We present the discovery of two Saturn-mass companions to HD 108147 and HD 168746 .
Both belong to the lightest ever discovered planets .
The minimum mass of the companion to HD 168746 is of only 0.77 the mass of Saturn and its orbital period is 6.4 days .
The companion to HD 108147 orbits its parent star in 10.9 days and its minimum mass is 1.34 that of Saturn .
Its orbit is characterized by a high eccentricity , e = 0.50 , indicating possibly the presence of a second companion .

The detection of Saturn-mass planets by means of the Doppler technique demands high radial-velocity measurement precision .
The two new candidates were discovered by means of the CORALIE echelle spectrograph .
The instrumental accuracy of CORALIE combined with the simultaneous ThAr-reference technique has reached a level better than 3 m s ^ { -1 } .
On many observed objects the precision is now limited by photon noise .
We present in this paper the weighted cross-correlation technique , which leads to an improvement in the photon noise of the computed radial velocity .
We discuss as well a modification of the numerical cross-correlation mask which reduces significantly the residual perturbation effects produced by telluric absorption lines .