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https://designers-guide.org/forum/YaBB.pl Measurements >> RF Measurements >> Single-side band mixer to measure I/Q accuracy https://designers-guide.org/forum/YaBB.pl?num=1203338485 Message started by neoflash on Feb 18th, 2008, 4:41am |
Title: Single-side band mixer to measure I/Q accuracy Post by neoflash on Feb 18th, 2008, 4:41am Hi, folks: I'm calculating how much spur will SSB mixer see, due to I/Q inaccuracy? For example, if there is 1 degree mismatch for I/Q, how much spur should I see? |
Title: Re: Single-side band mixer to measure I/Q accuracy Post by ACWWong on Feb 18th, 2008, 6:24am Spur will be about -41 dBc. In the absense of any other mismatches, nonlinearities or crosstalk you can calculate it by 20*LOG10[tan(IQphaseerror/2)] Often such things are represented by "image" sideband contours levels on IQ amplitude and phase mismatch Cartesian axis. |
Title: Re: Single-side band mixer to measure I/Q accuracy Post by neoflash on Feb 24th, 2008, 2:15am Thanks for the reply. I agree with -41dbc. However, I think the equation should be sin(delta) instead of tan(delta). They have similar value when mismatch (delta) is small. |
Title: Re: Single-side band mixer to measure I/Q accuracy Post by ACWWong on Feb 24th, 2008, 5:57am No it is tan(phaseerror/2) not sin It comes from the 10*LOG10{[1-cos(phaseerror)]/[1+cos(phaseerror)]} which is equal to 20*LOG10[tan(IQphaseerror/2)] Look at Razavi RF microelectronics for derivation or http://ieeexplore.ieee.org/iel5/4138799/4138800/04138864.pdf A key thing is that in a SSB IQ modulator error vectors which cause the "image" sideband, i.e quadrature phase error and quadrature amplitude error, are orthogonal. Therefore you can null both phase and amplitude error independantly. |
Title: Re: Single-side band mixer to measure I/Q accuracy Post by neoflash on Feb 25th, 2008, 3:33am Oh... Yes. I think i assumed cos(mismatch)=1 during derivitation. Thanks for the head up. |
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