| 摘要 |
A continuous-time tunable Gm-C architecture for a DELTA SIGMA modulator includes a tunable resonator and a low bit rate, high sample rate quantizer connected in a feedback loop. The resonator shapes the quantization noise spectrum so that the bulk of the quantization noise occurs outside the signal spectrum. A tunable Gm cell tunes the resonator's resonant frequency to maximize the modulator's SNR. The tunable Gm cell includes a fixed Gm cell having transconductance Gf, a current divider and a recombination circuit that together effectively multiply Gf by a factor alpha , where -1<= alpha <=1, without effecting the cell's common mode current Icm. A positive current source supplies Icm, while maintaining a common mode resistance of R/2 and a theoretically infinite differential mode resistance. Thus, the resonator's resonant frequency can be varied from DC to approximately 1 Ghz while maintaining a stable common mode operating point and improving the modulator's quality factor.
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