OPA810: Large-Signal Frequency Response vs Vo

THS3491 is your only option I think, 

Hi Michael 

Thank you for your reply. Will it be ok if I will connect THS3491 after the TIA stage employing OPA855?

Hi Michael

The one thing that I forgot to mention is that the output stage of my TIA is connected to a high pass RC filter. After that I need an amplification  with a gain of 7 and large signal bandwidth of 500MHz with a peak to peak swing of 4V. Can I connect the THS3491 after high pass  RC filter?

Hi PArveen,

why not showing a complete schematic? This would prevent us from guessing

Kai

Hi Kai

In this circuit I connected an OPA818 for 7V/V amplification. But when I checked the datasheet of the OPA818 I have found that the swing is limited to only 2Vpp at large signal bandwidth. Its slew rate is small. I need a swing of 4V peak to peak and large signal bandwidth of 500MHz.

0268.OPA855.TSC

Well the 4Vpp at 500MHz requires a min 6280V/usec slew rate and some margin beyond that. Only the THS3491 can do that -, then back up to the required gain there for the swing out of the prior stage to be within is slew rate

Hi Michael

I am using the formula to calculate slew rate:

Slew rate = 0.8*Vpeak*BW*2*phi = 0.88*2*500e6*2*phi = 3554V/µS. Is this not the correct way to calculate the slew rate?

I can compromise with the large signal bandwidth as well as peak to peak amplitude. Can you please suggest what would be the best OPAMP to use with OPA855 to get the maximum possible peak to peak swing and large signal bandwidth? For example I am ok to reduce the large signal bandwidth to 400MHz.

Hi Michael/Kai

Can I use OPA693 or OPA875 as an inverting amplifier after the OPA855 Transimpedance stage?

Please help me I will be grateful to you.  

Hello Parveen,

   You are able to interface those amplifiers with OPA855, but as Michael mentioned, the THS3491 has the slew rate needed to meet your specifications. Also, it looks like the same problem is being discussed at this e2e thread. I can assist there.

Thank you,

Sima 

Hi Sima

Thank you for reply. Can you clear my doubt that when I connected the THS3491 after the OPA855, is there any need to check the stability of the THS3491? I have checked the stability of the OPA855 separately, its phase margin is ok. Therefore, if I connect  the THS3491 in the noninverting configuration using the same values as mentioned is the datasheet in Table 2, page23 (RG =200 and RF= 798) after the OPA855 (TIA) stage. Further I want to know as mentioned in Figure 61 that the value of RT is 50 ohms. Is it a necessary condition? In my circuit the load on  the OPA 855 is 200 ohms. Therefore how can I match the source resistance?

Hi Parveen,

of course, you can do this and RT must not be 50R either. RT=50R is only necessary when driving the OPAmp with a 50R source in combination with a 50R cable (50R system).

Kai