Op Amp Amplifier with high input impedance and large voltage gain
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- Опубліковано 24 сер 2024
- How to design an amplifier with single Op Amp to simultaneously realize very high input impedance and large voltage gain? This circuit design video shows a practical method to design such analog amplifier using practical resistors. An example of this circuit is implemented with 2 mega Ohm resistors, one 50 Kohm potentiometer (variable resistor) and one smaller 500 Ohm resistor. The resulting circuit has two mega Ohm input impedance and -101 voltage gain. Both accurate and approximate formula for the voltage gain of the circuit are computed using a combination of Kirchhoff Circuit laws (KCL and KVL) and virtual short property of operational amplifier with negative feedback. Depending on target application, an analog potentiometer or a digital variable resistor (RDAC) can be used to realize variable gain for this amplifier.
One thing to consider is that while this is fine for DC or low frequency AC signals, with such high gain is you'll start to become bandwidth limited and lose gain at higher frequencies. If you need high frequency performance you're better off cascading two or more lower gain stages.
Thanks for sharing your thoughts. With the choice of components (discussed near the end of this video), this example circuit has an input impedance of 2M ohm and a gain of ~101. So the gain is not very high but nonetheless impressive for a single op amp design while having multi mega ohm input resistance. Nonetheless, to your point, properly designed cascade of two op amp stages should give us more flexibility and improved frequency response. Thank you.
THIS Channel is so precious! Thank you Prof
You are welcome! Thank you. Glad that this engineering channel is useful. For more circuit examples please see: Instrumentation Amplifier with Electronic Gain Control ua-cam.com/video/C4tghZ-q6Zs/v-deo.html
Push-Pull Power Amplifier with Op Amp, Sziklai Darlington Transistors ua-cam.com/video/8BFzsi7-Vbs/v-deo.html
Op Amp Amplifier with Electronic Gain Control ua-cam.com/video/NoNgQpbj77Y/v-deo.html
VCA: Voltage-Controlled Attenuator Overview ua-cam.com/video/cFzYZsPEtP0/v-deo.html
Power Amplifier Design (Class A) with Transformer ua-cam.com/video/gKlJrqGqeCI/v-deo.html
I hope these Circuit design and analysis videos are interesting and useful. 🙏
Very amazing thank you
You are welcome. Glad that you liked this video. For more examples please see my Analog Circuits & Op Amp videos collection.
This video shows a practical method to design an amplifier with single Op Amp to simultaneously realize very high input impedance and large voltage gain. For more examples please see the analog circuit and signal processing video playlist ua-cam.com/play/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt.html
And Digital Circuits and DSP playlist ua-cam.com/play/PLrwXF7N522y6cSKr0FmEPP_zQl011VvLr.html
Thanks for watching.
Thank you for video! Can this circuit be used in a mixer to amplify a microphone signal?
You are welcome. Depends on microphone type and requirements. But given 2M ohm input resistance, circuit draws sub micro amp level current from the unit source.
@@STEMprof ohhh
A large voltage gain means a small signal, right? 2meg input resistor (plus we have to use a same at a non inverting input) - that’s a very noisy element, which is not good for such signal. However it depends on the requirement of course. For a guitar pre-amp the worse the better 😂
Could you explain what you mean by, “for a guitar pre-amp the worse the better”. Thank you
@@rudygomez6996 Yeah ) That's funny, but guitarists all the time look for good distortions and fight against 50/60Hz hum. So, few less dB of S/N is nothing for them.
And they have high impedance coils, so need a very high impedance pre-amp input.
@@sc0or so you’re saying the noise created by this circuit wouldn’t bother guitarists because its nothing compared to a hum? What creates this hum? and why does 2meg input resistor create noise?
@@rudygomez6996 Sure, absolutely won't bother. A guitar pickup is an open inductor which captures a hum from wires around very well. There are symmetrical pickups called humbuckers, but they are not symmetrical enough, and the hum is audible anyway (but much less). High ohms resistors are noisy because of a chaotic electrons movement. 2meg resistor at a room temperature will generate about 4.5uVrms in a bandwidth of 10kHz. If a pickup max voltage is 4.5mV, that means a 60dB S/N. Not too much, not too little.
There is another kind of an electrical noise caused by a current, but it is remarkable only at high current values, where we don't talk about small signals.
@@sc0or Thank you for sharing your thoughts and good points. While extra care regarding noise is required in these very high input resistance op amp circuits, the voltage gain of amplifier is on the order of a nominal gain of 100. With that said, good point regarding noisy pre amp for Guitarists 😀