> >
> > Roy sends.
> >
> > > On Apr 26, 2019, at 11:01 AM, Barry <n4buq at knology.net> wrote:
> > >
> > > Hopefully this isn't too dumb of a question, but I was wondering how ramp
> > > (sawtooth) generators work ...
> > >
> > > This is confusing to me.  Capacitors don't charge linearly, do they, and,
> > > if that's true, then why is the ramp linear wrt time?
> 
> 
>