A question about Op-Amps

[1843]

Hi everybody,

We can get a special gain from an Op-Amp with several choices in Rinput and Rgain.
For example in Hammerhead if we change R26 to 1M and R24 to 10K, the gain(100) doesn't change...

Can I know what is the difference between these options?
Which option is better for an integrator circuit???

Best regards

[Carl-NC]

There are several trade-offs involved. First, a larger feedback resistor gives a slower amplifier. For the integrator, this is no big deal. Smaller resistors burn more power. Leakage currents have more effect when using large resistors. In the integrator, the cap value is inversely proportional to the feedback resistor, so a larger resistor means a smaller cap. But this is no big deal.

So, for the integrator stage, the values of R24 & R26 are not at all critical, as long as other components get scaled properly. I chose those values because I try to use common component values, and to put the circuit design smack in the middle of the spectrum of choices.

- Carl

[chemelec]

There are several trade-offs involved. First, a larger feedback resistor gives a slower amplifier. For the integrator, this is no big deal. Smaller resistors burn more power. Leakage currents have more effect when using large resistors. In the integrator, the cap value is inversely proportional to the feedback resistor, so a larger resistor means a smaller cap. But this is no big deal.

So, for the integrator stage, the values of R24 & R26 are not at all critical, as long as other components get scaled properly. I chose those values because I try to use common component values, and to put the circuit design smack in the middle of the spectrum of choices.

- Carl

Higher Resistance Values can also Increase Internal Noise.

[Carl-NC]

Higher Resistance Values can also Increase Internal Noise.

True! Noise is proportional to the squareroot of R26. In an integrator, it gets averaged out, but would not in an ordinary gain stage.

[1843]

Thanks Carl and Gary for reply.