OPA548: OPA548 output is abnormal

Hey Tom,

Thanks for reaching out. 

First, the OPA548 will likely be unhappy with 70V supply as the abs max is 60V:

Next, we have an important spec in the device datasheet, being full power bandwidth. 

This shows the maximum output voltage specified across frequency:

As we can see, we would be severely limited due to the maximum slew rate of the device. 

Tom Tom said:

I need to obtain a sine wave signal with an amplitude of 60Vpp at any frequency within the range of 10MHz to 60MHz, how should I proceed?

This type of requirement is best suited by a high speed amplifier, as the gain bandwidth of the OPA548 is just 1MHz typical:

I do not support the high speed amplifier portfolio, but I can say that this will likely be a somewhat challenging solution to realize.

My immediate thought is to leverage something like the THS3470, though even this device would be 64V abs max supply. 

Furthermore, this device would not have the large signal BW required to create up to 60MHz sine waves. 

For reference, to create a 60MHz 60Vpp sine wave, a ~12000V/us slew rate is required. This device would also need to drive the non-insignificant load present.

I can reassign to the high speed amplifier team if you would like. 

Do you have any further details on what this will be used for? What is the minimum load impedance?

Thanks,

Jacob

This signal drives a cable (total 0~0.12km) with a certain impedance per unit length. If operational amplifiers cannot be implemented, do you have any other recommended solutions?

Under the condition of a 2Vpp sine wave input amplitude, the current circuit that can output the highest frequency and voltage may not necessarily be OPA548. Can you send out the simulation results to take a look ？

Hey Tom, 

Thanks for the details on the transmission line. 

Op amps can certainly be used here, and it is great to see more details on the load. I saw mention of 60MHz, 60Vpp output, and relatively low load impedance, which would not be possible with any single chip TI amplifier that I know of. 

I am throwing this thread over to the HS amps team now, but I will follow along to make sure we realize a suitable design for your needs.

I am including a THS3470 Tina-Ti reference design in case you wanted to try some simulations using a faster high voltage device. 

sbomcq7.tsc

Thanks,

Jacob

Hi Tom,

I was able to look over the thread, and I agree with Jacob on his initial response regarding the slew rate required. However, I saw you mentioned 2Vpp, are there any details you can share on what is required in your application? Any information on the load would also be useful.

Best Regards,

Ignacio