# OPA350 behavior at high frequencies

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

Frequencies of (100Hz-10kHz)

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:

simulate this circuit – Schematic created using CircuitLab

• Have you checked the slew rate? That's often a gotcha – Scott Seidman Jul 5 '18 at 15:36
• 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. – Pllsz Jul 5 '18 at 15:37
• Try putting a 1 kohm load after the diode to 0 volts. – Andy aka Jul 5 '18 at 15:49
• My MacBook and iPhone is attenuating it’s signals at higher frequencies . Ahaha thought it was my op amp sorry guys. – Pllsz Jul 5 '18 at 16:08
• 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 – Jack Creasey Jul 5 '18 at 16:26