ABSTRACT
Bandpass ΣΔ modulation is a very power-efficient technique to realize RF analog-to-digital converters (ADCs) [1]. To cover a wide frequency range, BP ΣΔ ADCs with tunable center frequencies have been proposed [2]. One important challenge in designing a tunable BP ΣΔ ADC relies in varying the modulator’s feedback DAC coefficients to maintain the same signal transfer function (STF) and noise transfer function (NTF) for each center frequency, f0, in the complete tuning range, f0, of the ADC. The fact that the BP ΣΔ feedback DAC coefficients must be tuned for each center frequency has considerably complicated the modulator architecture. This resulted in a very large power consumption of 750 mW for a 1 GHz tuning range in [2], a rather low SNR of 40 dB with a bandwidth of 1 MHz for a 1.2 GHz tuning range in [3] or a very limited tuning range of 40 MHz in [4].
