Patent ID: 9276798
Filing Date: 2016-03-01
CPC Classification: H04L

Claim Text:
1. A Digital calibration circuit for joint-elimination of transmitter and receiver I/Q imbalances, comprising: a circuit receiving digital I and Q quadrature signals, said circuit comprising digital to analog converters receiving digital I and Q quadrature signals and transmitting analog I and Q quadrature signals on I and Q output channels; an initial output pre-compensation circuit providing digital I and Q quadrature signals to the circuit receiving the digital I and Q quadrature signals, and providing pre-compensation for the digital I and Q quadrature signals; an output mixer circuit converting the quadrature signals to an unbalanced RF output; the I and Q output channels further comprising a first pair of low pass filters between the digital to analog converters receiving digital I and Q quadrature signals and the output mixer circuit; a circuit receiving a signal as the unbalanced RF input; an input mixer circuit converting the received unbalanced RF input to analog I and Q quadrature signals; a circuit transmitting digital I and Q quadrature signals comprising analog to digital converters and a second pair of low pass filters between the input mixer circuit and the analog to digital converters, the circuit receiving analog I and Q quadrature signals from the input mixer circuit; a source follower amplifier connecting the unbalanced RF output with the unbalanced RF input; a source follower switch selectively connecting the unbalanced RF output to unbalanced RF input, establishing a feedback loop from the unbalanced RF output through the source follower amplifier to the unbalanced RF input; a local oscillator (LO) switchable to provide an LO signal to the output and input mixer circuits, wherein the LO adds an additional 90° phase shift between I and Q quadrature channels of the unbalanced RF input; a parameters estimator receiving the transmitted digital I and Q quadrature signals and providing estimations of I and Q quadrature imbalance conditions and providing a signal to the initial output pre-compensation circuit to balance I and Q components of the unbalanced RF output and further providing a signal to an input post-compensation circuit to balance the I and Q components of the compensated I and Q signals; and the input post-compensation circuit receiving the digital I and Q quadrature signals from the analog to digital converters and providing compensated I and Q signals.