A current-mirror opamp with switchable transconductances for low-power switched-capacitor integrators

In a switched-capacitor (SC) integrator, the opamp can be switched off during the sampling phase, to reduce the power dissipation. This paper proposes a switchable-opamp technique based on a current-mirror opamp with switchable transconductances. Whereas previous switchable-opamp methods can only be used in SC integrators with half delay, the proposed technique can be utilized in SC integrators with both half delay, and full delay. Furthermore, no special common-mode feedback (CMFB) circuits are required for the opamp. At high sampling frequencies, circuit simulations of SC integrators and discrete-time ΔΣ modulators demonstrate that power reductions of 30% can be achieved by using the proposed technique, with minimal effect on the gain error of the SC integrator and the SNDR of the ΔΣ modulator. This confirms that the proposed switchable-opamp technique does not limit the speed of the SC circuit.