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[MOVED] PMOS differential amplifiers

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silversgleaming

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I am a newbie here.
I am supposed to design an op-amp with gain of at least 20dB using aim SPICE.

I have the following differential amplifier
Untitled.png

with small differential gain as shown
Untitled.png

How do I improve the gain by modifying or adding some elements to the amplifier?
*All transistors must be pmos transistors.

Schematics are highly appreciated.

Thank you!
Franklin
 

hi,
You can simply use CS pair to improve the gain which is connected to ech outputs of differential pair...

Still you need more gain means, use cascode pair.........

Thanks
 

1、 use a small W/L of X3,X4 to increase the R;
2、use a little bais current ;
 

kenambo said:
hi,
You can simply use CS pair to improve the gain which is connected to ech outputs of differential pair...

Still you need more gain means, use cascode pair.........

Thanks
Click to expand...

So CS amplifier can be added to vout1 and vout2?
does using cascode pair mean adding 2 pmos transistors below X3 and X4?
 

silversgleaming said:
So CS amplifier can be added to vout1 and vout2?
does using cascode pair mean adding 2 pmos transistors below X3 and X4?
Click to expand...

yes ofcourse, CS pair can be added to each outputs....

You can use 2 PMOS pairs as cascode load but it cause some voltage headroom problem....

Still You can get high gain.... and

What is your operating frequency...?

Thanks...
 

kenambo said:
yes ofcourse, CS pair can be added to each outputs....

You can use 2 PMOS pairs as cascode load but it cause some voltage headroom problem....

Still You can get high gain.... and

What is your operating frequency...?

Thanks...
Click to expand...

Do you have the schematics? (without resistors)
The operating freq is 1Hz.

Thanks.
 

silversgleaming said:
Do you have the schematics? (without resistors)
The operating freq is 1Hz.

Thanks.
Click to expand...

operating frequency 1Hz.. is it...? May i know the purpose of getting high gain?

and Schematic ..... just add another one pair of P-Mos es under the X3 and X4 moses.. But you need to give a biasing voltage for this pair...

Anyway.... using PMOS and Nmos pair gives good results.... Try the above... and Make sure your operating frequency..

Thanks......
 
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