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Question Bank (3 marks) · Q12

Q.Show the circuit diagram by which we can obtain an output which is anti-logarithm of input.

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[!TLDR]

With the diode at the input and a resistor in feedback, Vo∝−antilog(Vin)V_o \propto -\text{antilog}(V_{in}).

Circuit: the input VinV_{in} is applied through a diode (or transistor junction) to the inverting (−) input, and a resistor RR forms the feedback from output to that node; the (+) input is grounded.

Derivation: The diode current set by the input is I=IseVin/ηVTI = I_s e^{V_{in}/\eta V_T}. This current flows through the feedback resistor RR, so

Vo=−IR=−RIs eVin/ηVTV_o = -I R = -R I_s\,e^{V_{in}/\eta V_T} …

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