Radio Frequency Integrated Circuit Design - Webs

Mixers
Table 7.5
Image Rejection for LO Phase Shifter
Tolerance Level for Resistance
and Capacitance Image Rejection
±20% >20 dB
±10% >27.4 dB
Nominal 69 dB
shift. It still provides image rejection of 20 dB even at 20% tolerance in the
values.
Table 7.6 shows that the polyphase filter with two stages also does an
excellent job at keeping the image suppressed, so this was a good choice for
the IF filter. If this filter is reduced to a first order as shown in Table 7.7, then
the image rejection suffers greatly. Thus, a second-order filter is required in
this case.
Example 7.7 Image Reject Mixer with Improved Gain
The gain of the image reject mixer has been reduced by 6 dB due to the presence
of the IF polyphase filter. Modify it to get the 6 dB of gain back.
Table 7.6
Image Rejection for IF Phase Shifter
Tolerance Level for Resistance
and Capacitance Image Rejection
±20% >25 dB
±10% >36.7 dB
Nominal 69 dB
Table 7.7
Image Rejection for IF Phase Shifter (First Order)
Tolerance Level for Resistance
and Capacitance Image Rejection
±20% >12.5 dB
±10% >18.2 dB
±5% >23.2 dB
Nominal 35 dB
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