The Research And Design Of Bandpass Sigma-Delta Modulator For Fiber Optic Gyroscope

With the advancement of wireless communication, fiber optic gyroscope and integrated circuit technology, the demand for high-resolution Analog-to-Digital Converters(ADCs) has been proliferated. Compared with the Nyquist ADCs, Sigma-Delta ADCs are insensitive to component mismatch. Thus, Sigma-Delta ADCs are widely used in high-resolution applications. Furthermore, for converting the narrowband IF or RF signals, the bandpass converters are more efficient than the lowpass counterparts. Therefore, the bandpass Sigma-Delta ADC is more popular in applications concerning the wireless communication and fiber optic gyroscope systems.The bandpass Sigma-Delta ADC consists of bandpass modulator and digital decimation filter, and its performance is mainly determined by the modulator. Moreover, the bandpass Sigma-Delta modulator’s performance is in turn dependent on its resonator. Therefore, it is imperative to design a good resonator structure in order to achieve high performance ADC. There are three major types of resonator structures, the Forward Euler structure, the Lossless Discrete Integrator structure, and the Double Delay(DD) structure. The DD structure is usually preferred over the other two structures being comparatively insensitive to capacitor mismatch. Hence, the DD resonator structure is able to realize a centre frequency precisely at one quarter of the sampling frequency. In addition, a DD resonator can be implemented using two series delay elements or a Pseudo-N-Path(PNP) architecture. In the two series delay elements, it needs two operational amplifiers to realize a DD resonator, thus increasing power consumption. Whereas in PNP architecture, the clocking scheme is too complex, and it makes the design more complicated and requires more area to implement the respective resonator.To address the above problems, the thesis proposes an improved DD resonator structure using one operational amplifier, and the clocking scheme is redesigned to be much simpler than the PNP structure. To verify the effectiveness of the improved DD resonator, a fourth order bandpass Sigma-Delta modulator is designed using standard 0.25μm CMOS technology. The simulation results show that a SNR of 116.7dB, a power consumption of 4.87 mW at 5V supply, and a FOM(Figure of Merit) of 11.17W/Hz are achieved.