For If Receiver Bandpass Simgma-delta Modulator

With the development of the wireless telecommunication technology and integrated circuit process, the analog-to-digital converters are advancing towards high speed, high resolution and low power. Compared to Nyquist ADC, Sigma-Delta ADC has some advantages when the resolution is high, because it's not restricted by the matching of the components. Especially for receivers, bandpass∑ΔADC based on∑Δmodulation can be used to digitize the narrowband intermediate frequency signals. It is suitable for the performance and integration of the receiver systems with the multi-mode potential.The implementation of a bandpass∑Δmodulator which is the key block of the bandpass∑ΔADC is explored in this research. From the basic theory of the∑Δmodulator, the principle of the bandpass∑Δmodulator achieving high accuracy in intermediate frequency is analyzed. Then, the behavioral model of the nonidealities is built by MATLAB Simulink toolbox, and the transfer function of the resonator considering nonidealities of the operational amplifier is proposed so as to optimize the performance of resonators. Finally, the circuit implementations of each block are discussed in detail and the method of layout design and test are described.A fourth-order switched-capacitor bandpass∑Δmodulator, which is implemented in a 0.13-μm standard CMOS process, is presented for digital intermediate-frequency (IF) receivers. The circuit operates at a sampling frequency of 100MHz. The measurement shows that signal-to-noise-and-distortion ratio (SNDR) and dynamic range (DR) achieve 68dB and 75dB, respectively, over a bandwidth (BW) of 200kHz centered at 25MHz, and the power dissipation is 8.2mW at 1.2V supply.