ADL5513 log amp undershoot

ADL5513 pulse response

I am using this device at 2.4 GHz driven with a balanced feed from a Minicircuits balun, to avoid log amp tails.

However, i see an annoying undershoot at the end of the pulse. The output of the log amp is buffered with an AD8051 and the undershoot appears at all power levels, with or without 22pF CLPF cap. Running off 5Vdc. Test source is an R&S SML03 sig gen, 400ns pulses between -60 and 0 dBm. Undershoot is present at the input of the video buffer amp.

The problem with the undershoot is that it eats into the rising edge of a second pulse that comes after the first.

Any ideas or is it to be expected?

Parents
  • 0
    •  Analog Employees 
    on Sep 19, 2017 6:32 PM
    • You may be running into the ADL5513's own slew rate limitations; video BW will be dominated by the 3pF cap that is internal to the device on the CLPF pin
    • Have you just been looking at the output of the AD8051 buffer? Have you traced the undershoot to the ADL5513 by probing right at the VOUT/VSET (I am assuming you have these shorted) node with a high impedance oscilloscope probe?
    • Is the 400ns the pulse width?  How long until the next pulse starts?
Reply
  • 0
    •  Analog Employees 
    on Sep 19, 2017 6:32 PM
    • You may be running into the ADL5513's own slew rate limitations; video BW will be dominated by the 3pF cap that is internal to the device on the CLPF pin
    • Have you just been looking at the output of the AD8051 buffer? Have you traced the undershoot to the ADL5513 by probing right at the VOUT/VSET (I am assuming you have these shorted) node with a high impedance oscilloscope probe?
    • Is the 400ns the pulse width?  How long until the next pulse starts?
Children
No Data