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# GAIN booster input problem

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#### ljy4468

##### Full Member level 4
boost input

Hi all~
I've a question about gain booster.
I'm using folded cascode amp with gain booster.
and gain booster circuit is single-ended folded cascode.
So need four single-ended folded cascode amp

Now, I've a question.
one of single ended amp's input is top mos drain.
Then, the other input????
Can I made a voltage using bias circuit????
If then, How can I determine voltage??

I wnat to know nbias1 & pbias3.....
How can I determine

nbias1 & pbias3 are chosen to make sure all transistors are operating in saturation mode.

For example, pbias has to be < Vdd - (2*|Vdsat| + |Vt|)
\]

Then, booster's inp and inn can have different DC bias??
or same dc voltage

just assume ur boost amp is completely ideal and having infinite gain and bw.
now, roughly determine how much voltage u want at the souce of ur cascode transistor.
for example: at pbias1=vs@pcasode=vdd-von@ptop~3-200mV~2.8V
put the same voltage (2.8V for pbias1) at the input to boost amp.. now due to to feedback
action (and high gain of boost amp: if u r able to bias ur boost amp properly) u will see
the voltage at casode node very close to wht u hav applied at the boost input.

<click helped me if i really helped u >

before designing a booster circuit,for the main circuit design we have to generate the pbias and nbias by using the wideswing bias circuits.,
when we are designing the booster circuit,without changing the bias conditions we shud design the circuit.,
care must be taken so that booster gbw shud be greater than main amplifier 3db frequency.

put the same voltage (2.8V for pbias1) at the input to boost amp.. now due to to feedback
action (and high gain of boost amp: if u r able to bias ur boost amp properly) u will see
the voltage at casode node very close to wht u hav applied at the boost input.

Oh...I didn't know that!
Thanks!!

ljy4468 said:
put the same voltage (2.8V for pbias1) at the input to boost amp.. now due to to feedback
action (and high gain of boost amp: if u r able to bias ur boost amp properly) u will see
the voltage at casode node very close to wht u hav applied at the boost input.

Oh...I didn't know that!
Thanks!!

i hope u r not kidding me bcaz this is the first lesson of any analog course..

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