A new SC differentiator for two-path bandpass ΔΣ modulator design

A new architecture of a fully differential switched capacitor (SC) differentiator is proposed as the building block of two-path bandpass SC ΔΣ modulators. Compared to other SC differentiators, the pole in its transfer function is not sensitive to capacitor mismatches, and there is less switch thermal noise in the new architecture. The opamp in the differentiator has a smaller capacitance load. Using the new SC differentiator, a fully differential fourth-order two-path SC bandpass ΔΣ modulator was built. The signal narrowband of the modulator is 200 kHz centered at 15 MHz. The effective sampling frequency is 60 MHz, double the physical clock frequency. The test circuit was implemented in 0.35-μm CMOS process. The measured signal-to-noise ratio is 77 dB. The power dissipation is 14.5 mW at a 3.0-V supply voltage.