Wireless communications has revolutionized the way the world conducts business, does commerce, or interacts with other people, even when they are on the move and without the wires and cables that have characterized the communications systems of old. Some of the problems with wireless communications, however, are the unwanted fluctuations, disruptions, interference, and other unstable transmitted signals that can be categorized as noise. Noise is a basic characteristic of modulated electromagnetic waves traveling through the atmosphere (the backbone of wireless communications). Noise can come either from external environmental causes or it can result from the performance of the electronic devices and components used to transmit and receive these signals. Over the years scientists have achieved significant milestones in noise-reduction technology in a bid to improve the quality of signals and information received in wireless communications.
As part of this initiative, Toshiba Corporation recently announced the development of a new noise reduction technology intended for wireless communications. This breakthrough can cut phase noise by as much as 90 percent as well as significantly reduce the jitter typical in radio frequency signals. This technology will be able to pave the way for the emergence of high-speed wireless communication chips and components for use with wireless LAN and WiMAX systems, thereby opening new doors to high-speed and noise-free wireless communications.
There are several potential causes for wireless noise, and most of these sources are inherent in the support processes and elements that make communications possible. Such sources include device and equipment temperatures, the condition of the electronic circuits, condition of the power supplies, and the frequency interference in between data signals. Because of this, total elimination of noise for transmitted wireless signals is almost impossible, as it can only be reduced to acceptable levels.
Previously, LSI chips used in wireless and mobile communications made use of phase-locked loop (PLL) systems. However, there has been demand and need to reduce circuit size, so manufacturers have migrated to all-digital time-to-digital converters (TDC) in their systems. The problem with this change is the increase in phase noise, which is inherent in the use of TDCs due to the large delay in the inverter circuits. On top of that, variations in the manufacturing processes can affect the performance of these highly-sensitive TDCs.
Such conditions might be tolerable in standard wireless communications, but if used with high-speed communication systems that require highly-accurate transmission of data signals, as in the case of WiMAX systems, reducing phase noise is an imperative.
To address this need in developing a more robust manufacturing process for TDCs with the capability to suppress phase noise, the technological experts at Toshiba developed a new process for manufacturing TDCs by making use of low-resistance conductors for integrating interpolation circuits. Making use of triple interpolation, the output signal of the frequency synthesizers is split into cycles, thus reducing the phase noise by up to 90 percent. The result is a stable all-digital PLL that is smaller than current analog PLLs, which can be used for mobile WiMAX transceiver systems.
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