Talk:Precision rectifier

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Are we ment to discuss moving the article here?? anyway, in any book I studied, the circuit that here is reported was always called 'super-diode'. I suggest precision rectifier to be a simple redirect to this page, as long as somebody else will invent a smarter way to rectify voltage :-) Alessio Damato 18:15, 3 December 2005 (UTC)

  • Results 1 - 10 of about 604 for "precision rectifier" [1]
  • Results 1 - 10 of about 315 for "super diode". [2]
Hmmm... — Omegatron 19:53, 3 December 2005 (UTC)
ok, I got it: then super-diode will be a redirect to 'precision rectifier'. I agree with that. Alessio Damato 13:23, 4 December 2005 (UTC)
I just never heard super diode before, but I guess it's pretty common. So I dunno. The name is fine, I guess. Plus we have to differentiate between precision half-wave and full-wave rectifiers. — Omegatron 17:57, 4 December 2005 (UTC)

Vin arrows[edit]

The Vin arrows on the two diagrams point outward rather as if they were emitting a signal. This doesn't seem right so perhaps they could be removed or made to point inward toward the amplifiers.--Hooperbloob 16:23, 22 January 2006 (UTC)

Good point. They should either be circles or the input arrow should be pointing in. — Omegatron 20:57, 22 January 2006 (UTC)
I see. I just used the notation my teachers use, but I will change it as soon as I have some time. I will add a full wave rectifier as well, just give me some time. Alessio Damato 10:49, 23 January 2006 (UTC)
Excellent. Thanks. Also note that I added a connection dot to the junction of four wires. These should always be present. — Omegatron 15:00, 23 January 2006 (UTC)

We should also draw a full-wave rectifier circuit, but I can't use xcircuit easily and I don't want to use two different circuit styles on the same page. — Omegatron 20:58, 22 January 2006 (UTC)

01:58, 6 February 2009 (UTC) (talk)==Saturation of the OpAmp output in the simple circuit==

Thanks for mentioning this behavior in the article. Quick sim with LTSpice.

File:Simple peak detector clips.PNG

Kender (talk) 00:06, 29 August 2008 (UTC) (talk) 01:58, 6 February 2009 (UTC)

Error in the simple circuit schematic[edit]

I think the positive and negative op-amp inputs are reversed in the simple circuit digram. (talk) 01:58, 6 February 2009 (UTC)

Yes, please clarify.. How can diode be open at negative input... it should be forward biased.. Garima Jaiswal (talk) 13:43, 4 October 2017 (UTC)

Frequency response of the improved circuit[edit]

The critical factor in the limit frequency (even for the improved circuit version) is not the gain-bandwidth product but the slew rate. This is because the output of the op-amp (the point between the two diodes) has to change from around -0.55V ÷ -0.6V to 0.55 ÷ 0.6V (depending on diode and the load current) every time the input signal changes its sign. Assuming for the opamp a typical slew rate value of 0.5 V/us (valid for 741, lm358...all general purpose amplifiers), this means the output needs around 2us ÷ 2.5us to reach the correct value. For a 10kHz sinewave (half-period of 50us), this translates in about 5% pause in the output signal, affecting the mean rectified value. Note that general purpose amplifiers have gain-bandwidth products of about 1 to 10MHz, or a 10kHz signal is well below this limit. (talk) 20:30, 18 November 2009 (UTC)Apass

I changed the wording to include slew-rate limitations; also note that National Semiconductor's Linear Brief 8 (by Robert C. Dobkin) includes such a circuit, using the LM101 with feed-forward compensation, that claims an accuracy of 1% from DC to 100kHz! (Pretty good for 1969, but no mention of signal level - this circuit is infamous for giving worse performance as signal level drops). Maitchy (talk) 05:07, 1 September 2010 (UTC)

History, Naming and Taxonomy[edit]

The NS LB8 mentioned above, dating from August 1969, is an early version of this circuit... does anyone have an earlier one? It was simply called a "Fast Half Wave Rectifier" then, but within a brief entitled "Precision AC/DC Converters". The naming of this particular circuit is neither "precision rectifier" or "super diode" about half the time in the popular text books... and is part of the bigger class of AC/DC converter circuits that include (say) back-diodes and auto-synchronous detectors and (particularly similar) several opamp rectifier circuits that rely on limited output swings by various means (no negative supply; special clamping opamps; knowledge of how to (mis)use compensation/bias pins to provide full-wave rectification, etc)... and these circuits are not often given particularly distinctive names (e.g. simply "Single-supply half- and full-wave rectifiers..." in Walt Jung's Op Amp Applications book). To add to the confusion, "Super diode" was a term used (admittedly some decades ago, and mostly in British literature) for a transistor connected as a diode, with base to collector.

There is a phrase "linearised rectifiers" that covers the general class of circuits (of which there are more than the ones given here), but I don't know how common that phrase is. I did a bit of research to find a formal classification/taxonomy naming system for such circuits, without success... can anyone find one published? Ideally, there should be an article that covers active and passive AC/DC converters, linking to this page, and to those like the True RMS converter for example (which currently is an orphan). Maitchy (talk) 05:07, 1 September 2010 (UTC)

Also, is it properly categorized as an electronic amplifier? ..or an analog circuit? The diagrams show op-amps in use but I think the actual gain settings used are tangential to the topic, right? --Hooperbloob (talk) 23:34, 19 September 2010 (UTC)
Hmmm - I agree it's probably not right to class it as an electronic amplifier. (talk) 05:37, 21 September 2010 (UTC)
Arguably this comes under category:signal processing and I support category:analog circuits. Gain is of the essence of this circuit, but I agree, it is not an amplifier. If one includes this in category:electronic amplifiers then every op-amp circuit in the book has to be included also. SpinningSpark 17:55, 21 September 2010 (UTC)

Addition please..[edit]

All this information could be found in any book. But can anyone add how actually the precision rectifier is working like an ideal diode.. Please cite an example showing how the feedback is taking place. And how could this setup could give outputs less than the cut-in voltage of the diode.

More about the basic circuit flaw.[edit]

The problem is not due to the output transistors. I used falstad's circuit simulator to test to see if perhaps the opamp itself could be modified to solve the problem. The problem appears related to the single capacitor. Increasing the capacitance increases the response delay. I found that limiting the maximum voltage the capacitor is exposed to will reduce the delay by some magnitudes: relocating the positive end to about 1.5V above the Vccnegative supply will reduce the capacitor current to an acceptable degree (more voltage above is required for greater input voltage at the max negative output, not sure to what degree this will effect the rest of the features of the opamp). The bandwidth will likely increase too. A delay will always exist while the capacitor is present. the ringing that occurs is due to the sharp rise (when the capacitor suddenly gets up to speed), which goes into the external circuit which rings. Charlieb000 (talk) 07:21, 2 March 2013 (UTC)