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A question related to a simple differential amplifier

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venn_ng

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Hey guys,

I have a question regarding a very simple differential amplifier. I have included the link below. Thanks for your help in advance.

**broken link removed**

Regards,
venn_ng
 

Effective Rload will be Rd*rds/(Rd+rds).

Gain=gm*Rload=gm/(1/Rd+1/rds)=1/{1/(gm*Rd)+1/(gm*rds)}.
So Gain is approximated as gm*Rd, since gm*rds >> 1.
 
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pancho_hideboo said:
Effective Rload will be Rd*rds/(Rd+rds).

Gain=gm*Rload=gm/(1/Rd+1/rds)=1/{1/(gm*Rd)+1/(gm*rds)}.
So Gain is approximated as gm*Rd, since gm*rds >> 1.
Click to expand...

Ha. It's called "tricky" for a reason. Try deriving using small-signal model using superposition. You will find something different.
 
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venn_ng said:
Why do you think? I am saying that the gain of the circuit is not equal to gm (Rd||rds)
Click to expand...

I apologize. I confused some weird phenomenon that I observed with this simplistic structure. What you said is correct.
 

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