Hi,
The circuit works fine for natural log, base 2 and 3 but it didn't work for any log base greater than 4. For any log base I adjust the differential gain with the feedback resistors which are dependent to the value of thermal voltage (and since every BJT model has a slight different thermal voltage, I didn't want to take it as a constant 26mV instead used a behavioral source to adjust the resistor value) according to the equations attached.
What I'd like to see at the output is when we use behavioral source as input such as pow(n, n) and step the n parameter which is the log base, the output voltage should be the value of n but it isn't working for values of n greater than 4.
The circuit works fine for natural log, base 2 and 3 but it didn't work for any log base greater than 4. For any log base I adjust the differential gain with the feedback resistors which are dependent to the value of thermal voltage (and since every BJT model has a slight different thermal voltage, I didn't want to take it as a constant 26mV instead used a behavioral source to adjust the resistor value) according to the equations attached.
What I'd like to see at the output is when we use behavioral source as input such as pow(n, n) and step the n parameter which is the log base, the output voltage should be the value of n but it isn't working for values of n greater than 4.
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