Question 12.8: Determine the output voltage for the log amplifier in Figure...
Determine the output voltage for the log amplifier in Figure 12–28 . Assume I_{\mathrm{R}} = 50 nA.
The input voltage and the resistor value are given in Figure 12–28 .
V_{\text {OUT }}=-(0.025 \mathrm{~V}) \ln \left(\frac{V_{\text {in }}}{I_{\mathrm{R}} R_1}\right)=-(0.025 \mathrm{~V}) \ln \left(\frac{2 \mathrm{~V}}{(50 \mathrm{nA})(100 \mathrm{k} \Omega)}\right)
=-(0.025 \mathrm{~V}) \ln (400)=-(0.025 \mathrm{~V})(5.99)=-\mathbf{0 . 1 5 0} \mathrm{V}
P R A C T I C E EXERCISE
Calculate the output voltage of the log amplifier with a +4 V input.
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