Adapting THS4524IDBT to THS4541IRGTT

Hello Albin,

If the input signal is differential then the gain of the FDA is simply Rf/Rg, where Rf is the feedback resistor and Rg is the input gain resistor. For example if figure 73 of the datasheet, the gain is 4.02V/V (ignore C1, C2 and Rm-  not relevant to this discussion).

Can you please confirm if the input signal in amp enabled mode is 2Vpp differential or 1Vpp differential. The ADC can accept a 2Vpp signal on 0.9V common-mode so I need to figure out whether the amplifier needs to be configured in a gain of 1V/V (0dB) or 2V/V (6dB). Once you confirm this I can send you a TINA schematic showing the resistor configuration.

Regards,

Samir

Hello Samir,

Thank you for your reply. It was much faster than expected. :)

In the "Amp enabled" mode it's 1Vpp (2V-3V). In "Amp disabled" mode it's 0.65Vpp (2.175-2.825V).

Based on the part number of the ADC, it can go up to 80Msps (with12/13 bit resolution), and the Xilinx FPGA that would receive the output from the ADC can handle both 65Msps and 80Msps. At a minimum we need 65Msps, so additional speed is bonus.

So, would you be able to keep the current resistor divider and capacitor configuration (Preferred) and just change the values to match the new THS4541IRGTT device?

Regardless, please also send the accuracy needed on the passive components. The currently used 4.99Kohm resistors have a 1% accuracy, but the rest have 10% accuracy. (Because it's so late in the layout phase I had to change the passive components to 0402 size to make them fit, without changing the PCB size.)

Looking forward to your answer.

Thanks,

-albin

Hi Albin,

 I am going to attach two circuits here - one checks the amplifiers loop gain for stability and phase margin and the other one can be used for checking the transient response and the ac closed loop gain of the circuit. As configured the bandwidth is around 92MHz with sufficient phase margin. 1% components would work out well. This will give the lower balance error compared to using 5% resistors.

I just want you to be aware that when changing from the THS4524 to the THS4541 you will need 4 discrete amplifier channels since the THS4541 is not available in a quad-channel version.

-Samir

THS4541_Ckt.TSC

THS4541_Stability Check.TSC

Hi Samir,

My TINA download, decompressing the ZIP-file and double clicking on the executable works (according to the windows task manager the install launcher is started each time), however nothing happens. No error messages and no window shows up. Starting it in administrator mode or in Windows XP mode gives the same result. I'm running Windows 7 in 64-bit mode.
I retried download and install it in root directory, but got the same result.

So, I can't see or use the TSC-files that you've sent.
Please send the circuits in PDF-version or even better in OrCAD format.

Thanks,

-albin

Hi Samir,

I was able to install TINA after PC reboot and simulate the TSC-files. Thanks
Very sorry. I found out from the Customer that the input frequency has been reduced to max 7MHz, so then I assume we can keep THS4524.
Please check that the voltage divider before the OpAmp in the schematic is correct.

Thanks,

-albin

Albin,
The THS4524 will work in the application now. You can use TINA TI to simulate your circuit and verify if it meets your requirements.
-Samir