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Build Function generator amplifier

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3A 15V
Do you need +/-15volts?
Do you need the amplifier to have 50 ohms output impedance like the amplifier in the 33220? (so you can drive coax)
Because you want 3 amps then you probably don't want 50 ohms output.
30Mhz....Do you want 30mhz bandwidth? Do you want 120mhz bandwidth so a 30mhz square wave looks some what square.
Distortion spec? The 33220 has good distortion.

Many of the parts that can do this job are not in production! If you build one then this is not a problem. If you want to go into production this is a big problem!
 
I'd like to drive with a high impedance output. Vpp I don't really need more than +/- 5V, so it's not a big concern.
the noise that I'm planning on feeding in is a sine wave and yes, my plan was to have a somewhat clean 30 MHz signal (I didn't realize I need to have that much more bandwidth to get a clean AC signals)
By distortion spec, did you mean the Vpp on AC signal? Then as mentioned earlier, it's only +/- 5V

I agree Ron, I'm really surprised that in today's technology, I can't find this kind of device in the market (or at least, none in my knowledge, after searching for a few days). This is gonna be a rather in house project than a production device, so we don't have to worry about that =)

Thanks for replying by the way, let me know if you have something in mind you'd like to share.
 
It would be helpfull if you could be a bit more definite about the specification of the signal you are trying to produce.

I am guessing 5v (RMS) sinewave at up to 30Mhz.

But what is the load?
Earlier you said 15v 3A, that infers a 5 ohm load.
What is it that you are trying to drive?

JimB
 
15 volt or +/-5 volts. That makes a big difference. If you want +/- 15 volts out then the output device (IC or transistors need to withstand 30 volts).
Most output amplifiers use 2x the supply because of back impedance. So they actually make 2x the voltage you need. So to drive 15 volts in a 50 ohm coax, inside the generator they make a 30 volt signal. The amplifier needs head room, so to make 30 volts you need a 40 volt supply. (short story; to make a signal generator with +/-15 volts output you will need +/-40 volts supplies and 90 volt parts. There are no fast 90 volts parts in production! I have spent many hours looking for them.


You said "I'd like to drive with a high impedance output." WHAT? Most signal generators drive through a 50 ohm resistor. (75 ohms if used for video) They can not drive 3 amps! So your amplifier needs to have a low impedance output! Not a 50 ohm impedance like the 33220 has.

I think you want to drive +/- 5 volts at up to 3 amps. With a output impedance of under 5 ohms. (maybe 0.5 ohms) I think you need current limit.

If you are only using a sign wave you need a amplifier that is very flat to 30mhz.
If you are using a square wave; it is made up of harmonics that will extend out a long way.
A 30mhz amplifier will reproduce a 30khz signal true. A 30mhz square wave will look like a sign wave. (or a ramp wave) Square waves have harmonics. With out the harmonics all you get is a sign wave.

I do know about the output amplifier in the 33220.
 
I guess I wasn't very clear in what I want, so I apologize

Here's the definite spec I'd like to have:

To amplify agilent 3320 signal to:
- drive 3 amp load
- DC level of 15V
- Ability to introduce noise of at least +/-5V to the 15Vdc (sine wave)

Ron, yes I understand that we need to supply the amplifier with more than the desired output voltage to assure it's not saturating. You're right on the impedance, I don't know what I was thinking, pardon my silly brain =).

I found this pdf that I could start my simulation with:
https://www.electro-tech-online.com/custompdfs/2012/04/buffer.pdf

I was looking at figure 2B. Using a OPA544 opamp and 1 ohm output impedance, I was able to drive a stable signals up to 275kHz. As warned, This circuit is only meant to work in a lower frequency. I'm still scratching my head trying to figure out a way to make a stable power amp that work in a high frequency region as well
 
- drive 3 amp load
- DC level of 15V
- Ability to introduce noise of at least +/-5V to the 15Vdc (sine wave)

3 amps -----OK
Do you want to output 15 volts DC with a sine wave on top of that?
What noise? Is the output of the signal generator noise?
"15Vdc (sine wave)" So is the 15V a sign wave or the +/-5V a sine wave?

