Subject: Logic Design

Topic: Biasing of BJT

Difficulty: Medium

Characteristics of Ideal Operational Amplifiers:

• Open loop Voltage Gain A0 is infinity.
• Infinity input resistance Ri so that almost any signal source can drive it and there is no loading of the preceding stage.
• Zero output resistance R0 so that the output can drive an infinite the number of other devices.
• Perfect Balance, i.e. the differential voltage in inverting and non-inverting terminals are zero.
• Zero output voltage when the input is zero.
• Infinity bandwidth so that any frequency signal from 0 to ∞ Hz can be amplified without attenuation.
• Infinity common-mode rejection ratio so that the output common-mode noise voltage is zero.
• Infinity slew rate so that output voltage changes occur simultaneously with input voltage changes.
• Zero drift of characteristics with temperature.

Characteristic of Practical Op-amp

• The open loop voltage gain A0 is maximum and finite, a typical value for the practical op-amp is considered to be 200,000.
• The input impedance Zi is maximum and is finite i.e. in the order of 100k or more.
• The output impedance Z0 is minimum, not zero, in the order of 100 or less.
• The CMRR is maximum and finite.
• Bandwidth is maximum and finite i.e. it can amplify dc to 1 MHz signal.
• A slight drift of characteristics due to the change in temperature , not null.
• Two terminal may be virtually ground, not Vd = 0 exactly, for all conditions.
• Maximum slow-rate and has the finite value.
• The output is negligible due to dc-bias when the input is zero.