This paper presents a technique for improving the SNR and resolution of complex bandpass ΔΣADCs which are used for wireless communication systems such as cellular phone, wireless LAN and Bluetooth. Oversampling and noise-shaping are used to achieve high accuracy of a ΔΣAD modulator. However when a multi-bit internal DAC is used inside a modulator, nonlinearities of the DAC are not noise-shaped and the SNR of the ΔΣADC degrades. For the conversion of complex intermediate frequency (IF) input signals, a complex bandpass ΔΣAD modulator can provide superior performance to a pair of real bandpass ΔΣAD modulators of the same order. This paper proposes a new noise-shaping algorithm--implemented by adding simple digital circuitry--to reduce the effects of nonlinearities in multi-bit DACs of complex bandpass ΔΣAD modulators. We have performed simulation with MATLAB to verify the effectiveness of the algorithm, and the results show that the proposed algorithm can improve the SNR of a complex bandpass ΔΣADC with nonlinear internal multi-bit DACs.

This paper presents a 0.5Vdd-step pumping method for Dickson-type charge-pump circuits that achieve high overall efficiency, including regulator circuitry, even at large output currents, and these circuits are targeted at mobile equipment applications. We have designed positive and negative charge-pump circuits which use a 0.5Vdd-step pumping method, are implemented with advanced control functions, and are fabricated with our custom CMOS process. Measured results showed that efficiency of a 2.5-stage positive charge-pump circuit before regulation is more than 93% (power supply Vdd=5 V, output voltage Vout=16.9 V 3.5Vdd, output current Iout=4 mA), and that of a 1.5-stage negative charge-pump circuit is 93% (power supply Vdd=5 V, output voltage Vout=-7.2 V -1.5Vdd, output current Iout=4 mA).