Talk:Operational amplifier applications

message: THis statement seems to convey very little useful info. I think its wrong anyway. I will delete unless it can be tightened up--Light current 01:15, 30 September 2005 (UTC)
thread_title:  Op amp o/p impedance 

message: In some other encyclopedias this material is splitted into several articles. To generate cross-language links, the header references are used (for instance, 
. Please avoid changing the headers without the real need. Audriusa 20:38, 2 January 2006 (UTC)
replies: text: Alternatively, feel free to change the section titles, just put an  to the old name in the same place. —TedPavlic (talk/contrib/@) 14:17, 6 January 2010 (UTC)
thread_title:  Important note: headers in use 

message: We should include Breakpoint generators here.--HappyEater 16:40, 19 May 2007 (UTC)
thread_title:  Hole in page 

message: In the explanation for the non-inverting amp, the resistor subscripts don't correspond to the picture.
"A third resistor, of value R_\mathrm{f} \| R_\mathrm{in}, added between the Vin source and the non-inverting input, while not necessary, minimizes errors due to input bias currents."
I looked everywhere for what the contributor meant by "R1||R2" and couldn't find any references besides: 'parallel-to' in geometry; and a logical OR operator in C programming. I don't think it means either of those and might possibly be a typo for "R1/R2". This needs to be verified by someone with more knowledge than myself.
:: The symbol means "impedance of the parallel combination of". That is, R_1 \| R_2 \triangleq (1/R_1 + 1/R_2)^{-1} = R_1 R_2 / (R_1+R_2). I've updated the document in the case you're talking about (for the inverting amplifier). I've also clarified the issues involving bias currents and input impedance. Some of the new comments there apply equally as well to any of the other OA circuits. —TedPavlic | (talk) 21:03, 19 November 2008 (UTC)
thread_title:  Typos in document 

message: I have often noticed a tendency to confusion around this term. I believe the usage is to call this circuit with an opamp and two matched pairs of resistors, a "Difference Amplifier".  "Differential Amplifier" is the term used to name the input stage inside the opamp, as you will see if you follow the link to that article. Friendly Person (talk) 13:31, 19 June 2008 (UTC)
thread_title:  "Differential Amplifier" 

message: If a fig is not provided for the "Zero level detector" "section", the section should be removed. —TedPavlic (talk) 14:35, 26 January 2009 (UTC)
thread_title:  Fig needed for "Zero level detector" 

message: The diagram for this is incorrect. One of the input buffer amplifiers has the '+' and '-' inputs transposed. 20.133.0.13 (talk) 13:37, 17 February 2009 (UTC)
replies: text: Good catch. I've notified the SVG author. —TedPavlic (talk) 13:51, 17 February 2009 (UTC)
thread_title:  Instrumentation Amplifier 

message: Sorry, I have removed the link to the page about Philbrick absolutely involuntarily. I have no idea how it has happened and I was unpleasantly surprised when I saw Zen-in's remark. Philbrick is a legend; I highly appreciate his achievements. Circuit-fantasist (talk) 15:35, 20 March 2009 (UTC)
thread_title:  About the link to Philbrick's page 

message: There is currently a page dedicated to the inverting amplifier configuration of the op amp.  The page doesn't seem to add much value beyond what is already in Operational amplifier applications or Operational amplifier.  Merge? Scottr9 (talk) 14:41, 23 April 2009 (UTC)
thread_title:  Merge Inverting Amplifier here 

message: There is an orphaned Log_amplifier page.  The quality of that page is awful, but I would suggest actually keeping it and merging it with the Logarithmic Output from this page (and hopefully improving the content of the log amp page!).  
Thus, Logarithmic output would have it's own main page and the section in this page could be excerpted from that article.  This would be similar to how the Operational_amplifier_applications#Precision_rectifier section is handled with the Precision_rectifier main page.
Furthermore, something should be done to connect the Logarithmic_video_amplifier page.
Marangu (talk) 13:21, 21 May 2009 (UTC)
thread_title:  Logarithmic output 

