Analog Logarithm Computer with Op Amp: How does it work?

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Analog circuit example discussed in this video computes Logarithm of the input positive signal voltage. The computed result appears as the output voltage of this circuit designed with Op Amps and BJT transistors. For more circuit examples including Analog Computers please see • Electrical Engineering...
This analog active circuit is designed using a matching pair of Bipolar Junction Transistors (BJT) and two operational amplifiers for instance Analog Devices LT1055/LT1056 JFET input Op Amps. The BJT transistors should be a matched pair in the same silicon substrate and in the same IC package so that they have the same PN junction properties and temperature. The proper choices of resistors in this example opamp circuit are also discussed in this video. A combination of Kirchhoff's circuit laws (KVL or Kirchhoff voltage law) , Shockley equation for PN junction , op amp virtual short and inverting and noninverting amplifier circuit topologies are applied to analyze this circuit and to prove Vout computes logarithm of the input voltage. For more circuit examples please see • Analog Computer solves... and Op Amp and Analog Circuits: • Electrical Engineering...
DSP and signal processing: • Digital Circuits and S...

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20 ноя 2023

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Комментарии : 28

@mr1enrollment 6 месяцев назад

I must be a nerd,... I enjoy the discussion - it reminds me of classwork 45 years ago. Good review of circuit analysis.

@STEMprof 6 месяцев назад

Thanks for watching. Glad that you enjoy this Logarithm Analog Computer. I'd say I'm a nerd too 🙂 . For more Op Amp circuits please see: Analog Exponential (Anti-Log) computer ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-kk2c7Gk3nW4.html Op Amp Analog Computer Differential Equation Solver: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ENq39EesfPw.html For more analog signal processing examples please see: ru-vid.com/group/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt I hope these Circuit videos are interesting as well. 🙋‍♂️

@STEMprof 7 месяцев назад

Thanks for watching. For more Analog Computer & Op Amp Circuit examples please see: Analog Exponential (Anti-Log) computer ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-kk2c7Gk3nW4.html Op Amp Analog Computer Differential Equation Solver: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ENq39EesfPw.html Analog Computer to Raise Signal to power n ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-IUTlBH1UraE.html Triangle Oscillator Op Amp circuit ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-JF5Up_cuL9k.html Push-Pull Power Amplifier with Darlington Transistors ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-866MYibo8yE.html Op Amp Analog Computer Differential Equation Solver: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ENq39EesfPw.html Full-Wave Rectifier ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-DJJMNU-CYcg.html. Differential Equation Solver Analog Circuit ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-R3X5AYNZGEI.html Diode-Amplifier VTC is analyzed in ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-vpGZkafxMJM.html ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-HeZRtnRXpEI.html presents a circuit with op amps and feedback loops to design an analog computer that solves a second order differential equation. For more analog signal processing examples see: ru-vid.com/group/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt I hope these Circuit design and analysis videos are helpful.

@Chupacabras222 7 месяцев назад

Fascinating again :)

@STEMprof 7 месяцев назад

Thank you again for watching. Glad that you also liked this video as well. For more analog signal processing examples please see: ru-vid.com/group/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt I hope you also enjoy these Circuit design and analysis videos as well 😀 🙋‍♂️

@ralvholmsen1254 7 месяцев назад

Youve done an impressive amount of work the last year or so. I do hope you like making them as much as i like to watch them :) Keep up the awesome work!

@STEMprof 7 месяцев назад

Thanks Ralv for watching and your encouraging comment. I am glad that you like my videos.🙏 It's also a fun challenge for me as well designing and solving interesting and useful problems. For example, next circuit that I will hopefully publish soon is a feedback amplifier with interesting nuances. I hope you like it as well 🙂. In the meantime, please see following links for more examples (hopefully you enjoy them as well): Op Amp Analog Computer Differential Equation Solver: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ENq39EesfPw.html Push-Pull Power Amplifier with Darlington Transistors ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-866MYibo8yE.html Triangle Oscillator Op Amp circuit ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-JF5Up_cuL9k.html And my Analog Circuits Videos Playlist: ru-vid.com/group/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt Thanks again 🙋‍♂️

@ralvholmsen1254 7 месяцев назад

@@STEMprof im looking forward to it!

@STEMprof 6 месяцев назад

Thanks Ralv. I hope you also liked recent circuit examples including the Feedback Amplifier with BJT ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-6dLMxpLNKv4.html , Op Amp Amplifier with Electronic Gain Control ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-NoNgQpbj77Y.html and Thermometer Circuit Design ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-55YsraFE0rg.html

@ralvholmsen1254 6 месяцев назад

i did indeed! Very interesting :)@@STEMprof

@STEMprof 6 месяцев назад

Glad that the circuit examples are interesting and you liked them. Thanks again for watching.

