3/1/2003BAE of 5 Additional Information on Op-Amp Specifications

3/1/2003BAE of 5 Additional Op Amp specifications Input Offset voltage – The apparent voltage offset at the input of the amplifier measured by determining the amp output (and dividing that output by the gain to calculate the input) when the differential input is shorted. (See the data sheet on the amp.) Common mode rejection ratio (CMRR) –Common mode is the average voltage of the two inputs on a differential amplifier. –Differential voltage is the voltage difference between the two inputs on a differential amplifier –Common mode rejection ratio is the ratio of the output of the amp subjected to a common voltage to the output of the amp subjected to the same level of differential input voltage. This would be zero in an ideal amplifier.

3/1/2003BAE of 5 Bandwidth – normally specified in terms of Gain – Bandwidth product (GBP). The amplifier behaves like a first order filter where the corner frequency is: The transfer function for an Op Amp may be written as: Computation of Gain Bandwidth Product

3/1/2003BAE of 5 Frequency Response for an Op Amp Substituting j  for s and computing the non-transient response: Corner frequency occurs where the  term under the root becomes significant with respect to the 1/A 2 term

3/1/2003BAE of 5 Bandwidth Graphically