A Novel Analog Switch for High Precision Switched-Capacitor Applications

The performance of a switched capacitor circuit strongly depends on its analog switches. This paper introduces a new technique to design a high precision analog MOS switch for switched-capacitor applications. To satisfy the accuracy requirements of the switch, a novel technique is proposed to minimize the charge injection and clock feed-through errors by using a very simple structure. Moreover, an innovative approach to increase the off-resistance of the switch and consequently minimizing its leakage current is presented. In order to evaluate the performance of the proposed switch, simulations are done in a 18μm standard CMOS technology. The on-resistance of the proposed switch is less than 560Ω over entire input signal range which completely satisfies the tracking bandwidth requirements. In addition, since the proposed switch provides an ultra-high off-resistance in the range of several GΩs, the leakage current of the proposed switch is negligible. Simulation results also show that switch induced errors are significantly eliminated by using the proposed cancellation technique. The output error charge due to charge injection and clock feed-through over a wide range of the input signal variation is less than 1.6fC. Moreover, simulation results show that the proposed switch achieves signal to noise plus distortion ratio (SNDR) of 80.55dB, effective number of bits (ENOB) of 13.08, total harmonic distortion (THD) of -81.41dB and spurious-free dynamic range (SFDR) of 87.7dB for a 2.5MHz sinusoidal input of 800mv peak-to-peak amplitude at 200MHz sampling rate with a 1.8V supply voltage.