Question
Download Solution PDFWhich of the following is not true for an ideal operational amplifier ?
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFThe ideal op-amp has the following characteristics:
- Input impedance (Differential or Common-mode) = Infinity
- Output impedance (open loop) = 0
- Voltage gain = Infinity
- Infinite Bandwidth
- Common-mode voltage gain = 0
- Vout = 0 when both inputs are at the same voltage, i.e. (zero "offset voltage")
- Output can change instantaneously (Infinite Slew Rate)
- The purpose of bias current is to achieve the ideal behavior in op-amp which is high CMRR, high differential gain, and high input impedance
CMRR (Common mode rejection ratio) is defined as the ratio of differential-mode voltage gain (Ad) and the common-mode voltage gain (Ac).
Mathematically, this is expressed as:
\(CMRR = \frac{A_d}{A_c}\)
Ad = Differential gain
Ac = Common mode gain
Note: Ideally, the common-mode gain of the Op--Amp should be zero., i.e. it must give a zero output for common input at both the inverting and non-inverting terminal. ∴ The CMRR of an ideal Op-Amp is infinity.
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