SaM - Operational Amplifier

Remeber:

• Non-Idealities of Operational Amplifier
  • $Z_{in}$ : input resistance, $Z_{in}\in [100\text{k}\text{ohm}÷1\text{M}\text{ohm}]$, usually we consider it $\simeq \infty$.
  • $Z_{out}$ : output resistance, $Z_{out}\in [100\text{ohm}÷20\text{k}\text{ohm}]$, we usually consider it $\simeq 0$.
• Open Loop Frequency Response Formula:$V_{out}=(V^{+}-V^{-})\cdot \frac{A_{DC}}{1+j\frac{f}{f_H}}$Where:
  • $A_{DC}$ : open loop gain (ideally infinite, in reality $\in [10^5÷10^6]$).
  • $f_H$ : cut-off frequency $(f_H\in [1\text{Hz}÷1\text{MHz}])$.

A “real world amplifier” can be modelled by adding the “bias currents” ($I_{\text{bias}}$) and “input offset voltage” ($V_{io}$):

• $V_{io}\in [\mu \text{V}÷\text{mV}]$
• $I_{\text{bias}}$ : input bias current, $I_{\text{bias}}\in [\text{fA}÷\mu \text{A}]$ (Remember: $\text{f}=10^{-15}$, $\mu =10^{-6}$).

Here are some circuits we have seen that use an operational amplifier:

• SaM - Inverting Operational Amplifier
• SaM - Non-Inverting Operational Amplifier
• SaM - Charge Amplifier
• SaM - AC-Coupled Amplifier
• SaM - Differential Amplifier
  • SaM - Instrumentational Amplifier

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Memory Card

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• Basic General Structure of an OP Amp (Operational Amplifier):
  
• Equivalent Circuit:
  
  • Usually the resistances assume this values:
    • $Z_{in}\simeq \infty$
    • $Z_{out}\in [100\text{ohm},20k\text{ohm}]$, we usually consider it $\simeq 0$
• Open Loop Frequency Response Formula:$V_{out}=(V_2-V_1)\cdot \frac{A_{DC}}{1+j\frac{f}{f_H}}$Where:
  • $A_{DC}$ : Open Loop Gain, ideally infinite, in reality $\simeq [10^5÷10^6]$.
  • $f_H$ : Cut-Off Frequency, it can assume a wide range of values $\simeq [1\text{Hz}÷1\text{MHz}]$.
• Bode Plot of the Open Loop Frequency Response