Patent ID: 7675445

Claim:
A conversion method for an analog-digital conversion device having two channels, I and Q respectively, in quadrature, each comprising an input and an associated output, for converting a complex analog input signal into a complex digital output signal by an analog-digital converter, each output being fed back onto said associated input so as to form a first and a second feedback loops each comprising a digital-analog converter, said device comprising a complex filter with a first stage and a last stage, said method comprising, on each of said channels, the steps consisting in: sampling an analog input signal; performing a signal integration of the sampled signal in said first stage of the filter in order to deliver an output signal from the first stage, said integration not introducing any substantial delay; performing a signal integration in the last stage of the filter in order to deliver an output signal from the last stage; introducing a substantial delay at the output of the last stage and converting the output signal from the last stage into a digital signal over several bits by said analog-digital converter; injecting said digital signal into the feedback loop of said channel; converting the digital signal into a feedback signal by said digital-analog converter; injecting said feedback signal into at least said first stage of said complex filter wherein the step consisting in performing a signal integration in the first stage of the complex filter comprises the steps consisting in: adding together the following signals on the channel I: the input signal of the channel I, the feedback signal of the channel I, the output signal of the first stage of the channel I substantially delayed and multiplied by a coefficient 1/G, the output signal of the first stage of the channel I substantially delayed and multiplied by a coefficient of value 1/G*(cos θ−1), and the output signal of the first stage of the channel Q substantially delayed and multiplied by a coefficient 1/G*(−sin θ); adding together the following signals on the channel Q: the input signal of the channel Q, the feedback signal of the channel Q, the output signal of the channel Q of the first stage substantially delayed and multiplied by a coefficient of value 1/G the output signal of the channel Q of the first stage substantially delayed and multiplied by a coefficient of value 1/G*(cos θ−1), and the output signal of the channel I of the first stage substantially delayed and multiplied by a coefficient 1/G*(sin θ); where θ is equal to 2πfz/fs, where fz is a frequency corresponding to a zero of the transfer function of the filter and fs is the sampling frequency of the signal; where G is the gain of the first stage.