wide band amplifiers + paper

hello freinds,

I am working on wideband amplifiers

during study this paper, i don't understand why it say "the changes in gm"

gm1,2 does not has any change? why not consider?

this is the paper: "A Wideband Analog-Controlled Variable-Gain
Amplifier With dB-Linear Characteristic
for High-Frequency Applications" (2016)

the shot of paper is here:

anyone can help me to understand?

tnx in advance!

Hi,
by changing control voltage Vcn that applied to the gates of M4,M5 you can change its current Ids and respectively its gm