Design amplifier

[missgurlmia]

Hi everyone,im from malaysia and very3 new here.As i read bout this site,i know,lots of my new frens here know the best bout electronic..Can u guys please help me??
thank you~~~

Design amplifier with following specifications:
1- voltage gain > 150 000 open loop
2-high input impedance for differential mode & input impedance more than 150M ohm
3-should be no DC voltage at output for zero input voltage
4-output stage should be able to handle more than 50mA of current
5-power consumption of the device should be less than 25 mW
6-bandwidth of amplifier should be 250k Hz
7-some means of protection should be provided for short circuit

*must use min numbr of components
*min number of passive device
*max value of resistor should be less than 10k ohm
*use ±12V for supply voltages
*no capacitor should be used unless its use is justified

 

[crutschow]

It would seem you are supposed to design an op amp, which is a difficult task. A good place to start would be to look for op amps with characteristics similar to what you need and see if the data sheet shows a schematic. Use that as a start for your design.

 

[moffy]

When you specify a bandwidth for an amplifier you need to also specify the gain. Op Amps have a relatively constant Gain Bandwidth Product (GBW) which means you get more gain at lower frequencies, up to the maximum, and less at higher frequencies.

crutschow is right as you are designing a classic opamp, the cap and resistor limitations sound like ic fabrication restrictions. Unfortunately with discrete devices you can't use a lot of the tricks that ic fabricators can. You might need to use a matched JFET to get the required input impedance.

Discreet audio amplifiers are normally simplified op amps so you could start there.

 

[MikeMl]

There is also a "Homework Forum" for questions like this one.

 

[audioguru]

Why do teachers ask little kids to design a complicated opamp?
When the little kids (and the teacher) know nothing about electronics?

 

[crutschow]

Why do teachers ask little kids to design a complicated opamp?
When the little kids (and the teacher) know nothing about electronics?

I think you answered your own question. The teachers don't know enough to realize how complicated the design of an op amp is.