Looking for op amp that supports large gain/bandwidth

In summary, the student is seeking help with finding an operational amplifier that can be cascaded to achieve a total gain of 100,000 or 100dB at a frequency of 1.5 MHz. They are building an RF amplifier for an AM radio. They have encountered issues with amplification and suspect it may be due to bandwidth limitations. The most gain achieved so far is 1,000. The responder suggests that achieving 100dB gain at 1MHz on a breadboard may be difficult due to parasitic feedback and recommends using a construction technique similar to that of a spectrum analyzer. They also inquire about the student's application and mention the potential need for AGC or changeable gain/attenuation.
  • #1
max.L
1
0

Homework Statement



I need help with finding an operational amplifier that could be cascaded with itself to produce a total gain of around 100,000, or 100dB. It also needs to be operational up to 1.5 MHz. This is for an rf amplifier for an AM radio I am building.


Homework Equations





The Attempt at a Solution



Most amplifiers seem to amplify correctly during the first stage, but the second stage either doesn't amplify at all or it seems to drop almost back to the input values. This could be due to bandwidth issues I suppose. The most gain I've been able to achieve is 1,000. Thank you for your time.
 
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  • #2
max.L said:

Homework Statement



I need help with finding an operational amplifier that could be cascaded with itself to produce a total gain of around 100,000, or 100dB. It also needs to be operational up to 1.5 MHz. This is for an rf amplifier for an AM radio I am building.


Homework Equations





The Attempt at a Solution



Most amplifiers seem to amplify correctly during the first stage, but the second stage either doesn't amplify at all or it seems to drop almost back to the input values. This could be due to bandwidth issues I suppose. The most gain I've been able to achieve is 1,000. Thank you for your time.

You are not going to get 100dB gain at 1MHz with opamps on a simple breadboard. Parasitic feedback from the output stages will cause oscillations or other problems with the input stages.

If you look at the internals of a spectrum analyzer, you will see multiple shielded modules with shielded coax connections between them. If you want 100dB gain, you will most likely need to use a similar construction technique, including a lot of power supply filtering and isolation.

I'll see if I can find some pictures of spectrum analyzer internals. Can you say more about your application? Will you be needing AGC as part of the amplifier chain? Or non-automatic but changeable gain/attenuation like a spectrum analyzer?
 
  • #3
OTOH, you will have fewer problems at 1MHz versus 100MHz. I don't know for sure, but I'm guessing that commercial AM radio receivers have around 60-70dB gain, with only modest isolation and shielding between stages.
 

FAQ: Looking for op amp that supports large gain/bandwidth

What is an op amp and what is its purpose?

An op amp, short for operational amplifier, is an electronic component used in circuits to amplify and process signals. Its purpose is to perform mathematical operations on input signals, such as amplification, addition, subtraction, and integration.

What does it mean for an op amp to support large gain/bandwidth?

The gain of an op amp is a measure of its ability to amplify an input signal. The bandwidth refers to the range of frequencies that the op amp can accurately amplify. A large gain/bandwidth means that the op amp can amplify a wide range of frequencies with high accuracy.

Why would someone need an op amp that supports large gain/bandwidth?

An op amp with large gain/bandwidth is useful in applications where a wide range of frequencies need to be amplified, such as in audio and instrumentation circuits. It can also be used in circuits where precise amplification is necessary, such as in medical and scientific equipment.

What are some factors to consider when choosing an op amp with large gain/bandwidth?

Some important factors to consider are the op amp's gain bandwidth product (GBW), which determines the maximum gain and frequency range, its slew rate, which refers to how fast it can respond to changes in the input signal, and its noise level, which can affect the overall accuracy of the amplified signal.

Are there any trade-offs when using an op amp with large gain/bandwidth?

Yes, there are trade-offs to consider. Op amps with large gain/bandwidth tend to be more expensive and consume more power compared to those with lower gain/bandwidth. They may also be more sensitive to noise and require careful circuit design to prevent oscillations and instability.

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