Bandpass delta-sigma modulators (BPDSMs) make the perfect solution for contemporary receiver systems. They digitize analog signals from the intermediate frequency, allowing more versatility within the digital back finish. Figure 1 contrasts a conventional receiver signal processing chain with what BPDSM system. Inside a BPDSM system, high-frequency narrow band signals are transformed into digital form without prior lower-conversion to baseband [1 ]. This pushes the signal processing burden towards the digital domain and improves both system’s simplicity and it is power use.
BPDSMs could be recognized either in continuous-time (CT) or discrete-time (DT) fashion. The CT structure enjoys certain advantages over its DT counterpart [2 ]. 1) it can achieve lower noise and linearity 2) it relaxes the gain-bandwidth requirement around the op amps 3) it offers intrinsic anti-alias filtering. Therefore, CTBPDSM supplies a more power-efficient solution for wideband and resolution analog-to-digital conversion.
This project concentrates on the style of a CTBPDSM that may acquire a signal-to-noise ratio (SNR) well over 80dB having a signal bandwidth of 25MHz, a sampling rate of 1GHz, along with a center frequency at 250MHz. Figure 2 shows the modulator architecture. A cascaded resonator feedback (CRFB) topology is utilized to understand a set in-band signal transfer function. An 8-th order noise transfer function is implemented with four active RC resonators in cascade. The task is based on the style of the continual-time bandpass loop filter with low power and linearity needs. To ensure that resonators to possess top quality factor, op amps have to maintain high gain in the center frequency.
To do this goal, we adopt a 4-stage op amp with feed-forward gm-C compensation [3 ]. We’ve developed techniques to help make the op amps more power efficient and stable. We’re also investigating Pavan’s method [4 ]. which will help make amends for loop filter non-idealities by tuning feedback coefficients.
- R. Schreier and G. C. Temes, Understanding Delta-Sigma Data Converters. Hoboken: John Wiley Sons. Corporation. 2005. [↩ ]
- K. Philips, “Continuous-time Sigma-Delta ADCs,” Philips Research Laboratories, Eindhoven, holland. [↩ ]
- G. Mitteregger, C. Ebner, S. Mechnig, T. Blon, C. Holuigue, and E. Romani, “A 20-mW 640-MHz CMOS Continuous Time DS ADC With 20-MHz Signal Bandwidth, 80-dB Dynamic Range and 12-bit ENOB,” IEEE Journal of Solid-Condition Circuits. vol. 41, no. 12, pp. 2641-2649, 12 ,. 2006. [↩ ]
- S. Pavan, “Systematic Design Centering of Continuous Time Oversampling Converters,” IEEE Transactions on Circuits and Systems – II: Express Briefs, vol. 57, no. 3, pp. 158-162, Marly. 2010. [↩ ]
Table of Contents