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III. Gm-C Filtering - Epublications - Université de Limoges

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g<br />

V<br />

m3<br />

in<br />

+ g′<br />

′ V<br />

3<br />

m3<br />

in<br />

Replacing:<br />

3<br />

g 1g<br />

2r<br />

⎛<br />

0<br />

3 g 1r0<br />

g 1r<br />

⎞<br />

m m<br />

m<br />

m 0<br />

3 3<br />

3 1 jr0C<br />

bω<br />

( αVin<br />

βV<br />

) ⎜ ′<br />

⎛ ⎞<br />

+<br />

=<br />

+ in + gm<br />

2 + g′<br />

′<br />

⎟<br />

m2<br />

( αVin<br />

+ βVin<br />

) + ( αVin<br />

+ βVin<br />

)<br />

1 jr0C<br />

aω<br />

⎜ 1 jr0C<br />

aω<br />

⎜<br />

1 jr0C<br />

aω<br />

⎟<br />

+<br />

+<br />

⎟<br />

r0<br />

⎝<br />

⎝ + ⎠ ⎠<br />

(<strong>III</strong>.15)<br />

Thus, this leads to:<br />

α<br />

m3<br />

= ,<br />

gm1g<br />

m2r0<br />

1 + jr0C<br />

bω<br />

+<br />

1 + jr C ω r<br />

which corresponds to the gain of the filter transfer function.<br />

0<br />

a<br />

g<br />

- 86 -<br />

0<br />

(<strong>III</strong>.16)<br />

The second equation gives:<br />

3<br />

g 1g<br />

2r<br />

⎛<br />

0 g 1r0<br />

g 1r<br />

⎞<br />

m m<br />

m<br />

m 0<br />

3 1 jr0C<br />

bω<br />

gm3<br />

β<br />

⎜ ′<br />

⎛ ⎞ +<br />

′′ =<br />

+ gm<br />

2 + g ′′<br />

⎟<br />

m2<br />

α + β<br />

1 jr0C<br />

aω<br />

⎜ 1 jr0C<br />

aω<br />

⎜<br />

1 jr0C<br />

aω<br />

⎟<br />

(<strong>III</strong>.17)<br />

+<br />

+<br />

⎟ r0<br />

⎝<br />

⎝ + ⎠ ⎠<br />

Hence,<br />

β<br />

g ′′<br />

This finally gives:<br />

⎛<br />

− ⎜ g<br />

g ′′<br />

m1<br />

0<br />

m1<br />

0<br />

3<br />

m3<br />

m2<br />

m2<br />

⎜ 1 + jr0C<br />

aω<br />

⎜1<br />

jr0C<br />

aω<br />

⎟ ⎟<br />

⎝<br />

⎝ + ⎠<br />

=<br />

⎠<br />

(<strong>III</strong>.18)<br />

gm1g<br />

m2r0<br />

1 + jr0C<br />

bω<br />

+<br />

1 + jr C ω r<br />

0<br />

r<br />

a<br />

⎛<br />

+ g′<br />

′ ⎜<br />

0<br />

g<br />

r<br />

3<br />

⎞ ⎞<br />

⎟ ⎟α<br />

3<br />

3<br />

⎛ g 1 2 0 1 ⎞ ⎛<br />

⎞<br />

0 ⎜ ′′ ⎛ ⎞<br />

m gm<br />

r + jr Cbω<br />

gm1r0<br />

gm1r0<br />

3<br />

g ′′<br />

′<br />

⎟<br />

m3<br />

⎜ +<br />

2<br />

2<br />

3<br />

1<br />

⎟ − gm<br />

+ gm<br />

⎜<br />

0<br />

0<br />

1<br />

⎜<br />

0 1 ⎟ gm<br />

⎝ + jr C<br />

⎠ +<br />

⎟<br />

aω<br />

r<br />

jr C<br />

⎝<br />

aω<br />

⎝ + jr0C<br />

aω<br />

⎠<br />

β =<br />

⎠<br />

4<br />

, (<strong>III</strong>.19)<br />

⎛ g 1g<br />

2r0<br />

1 + jr ⎞<br />

m m<br />

0Cbω<br />

⎜ +<br />

1<br />

⎟<br />

⎝ + jr0C<br />

aω<br />

r0<br />

⎠<br />

which corresponds to the third or<strong>de</strong>r non-linear term.<br />

Determining by <strong>de</strong>sign the achievable IIP3 of all transconductors leads to the various<br />

gmi3, thanks to the formula:<br />

4 IIP3<br />

g ′′ mi = . gmi<br />

. 10 . (<strong>III</strong>.20)<br />

3<br />

β and α can thus be computed and this gives the achievable IIP3 of the filter.

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