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

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

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II.3 Towards a Fair Figure-of-Merit<br />

II.3.a Required Parameters to Handle a Fair Comparison<br />

To be able to compare the performances of the various structures of RF filters (passive<br />

LC, Gyrator-C, <strong>Gm</strong>-C, n-path filters or else) that may be found in the literature, a common<br />

reference figure is nee<strong>de</strong>d. This figure, called figure-of-merit (FOM), should take into account<br />

all parameters related to the specifications discussed in introduction, which are:<br />

- RF dynamic range: linearity and noise;<br />

- Frequency tuning range;<br />

- Selectivity: quality factor, harmonics and adjacent channels rejections;<br />

- Maximum working frequency.<br />

Some other aspects might as well be taken into account, such as the process<br />

variations, the gain at the central frequency or even the area occupied by the circuit.<br />

II.3.b Study of the Figures-of-Merit Found in the Literature<br />

Let’s have a look at some FOMs found in the literature. In [II.5], K. Kwon et al, a<br />

FOM for linear and low-noise low-pass filters is presented. Their FOM is the following:<br />

OIP3.<br />

f max . TR.<br />

N<br />

FOM = (II.29)<br />

( F −1)<br />

Pdc<br />

where F is the noise factor, Pdc/N is the power consumption per pole and TR is the frequency<br />

tuning range.<br />

The quality factor of the filter, for a band-pass, is an important parameter to consi<strong>de</strong>r<br />

and is not taken into account in this FOM. Although too high power consumption would be an<br />

issue, it is not a primary specification since TV is not a portable application. Input parameters<br />

would also be preferred because of their in<strong>de</strong>pen<strong>de</strong>nce of the filter gain.<br />

Another FOM is introduced in [II.6]. After having <strong>de</strong>scribed a passive band-pass filter,<br />

F. Dülger et al. have introduced the following figure-of-merit, which is taken in dB:<br />

N.<br />

SFDR.<br />

f 0.<br />

Q<br />

FOM dB = (II.30)<br />

Pdc<br />

where Pdc/N is still the power consumption by pole, SFDR is the Spurious Free Dynamic<br />

Range.<br />

However, this FOM does not take into account the frequency tunability. There is<br />

reference neither to linearity nor to noise in this figure, which makes this FOM not suitable<br />

for the previously <strong>de</strong>scribed purposes.<br />

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