Current Feedback Operational Amplifier, High Gain

[torbai]

Current Feedback Operational Amplifier can offers high bandwidth. However, when I look up a datasheet of a CFOPA, I find that the gain of the example circuit is not high(maybe Av = 2 or 5). Why?
If I want G = 20dB or 40dB (BW = 100MHz, for example), it is posible?

 

[barry]

For 40dB, you're going to need an amp with a GainBandwidthProduct of 10GHz. Good luck. 20 dB should be no problem (AV=10)

The reason the example circuit had AV of 5 was because it was an example of an amplifier with a gain of 5.

 

[crutschow]

CFOPAs don't have the normal gain-bandwidth limit of the common voltage-mode op amp so getting 20dB or 40dB at 100MHz should be doable. What is the number of the amp you looked at?

 

[torbai]

CFOPAs don't have the normal gain-bandwidth limit of the common voltage-mode op amp so getting 20dB or 40dB at 100MHz should be doable. What is the number of the amp you looked at?

I'm looking at Texas Instruments THS3001

 

[crutschow]

If you look at page 19 of the data sheet you will see a discussion of gain resistors. These amps are typically used at lower gains but you should be able to increase the gain above 5 by lowering the gain resistor. The feedback resistor should be selected for the response you want (as shown in Figure 33) and then the gain resistor (Rg) selected for the desired gain.

It is likely not practical to try to get more that 20dB (Av=10) from one amp so you would need two in series to get 40dB. Note that a high frequency amp with that much gain is very prone to oscillations so a careful layout using a PCB with a ground plane is mandatory. Read this for information on layout. You might want to buy one of those EVAL boards for initial testing of the amp.

 

[torbai]

If you look at page 19 of the data sheet you will see a discussion of gain resistors. These amps are typically used at lower gains but you should be able to increase the gain above 5 by lowering the gain resistor. The feedback resistor should be selected for the response you want (as shown in Figure 33) and then the gain resistor (Rg) selected for the desired gain.

It is likely not practical to try to get more that 20dB (Av=10) from one amp so you would need two in series to get 40dB. Note that a high frequency amp with that much gain is very prone to oscillations so a careful layout using a PCB with a ground plane is mandatory. Read this for information on layout. You might want to buy one of those EVAL boards for initial testing of the amp.

Thank you very much