help on omp circuit design

[silvermirror]

I saw a circuit schematic, and I was confused...

In the circuit, there are two stage omp connect together, and they are the same omp. The first stage is a differential amplifier with the gain (10/43), and the second stage is a non-inverting amplifier with the gain (1/40)

I dont understand why there are two stages to do a differential amplifier work. The gain of first stage is almonst 1/4, and the second stage is 40. why not put the gain in the first stage?

 

[anujgupta.gcet]

To meet given amplifier specifications the need often arises to design the amplifier as a cascaded of two or more stages. The stages are usually not identical; rather each is designed to serve a specific purpose. For instance, the first stage is usually required to have a large input resistance, and the final stage in the cascade is usually designed to have a low output impedance.

Added after 6 minutes:

To avoid losing strengths at the amplifier input where the signal is usually very small, the first stage is designed to have a relatively large input resistance, which is much larger than the source resistance. The second stage need not to have such a high input resistance; rather here we need to realize the bulk of required voltage gain.

Added after 2 minutes:

please see section 1.5.2 Cascaded Amplifiers and Example 1.3 of SEDRA SMITH Microelectronics for further details.

i hope u got ur answer now.

 

[silvermirror]

thank you!

These two stages use the same omp.
so the input impedence should be the same, right?

To meet given amplifier specifications the need often arises to design the amplifier as a cascaded of two or more stages. The stages are usually not identical; rather each is designed to serve a specific purpose. For instance, the first stage is usually required to have a large input resistance, and the final stage in the cascade is usually designed to have a low output impedance.

Added after 6 minutes:

To avoid losing strengths at the amplifier input where the signal is usually very small, the first stage is designed to have a relatively large input resistance, which is much larger than the source resistance. The second stage need not to have such a high input resistance; rather here we need to realize the bulk of required voltage gain.

Added after 2 minutes:

please see section 1.5.2 Cascaded Amplifiers and Example 1.3 of SEDRA SMITH Microelectronics for further details.

i hope u got ur answer now.

 

[anujgupta.gcet]

i suppose the input impedance depends on various other factors other than the type of op-amp. You said that the gain of two amplifiers is different. That means there resistance must also be different for different opamp.

 

[charkyriak]

maybe you could upload the schematic in order for us to understand and consequently explain better...

 

[anujgupta.gcet]

hello charkyriak...
this time its not possible to upload any schematic. but u can ask me ur doubts regarding the amplifiers.
i have already mention the name of book " SEDRA SMITH" for self guidance.

 

[Sadegh.j]

The first stage increases the band width of your circuit

 

[standup]

can't understand the question?Can anyone upload a picture to explain?