Looking for a variable gain amplifier

[cyberblak]

Variable gain amplifier

Hi,

Does anyone know an amplifier or a circuit that can provide a 60dB adjustable gain with a > 35MHz bandwidth?

Thanks,

cyberblak

 

[jasnoch]

Re: Variable gain amplifier

Take a look at the VGAs from Analog Devices. No one amplifier gives you 60db of gain but you could put two in series. Link for these is at:

**broken link removed**

 

[cyberblak]

Re: Variable gain amplifier

I thought of using two amps in series, but how could I adjust the gain from 0dB to 60dB from one potentiometer then?

Thanks,

cyberblak

 

[jasnoch]

Re: Variable gain amplifier

You can just connect the gain control voltage lines from both the amplifiers together and feed the same control voltage into both. Make sure that the second amplifiers input will not be overloaded by the first amplifiers output. The voltage gain slope will be twice as steep when the amplifiers are in series.

 

[cyberblak]

Re: Variable gain amplifier

Thank you very much jasnoch, your answers were of great help!

By any chance, do you know a manufacturer that offers cheaper VGAs than Analog?

I found one that'll be perfect, but wow, it's expensive...! Of course, if it's the one that I need, it'll do...

cyberblak

 

[jasnoch]

Re: Variable gain amplifier

Hi Cyberblak,

Glad to help. Other companies making VGA chips would be Linear Tech and National but I think you'll find them around the same price range. On the prices of Analog Device parts; they have a fairlywide selection. Some are real specialized, like very low noise and distortion for ultrasound applications and hence expensive. But would something like two AD8324's in series work? They are fairly cheap.

 

[cyberblak]

Re: Variable gain amplifier

Unfortunately no... but thank you anyway! I'll stay with the one I found...