Patent ID: 7183956

Claim:
Apparatus for converting digital input signals directly to a radio-frequency (RF) analog signal for transmission, without use of RF upconversion, the apparatus comprising: an upsampler, for taking the digital input signals at input sample rate and converting them by interpolation to upsampled digital input signals at a sample rate of N times the sample rate, where the sample rate of the upsampled digital input signals is greater than the input sample rate, the upsampler comprising: a multiplexer having N inputs and a single output; combinatorial logic for manipulating two consecutive digital input signals and applying selected positive or negative versions of the two consecutive signals to the N inputs of the multiplexer; and a counter coupled to the multiplexer and configured to generate cyclically control signals of values 1 through N, at a rate N times the input sample rate, wherein the multiplexer outputs a succession of upsampled digital signals selected from each multiplexer input in turn, at a rate of N times the input sample rate; a delta-sigma modulator for receiving the upsampled digital input signals and transforming them to output digital signals having a lower resolution than the digital input signals; and a digital-to-analog converter, for converting the output digital signals to RF analog form for transmission.