Page 333 - Complete Wireless Design

Mixer Design

332 Chapter Seven

When the active mixer is utilized in any up-conversion role, the input and
output ports do not change as they would for a passive DBM. The input port
will still be for the RF, while the output port will still be for the IF. However,
since the IF port is generally capable of less than half (to as low as one-fifth)
of the output frequency that the RF input port is capable of, then up-conver-
sion (at least with any gain), will be limited to the rated output frequency of
the IF port. Thus, most active IC mixers will be incapable of being used for up-
converting a signal beyond 1 or 2 GHz.
Since most active MMIC mixers are much less sensitive to port mismatches
than passive diode models, the LO input to the active mixer will normally not
require an external buffer amplifier, nor will the IF port need a diplexer. But
many IC active mixers will have DC voltages present at all ports, necessitat-
ing a series blocking capacitor at the RF, IF, and LO ports.

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