CHAPTER 1: INTRODUCTION TO OPERATIONAL AMPLIFIERS. Objectives. Describe basic op-amp characteristics. Discuss op-amp modes and parameters. Explain negative feedback. Analyze inverting, non-inverting, voltage follower and inverting op-amp configurations. BASIC OP-AMP. Symbol and Terminals.
Figure 1a: Symbol
Figure 1b: Symbol with dc supply connections
circuit element designed
to perform mathematical
Operations of addition,
741 general purpose op-amp made by Fairchild Semiconductor
The op amp is built using VLSI techniques.The circuit
diagram of an LM 741 from National Semiconductor is
Taken from National Semiconductor
data sheet as shown on the web.
Internal circuitry of LM741.
+The Ideal Op-Amp
Figure 2a: Ideal op-amp representation
A) Single-Ended Input
where Aol = open-loop voltage gain
Acm = common-mode gain
A certain op-amp has an open-loop voltage gain of 100,000 and a common-mode gain of 0.2.
Determine the CMRR and express it in decibels.
Answer: a) 500,000 b) 114dB
V2Input Bias Current
Figure 4a: Input bias current is the average of the two op-amp input currents.
Figure 4b: Differential input impedance
Figure 4c: Common-mode impedance
Figure 4d: Op-amp output impedance
Figure 4e: Test circuit
–Vmax to its upper limit +Vmax, once the input step is applied.
Figure 4f: Step input voltage and the resulting output voltage
Where ∆Vout = +Vmax-(-Vmax).
Figure 5: Noninverting amplifier
Determine the gain of the amplifier in figure below. The open-loop voltage gain of the op-amp is 100,000.
Figure 6: Op-amp voltage-follower
Figure 7: Inverting Amplifier
Given the op-amp configuration in figure below, determine the value of Rf required to produce a closed-loop voltage gain of -100.
Answer: 220 kΩ
Where Zin is the open-loop input impedance (internal) of the op-amp (without feedback connection)
Generally, assumed to be Ri
Generally, assumed to be 0
Note that the output impedance has the same form for both amplifiers.
Answer: (a) Zin(NI)=17.5GΩ, Zout(NI)=8.6mΩ, (b) Acl(NI) = 23.0
Find the values of the input and output impedances in Figure below. Also, determine the closed-loop voltage gain. The op-amp has the following parameters: Aol = 50,000; Zin = 4MΩ; and Zout = 50 Ω
Answer: Zin(I)=1.0kΩ, Zout(I)=980mΩ, Acl(I)=-100