(A) Low-noise, high-gain transmitter design for spin-torque wireless communication

Abstract

Since Slonczewski proposed a new mechanism for exciting the magnetic state of a ferromagnet and a nano-structure that generates spin transfer torque in 1996 [1], various researches have been carried out to utilize this quantum mechanics effect efficiently. STT-MRAM and Spin-torque-nano-oscillators (or Spin-transfer-nano-oscillators, STNOs) are two representative applications using spin transfer torque. Especially STNOs have been investigated as one of the next-generation oscillators. Conventional LC-tank oscillators which are widely used in today’s wireless transceivers limit the possibility of shrinking the chip size. However, STNOs are normally 50 times smaller than the conventional LC-tank oscillators, and have wide frequency tuning range. With these two superiorities, STNOs can replace the position of LC-tank oscillators if STNOs make up for their low output power and high phase noise properties. This thesis presents a low-noise, high-gain wideband transmitter for OOK STNO communication. The designed OOK transmitter consists of LNA and RF-amplifier, and OOK modulation method is selected to overcome the high phase noise characteristic of STNO. Unlike other transmitter, low-noise amplifier (LNA) is used at first stage considering low output power of STNO and RF-amplifier is added for large amplifying. Using resistive feedback with PSCNMIM method, the noise and input of LNA is simultaneously matched in wideband frequency range from 3 GHz to 4GHz. This wideband matching covers the oscillating frequency of STNOs. which has wide tuning range. RF amplifier also designed using resistive feedback topology for wideband matching and eliminate the noise matching to increase the total transmitter gain. Because proposed transmitter has an oscillation issue that general high-gain amplifiers have, we devised two different ground layout for perfect ground and perfect isolation to lower the possibility of oscillation and made two transmitters without oscillation applying theses ground layout. Measured transmitter gain and noise figure is 34 dB and 4 dB with 9.2 mW power consumption. Wireless communication experiment is done using designed transmitter. Measured output power output power of STNO is -82 dBm at 3.3 GHz and signal was successfully transmitted to receiver when transmitter module sends 1MHz data signal. Maximum communication distance is 1 m and calculated maximum data rate is 8.5 Mbps.