Patent ID: 8548091

Claim:
A transmit chain comprising: a transmit path comprising: a pre-correction module for receiving an input signal and applying a correction to the input signal to correct for errors introduced in the transmit path and outputting pre-corrected quadrature signal components; a quadrature up-converter for up-converting the pre-corrected quadrature signal components; an observation path comprising: a coupler for receiving a portion of the up-converted quadrature signal components and outputting a coupled signal; a quadrature down-converter for down-converting the coupled signal to baseband quadrature signal components; a post-correction module for applying distortion to the baseband quadrature signal components to correct for errors introduced by the observation path; the transmit chain further comprising: a local oscillator signal source which is arranged to provide the quadrature up-converter and the quadrature down-converter with a local oscillator signal and wherein the local oscillator signal source is operable in: a first state in which the local oscillator signal is applied to the quadrature up-converter and the quadrature down-converter; and a second state in which the local oscillator signal is applied to the quadrature up-converter and the quadrature down-converter and a phase shift is made to the local oscillator signal applied to quadrature up-converter or the quadrature down-converter compared to the first state; a processor arranged to: monitor properties of the baseband quadrature signal components while the local oscillator signal source is operating in the first state and while the local oscillator signal source is operating in the second state; determine a correction to apply to the baseband quadrature signal components at the post-correction module, based on the monitored properties of the quadrature down-converted signal components, to correct for errors introduced by the observation path; determine a correction to apply to the input signal at the pre-correction module, based on the monitored properties of the quadrature down-converted signal components, to correct for errors introduced in the transmit path.