Digital RF converter, digital RF modulator and transmitter including the same

A digital RF modulator, comprising:

• a pulse shaping digital filter configured to receive digital signals of a baseband and pulse-shape only digital signals included in a communication bandwidth;
• a sigma-delta modulator configured to perform sigma-delta modulation on least-significant n bits among the pulse-shaped signals;
• a decoder configured to decode the sigma-delta modulated n bits to a thermometer code, decode the intermediate k bits among the pulse shaped signals to a binary code, and decode the most-significant m bits among the pulse-shaped signals to a thermometer code;
• and
• a digital RF converter configured to segment the decoded n bits, the decoded k bits, and the decoded m bits and perform digital-to-analog conversion thereon, perform the digital-to-analog conversion on the decoded n bits at the same sampling frequency as that of the sigma-delta modulator, and perform the digital-to-analog conversion on the decoded k bits and m bits at a sampling frequency lower than that of the sigma-delta modulator.

A direct up conversion transmitter, comprising:

• a first digital RF modulator configured to modulate and output certain bits of in-phase signals at a different sampling frequency than remaining bits of the in-phase signals;
• a second digital RF modulator configured to modulate and output certain bits of quadrature signals at a different sampling frequency than remaining bits of the quadrature signals;
• a carrier signal generator configured to generate carrier signals required to modulate the in-phase signals and the quadrature signals;
• a differential-single output converter configured to convert the modulated in-phase signals and quadrature signals into a single output signal;
• a filter configured to remove cosine signals and spurious waves included in the single output signal;
• and
• a power amplifier configured to amplify and output the power of the filtered signal.