OPERATIONAL AMPLIFIERS

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OPERATIONAL AMPLIFIERS

 
Nodal analysis can be used to perform op amp circuit analysis.

Ideal op amps assume the following properties:

  * Infinite open loop gain

    * Zero output impedance

  * Infinite input impedance

    * Infinite bandwidth
Differentiating

Inverting

 Differential
 

Non-Inverting

Integrating

 

OPAMP NOISE FIGURE

These equations calculate the noise figure of an opamp using parameters provided by vendors at the operating frequency and gain configurations. Be sure to note units both for the input parameters and for the equations, or you will end up with really bad results.
 
Approximation Formula
VNOISE = Noise voltage density, i.e.  pA/sqrt(Hz)
INOISE = Noise current density, i.e.  nV/sqrt(Hz)
RS = Source resistance, i.e. 50 W
k = Boltzmann's Constant = 1.380 662 x 10-23 J/K
T = Ambient temperature in Kelvin

The example to the right uses T = 25 °C
  = 298.15 K

 
Complete Non-Inverting Opamp Noise Figure Formula (for RS = RT)

Complete Inverting Opamp Noise Figure Formula (for RS = RT)

ENI = Input noise voltage
IBN = Non-inverting input noise current
IBI = Inverting noise current
RS = Source resistor
RT = Termination resistor
RF = Feedback resistor
RG = Gain setting resistor