message: The text on power supply design contained some very odd wording that I regard as meaningless. I have edited to remove the offending text, but if anyone can supply a meaningful alternative then please insert.   —Preceding unsigned comment added by 86.53.81.124 (talk) 16:52, 28 December 2009 (UTC)
replies: text: Restored from your edit and tried to add some clarity. You can find an example circuit that uses current on the OA rails as an input to an external amplifier in Horowitz and Hill. In particular, look at the notable examples (the gray section) at the end of the operational amplifier section. There is a high gain amplifier there (provided without explanation) that matches the text I've inserted. —TedPavlic (talk/contrib/@) 06:02, 29 December 2009 (UTC)
thread_title:  Power supply design 

message: Regarding to the sign of the feedback, there are two kinds of circuits with feedback - circuits with negative feedback (e.g., inverting and non-inverting amplifier) and circuits with positive feedback (e.g., non-inverting and inverting Schmitt trigger).
Regarding to the way of feedback applying, there are two kinds of circuits with feedback - circuits with parallel feedback (inverting amplifier and non-inverting Schmitt trigger) and circuits with series feedback (non-inverting amplifier and inverting Schmitt trigger).
In circuits with parallel feedback (look at the picture of the inverting amplifier above and at the picture of the non-inverting Schmitt trigger here), the op-amp's output and the input voltage source are connected through the feedback circuit (the resistors R1 and R2). As a result, the op-amp passes a current through the input source; so, the circuit impacts the input source. Note that in circuits with parallel negative feedback (inverting amplifier) the two voltage sources are connected in the same direction travelling through the circuit; so their voltages are added; in circuits with parallel positive feedback (non-inverting Schmitt trigger) the two voltage sources are connected in the opposite direction; so their voltages are subtracted. Now look at the circuit of NIC (more precisely, it is a VNIC) that is a typical S-shaped negative resistor, and you will see the same phenomenon there - the op-amp's output and the input voltage source are connected through the positive feedback circuit (the resistors R3 and the internal resistor of the input source Vs). That is why the non-inverting Schmitt trigger behaves as a (an S-shaped) negative resistor. See also Linear Mode of Current Inversion NIC and Bistable Mode of Current Inversion NIC.
In circuits with series feedback (look at the picture of the non-inverting amplifier above and at the picture of the inverting Schmitt trigger here), there is no connection between the op-amp's output and the input voltage source. So, no current flows between them and these circuits do not possess a negative resistance; they have extremely high input resistance. Circuit dreamer (talk) 20:33, 30 March 2010 (UTC)
replies: text: This idea you have, that almost everything in electronics is due to a negative resistance was pretty much talked to death a while ago.   It is OR and your own POV.   No-one else subscribes to your theory, sorry.  Also, I thought you had agreed to not post anymore of your "circuit ideas".  Zen-in (talk) 00:32, 31 March 2010 (UTC)
thread_title:  About the two Schmitt trigger versions 

message: I just cleaned up (I think) some commentary at the section on the "Inverting differentiator", but I'm not sure why it's there. The commentary isn't about issues implementing differentiators with operational amplifiers. Instead, it's about using differentiators in larger feedback loops. This may be a topic of interest, but it probably doesn't belong on this page and probably deserves a richer discussion. So should it be removed? Shouldn't this page just give the outline of the implementation of an OA-based inverting differentiator? —TedPavlic (talk/contrib/@) 15:57, 12 July 2011 (UTC)
thread_title:  Feedback commentary at inverting differentiator&nbsp;&ndash; needed? 

message: Zero crossing threshold detector duplicates a section here and should be merged for context. --Wtshymanski (talk) 22:03, 28 November 2011 (UTC)
thread_title: Suggest merge

message: I have edited section "Inverting Integrator" to incorporate much of article Op amp integrator, per the suggestion in the banner at the beginning of this section. I have not attempted to merge in that article's section "Frequency response" nor "Applications" nor its reference. This work is a first cut and needs to include the derivation of the transfer function for each of the two circuits and it needs to include substantiation for the statement about the value of Rn.
I read the discussion above, titled "About the op-amp inverting integrator" and gave thought to how the concerns voiced there bore on the section. I hope I have addressed them reasonably well.
ArthurOgawa (talk) 09:01, 24 February 2014 (UTC)
thread_title:  Section "Inverting Integrator" has acquired most of article [[Op amp integrator]] 

