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

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

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201.<br />

B.1.d Example<br />

Let’s consi<strong>de</strong>r a differential pair ma<strong>de</strong> with bipolar transistors as <strong>de</strong>picted in Figure<br />

Figure 201. Differential pair<br />

The output voltage is then given by :<br />

⎛ Vin<br />

Vout<br />

= RI e tanh<br />

⎜<br />

⎝ 2U<br />

T<br />

⎞<br />

⎟<br />

⎠<br />

(B.22)<br />

Developing this expression leads to:<br />

⎛ Vin<br />

V ⎜<br />

out = RI e ⎜<br />

⎝ 2U T<br />

3<br />

Vin<br />

⎞<br />

− ⎟<br />

3<br />

24U<br />

⎟<br />

T ⎠<br />

(B.23)<br />

Hence,<br />

Thus, one gets:<br />

Rc<br />

I e<br />

k1<br />

2U<br />

T<br />

= (B.24)<br />

Rc<br />

I e<br />

k 3 = − 3<br />

24U T<br />

(B.25)<br />

4 k1<br />

IIP3 = = 4U<br />

T<br />

(B.26)<br />

3 k<br />

3<br />

- 194 -

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