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

[@mr1enrollment]

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

[@STEMprof]

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 kzbin.info/www/bejne/oZyVlGp9oJihjZY Op Amp Analog Computer Differential Equation Solver: kzbin.info/www/bejne/e3_UZGx7mtiZhtk For more analog signal processing examples please see: kzbin.info/aero/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt I hope these Circuit videos are interesting as well. 🙋‍♂️

[@ralvholmsen1254]

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]

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: kzbin.info/www/bejne/e3_UZGx7mtiZhtk Push-Pull Power Amplifier with Darlington Transistors kzbin.info/www/bejne/bmeZfoyfl9Rrr6c Triangle Oscillator Op Amp circuit kzbin.info/www/bejne/gHeYhqOVmNp_b80 And my Analog Circuits Videos Playlist: kzbin.info/aero/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt Thanks again 🙋‍♂️

[@ralvholmsen1254]

@@STEMprof im looking forward to it!

[@STEMprof]

Thanks Ralv. I hope you also liked recent circuit examples including the Feedback Amplifier with BJT kzbin.info/www/bejne/bJWvfqumgbN-rJY , Op Amp Amplifier with Electronic Gain Control kzbin.info/www/bejne/hKCxmISml89qbbs and Thermometer Circuit Design kzbin.info/www/bejne/a2a8pKWXe6pjqMk

[@ralvholmsen1254]

i did indeed! Very interesting :)@@STEMprof

[@STEMprof]

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

[@STEMprof]

Thanks for watching. For more Analog Computer & Op Amp Circuit examples please see: Analog Exponential (Anti-Log) computer kzbin.info/www/bejne/oZyVlGp9oJihjZY Op Amp Analog Computer Differential Equation Solver: kzbin.info/www/bejne/e3_UZGx7mtiZhtk Analog Computer to Raise Signal to power n kzbin.info/www/bejne/f4a3nXV-Zrqll6c Triangle Oscillator Op Amp circuit kzbin.info/www/bejne/gHeYhqOVmNp_b80 Push-Pull Power Amplifier with Darlington Transistors kzbin.info/www/bejne/bmeZfoyfl9Rrr6c Op Amp Analog Computer Differential Equation Solver: kzbin.info/www/bejne/e3_UZGx7mtiZhtk Full-Wave Rectifier kzbin.info/www/bejne/enutfoGLYqiMmck. Differential Equation Solver Analog Circuit kzbin.info/www/bejne/iGS7ZnSPg796e6s Diode-Amplifier VTC is analyzed in kzbin.info/www/bejne/rKGqi56Xm92AgK8 kzbin.info/www/bejne/fpa9g6ekh72je6s 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: kzbin.info/aero/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt I hope these Circuit design and analysis videos are helpful.

[@marcorademan8433]

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]

Thanks for watching and sharing your thoughts. In line with your point, please watch kzbin.info/www/bejne/oZyVlGp9oJihjZY 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 kzbin.info/aero/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt . I hope these Circuit design and analysis videos are helpful.

[@marcorademan8433]

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

[@STEMprof]

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

[@Elyas_Fix]

Thanks 🎉

[@STEMprof]

You're welcome. Thanks for watching. For more Analog Computer & Op Amp Circuit examples please see: Analog Exponential (Anti-Log) computer kzbin.info/www/bejne/oZyVlGp9oJihjZY Op Amp Analog Computer Differential Equation Solver: kzbin.info/www/bejne/e3_UZGx7mtiZhtk Push-Pull Power Amplifier with Darlington Transistors kzbin.info/www/bejne/bmeZfoyfl9Rrr6c I hope these Circuit videos are interesting.

[@Chupacabras222]

Fascinating again :)

[@STEMprof]

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

[@tristanboyle4450]

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]

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

[@STEMprof]

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 kzbin.info/www/bejne/f4a3nXV-Zrqll6c I will post more examples soon. I hope this is helpful.

[@andreasn6432]

How do you realise T1 and T2 in practik?

[@STEMprof]

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 kzbin.info/www/bejne/a2a8pKWXe6pjqMk .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 kzbin.info/aero/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt Thanks again for your interest and question. I hope this explanation and additional circuit examples are helpful. 🙏🙋‍♂

[@ramy8338]

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

[@STEMprof]

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.

[@qemmm11]

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

[@STEMprof]

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: kzbin.info/aero/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt I hope this explanation and Circuit design and analysis videos are helpful.

[@k7iq]

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

[@STEMprof]

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 kzbin.info/www/bejne/e3_UZGx7mtiZhtk 🙋‍♂️