Low-voltage Switched-capacitor Resonators

The recent explosion of interest in wireless personal communication systems motivates the development of fully integrated radio receivers. The parallel reduction of the feature sizes in CMOS technology, and hence higher levels of integration. enable the combined integration of a bandpass or baseband analog-to-digital converter with the traditional front-end receiver building blocks. While ths trend advances the digital technology, one of the key analog limitations of state-of-the-art submicron CMOS technologies remains the restricted power-supply voltage, limited by the low junction breakdown voltage of the high density CMOS process and by the thin gate oxide, prone to voltage stress. There exist many resonator circuits to implement SC bandpass AX modulators and filters for high-frequency communication applications, such as the “lossless-discrete integrator” (LDI) and “forward-Euler” (FE) types [I], two-delay loop (TDL) [2], [5], low-pass filter [3], high-pass filter based [4] and pseudo-two-path (P2P) types [6] . The most recent ones use P2P and TDL techniques, with double sampling to increase the sampling frequency. In these previous implementations, the minimum available power supply voltage was 3 V. In our previous work [7], we have shown the LV implementations of SC ADCs and low-pass filters based on the unity-gainreset (UGR) technique. Compared to the switched-opamp technique [SI, this technique is suitable for operating at higher speeds, by keeping the opamp in its active operating region at all times. In this paper, we present four different LV resonator circuits, which are functional with supply voltages down to 1 V. They are compared based on their robustness with respect to the finite gain and bandwidth of the opamps used. SWITCAP2 simulations have been performed to see the effects of the analog imperfections on their frequency responses. , The typical resonator transfer function for a band center at fc lock/4 with unit delay from input to output is given by