Is this Amplification Circuit Possible?

Thread Starter

DavAerElectr

Joined Nov 5, 2023
1
View attachment path1.jpg
I don't know much about opamps.
The idea is to use various opamps in series, with different charateristics according to the input voltage, but with the main goal to increase the peak voltage,let's 5 or more volts, and mostly keep the sine wave frequency of the orginal circuit. Is this possible?. Assume you have all the necessary power source to power the opamps.
 

Alec_t

Joined Sep 17, 2013
14,214
Welcome to AAC!
It is certainly possible to have multiple stages in series, each stage comprising an op-amp with, for example, an individual gain or phase response. Is that the sort of thing you mean?
 

Jerry-Hat-Trick

Joined Aug 31, 2022
494
I’m thinking, for 20Mhz you’ll need high frequency op amps and I’m wondering why you need multiple stages? Maybe you could share your objective, i.e what voltage and current is the input and what voltage and current are you hoping for as the output after two transformer stages?
 

k1ng 1337

Joined Sep 11, 2020
910
This is a good problem for LTspice circuit simulator. You can model ideal components or choose existing opamps. If you haven't already, attempt to solve this problem on paper with basic opamp equations because the diagram is apparently increasing the amplitude of the signal while keeping the phase and frequency the same. This can be accomplished by a single op amp or as many stages as you want.

This begs the question as to why you want to have multiple opamp stages when an single opamp is capable of near infinite gain. Unless you have a specific goal, having more stages will at the very least introduce a propagation delay. What are you getting in return for this delay and the other parasitic losses / interference generated by the additional circuitry?
 

Audioguru again

Joined Oct 21, 2019
6,608
I have never used an opamp for your 20MHz radio frequency.

An OPA134 is a very good wideband audio opamp. Its voltage gain is 1 million times up to 10Hz, is 10 thousand times at 1kHz, is 10 times at 1Meg Hz and is zero (like a piece of wire) at 10meg Hz. Its slew rate converts a sinewave into a triangle wave at a few hundred-thousand Hz.
It is overloaded if its load resistance is less than about 470 ohms.
 

BobTPH

Joined Jun 5, 2013
8,661
If the height of the waveforms shown in your diagram reflect the actual magnitude ratios, a single opamp can give you that gain, but not at 20MHz. At that frequency any gain above one would be a specialty item.
 

WBahn

Joined Mar 31, 2012
29,857
I have never used an opamp for your 20MHz radio frequency.

An OPA134 is a very good wideband audio opamp. Its voltage gain is 1 million times up to 10Hz, is 10 thousand times at 1kHz, is 10 times at 1Meg Hz and is zero (like a piece of wire) at 10meg Hz. Its slew rate converts a sinewave into a triangle wave at a few hundred-thousand Hz.
It is overloaded if its load resistance is less than about 470 ohms.
So... it sounds like the OPA134 would be a horrible choice for his application. Why even mention it?
 

WBahn

Joined Mar 31, 2012
29,857
View attachment 306800
I don't know much about opamps.
The idea is to use various opamps in series, with different charateristics according to the input voltage, but with the main goal to increase the peak voltage,let's 5 or more volts, and mostly keep the sine wave frequency of the orginal circuit. Is this possible?. Assume you have all the necessary power source to power the opamps.
You need to supply a LOT more information if you want to get useful information back.

There are lots of opamps out there that are designed to operate at these frequencies and higher.

Whether you need multiple stages depends on what your requirements are. What is your input signal source? What amplitude? What output impedance? What output impedance do you need from your final opamp stage? What is it that you are driving (and just knowing that it's a transformer isn't good enough).
 

MisterBill2

Joined Jan 23, 2018
17,790
This is a good problem for LTspice circuit simulator. You can model ideal components or choose existing opamps. If you haven't already, attempt to solve this problem on paper with basic opamp equations because the diagram is apparently increasing the amplitude of the signal while keeping the phase and frequency the same. This can be accomplished by a single op amp or as many stages as you want.

This begs the question as to why you want to have multiple opamp stages when an single opamp is capable of near infinite gain. Unless you have a specific goal, having more stages will at the very least introduce a propagation delay. What are you getting in return for this delay and the other parasitic losses / interference generated by the additional circuitry?
There is a limiting factor for many devices, that is the gain-bandwidth product. It is totally brutal at enforcing reality on us. I wil leave it to those who can describe it more elequantly than me to explain it.
 

k1ng 1337

Joined Sep 11, 2020
910
There is a limiting factor for many devices, that is the gain-bandwidth product. It is totally brutal at enforcing reality on us. I wil leave it to those who can describe it more elequantly than me to explain it.
Agreed but TS asked 'a is this possible?' question so I suggested a simulator. I'm fond of LTspice for its ability to easily answer these kinds of questions due to its computational power. The program is set to be near to reality and many parameters including GBP can be modified to deviate from the ideal value.

I often find it useful to reverse engineer a circuit starting with a spice simulation because I put my trust in the people over at Analog Devices to effectively orient the ignorant me during my experiments... "If we knew exactly what we were going to find, we would know exactly how to design the study!"

Simulating Gain-Bandwidth—the generic op amp model - The Signal - Archives - TI E2E support forums
 

MisterBill2

Joined Jan 23, 2018
17,790
The example that I had recalled was an IF amplifier for a SSB receiver. There were three stages and the explanation was that while one stage could provide the required gain at a lower frequency, at the higher frequency it took three stages of the same high frequency op-amp for that gain without distortion, because of the GBW limitations. That is at least partly because of slew-rate limitations that are a real bother some times.
 

WBahn

Joined Mar 31, 2012
29,857
Because its works well it is popular and millions have been sold.
Where is a circuit that uses an opamp for 20MHz?
But you've made it clear that it is NOT going to work well for the TS's needs.

Not everything in the world is audio. TI has been making opamps for use at RF for at least three decades, and they are certainly not alone.
 

MisterBill2

Joined Jan 23, 2018
17,790
But you've made it clear that it is NOT going to work well for the TS's needs.

Not everything in the world is audio. TI has been making opamps for use at RF for at least three decades, and they are certainly not alone.
Lots of circuits use op-amps for megahertz signals. There is a whole lot of electronics that is not "audio", and a fair amount is not even communications. All sorts of medical equipment, and even data recording equipment.
Receivers for all sorts of frequencies use 20 or 21.4 mhz amplifiers and have used them for a few decades.
 
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