message: Since Wikipedia is suppose to be helpful for "newbies", an important topic seems to be missing from this article and its parent operational amplifier article, which is how to properly terminate unused op-amps.  I'm not sure which article it belongs, but I think a section should be created to address this important design issue, including the need for a drawing similar to "this drawing" which came from "this article".  Please discuss and someone please add to the correct article.  Thanks!  • Sbmeirow • Talk • 16:09, 24 July 2014 (UTC)
replies: text: I deleted it from op amp. WP is not supposed to be a tutorial or a how to guide, so the material doesn't really belong in WP. This article appears to be a how to, so I left the EL in. Glrx (talk) 23:37, 25 July 2014 (UTC)
replies: text:  Proper design is NOT a "how to" guide.  Maybe we should delete all the schematic drawings and calculations in all opamp articles, since they obviously show/tell a person "how to" make an opamp do "Negative feedback", "Inverting Amplifier", "Closed loop", and so on.  I'm amazingly amazed at the deletion of this useful information.  • Sbmeirow • Talk • 08:41, 26 July 2014 (UTC)
thread_title:  Properly terminating unused op-amps missing from articles 

message: I wonder if someone could add the current-to-voltage converter configuration to this page? I was surprised to come here and not find it. 
It's described here: https://en.wikipedia.org/wiki/Transimpedance_amplifier 
For what it's worth, it's the fourth one on the corresponding french wikipedia page: http://fr.wikipedia.org/wiki/Montages_de_base_de_l%27amplificateur_op%C3%A9rationnel "Convertisseur courant à tension" = "Converter of current to voltage".  Gwideman (talk) 19:03, 29 April 2015 (UTC)
thread_title:  Current-to-Voltage "transimpedance" application is missing 

