The circuit in Figure P4–40 has a diode in its feedback path and is called a ‘‘log-amp’’ because its output is proportional to the natural log of the input.

(a) Show that vO ¼ VT‘nð1 þ vS=ðRSIOÞÞ if the i-v characteristics of the diode is iD ¼ IOðevD=vT 1Þ.

(b) Using MATLAB plot vO versus vS for RS¼10 kV, IO¼2 1014Aand VT0.026 V. Plot your results on a semilog plot for 106 V vS 100 V.

Transcribed Image Text:

+ VS Rs iD w FIGURE P4-40 + + VD Vo