Phase-to-frequency conversion for polar transmitters
View Patent ↗The present invention relates to a polar transmission method and a polar transmitter for transmitting phase and amplitude components derived from in-phase (I) and quadrature-phase (Q) components of an input signal. A first conversion is provided for converting the in-phase (I) and quadrature-phase (Q) components into the phase and amplitude components at a first sampling rate. Additionally, a second conversion is provided for converting the phase component into a frequency component, wherein the second conversion comprises a rate conversion for converting the first sampling rate into a lower second sampling rate at which the frequency component is provided. Thereby, the second sampling rate can be used as a lower update rate in a digitally controlled oscillator in order to save power or because of speed limitations, while the surplus phase samples obtain due to the higher first sampling rate enable better approximation of the phase component after the digitally controlled oscillator. This better approximation accounts for a cleaner spectrum around the synthesized channel.
1. A polar transmitter for transmitting phase and amplitude components derived from in-phase and quadrature-phase components of an input signal, said transmitter comprising:
a first converter for converting said in-phase and quadrature-phase components into said phase and amplitude components at a first sampling rate; and
a second converter for converting said phase component into a frequency component, and for rate-converting said first sampling rate into a lower second sampling rate at which said frequency component is provided.
2. The polar transmitter according to claim 1 , wherein said second converter comprises an interpolator for interpolating input samples of said phase component at said first sampling rate by a first factor, a reconstruction filter for filtering the interpolated samples, and a down-sampler for down-sampling calculated samples of said frequency component by a second factor.
3. The polar transmitter according to claim 1 , wherein said second converter comprises a frequency calculator for calculating said frequency component by using a currently realized sample of said phase component so that the distance between input samples of said phase component at said first sampling rate and a linearly interpolated phase during a predetermined number of sampling intervals is minimized.
4. The polar transmitter according to claim 3 , wherein said frequency calculator is adapted to obtain a quantized frequency component by mapping a calculated frequency component to a closest available quantization value.
5. The polar transmitter according to claim 3 , wherein said frequency calculator is adapted to calculate the next realized sample of said phase component based on said currently realized sample of said phase component and said quantized frequency component.
6. The polar transmitter according to claim 1 , wherein said second converter comprises switching means for comparing a frequency component obtained from upcoming samples of said phase component with a predetermined threshold value, and for switching between said rate conversion and a linear approximation without rate conversion, in response to the result of said comparison.
7. The polar transmitter according to claim 1 , wherein said frequency component is supplied to a digitally-controlled oscillator.
8. A method of transmitting phase and amplitude components derived from in-phase and quadrature-phase components of an input signal, said method comprising:
a first conversion step for converting said in-phase and quadrature-phase components into said phase and amplitude components at a first sampling rate; and
a second conversion step for converting said phase component into a frequency component, wherein said second conversion step comprises a rate conversion step for converting said first sampling rate into a lower second sampling rate at which said frequency component is provided.
9. A computer program product comprising code means for generating the steps of method claim 8 when run on a computer device.