2
\$\begingroup\$

The INA143 difference amplifier datasheet states that the device supports G=10 and G=0.1 when connected in difference amplifier configuration. However, the datasheet only gives specifications for the G=10 case.

The bandwidth there is given as 0.15MHz for the G=10 case (where the internal op amp will see a gain of 11), but I'm interested in the bandwith at G=0.1 (where the op amp's gain is 1.1). Given that op amps typically have a 20db/decade gain/frequency relation, can I extrapolate that the bandwidth in the G=0.1 configuration will likely be around 1MHz or above?

I plan to use the amplifier inside a feedback loop, so good bandwidth will be essential for stability.

\$\endgroup\$
  • 2
    \$\begingroup\$ It doesn't look like they say. \$\endgroup\$ – Andy aka Feb 10 '15 at 12:32
  • \$\begingroup\$ Is your application cost sensitive? For a few dollars more there are faster instrumentation amps. \$\endgroup\$ – George Herold Feb 10 '15 at 15:03
  • \$\begingroup\$ It's not particularly cost-sensitive. \$\endgroup\$ – Medo42 Feb 10 '15 at 15:09
  • \$\begingroup\$ One thing to look out for though is that the input voltage is up to +-30V on the positive input. With the default three amplifier configuration, the in-amp would have to run from +-30V supplies. It seems far easier to find diff-amps which support that range, since they divide the voltage down before it reaches an amp. \$\endgroup\$ – Medo42 Feb 10 '15 at 15:14
1
\$\begingroup\$

I would expect the gain-bandwidth product to be a constant, but it's worth comparing the two on the bench before designing it in (I suggest measuring both the gain-of-10 -3dB point and the gain-of-0.1 -3dB point to have a point of comparison with the datasheet limits).

Note that the slew rate is typically a fairly good 5V/us, but you'll run into that at high amplitudes.

\$\endgroup\$
  • \$\begingroup\$ Thanks for the answer. The slew rate doesn't limit me here, because the controlling amplifier itself is pretty slow. 0.5V/µs would probably be enough already. \$\endgroup\$ – Medo42 Feb 10 '15 at 15:08
1
\$\begingroup\$

I suppose the opamps are unity-gain compensated. Therefore, it is logical to assume that the closed-loop bandwidth in case of G=0.1 will be app. 10 times larger that for G=10. To be somewhat conservative, I would expect 1.2...1.5 MHz.

\$\endgroup\$
  • \$\begingroup\$ The op-amp inside the diff-amp doesn't actually see a gain below 1 in the G=0.1 diff-amp configuration. \$\endgroup\$ – Medo42 Feb 10 '15 at 15:54
  • \$\begingroup\$ Ohh - it seems that there was something like a "short" in my brain. Yes - it`s nearly a unity gain configuration. Thank you for correcting me. I will edit my answer correspondingly. \$\endgroup\$ – LvW Feb 10 '15 at 16:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.