I think you want 15V power that has a 'noise' added to it. The noise comes from the Agilent box.
 
3 amps -----OK
Do you want to output 15 volts DC with a sine wave on top of that?
What noise? Is the output of the signal generator noise?
"15Vdc (sine wave)" So is the 15V a sign wave or the +/-5V a sine wave?

I think you want 15V power that has a 'noise' added to it. The noise comes from the Agilent box.

Yes you are correct sir. 15Vdc with +/-5V sine wave on top of it.

By noise, I was referring to the sine wave that's riding on top of the DC signal
 
I see several options.
1) Make a amplifier that can output 0 to 20 volts. 20=15+5
2) Make a power supply that is 0 to 15 volts. On that supply float a +/-5 volt amplifier.
3)?

The reason I am trying to keep the high speed amplifier to +/- 5V is that high speed amplifiers do not do well with high voltage. There is a voltage/time (slew rate) problem in amplifiers. A LM741 amplifier can change its output at only 1V/uS. There are amplifiers that can move 1000V/us or 1V/nS but they can not handle high voltage.

You can add emitter flowers, like in the pater of post#4, or parallel ICs. I have used 4 ICs in parallel to boost current.

I like current feedback amplifiers for this application.

Here is a parts to think about.
LT1206
It has a large current output. (not what you need but..)
Good bandwidth.
Fast slew rate.
10 to 30 volt supply.
Many packages, some will work with heat sinks.
If Rfeedback is 1.2k then -1db point is 30mhz.
 
I see several options.
1) Make a amplifier that can output 0 to 20 volts. 20=15+5
2) Make a power supply that is 0 to 15 volts. On that supply float a +/-5 volt amplifier.
3)?

The reason I am trying to keep the high speed amplifier to +/- 5V is that high speed amplifiers do not do well with high voltage. There is a voltage/time (slew rate) problem in amplifiers. A LM741 amplifier can change its output at only 1V/uS. There are amplifiers that can move 1000V/us or 1V/nS but they can not handle high voltage.

You can add emitter flowers, like in the pater of post#4, or parallel ICs. I have used 4 ICs in parallel to boost current.

I like current feedback amplifiers for this application.

Here is a parts to think about.
LT1206
It has a large current output. (not what you need but..)
Good bandwidth.
Fast slew rate.
10 to 30 volt supply.
Many packages, some will work with heat sinks.
If Rfeedback is 1.2k then -1db point is 30mhz.

Thanks for the suggestion! By the way, did you encounter some problems when you paralleled op amps?? I heard it can get messy and based on page 4 in the site I mentioned earlier, it's not recommended due to potential of mismatching. I'll do my homework here too and research on google
 
Paralleling amplifiers:
In my case:
1 amplifier driving 50 ohms to the output connector can handle X amount of current.
2 amplifiers each with 100 ohms to the output connector can handle 2x of current.
4 amplifiers each with 200 ohms to the output connector can handle 4x of current.

In each case the output impedance is 50 ohms.

There are problems paralleling amplifiers with out the a resistor network on the outputs. There are numerous examples in production at high end test equipment companies using parallel amplifiers (using resistor summing).
 
It sounds like you want to introduce a sine wave signal into (onto) a DC output, and you are calling the sine wave signal "noise". Is this for some kind of compliance testing?

ak
 
Is this for some kind of compliance testing?
This is a old dead thread from 2012. We do not know much.
I have use something almost like this to see the frequency response of a power supply. Example; 15 volt + 0.5V signal. Sweep the signal from dc to (khz or mhz) and look how much of the signal gets to the output.
This is how you measure supply ripple rejection on op-amps. OR Look at the LM7805 data sheet. There is a input to output rejection ratio.
upload_2018-5-5_16-12-6.png

I also use this to see if the error amplifier is stable.
 
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