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I just recently bought a OPA350 OP-AMP due to its fast recovery speed that I need for my application (Precision Rectifier), it just arrived today and I went to go test the circuit. However weir behavior is starting to surface at high frequencies...but this time it's the Vpk-pk.

Datasheet: OPA350


Output at 584 Hz

Frequencies of (100Hz-10kHz)


Output at 21 kHz

Frequencies of (20kHz)


As you can see the \$Vpk-pk\$ took a beating at 20kHz and I thought this was due to the bandwidth of the OP AMP, however it's stated to be 30MHz. It also gets much noisier as well.

GBW EQUATION:

\$F_c=\frac{30MHz}{1}=30MHz\$

so the flatness should decade 6dB/sec after 30MHz ish, but why is it doing it around 20kHz?

SLEW RATE EQUATION:

\$SR = 20kHz*2*\pi\$
\$SR = 0.127V/uS\$

The OP AMP is rated for 22V/uS

Schematic:

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ Have you checked the slew rate? That's often a gotcha \$\endgroup\$ – Scott Seidman Jul 5 '18 at 15:36
  • \$\begingroup\$ Its more than enough :/ its faster than my old OP AMP which was slower.. the Slew rate is at 22V/uS should be more than enough. \$\endgroup\$ – Pllsz Jul 5 '18 at 15:37
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    \$\begingroup\$ Try putting a 1 kohm load after the diode to 0 volts. \$\endgroup\$ – Andy aka Jul 5 '18 at 15:49
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    \$\begingroup\$ My MacBook and iPhone is attenuating it’s signals at higher frequencies . Ahaha thought it was my op amp sorry guys. \$\endgroup\$ – Pllsz Jul 5 '18 at 16:08
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    \$\begingroup\$ It's worth noting that your negative excursion of the input signal is taking the input below gnd by more than recommended. I'd also replace the In4148 with a much lower Vf diode to get more signal output capability. This may help: ww1.microchip.com/downloads/en/AppNotes/01353A.pdf \$\endgroup\$ – Jack Creasey Jul 5 '18 at 16:26

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