Fujitsu Laboratories advances communication and memory technology

Fujitsu Laboratories advances communication and memory technology

Researchers at Fujitsu Laboratories have been busy on three fronts. First, they have developed, for tuners in terrestrial digital television receivers, a frequency synthesizer that features a reduction of circuit size to one-third that of conventional circuits and eliminates the need for external components. The new synthesizer uses a “circulating register” modulator, which has lower noise than conventional delta-sigma modulators. For the design, seven registers are lined up in parallel, resulting in accurate reception of 3/7th-MHz frequency intervals that are used in digital TV broadcasts in Japan. This design aids noise suppression and eliminates the need for an external filter circuit.

Secondly, Fujitsu and the University of Toronto have developed a new processing method for gigabit/s-class wire-line transceiver chips that uses digital to replace previously required analog circuits. The technology detects variations in the delay time of the input signal and, based on that, automatically adjusts the receive timing.

And third, again working with the University of Toronto, Fujitsu researchers have developed a high-reliability read-method for use with spin-torque-transfer MRAM (magnetoresistive random access memory). Reading the MRAM’s magnetic tunnel junction (MTJ) state involves applying a voltage to the junction to discover whether it is in a high- or low-resistance state. However, a relatively high voltage needs to be applied and the current passed at this voltage leaves little difference between the read and the write current. Any fluctuation in the electrical characteristics of individual MTJs could cause an erroneous change the direction of magnetization.

A newly developed read method uses a negative resistance that is intermediate between the MTJ’s high and low resistance on a parallel circuit (see figure ). If the MTJ is in a high-resistance state, this circuit exhibits negative-resistance characteristics. If the MTJ is in a low-resistance state, it exhibits normal-resistance characteristics. These characteristics allow the resistance value to be read at lower voltages than before, suppressing the false read problem and resulting in an MRAM that is insusceptible to erroneous writes. For more information see www.fujitsu.com/global/news.

Jim Harrison