Op-amp

Operational amplifier
An operational amplifier (often op-amp or opamp) is a high- electronic voltage  with a  and, usually, a  output. In this configuration, an op-amp produces an output potential (relative to circuit ground) that is typically hundreds of thousands of times larger than the potential difference between its input terminals.

The popularity of the op-amp as a building block in s is due to its versatility. By using, the characteristics of an op-amp circuit, its gain, input and , etc. are determined by external components and have little dependence on s or  in the op-amp itself.

Op-amps are among the most widely used electronic devices today.

In the non-inverting amplifier on the right, the presence of negative feedback via the Rf, Rg determines the closed-loop gain ACL = Vout / Vin. Equilibrium will be established when Vout is just sufficient to "reach around and pull" the inverting input to the same voltage as Vin. The voltage gain of the entire circuit is thus 1 + Rf/Rg. As a simple example, if Vin = 1 V and Rf = Rg, Vout will be 2 V, exactly the amount required to keep V- at 1 V. Because of the feedback provided by the Rf, Rg network, this is a closed-loop circuit.

Log amplifier
A log amplifier is an amplifier for which the output voltage Vout is K times the natural log of the input voltage Vin. This can be expressed as,


 * $$V_\text{out} = K \ln\left(\frac{V_\text{in}}{V_\text{ref}}\right)$$

where Vref is the normalization constant in volts and K is the scale factor.

The logarithm amplifier gives an output voltage which is proportional to the logarithm of applied input voltage. To design a logarithm amplifier circuit, high performance op-amps like LM1458, LM771, LM714 are commonly used and a compensated logarithm amplifier may include more than one.



The relationship between the input voltage $$V_\text{in}$$ and the output voltage $$V_\text{out}$$ is given by:


 * $$V_{\text{out}} = -V_\text{T} \ln \left(\frac{V_\text{in}}{I_\text{S} \, R} \right)$$

where $$I_\text{S}$$ and $$V_\text{T}$$ are the saturation current and the thermal voltage of the diode respectively.