Analog Modulator Circuit Explained

An Analog Modulator is Explained and the circuit operation is analyzed in this Video which is the 212th video in the Circuit Design Playlist. This Analog Modulator circuit implements Analog Multiplication of signals to achieve amplitude modulation (AM). The Circuit consists of three operational amplifiers, and three differential matched NPN BJT transistor pairs effectively forming a variant of the Gilbert Cell. This video discusses and answers the following topics: How does this example of Analog Modulator work? DC analysis, and how to quickly compute the AC small signal input-output Voltage Formula showing that output voltage signal is proportional to the product of the first input signal and the sum of the second and third input signal. All input voltages are considered as small signal. There are two symmetric positive and negative DC voltage supplies in this example. A combination of superposition, KVL, KCL and op amp virtual short are used to compute and show that Vout is proportional to V1*(V2+V3).

[@STEMprof]

An Analog Modulator is Explained and the circuit operation is analyzed in this Video. For more Analog circuits and signal processing videos see: PhotoDiode Amplifier with Data Compression Explained ua-cam.com/video/hqrRx2ufAwg/v-deo.html
Analog Logarithm Computer with Op Amp ua-cam.com/video/RpKEq5WyoLg/v-deo.html
Instrumentation Amplifier with Electronic Gain Control ua-cam.com/video/C4tghZ-q6Zs/v-deo.html
Temperature-Compensated Programmable Current Source ua-cam.com/video/QY48IQXJIRI/v-deo.html
Analog Exponential (Anti-Log) computer ua-cam.com/video/kk2c7Gk3nW4/v-deo.html
Analog Multiplier Circuit (4-quadrant) ua-cam.com/video/VP53A2zpVMQ/v-deo.html
Analog Computer to Raise Signal to power n ua-cam.com/video/IUTlBH1UraE/v-deo.html
Analog Computer: Signal Division Calculator ua-cam.com/video/2axI5l3cf6c/v-deo.html
Op Amp Analog Computer Differential Equation Solver: ua-cam.com/video/ENq39EesfPw/v-deo.html
For more analog signal processing examples see: ua-cam.com/play/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt.html
I hope these Circuit videos are interesting.

[@FRED82627]

Excellent tutorial. Thanks a lot!!

[@STEMprof]

You are welcome! Glad that you liked this Analog Modulator Video. For more analog signal processing examples please see ua-cam.com/play/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt.html Playlist.

[@JaenEngineering]

The BJT layout is basically a Gilbert Cell

[@STEMprof]

Thanks for comment. That's also mentioned in the video see 33:40.

[@bobdoritique7347]

Merci!

[@STEMprof]

You're welcome! You might also like the following related videos: Analog Multiplier Circuit (4-quadrant) ua-cam.com/video/VP53A2zpVMQ/v-deo.html
Analog Computer to Raise Signal to power n ua-cam.com/video/IUTlBH1UraE/v-deo.html
Analog Computer: Signal Division Calculator ua-cam.com/video/2axI5l3cf6c/v-deo.html
Op Amp Analog Computer Differential Equation Solver: ua-cam.com/video/ENq39EesfPw/v-deo.html
Thank you.

[@bobdoritique7347]

@@STEMprof Cool! Very interresting, i will look your video. Thanks a lot.

[@STEMprof]

@@bobdoritique7347 My pleasure, Hope the additional circuit videos are interesting as well.

[@fouazhdib6813]

hi sir , In the video at minute 17:24, I would like to understand why in the ib2 statement you took the volt values of rb1 and r to be positive
and my understanding is that they are negative Therefore, the expression of v1 will be -v1/100 .

[@STEMprof]

@fouazhdib6813 Good question. Given that V1 is applied to the base of NPN transistor T2, as V1 voltage increases, the base current of T2 increases as well. Therefore ib2 = v1/(100+2rb). Here are a few more examples of differential amplifiers: Instrumentation Differential Amplifier ua-cam.com/video/2xJpqfexsPg/v-deo.html
Differential Amplifier Gain, CMRR ua-cam.com/video/z8f7iZei5cY/v-deo.html
Differential Amplifier Design with BJT & JFET transistors ua-cam.com/video/zKgSYvk7JAM/v-deo.html
I hope these videos are helpful.