How to design 2decade BJT-OPAMP cascade inverting voltage amplifier?

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Discussion Overview

The discussion revolves around designing a two-decade BJT-opamp cascade inverting voltage amplifier using a single BJT, a UA741 opamp, and a 12V power supply. Participants explore circuit specifications, including gain, input/output impedance, and frequency response, while seeking guidance on circuit configuration for a final year project.

Discussion Character

  • Homework-related
  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant requests assistance in designing a circuit that meets specific output requirements, including a maximum voltage gain of -500 and a bandwidth of 200-20kHz.
  • Another participant questions the output impedance specification, suggesting it may be a typographical error.
  • Some participants express uncertainty about how to connect the opamp and BJT, indicating a need for guidance on circuit configuration.
  • There is mention of previous research on a two-BJT circuit, with a request for ideas on adapting it to use one BJT and one UA741 opamp.
  • One participant acknowledges the need to prove the output of the circuit, despite having access to the UA741 datasheet for specifications.
  • Another participant suggests that two UA741s in series could meet the specifications, hinting at the limitations of using a single opamp.
  • Some participants discuss the relevance of a cascode configuration in the context of the circuit design.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the circuit design and specifications. There is no consensus on the necessity of the BJT in the circuit, and multiple approaches are proposed without resolution.

Contextual Notes

Participants indicate uncertainty about certain specifications and the rationale behind using specific components. The discussion includes references to circuit simulation tools and the need for further refinement to meet project requirements.

Who May Find This Useful

Students and practitioners interested in circuit design, particularly those working with opamps and BJTs in amplifier configurations.

badrie2004
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Can somebody help me to find this kind of circuit.im really appreciete your help

Specification
Only one bjt,one opamp ua741 and asingle power supply of 12v must be used. A 10k ohm load and an input signal will be connected via capacitors to the amplifier. The max voltage gain is about -500.imput impedance is about 600 ohm.output impedance is about 10k ohm.the low cut off frequency is about 200hz and the high cutoff frequency is about 20khz(bandwith of 200-20khz ;2decades).the maximum pek-to-peak(mpp) output voltage without clipping is more or equal to 6v.make sure that the opamp must not produce a low rate distortion at less or equal 20khz.
Please I need this for final year project
 
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Thread moved from EE to Homework Help.

Welcome to the PF, badrie. Can you show us your initial approach to this question? What can you tell us about common connection diagrams for opamps in the inverting configuration? Do you have an idea where they want you to use the BJT?

Also, could you double-check the specifications -- specifically the output impedance. A Zout of 10k Ohms sounds like a typographical error...
 
TQ bekeman for your reply.
for your information i need to design this circuit so that i can get the output like in specification.that means that i need to prove that my circuit can be produce same output that in question.this circuit just need to prove the output.

for ur information,i don't know how to connect between opamp and the bjt. that y i need some idea from u.yeah the output impedance is 10k OHM.

i already do some the research. but i only get "2decade BJT cascade inverting voltage amplifier". this circuit use two bjt.i do appreciate if u give me some idea how to change it into "one BJT and one ua741(opamp)
 
badrie2004 said:
TQ bekeman for your reply.
for your information i need to design this circuit so that i can get the output like in specification.that means that i need to prove that my circuit can be produce same output that in question.this circuit just need to prove the output.

for ur information,i don't know how to connect between opamp and the bjt. that y i need some idea from u.yeah the output impedance is 10k OHM.

i already do some the research. but i only get "2decade BJT cascade inverting voltage amplifier". this circuit use two bjt.i do appreciate if u give me some idea how to change it into "one BJT and one ua741(opamp)

Show us your circuit with 2 BJTs and the opamp.

Also, here's a Quiz Question -- why do you need a BJT at all, given these specifications? There's one specification (and one corresponding graph in the 741 datasheet) that would be the only reason that it would be used here...

Remember, we will not do the work for you. We can offer tutorial assistance. What courses in opamps and transistors have you taken to support your work on this "senior project"?
 
tq bekeman..
when i read about ur reply, it force me to open again my electronic book.since i majoring in electronic,so i have to refresh back my knowledge.

i already got the circuit and try it using PSpice.i juz need to do some touch up to meet the specification

actually i really dun understand why i need to prove the output.i already read the 741 data sheet and it already show all the specification.

anyway tq for ur assistance.i appreciete it. hope u delight to help me.
 
badrie2004 said:
tq bekeman..
when i read about ur reply, it force me to open again my electronic book.since i majoring in electronic,so i have to refresh back my knowledge.

i already got the circuit and try it using PSpice.i juz need to do some touch up to meet the specification

actually i really dun understand why i need to prove the output.i already read the 741 data sheet and it already show all the specification.

No, there is at least one specification in your assignment that is not met by just the 741 alone. Hint -- two 741s in series would be able to meet the specification.

Another hint -- why does the 2 BJT circuit use a cascode configuration? The answer is related.
 
ok..i understand that.

i got some idea how to connect 741 and the bjt. about using two 741 idea is correct.i no doubt about it.but i only need to use one opamp. i will work on it more. tq.wish me luck
 

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