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THS4521 Frequency response inverting output

R. Scalick
Prodigy 160 points
Other Parts Discussed in Thread: THS4521, THS4541

Hallo,

I have added simulation results.....

I have done a Tina simulation with a THS 4521.  (Gain 1V/V; with 4pcs of 1k resistors;  both Inputs are AC decoupled with 100n caps; single ended input signal 500mV: 5V supply voltage; Vocm=2,5V; output differently loaded with 1k. )

I have done the AC transfer characteristic from 10MHz to 100MHz and i got on the + output a frequ response -6dB to -7dB....if I measure at the - output I get  a frequ. response from -6 to -10dB. 

What is the reason for this 3dB difference between the output channels and why is the inverting output not so flat like the non  inverting output.

kind regards

Rudi

  • 0
    TI__Genius 15975 points

    Hello Rudi,

    The 3dB difference between the output channels is due to one of the feedback paths (from inverting output to non-inverting input for THS4521) being bandwidth limited compared to the other, which is partially responsible for the roll-off of the frequency response in unity gain. Please note that this happens outside the linear operating frequency of the THS4521.

    Best Regards,

    Rohit

  • 0 in reply to Rohit Bhat
    Prodigy 160 points

    Hi Rohit,

    many thanks for your info.

    That means for me: If this component is used with a gain of 1V/V with 0.2V input voltage the gain bandwidth product is not the 145MHz ! Where can I find the "true" bandwidth in the datasheet for this application ?

    kind regards

    Rudi

     

     

     

  • 0 in reply to R. Scalick
    TI__Genius 15975 points
    Hello Rudi,

    The gain bandwidth product (GBP) for the part would still be 145MHz with gain of 1V/V and 0.2V input, since for an FDA the GBP is determined by the difference between the two output ports differentially, rather than calculating it single-ended on each output ports.

    What do you mean by the "true" bandwidth of the part? Do you mean the linear operating frequency of the part?

    Best Regards,
    Rohit
  • 0 in reply to Rohit Bhat
    Prodigy 160 points

    Hi Rohit,

    I mean up to which frequency (within a +-0,5dB frequency response flatness) can this component be used. 

    (single ended to differentally, Gain1, .....)

    kind regards

    Rudi

     

     

     

  • 0 in reply to R. Scalick
    TI__Genius 15975 points

    Hi Rudi,

    Looking for a +/-0.5dB frequency response flatness for THS4521 would be close to 40MHz. If you looking for a frequency response flatness of +/-0.5dB up to 145MHz, I would recommend looking into the THS4541.

    Best Regards,

    Rohit