A 16b 12GS/S single/dual-rate DAC with successive bandpass delta-sigma modulator achieving <-67dBc IM3 within DC-to-6GHz tunable passbands

The agile allocation of signal bands over RF frequencies and high in-band spectral purity (both SFDR and NSD) can enable higher-order modulation in high-throughput flexible wireless/wireline transmitters, where signals are often channelized at certain center frequencies. Using a Nyquist DAC to cover the entire signal spectrum is thus unnecessary, as this trades the achievable dynamic range with the bandwidth. For such applications, a narrowband Nyquist DAC followed by a mixer, RF mixing DAC [1], or exploiting higher Nyquist zones [2] are typically adopted; these are either limited by deliverable output power or nearby spectral images due to lower input data rates. A dual-rate hybrid DAC [3] uses a delta-sigma modulated LSB path to compensate for the non-idealities of the Nyquist path, allowing high linearity and a low noise floor within the Nyquist band while limiting out-of-band quantization noise. Still, this only synthesizes the baseband signal and is difficult when covering wide RF spectra due to the DSM OSR requirements.