quad_p1quad.pdfImage reject mixers Recall that the image problem for downconverting mixers is not fully solved by the use of preselection filtering. Filters do not have adequate rejection and require extra space and power. Recall that an image signal often comes from an out-of-band source which may be another transmitter or might be due to a spurious signal generated in the receiver itself. A widely used alternative is to employ phase cancellation to reject images. To the extent that accurate phase and amplitude matching can be obtained, very high image reject ratios can be obtained. IRR is defined in the equation below: 10 logIMAGERFPIRRP= The image rejection process is incorporated into the mixer through the use of in-phase and quadrature signals. To understand how this process works, we must begin with a brief review of quadrature signals. For a good exposition of quadrature signals and image rejection, follow the link, download and read: Quadrature Signals: Complex, But Not Complicated, by Richard Lyons. http://www.dspguru.com/info/tutor/quadsig.htm Next, let’s quickly review quadrature signals and then apply to analog IR mixers. freqfreqRLIFIM12RLIMIFfreqfreqRLIFIM122RLIMIFDot"r",c-t",nve"t A-QQ€*b'l.o-uJtJU -a' - j nit't'tL(IvJles,rc€{ ?-t 9"?' a-l/q^rn c{\AtA/'he-n/\e+'Ji uiq*j tjotrt tstiPo tg gln nro 9,'l fcr c6uv'4uoAaYrrv fU'q$(9 t++l-{\7_lIn{)-vli-*,21r *,"'I )-4/\vrz t?u -It ?, 7ttl . loy{zo*49'/tr& +4v 7 nu'a rfioV'ar8o -tv rytarto +45 j zu' .21oyrt u *45 5y/eg -t QY ? \vt " 0v/tu-+t :vtta +eF ZY'zo - +s 5v'zo +4f Zvt ztw-1E )VtArS+ qE jvtltwvryli$Va'v e'r^Ve d"' (*ece*h'a)v!.?:177'r'1{*:.yrttCD++5 ) '.+,,zl zozvtt4Drlz,/'/lg0pos f q,%Di ^fi tho$L iJ ,,^er4eA ; 6r.'ul 'po9"hv'o f*{ ve'aq 'rgu9f'' ,! cDi};ltnff -It-ClkABDD QCLK QABD QCLK
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