Digital Modulation #7. What is QPSK Channel Impairment: Quadrature Error, IQ Imbalance & Offset.
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IQ Imbalance
Difference in gain between the I & Q signal components
Asymmetric constellation. Skewed or Stretched Constellations (non-square shapes)
Quadrature Error
quadrature error is the deviation from angle
for an ideal modulator, the quadrature offset is 0o
skewed constellation phase skew
Imperfect Local Oscillator (LO)
The I and Q carriers may not be exactly 90° apart due to phase imbalances
I/Q Offset / Carrier Leakage
In a constellation diagram, I/Q offset (also known as carrier leakage) refers to a distortion where the entire constellation is shifted away from its ideal origin (0,0 point) due to a DC offset in the I (in-phase) and/or Q (quadrature) channels.
DC offsets introduced in the I and Q paths