A noise isolation passive mixing apparatus is designed to mitigate noise
contribution from intermediate frequency (IF) filters and amplifiers in a
radio frequency translation stage. Common-gate configuration devices are
inserted between passive mixer output and input of a transimpedance
amplifier. In this way, circulation of the input-referred noise of the
transimpedance amplifier is decreased, because of the relatively high
output impedance of the common-gate devices, and the noise figure of the
mixing apparatus can be improved. Since the radio frequency signal still
sees low impedance, a radio frequency transconductance (RF gm) stage can
be removed from the mixing apparatus, reducing current consumption. A
double-balanced mixing apparatus with this general architecture may be
implemented in a 0.18 micrometer CMOS technology and used in a low-IF
global positioning system operating at 1.575 GHz, in an access terminal
of a cellular communication system, and in other systems.