differential amplifier

The differential amplifier stage can be implemented using PMOS input differential pairs or using NMOS input differential pairs. Can you tell the difference between them and the advantages and disadvantages of both approaches. , can you tell me what do you prefer in designing the differential amplifier (PMOS or NMOS pairs)?

Dear abdou8_x
Hi
I think in fact it is not any important difference between them.
Respect
Goldsmith

---------- Post added at 18:30 ---------- Previous post was at 18:28 ----------

BTW , the NMOS pairs have better specifications instead of PMOS.

The main problem with PMOS is that the mobility of holes is lesser. So gm is also lesser in PMOS. Hence the gain is reduced in PMOS when compared to NMOS. That's the reason why we see more NMOS circuits in our books.

Hi abdou8_x!
Normally, PMOS-pair and NMOS-pair are the same, maybe diff.pair used a lot in error amplifier and opamp...=> it depends on the output stage of your circuit. Also, it depends on your specification design. For example: Gm, slew rate, output swing, phase margin, gain margin, DC gain, bandwidth, CMRR, PSRR...by hand calculation, you can see the different btw for example OPAMP using PMOS-pair and NMOS-pair to get each parameter above.

To understand more and get more clear, i think you should simulate your problems a lot.

Hope this help!

The primary consideration for the type of input stage to choose is the icmr.
Area, noise and offset are some other secondary considerations.

abdou8_x said:

The differential amplifier stage can be implemented using PMOS input differential pairs or using NMOS input differential pairs. Can you tell the difference between them and the advantages and disadvantages of both approaches. , can you tell me what do you prefer in designing the differential amplifier (PMOS or NMOS pairs)?

Click to expand...

Hi friend....

NMOS is built with n-type source and drain and a p-type substrate, while PMOS is built with p-type source and drain and a n-type substrate. In a NMOS, carriers are electrons, while in a PMOS, carriers are holes. When a high voltage is applied to the gate, NMOS will conduct, while PMOS will not. Furthermore, when a low voltage is applied in the gate, NMOS will not conduct and PMOS will conduct. NMOS are considered to be faster than PMOS, since the carriers in NMOS, which are electrons, travel twice as fast as holes, which are the carriers in PMOS. But PMOS devices are more immune to noise than NMOS devices. Furthermore, NMOS ICs would be smaller than PMOS ICs (that give the same functionality), since the NMOS can provide one-half of the impedance provided by a PMOS (which has the same geometry and operating conditions).


Hope, this is helpful to you...

hey
i think there is no particular difference between nmos and pmos differential pair
but the only difference exist is due to different nature of pmos and nmos based upon there structure and elctronic configuration