Interpolation method for polar signals in radio frequency transmitters

A lookup table (LUT) based interpolator circuit, comprises:

• a LUT circuit comprising an LUT configured to store a plurality of normalized phase angles or a plurality of normalized radius values or both, wherein each of the normalized phase angle and normalized radius value has a respective LUT index value associated therewith;
• and
• an address generating circuit configured to:
• receive an input IQ signal comprising a plurality of input IQ samples at a first sampling rate;
• and
• generate a set of LUT index values at a second, different, sampling rate, in order to access a set of normalized phase angles or a set of normalized radius values or both, corresponding to the set of LUT index values from the LUT, wherein the set of LUT index values is generated based on the received input IQ signal and an information of a required interpolation ratio,
• wherein the normalized phase angles and the normalized radius values are obtained based on a normalized IQ trajectory of the input IQ samples, the normalized IQ trajectory being obtained by rotating an IQ trajectory of the input IQ samples by an angle of a normal vector to the IQ trajectory.

An apparatus for mapped linear interpolation of polar signals in RF transmitters, comprises:

• a displacement calculation circuit configured to:
• receive an input IQ signal comprising a plurality of input IQ samples at a first sampling rate;
• and
• normalize an IQ trajectory associated with the input IQ samples, determine a set of normalized displacement values comprising a set of values associated with a normalized displacement corresponding to each sampling point on the IQ trajectory, based on the received input IQ signal and an information of a required interpolation ratio, wherein the normalized displacement is x/d, where x is a displacement of the sampling point along the normalized IQ trajectory and d is a distance of the normalized IQ trajectory from an origin of IQ plain;
• and
• an output generation circuit configured to:
• generate a set of interpolated polar samples at a second, different sampling rate based on a mapping between the set of the normalized displacement values, and one or more predefined functions of the normalized displacement indicative of phase angle values of the interpolated polar samples or radius values of interpolated polar samples or both, associated with the input IQ signal.