Sriram Murali

Highly-linear FM transmitter for mobile application in 65nm CMOS

An FM frequency synthesizer and antenna driver with >63dB SNR, <0.1% THD, and −dBc out-of-band emissions at 124dBµV output swing in 65nm digital CMOS is described. The optimized FLL incorporates a DCO with a highly linear capacitor array and flicker noise reduction techniques. Cascaded filtering and a segmented driver improve efficiency and tuning range with minimal high-order distortion.

Effect of protective coating on marginal integrity of nanohybrid composite during bleaching with carbamide peroxide: A microleakage study

AIM The aim of the study was to evaluate the microleakage on the marginal integrity of nanohybrid composite during bleaching with carbamide peroxide after applying a protective coating of G-Coat plus (GC, Japan). MATERIALS AND METHODS Class V cavities were prepared and restored with nanohybrid composite restoration in 60 freshly extracted noncarious premolars extracted for orthodontic reasons. Then they were divided into 3 groups. Group 1 - bleaching with carbamide peroxide without G coat plus (n = 20), Group 2 - bleaching with carbamide peroxide with G-Coat plus (n = 20), Group 3 - without bleaching procedure (n = 20) (control group). In Group 2, G coat plus was applied over the restorative surface and margins. Then all teeth in Groups 1 and 2 were taken and mounted in dental stone. Bleaching trays were custom fabricated over the cast with the help of a heated vacuum-forming machine. 10% carbamide peroxide (opalescence PF) was applied over the tooth, and the bleaching process was done for about 2 weeks. Then all samples underwent thermocycling and were then immersed in the 2% methylene blue solution for 24 h and observed under a stereomicroscope to evaluate the amount of dye penetration. Data were compared using Kruskal-Wallis test and Mann-Whitney test using SPSS Inc.; Chicago, IL, USA, Version 17.0. RESULTS Mann-Whitney test shows that the difference in microleakage between Group 1-Group 2 and Group 2-Group 3 is statistically significant (P < 0.05). CONCLUSION Significant reduction in microleakage was seen in Group 2 when compared to other groups.

Overmodulation protection in FM transmitters

The FM radio broadcast standard mandates the use of an audio pre-emphasis filter prior to frequency modulation, to enhance robustness against noise coloration inherent to FM reception. The standard also places a restriction on the maximum frequency deviation that can be imparted by a message signal modulating the FM carrier, to limit the occupied bandwidth of the broadcast signal. Because of the frequency dependent gain profile of the pre-emphasis filter, an audio signal, even if amplitude limited prior to pre-emphasis, is not guaranteed to remain so after pre-emphasis. Hence, there arises a need for a gain control mechanism specifically tailored to handle pre-emphasized audio in any FM broadcast system, to prevent overmodulation. In this paper, we present a novel, low-complexity, digital adaptive filter based algorithm for overmodulation protection in FM radio transmission.