Question

Problem 3: a) For the inverting amplifier designed using low noise amplifier AD743 shown on the bottom of the page with Ri=10kOhm and Rf=220kOhm, what should be the value of the resistor connected to the non-inverting input (R2) to minimize the output offset due to input bias current? b.) Even if the R2 value you calculated is used, could there be an output offset due to a difference between the two input bias currents? What is the maximum value of this output offset for this amplifier? (Hint: find out the maximum difference between the input bias currents from its data sheet and calculate the output voltage offset that this causes in this specific amplifier design. To do this, consider the input offset current multiplied by R2 as a voltage source connected in series to the non-inverting input, and find the output offset voltage by multiplying this input source with the amplifier’s gain from the noninverting input to the output). Problem 4: If we limit the BW of the amplifier in Prob. 3 using a low-pass filter with a cut of frequency of 10kHz, what would be the output noise (in rms units) due to the input current and voltage noise values plus the thermal noise of R1//Rf and R2 ? Input signal is a noiseless voltage source. Ignore the 1/f and popcorn noise (Hint: use Equ. 3.18 in the book, note the thermal noise due to both R1/Rf and R2 need to be incorporated into the equation separately).

Answer 1

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