message: I have moved most html comments (WP:HIDDEN) from the article to here for consideration. It is not satisfactory for the article to retain these long-term, and the material looks to be too "tutorial" in nature for an encyclopedic article.
----
An inverting amplifier inverts and scales the input signal. As long as the op-amp gain is very large, the amplifier gain is determined by two stable external resistors (the feedback resistor Rf and the input resistor Rin) and not by op-amp parameters which are highly temperature dependent. In particular, the Rin–Rf resistor network acts as an electronic seesaw (i.e., a class-1 lever) where the inverting (i.e., −) input of the operational amplifier is like a fulcrum about which the seesaw pivots. That is, because the operational amplifier is in a negative-feedback configuration, its internal high gain effectively fixes the inverting (i.e., −) input at the same 0 V (ground) voltage of the non-inverting (i.e., +) input, which is similar to the stiff mechanical support provided by the fulcrum of the seesaw. Continuing the analogy,
* Just as the movement of one end of the seesaw is opposite the movement of the other end of the seesaw, positive movement away from 0 V at the input of the Rin–Rf network is matched by negative movement away from 0 V at the output of the network; thus, the amplifier is said to be inverting.
* In the seesaw analogy, the mechanical moment or torque from the force on one side of the fulcrum is balanced exactly by the force on the other side of the fulcrum; consequently, asymmetric lengths in the seesaw allow for small forces on one side of the seesaw to generate large forces on the other side of the seesaw. In the inverting amplifier, electrical current, like torque, is conserved across the Rin–Rf network and relative differences between the Rin and Rf resistors allow small voltages on one side of the network to generate large voltages (with opposite sign) on the other side of the network. Thus, the device amplifies (and inverts) the input voltage. However, in this analogy, it is the reciprocals of the resistances (i.e., the conductances or admittances) that play the role of lengths in the seesaw.
Hence, the amplifier output is related to the input as in
:V_{\text{out}} = -\frac{R_{\text{f}}}{R_{\text{in}}} V_{\text{in}}\!\,.
So the voltage gain of the amplifier is A = -R_{\text{f}}/R_{\text{in}} where the negative sign is a convention indicating that the output is negated. For example, if Rf is 10 kΩ and Rin is 1 kΩ, then the gain is −10 kΩ/1 kΩ, or −10 (or −10 V/V).Basic Electronics Theory, Delton T. Horn, 4th ed. McGraw-Hill Professional, 1994, p. 342–343. Moreover, the input impedance of the device is R_{\text{in}} because the operational amplifier's inverting (i.e., −) input is a virtual ground.
In a real operational amplifier, the current into its two inputs is small but non-zero (e.g., due to input bias currents). The current into the inverting (i.e., −) input of the operational amplifier is drawn across the Rin and Rf resistors in parallel, which appears like a small parasitic voltage difference between the inverting (i.e., −) and non-inverting (i.e., +) inputs of the operational amplifier. To mitigate this practical problem, a third resistor of value R_{\text{f}} \| R_{\text{in}} \triangleq R_{\text{f}} R_{\text{in}} / (R_{\text{f}} + R_{\text{in}}) can be added between the non-inverting (i.e., +) input and the true ground.Malmstadt, Enke and Crouch, Electronics and Instrumentation for Scientists, The Benjamin/Cummings Publishing Company, Inc., 1981, , Chapter 5. p. 118. This resistor does not affect the idealized operation of the device because no current enters the ideal non-inverting input. However, in the practical case, if input currents are roughly equivalent, the voltage added at the inverting input will match the voltage at the non-inverting input, and so this common-mode signal will be ignored by the operational amplifier (which operates on differences between its inputs).
----
Amplifies a voltage (multiplies by a constant greater than 1)
:V_{\text{out}} = V_{\text{in}} \left( 1 + \frac{R_2}{R_1} \right)\,
* Input impedance Z_{\text{in}} \approx \infin
** The input impedance is at least the impedance between non-inverting (+) and inverting (-) inputs, which is typically 1 MΩ to 10 TΩ, plus the impedance of the path from the inverting (-) input to ground (i.e., R_1 in parallel with R_2).
** Because negative feedback ensures that the non-inverting and inverting inputs match, the input impedance is actually much higher.
* Although this circuit has a large input impedance, it suffers from error of input bias current.
** The non-inverting (+) and inverting (-) inputs draw small leakage currents into the operational amplifier.
** These input currents generate voltages that act like unmodeled input offsets. These unmodeled effects can lead to noise on the output (e.g., offsets or drift).
** Assuming that the two leaking currents are matched, their effect can be mitigated by ensuring the DC impedance looking out of each input is the same.
*** The voltage produced by each bias current is equal to the product of the bias current with the equivalent DC impedance looking out of each input. Making those impedances equal makes the offset voltage at each input equal, and so the non-zero bias currents will have no impact on the difference between the two inputs.
*** A resistor of value
***:R_1 \| R_2 \triangleq \left(\frac{1}{R_1} + \frac{1}{R_2}\right)^{-1} = \frac{ R_3 R_2 }{ R_1 + R_2 },\,
**:which is the equivalent resistance of R_1 in parallel with R_2, between the V_{\text{in}} source and the non-inverting (+) input will ensure the impedances looking out of each input will be matched.
*** The matched bias currents will then generate matched offset voltages, and their effect will be hidden to the operational amplifier (which acts on the difference between its inputs) so long as the CMRR is good.
** Very often, the input currents are not matched.
*** Most operational amplifiers provide some method of balancing the two input currents (e.g., by way of an external potentiometer).
*** Alternatively, an external offset can be added to the operational amplifier input to nullify the effect.
*** Another solution is to insert a variable resistor between the V_{\text{in}} source and the non-inverting (+) input. The resistance can be tuned until the offset voltages at each input are matched.
*** Operational amplifiers with MOSFET-based input stages have input currents that are so small that they often can be neglected.
----
----
I left the following two comments (shown in green here) for later investigation:
*The relationship between input signal and output signal is now:
:V_{\text{out}}(t_1) = V_{\text{out}}(t_0) - \frac{ 1 }{R_{i}C_{f}} \int_{t_0}^{t_1}V_{\text{in}}(t)\, \operatorname{d}t 
* Single supply op-amp circuit collection 
Johnuniq (talk) 06:35, 7 November 2015 (UTC)
thread_title:  Comments removed from article