• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 46 subscribers
  • Views 447 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Fully Differential Amplifier, Single Supply Problem compared to Dual Supply

William Lu61122
Prodigy 10 points
Other Parts Discussed in Thread: THS4500, THS4130, THS4521

Hello, I'm using a FDA to reject a 2.5V offset of my signal and amplify the signal such that when it goes through a peak detector, it'll be at 5V.

When using dual supply, I am able easily achieve this.

However, when changing the configuration to a single supply, the signal will clip if I try to make it 5V.

I display my schematic and plots in the file.

6165.Doc1.pdf

I was wondering if there was a way to solve this?

On a side note, the PD pin of THS4521 says the max is 2.1V but I'm only allowed to use 2.5 and 5V power supplies. I was wondering If I can shove 2.5V down the PD pin like I did in the simulation.

  • 0
    TI__Genius 17905 points

    William,

    In the dual supply case, you are using +/-5V supplies which violates the 5.5V max supply voltage of the THS4521. The model does not reflect this supply limit and is providing a wider output voltage range with this +/-5V supply than with the single 5V supply. With a 5V single or split (+/-2.5V) supply, the THS4521 will achieve ~4.6Vpp output voltage swing at each leg of the differential output for a differential output swing of about 9 Vpp. A limitation of the voltage level of the signal after the peak detect is the voltage drop due to the rectifying diodes (~1.4V through two diodes in either direction). If you were not tied to 5V, you could use one of our higher supply voltage FDAs such as the THS4130 or THS4500/1/2/3 to get a wider range. Otherwise, you might try replacing the diode with one with a lower forward voltage and/or just do a half-wave rectification.

    For the PD pin, the 2.1V is the maximum enable threshold voltage, not the maximum allowed voltage at the pin, so 2.5V is perfectly fine to use on that pin.