@user-pt8wj8xc4q 6 месяцев назад

Thanks 🎉

@STEMprof 6 месяцев назад

You're welcome. Thanks for watching. For more Analog Computer & Op Amp Circuit examples please see: Analog Exponential (Anti-Log) computer ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-kk2c7Gk3nW4.html Op Amp Analog Computer Differential Equation Solver: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ENq39EesfPw.html Push-Pull Power Amplifier with Darlington Transistors ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-866MYibo8yE.html I hope these Circuit videos are interesting.

@k7iq 7 месяцев назад

Had to turn on CC when you said Logarithm there at first. It's OK 😀

@STEMprof 7 месяцев назад

Thanks for watching & your comment. Glad that you are interested in this Analog Computer Op Amp circuit that computes Logarithm of the input signal. For more examples of Analog Computers please see ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ENq39EesfPw.html 🙋‍♂️

@tristanboyle4450 7 месяцев назад

What is the first op amp actually doing ? is it just making it possible to achieve ic1 with a complete voltage drop across R? is that very different to the circuit with no first op amp? thanks for the video

@tristanboyle4450 7 месяцев назад

this may be better answered by watching a basic intro..but ill leave it.

@STEMprof 7 месяцев назад

Thanks for watching and your good question. As you also noted, We need to inject a current into the collector of the BJT transistor proportional to input voltage V1. The first operational amplifier takes care of that by forcing input voltage V1 across the resistor R. For a related example please see Analog Computer that Raises Signal to power n ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-IUTlBH1UraE.html I will post more examples soon. I hope this is helpful.

@marcorademan8433 6 месяцев назад

Surely this circuit is too temperature sensitive for any practical use? I've seen designs using an IC with multiple BJTs (4), where the remaining BJTs are hooked up in a feedback configuration with a very stable voltage reference, such that the BJTs used in the sensitive circuit remains at a stable temperature. A stable voltage reference will be required to fix a Vbe voltage with a current produced by feedback with respect to the reference, thereby acting as a heater for the other monolothic BJTs.

@STEMprof 6 месяцев назад

Thanks for watching and sharing your thoughts. In line with your point, please watch ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-kk2c7Gk3nW4.html which is Transistor-Tempco Resister Temperature Compensated Anti-Log Analog Computer. This example highlights a temperature compensation technique for these circuits. For further examples please see ru-vid.com/group/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt . I hope these Circuit design and analysis videos are helpful.

@marcorademan8433 6 месяцев назад

@@STEMprof Thank you! I'll give it a watch. You are one of few channels which cover more advanced application circuits.

@STEMprof 6 месяцев назад

@@marcorademan8433 Thanks for watching & your interest. Glad that you like my videos.

@StandforAjdetray 7 месяцев назад

Because Bjt on , and then inverting amplifier output=-0.7v.

@STEMprof 7 месяцев назад

Thanks for watching and sharing your thoughts. That is not correct because there is a resistor connecting output of the first op amp to emitter of BJT. So while emitter of BJT is at -Vbe=VT*log(Ic/Is), the output of op amp is less due to further voltage drop across the one kilo ohm resistor that connects emitters to op amp1. For more circuit examples please see: ru-vid.com/group/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt I hope this explanation and Circuit design and analysis videos are helpful.

@andreasn6432 6 месяцев назад

How do you realise T1 and T2 in practik?

@STEMprof 6 месяцев назад

hanks for watching and your good question. For similar example involving matched BJT transistors please see Thermometer Circuit Design with Op Amp and BJT transistor ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-55YsraFE0rg.html .Answering your question, for practical implementation we have to use Matched Monolithic Dual or Quad Transistors (in single package) that are available to purchase online from say Mouser.com . For example Analog Devices MAT14ARZ-R7 is a quad monolithic NPN transistor that offers decent parametric matching for precision amplifier. And as another example, OnSemi (Fairchild) MMPQ2907A Quad PNP and FMB2907A Dual matched PNP transistors packages are also available to order from Mouser.com. For more examples please see ru-vid.com/group/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt Thanks again for your interest and question. I hope this explanation and additional circuit examples are helpful. 🙏🙋‍♂

@ramy8338 7 месяцев назад

If the base of T1 is connected to ground doesn't that mean that T1 is an open switch hence no current flowing ?

@STEMprof 7 месяцев назад

Thanks for watching and your follow-up question. BJT transistor T1 with grounded base can operate normally in this circuit because Op Amps have positive and negative supplies and therefore output voltage of op amp becomes the needed negative value so that emitter of T1 transistor is at proper negative value to keep T1 operational. I hope this explanation is helpful.