An energy-efficient ΔΣ modulator using dynamic-common-source integrators

An energy-efficient ΔΣ modulator has been investigated by using dynamic-common-source integrators. Instead of the virtual short commonly used in conventional opamp-based integrators, the novel integrator used the fact that when a MOSFET turns off from its on-state, the voltage difference between the gate and source approaches to the threshold voltage, which is virtually constant after the charge redistribution. No static currents flow in the present integrator, resulting in high energy efficiency. An FOM of 29 fJ/comv-step was estimated by our transistor-level circuit simulation assuming a 0.18-μm standard CMOS technology with an SNDR, a bandwidth and a sampling frequency of 82.6dB, 20 kHz and 5 MHz, respectively.