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LT 1167 Adding a capacitor in series with the Rg (gain resistor)

Category: Hardware
Product Number: LT1167

I am using a LT1167 Instrumental Amplifier (IA) and using the out put to be used in 3 DC-DC converters to current share. What effect would it have in bandwidth or noise if I add a capacitor in series with the Rg (gain resistor) ? 

I have already researched about this and so far I was unable to find anything about this. I have attached a screenshot I of the LTSpice simulation. 
Please let me know if you know. 

Thank you 

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  • Hi,

    This technique is typically used in audio inamp applications, when only AC gain is needed. This is an example from the System applications guide, Audio applications:

    If you want to calculate the gain versus frequency of your circuit, just replace the R1 value with the equivalent impedance of the series connected R1 and C1 in the gain equation (and take the absolute value). At low frequencies the gain is close to unity (at DC it is unity). At higher frequencies, when the impedance of the capacitor gets less than R1, the gain is determined by R1. Just run an AC simulation to see this.

    So due to the capacitor the bandwidth is only affected at low frequencies (the lower limit is 1/(2*π*R1*C1), the higher is not affected).

    I don’t think that the noise will be increased, since the gain is never higher than the gain without the capacitor (because the impedance is in the denominator of the gain equation). Instead, it will be less, mainly at low frequencies.

    I think the capacitor is only needed, if the inamp output offset is too large at the required gain. So not in your application.