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INA111: About Gain vs Frequency

Tsukui Yusuke
Guru 21930 points
Part Number: INA111
Other Parts Discussed in Thread: OPA192

Hi,

We are considering using this device.
While checking the graph information, I found a peculiar characteristic.
Could you tell me about Gain vs Frequency graph?

1.
The amplification factor increases in the range of 1MHz to 2MHz under the condition of "Gain = 1".
Is this phenomenon unique to INA111?
Could you tell me the reason why the amplification factor increases at the point of "⓵"?
And Does this increase phenomenon depend on individual differences and temperature?

2.
Under the condition of "Gain ≥ 10", the amplification factor increase phenomenon does not occur.
Is there any reason why the increase phenomenon does not occur at the "②" point?
Is it possible that it will occur due to temperature or individual differences?



Best regards,
Yusuke



  • 0
    TI__Guru 56451 points

    Hi Yusuke-san,

    Q:  Is this phenomenon unique to INA111?

    Could you tell me the reason why the amplification factor increases at the point of "⓵"?
    And Does this increase phenomenon depend on individual differences and temperature?

    All instrumentation amplifiers have this phenomenon at lower Gain (Gain=1). The point of interested in Q or gain peaking is resulted from feedback resistor (25kOhm) interacting with the input and output capacitance, typically in an order of 1-2pf, which it introduces a second pole near the corner frequency. I do not have data to present the temperature effects on the Q, but it is believed that the effect is minimum. I do not have the information of op amps used in INA111 part. 

    I am demonstrating the phenomenon with a known OPA192 op amps, you can see the effect via simulation. In addition, the bode plot in the last stage differential op amp is products of the analog front end in 3-op amp Instr. configuration. Typically, the front end op amps use high BW types because of high gain requirements in instr. amplifier. 

    Q: Under the condition of "Gain ≥ 10", the amplification factor increase phenomenon does not occur.
    Is there any reason why the increase phenomenon does not occur at the "②" point?
    Is it possible that it will occur due to temperature or individual differences?

    When instr. gain increases, two things are happening. The cutoff frequency is lowered due to GBP, and the two poles starts to separate due to lower Rg value. So the Q effect starts to minimized in higher gains (Q<1).

    I am enclosing the Tina simulation and you may be able to understand the interaction better, if you perform the simulation. 

    /cfs-file/__key/communityserver-discussions-components-files/14/use-OPA192-built-instr-amplifier-10312020.TSC  

    If you have additional questions, please let us know.

    Best,

    Raymond