Level Detectors, Absolute Value, Peak and RMS

[mediatechnology]

This is a collection in pictures. I'll add text later.


Ron Mancini, TI


AD536 Absolute Value


Comparator-based peak detector


Comparator-based peak detector with NPN Boost


A diode simulator


Current rectifier and frequency doubler


The discontinued GAP-01 as a rectifier.


A two-color overload indicator


A peak flasher. Note the pinout error on the bottom TL074.


A log peak detector. Two channels shown. Crazynightowl may recognize this one.


Peak-to-peak detector


The AD823 op amp used as a rectifier


AD823 rectifier output


D-R Compressor Shunt rectifier


An early dbx rms detector from the patent application.


A dbx rms detector using the CA3083.


Stephen Woodward, rms detector with differential input


dbx 902 rms using transistor array


bcarso symmetrical rectifier


Graeme symmetrical rectifier

Note: The above rectifier circuit has been attributed to SSL by Rod Elliot but I first saw it in the 1973 edition of "Applications of Operational Amplifiers," Jerald Graeme, Burrr Brown. It is used in the SSL Phase Meter.


Boss SG-1 Rectifier

[Crusty]

This one shows how to select positive, negative, or full-wave peaks:

http://www.edn.com/article/CA6339250.ht ... ryid=44217

And from the reference, a neat envelope follower technique (scroll down to 2nd article):
http://www.edn.com/contents/images/122602di.pdf

[mediatechnology]

Here's another one I just found in a stomp box:



The 100K is a pullup to 1/2 V+, the 10K collector load is to V+. The base series resistor, off-screen and not shown, is 22K. This looks a little like the Boss SG-1 sent to me by clintrubber.

[mediatechnology]

Biased Diode Rectifier


"Applications of Operational Amplifiers," Third Generation Techniques," Jerald Graeme, Burr-Brown, 1973, Figure 4.18.

Using a THAT340 with D1 and D2 as diode-connected transistors this circuit rocks as a half-wave rectifier.
I used an LME49860.
A second summation stage, not shown, makes this an absolute value circuit.
I lowered the 10K bias resistors to 2K2.
D1 should thermally track Q1 and D2 should track Q2 but D1/Q1 and D2/Q2 do not need to be in the same package.

[JR.]

As usual thanks Wayne (the librarian).. This thread has every precision rectifier and peak detector ever designed ... [ rim shot }... Of course not that would be a herculean task, for no reason other than the fact that design engineers suffer from NIH syndrome, so even when some perfectly useful prior art exists they will still design their own different way.

I've seen some clever use of biased rectification (to reduce diode drop lag) in some of Paul Buff's log side chain dynamics designs.

I did some variant stuff in my LOFTECH TS-1 to deal with opamp GBW product. Trying to slew +/- a diode drop for a precision rectifier gets increasingly difficult for low level high frequency. (I had to do some extra work to only be down -3dB at 20kHz for -60 dBu. )

While I don't know if i can find one, I vaguely recall making (or trying to) a one opamp bi-color detector for some console design. Trust me you don't want to throw a bunch of circuitry at several tens of these inside a console.

I seem to recall other discussion of this stuff in threads around this forum, probably hijacks occurring other threads.

This is certainly comprehensive and enough for anybody to need time to digest.

JR

[JR.]

bi-bolor.jpg (78.04 KiB) Viewed 485 times

Well what do you know... Here is my one (cheap) opamp bi-color signal present/overload circuit from an old AMR console.

IIRC this used a 2 lead bi-bolor LED so green in one polarity, red the other, looks like I have hold time built into the OL so narrow spikes can be seen.

Not shown are multiple small signal diodes between "SMPLE" and several different signal nodes (cathodes connected together and to SMPLE). .

JR

PS: Looks like a lot of parts to me now, but this was an actual production circuit so tweaked to look good for a $10k-20k console.

[mediatechnology]

Here is my one (cheap) opamp bi-color signal present/overload circuit from an old AMR console.

Thanks! I'm going to have to stare at that one for awhile.

I've seen some clever use of biased rectification (to reduce diode drop lag) in some of Paul Buff's log side chain dynamics designs.

This is the DynaMite detector:


Valley People Dynamite Detector

[JR.]

Yup, exactly,, That one Buff schematic is a nice object lesson in smart log domain design. Some subtle stuff going on in there, and I suspect many got in trouble trying to copy it without understanding details. While he was not allergic to using lots of trim pots... a habit Peavey broke me of.

My signal preset/clip circuit is crude stone age stuff by comparison.

JR

[tubegeek]

Excuse me, Wayne, but in another thread, JR had assigned me to design my own peak detector. You've TOTALLY screwed THAT up.

Now, I do NOT suffer from NIH and this is an embarrassment of riches. Thank you.

But it seems like I'm going to miss a learning opportunity..... of course, understanding what these circuits DO is not a bad one either...

-j

[mediatechnology]

But it seems like I'm going to miss a learning opportunity..... of course, understanding what these circuits DO is not a bad one either...

Just build all of them and figure out which is best. You'll learn a lot from it.

Symetrix used the Buff log detector though there does seem to be a bias resistor missing.


Symetrix 425 Level Detector