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I-Q Modulator/Demodulator Sideband Rejection Analysis

Often sideband rejection can be measured more accurately than the phase error Δ, (90° ± Δ), I Port relative to Q Port. It is possible to calculate the phase error if the sideband rejection is given, as follows:

therefore,

Example 1: What is the phase error for the image rejection of Z = 15 dBc?

Of course, the equation above assumes that other spurs (such as two tone intermod) are negligible and quite lower than the image rejection. If other spurs are high enough relative to image rejection, then the phase error can be measured as follows:

Example 2:

Where sin^{-1}w is intermod product (dBc), sin^{-1}u is the other erroneous signal close to the fundamental frequency, using (Example1) for determining errors.