Radio Frequency Integrated Circuit Design - Webs

218 Radio Frequency Integrated Circuit Design
Figure 7.18 Series LC between mixer outputs.
Figure 7.19 Parallel RC circuit across the output.
to use a filter after the mixer in the transmitter to get rid of the unwanted
sideband for the up-conversion case. Similarly, it is possible to use a filter before
the mixer in a receiver to eliminate unwanted signals at the image frequency
for the down-conversion case. Alternatively, a single-sideband mixer for the
transmit path, or an image reject mixer for the receive path can be used.
An example of a single-sideband up-conversion mixer is shown in Figure
7.21. It consists of two basic mixer circuits, two 90° phase shifters, and a
summing stage. As can be shown, the use of the phase shifters and mixers will
cause one sideband to add in phase and the other to add in antiphase, leaving
only the desired sideband at the output. Which sideband is rejected depends
on the placement of the phase shifts or the polarity of the summing block. By
moving the phase shift from the input to the output, as shown in Figure 7.22,