<Bike>
the text you got that from doesn't explain?
<Bike>
razavi, ok.
<Bike>
he has the expression for Gm right there as 4.11. i... don't want to work out the calculus or anything to prove it's a maximum, but it seems intuitive enough
<promach>
Bike: intuitive enough? how ?
<Bike>
increasing the voltage difference increases the subtrahend in the numerator faster than it shrinks the denominator
<Bike>
i guess i'm not sure how to make it intuitive in actual electrical terms, though
<Bike>
i feel there should be some obvious reason the current difference versus voltage difference curve is sigmoidal, but i can't think of it :/
<promach>
Bike: I am referring to Gm versus delta-Vin curve
<Bike>
i know
<promach>
let me do more research, I will come back to you
<Bike>
it's shaped like a hump because id/vd is sigmoidal
<promach>
what ?
<Bike>
s-shaped. all the curves in 4.14
<Bike>
you can see that they're steepest at 0 Vd, meaning Gm is highest there.
<promach>
I see
<promach>
but the x-axis is labelled delta-Vin
<promach>
not Vin alone
<promach>
Bike:
<Bike>
uh, yeah. same as the Gm graph.
<Bike>
the Gm graph is the derivative of 4.14.
<promach>
Bike: I got to run now. I am still confused why it still work out with x-axis labelled as delta-Vin instead of Vin
<Bike>
what
<promach>
delta-Vin
<promach>
x-axis
<Bike>
i mean there's nothing called "Vin" for one, ther's two voltage inputs
<promach>
delta-Vin = V(in2) - V(n1)
<Bike>
yes...
<promach>
I got to run now. I am still confused on the axis label
<promach>
x-axis
<Bike>
it's a differential amplifier. the input is differential.
<promach>
I know
<promach>
but...
<promach>
when delta-Vin = 0, Id1 = Id2
<promach>
I see
<promach>
ok, I got it now
<Bike>
um. good, i guess.
<promach>
let me figure out the maths behind equation 4.11
<Bike>
maybe you're not clear on what transconductance is?