early Saturation in OpAmp!

Hi guys



In a non-inverting op-amp, Vout=(1+R1/R2)Vin. Assuming Vsupply=±Vcc, Vout is supposed to swing up to ±Vcc
(Right?). While that's ideal and I don't expect Vout reaches ±Vcc; the Vout I see in the simulation, saturates far before ±Vcc.

Here are the parameters (exactly according to the datasheet):
op-amp: THS3091
R1=1000 Ω
R2=250 Ω
Vsupply=±5v

Vin=1 Vp-p sine wave @ 1 MHz
while Vout should be 5 Vp-p, it saturates at around 3 Vp-p. (As a solution, I could change the Vsupply=±5v to ±8v to have non-saturated output. But, increasing the Vsupply in the design is not allowed)

Here is the question:
Is this early saturation at 3v inevitable OR I am doing some mistakes in this simple design?


Thanks a lot, in advance
Politecnico

I would expect Vo= 4Vpp at least as shown in spec. What is your load R? 100?

Beyond 4Vpp that THD rises and slew rate well below limit , what about lower frequency response? Does it saturate the same?

Thanks a lot for your reply.
Assume Rload=100 Ω, according to the right side plot you attached, Vout can not swing beyond ~3.1V ! So, what does Vout=4 Vpp at the left side plot mean?

SunnySkyguy said:

I would expect Vo= 4Vpp at least as shown in spec. What is your load R? 100?

Beyond 4Vpp that THD rises and slew rate well below limit , what about lower frequency response? Does it saturate the same?

View attachment 109011

Click to expand...

For the output to go near the rail voltages you need a rail-to-rail input and output type op amp.

Edit: How close a RR amp goes to the rail voltage depends upon the value of the load resistance (including any feedback resistance).

Be careful! SunnySkyguy mentioned 4VPP, which is -2V...+2V. But you mean that the output doesn't go beyond +3.1V, which would mean ~6Vpp! As you can see from the datasheet excerpt, the output goes into saturation at exactly +3.2V/-3V. So your findings perfectly match the datasheet values and are absolutely inevitable when using this Opamp.