[sdiy] Waveshapers based on Max-min operations (Re: Simple circuit challenge: |a-b|)

Fri Oct 18 20:53:50 CEST 2024

Dear Osamu Sam & list,

Thanks again for sharing! Using the schematic in your first link, I have
simulated your full-wave rectifier in Spice and compared it to a commonly
used 2-opamp precision rectifier circuit (Figure 4 on this page
https://sound-au.com/appnotes/an001.htm). It seems to perform very well (on
1kHz sine), and seems to even outperform the standard precision rectifier
on high frequency accuracy (20kHz sine). This comparison made me wonder
about a couple of things though:

1) Noise performance: probably due to the large 1M resistors around the
opamp, the noise performance seems below that of the 2-opamp rectifier. In
simulation I could lower the 1Meg resistors around the opamp to 100K,
without much apparearant harm to the quality of the output, but benefits
to noise performance. What is the reason for the proposed 1M values?
2) The other circuit: on the bottom of the schematic on your website
there's an alternative circuit, with a note "My older design seems a little
more precise". In my simulation however, it is much less precise... What
did I do wrong?
3) How important is diode matching?
4) How important is voltage accuracy of +V and -V (being tied to the diode
bridge via 100K)?

Otherwise, this is a gem of a circuit that I will definitely keep in mind!

Rutger

Op vr 4 okt 2024 om 18:10 schreef Sean Ellis <tensiontype at hotmail.com>:

> Fantastic ideas, the full wave rectifier is so simple. I dont quite
> understand how the absolute value circuit works, might have to simulate it.
>
> Great stuff :)
>
> ------------------------------
> *From:* Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of
> houshu--- via Synth-diy <synth-diy at synth-diy.org>
> *Sent:* Thursday, 3 October 2024 4:26 PM
> *To:* Rutger Vlek <rutgervlek at gmail.com>
> *Cc:* SDIY List <Synth-diy at synth-diy.org>
> *Subject:* [sdiy] Waveshapers based on Max-min operations (Re: Simple
> circuit challenge: |a-b|)
>
> Hello Rutgers and List,
>
> I designed variations of Max-min based waveshapers, which may be of your
> interests.
> They are quite simple and quite precise.
>
> Explanations are in Japanese, but I guess schematics and waveforms are
> sufficient information for you.
>
> Full-Wave Rectifiers (Absolute Value) Based on Max-Min Operation.
>
> https://apac01.safelinks.protection.outlook.com/?url=https%3A%2F%2Funderstandcircuit.seesaa.net%2Farticle%2F505024372.html&data=05%7C02%7C%7C5afc30a132a54417a92408dce3fa480b%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638635911325026475%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=D6%2FNwIyy2e%2BcKTm86K7dGlVJp5cPQQSLsyVZWkgiwic%3D&reserved=0
> <https://understandcircuit.seesaa.net/article/505024372.html>
>
> Single Opamp Wavefolder with Folding Threshold Control.
>
> https://apac01.safelinks.protection.outlook.com/?url=https%3A%2F%2Funderstandcircuit.seesaa.net%2Farticle%2F505024822.html&data=05%7C02%7C%7C5afc30a132a54417a92408dce3fa480b%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638635911325039849%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=GgMfNzMVO3lLjpO3EK6jt%2Bea4St%2FIigMid0XJFjJLtM%3D&reserved=0
> <https://understandcircuit.seesaa.net/article/505024822.html>
>
> Wave Multiplier with Folding Threshold Control.
>
> https://apac01.safelinks.protection.outlook.com/?url=https%3A%2F%2Funderstandcircuit.seesaa.net%2Farticle%2F505024858.html&data=05%7C02%7C%7C5afc30a132a54417a92408dce3fa480b%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638635911325047338%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=mIBfUGhoga38%2B5KyCucJjlSWvQV9IzRaI7PuOzD7c3w%3D&reserved=0
> <https://understandcircuit.seesaa.net/article/505024858.html>
>
> Absolute Value of Difference with Single OP Amp.
>
> https://apac01.safelinks.protection.outlook.com/?url=https%3A%2F%2Funderstandcircuit.seesaa.net%2Farticle%2F503838897.html&data=05%7C02%7C%7C5afc30a132a54417a92408dce3fa480b%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638635911325054556%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=Ocnt3Bm8RDHy3yANTgwfhtp99Y8Rj9j2bUjhZ7xoxqc%3D&reserved=0
> <https://understandcircuit.seesaa.net/article/503838897.html>
>
> Best,
> Osamu Sam HOSHUYAMA
> Kawasaki, JAPAN
>
>
>
> ------ Original Message ------
> 差出人: "Rutger Vlek" <rutgervlek at gmail.com>
> To: "houshu at muj.biglobe.ne.jp" <houshu at muj.biglobe.ne.jp>
> Cc: "SDIY List" <Synth-diy at synth-diy.org>
> 送信済み: 月曜日, 2024/4/1  19:32
> 件名: Re: [sdiy] Simple circuit challenge: |a-b|
>
> Thanks everyone for the suggestions!
>
> I agree with Roman, the Graetz bridge solution is very elegant, thanks
> for sharing Osamu! Will keep you posted on progress with this circuit.
> If the prototype works as expected, I'll share the details here on the
> list.
>
>
> Rutger
>
>
> Op do 28 mrt 2024 om 03:43 schreef houshu at muj.biglobe.ne.jp
> <houshu at muj.biglobe.ne.jp>:
>
>       Hello Rutger and List,
>
> Here is my solution.
> |a-b| = Max(a,b) - min(a,b).
> If output offset is acceptable, we can omit D5, D6, and R7.
> Impedance of inputs should be low.  When one of inputs is open, output
> is a little distorted.
> Sam HOSHUYAMAKawasaki, Japan.
>
>
>
> ------ Original Message ------
> 差出人: "Rutger Vlek via Synth-diy" <synth-diy at synth-diy.org>
> To: "SDIY List" <Synth-diy at synth-diy.org>
> 送信済み: 金曜日, 2024/3/22  04:50
> 件名: [sdiy] Simple circuit challenge: |a-b|
>
> Dear list,
>
> while hobbying on an experimental design, I'm looking for a simple
> analog circuit to give me the absolute value of the difference between
> two signals (mathematically written as |a-b|).
>
>
> I already have a working circuit, but it's rather big for my needs. It
> uses an inverting opamp to invert signal A, followed by a bog-standard
> full wave precision rectifier circuit where -A and B are summed together
> and being rectified. The total is 3 opamps, 2 diodes and 9 resistors. As
> I need to repeat the circuit many times in the final application, I'm
> wondering: is there anything simpler that can do this?
>
>
> Requirements:
> - working across full audio range
> - distortion as consequence of diode drops is no problem (might even be
> beneficial!)
>
>
> Many thanks for any suggestions!
>
>
> Regards,
>
>
> Rutger
>
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