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mulit stage amplifier vs single stage

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malik_123

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single stage amplifier

referring to this schematic
https://instruct1.cit.cornell.edu/c...6/XL76_SL362/XL76 SL362/index.html#schematics
one question arise in my mind

this person is using three stage amplification to get the gain of 1000

what if some one uses just one stage to get the same gain

like using 1k and 1000k resistor ?

Added after 3 minutes:

what could be the disadvantages , one could face if he uses just one stage amplifier to get 1000 time gain
 

three stage amplifier

To mention an obvious disadvantage, LMC7111, that's used in the circuit, has a GBW (gain bandwidth product) of 50 kHz, so the amplifier bandwidth with gain of 1000 is about 50 Hz. Most likely less than intended.

It's no problem to achieve a gain of 1000 in a single stage with an appropriate fast audio OP. (But 1000 is typically too high for a microphone amplifier).

You shouldn't use however fast OPs in breadboard design without any bypass caps, as presented in the link.
 
what is single stage amplifier

malik_123 said:
what could be the disadvantages , one could face if he uses just one stage amplifier to get 1000 time gain
Click to expand...

Another problem could arise in connection with offset properties of the opamp.
For example, 2mV input offset cause 2 V offset at the output (in case of a gain of 1k).
This estimation even neglects offset current effects.
But, of course, the final design depends on the opamp used, the supply voltages and the operating frequencies.
 
single stage amplifier

The lousy opamp that is used has a max gain of only 150 to 400. Most ordinary opamps have a max gain of 200,000.
This opamp has no high frequency response.
But its supply current is almost nothing and it works when the supply is as low as 2.7V.
 

3 stage amplifiers

Another problem could arise in connection with offset properties of the opamp.
Click to expand...
Yes. I didn't mention it, because I would never set the DC gain to 1000 rather than providing a high-pass roll-off for the AC gain. The said three-stage amplifier however has DC coupling between the stages, resulting in a DC gain of 100.
 

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