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Radio Frequency Integrated Circuit Design - Webs

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220 <strong>Radio</strong> <strong>Frequency</strong> <strong>Integrated</strong> <strong>Circuit</strong> <strong>Design</strong><br />

Figure 7.22 An image reject mixer.<br />

Figure 7.23 Weaver image reject mixer.<br />

result, this architecture is less sensitive to amplitude mismatch in the phaseshifting<br />

networks and so image rejection is improved. The disadvantage is the<br />

additional mixers required, but if the receiver has a two-stage downconversion<br />

architecture, then these mixers are already present and so there is no penalty.<br />

7.10.2 Generating 90� Phase Shift<br />

Several circuits can be used to generate the phase shifts as required for singlesideband<br />

or image reject mixers. Some of the simplest are the RC circuits shown<br />

in Figure 7.24. The transfer functions for the two networks are simply

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