In the circuit shown below , the output voltage is proportional to
a) ln V(in) b) exp(V(in)) c) |V(in)|
d) -|V(in)|

Question

In the circuit shown below , the output voltage is proportional to
a) ln V(in)      b) exp(V(in))     c) |V(in)|
d) -|V(in)|

anonymous · Answer

|dw:1420619373898:dw|

anonymous · Answer

@Vincent-Lyon.Fr @perl @iGreen @mathmate

perl · Answer

i am looking for a formula to use

anonymous · Answer

We know for this circuit that $$V _{o} =-( R _{diode}/ R)*V _{i}$$ How does the characteristic resistance of the diode vary?

anonymous · Answer

no resistance. when it is forward biased.

anonymous · Answer

when it is reversed biased , it does not allow the current to pass.
now, how to proceed?

radar · Answer

This is a "log amplifier"

anonymous · Answer

When it is forward biased there is a distinct relationship between current and voltage over a limited range of voltages near the conduction point

radar · Answer

The choice A would be correct if it was preceded by a negative sign, as it is an inverting log amp.

radar · Answer

radar · Answer

Vout = -Vt In(Vin/IsR)

radar · Answer

Where Vt is the thermal voltage, Is is saturation current, Vin is the input voltage.

vincent-lyon.fr · Answer

I would say a) as well.

anonymous · Answer

answer is option (c)

anonymous · Answer

where |Vin| means modulus of Vin