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OPA350: OPA 350

Mohd Khairul Akhtar Mohd Yahaya
Prodigy 10 points
Part Number: OPA350

Tool/software:

I tried using OPA350 to work as both amplifier and buffer, but it doesnt work. 

Both R = 1k ohm, expected gain of 2. Supplied with +5V. Added 0.1 uF bypass capacitor from V+ to GND. Added feedback capacitor as an attempt to stabilize it (but without it there seems to be no effect as well)

 

Below is the input and output. The amplification doesnt tally with the expected gain of 2?

Since the datasheet specify the OPA350 is unity gain stable, I tried to configure it as buffer as well.

  

The output doesnt give the same waveform as the input. And it looks the same output when I configured it as op amp (the scope picture above).

Where did it go wrong?

  • 0
    TI__Guru 67601 points

    Mohd,

    You need to show your power supply.  For a single 5V supply, you must shift up the input (see Vcm) to make sure that the output is within OPA350 linear range - see below.      As expected, the OPA350 shows that it is in fact in the gain of 2.

    It is not clear to me what is your input signal. If it is a short duration pulse of less than us, the feedback RC will filter the signal at fc of around 402kHz and thus any signal shorter than 2.5us will be attenuated - see below.

    Running transient simulation shows 10MHz square input signal being attenuated from gain of 2 to gain=~1.2 (from +/-200mV down to +/-120mV) -  see below.

    Replacing the 560pF feedback cap with 9pF properly compensates (CF=Cin_diff+Cin_cm) the op amp with effective bandwidth of around 25MHz - see below.

    With the above compensation, OPA350 may easily pass the small-signal of 10MHz without any attenuation - see below.

    OPA350 single supply.TSC

    OPA350 AC bandwith.TSC

    OPA350 transient response.TSC