Digital quadrature transmitter using generalized coordinates

摘要

In one embodiment, a sequence of a plurality of pairs of in-phase (I) and quadrature (Q) modulated signal samples are applied to a radio frequency digital-to-analog converter (RFDAC) for upconversion. A phase of a local oscillator (LO) signal supplied to the RFDAC is selected according to a quadrant determined by signs of a given pair of I and Q modulated signal samples. The selected phase of the LO is supplied to the RFDAC for use in upconverting the sequence of I and Q modulated signal samples. In another embodiment, a current steering DAC is used for directly upconverting the I and Q modulated signal samples. A clock signal at four times the LO frequency is supplied to a counter and to the current steering DAC. One of the I and Q modulated signal samples and negative I and negative Q modulated signal samples is selected for supply to an input of the current steering DAC based on a count state of the counter.

主权项

1. A method used in a digital quadrature transmitter, comprising:
generating a plurality of pairs of in-phase and quadrature modulated signal samples to be successively applied to a radio frequency digital-to-analog converter (RFDAC) for upconversion; selecting a phase of a local oscillator signal according to a quadrant determined by signs of a given pair of in-phase and quadrature modulated signal samples; supplying the selected phase of the local oscillator signal to the radio frequency digital-to-analog converter (RFDAC) for use in upconverting the in-phase and quadrature modulated signal samples; translating the in-phase and quadrature modulated signal samples to thermometer coded outputs that are supplied to inputs of the RFDAC to select transistors to be turned on in the RFDAC; and time-dithering the in-phase and quadrature modulated signal samples to produce resolution-increased versions of the in-phase and quadrature modulated signal samples.