Problem: Design a voltage amplifier with an input impedance greater than 1MQ, an
ID: 2248107 • Letter: P
Question
Problem: Design a voltage amplifier with an input impedance greater than 1MQ, an output impedance less than 100 and a voltage gain of +50 V/V You must demonstrate (via LTSpice) that your amplifier meets the specifications. Use the methods learned in lab to show the input and output impedance specifications are achieved. You are to use 'real" (not ideal) components to design your amplifier. You should minimize cost. To determine component prices you may find http://www.mouser.com/ p://www.digikey.com/ http://www.newark.com/ and http://www.ameco.com/to be useful sources of information.Explanation / Answer
We shall use an OP Amp to design the circuit, as we know that Op Amps have high gain, low or almost zero output impedance and high input impedance. Please go to the link https://media.digikey.com/pdf/Data%20Sheets/Texas%20Instruments%20PDFs/LM741_Series_Rev_July_2016.pdf and refer Page 9 for a circuit that shows noninverting voltage amplifier using Op Amp. The gain of the circuit is given by Av = 1+(R2/R1). Since Av = 50
50 = 1+(R2/R1)
49=R2/R1
R2=49R1
Choosing R1=1K and R2=49K. Since, 49K resistors are not available readily in market, we choose one 47K and two 1K resistors to get 49K resistor that is have the two 1K and one 47K resistors in series. So, to construct the voltage amplifier, we need one Operational Amplifier, one 47K resistor and three 1K resistors.
For the OP Amp, we shall go for LM741 which has about 75 ohm input impedance and 2M ohm output impedance. After searching for the respective components online at four stores Digikey, Mouser, Newark and Jameco, we shall buy the components given below with respective manufacturer part number.
1. LM741CN/NOPB OpAmp from Jameco Unit Price is $0.59
2. CF14JT1K00 1K resistor from Digikey Unit Price $0.1
3. CF14JT47K0CT-ND 47 K resistor from Digikey Unit Price $0.1
Total Price = $0.59 +3*$0.1+$0.1 =$0.99
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