Spin Torque Oscillator (STO) is a promising technology for microwave and radar applications due to its large tunability, miniature size, high operation frequency, high integration level, etc. However, the technology comes also with issues and challenges,such as low output power and spectrum impurity. For instance, in order to apply the STO technology into communication systems, an amplifier is required to compensate the STO’s low output power.
This project presents an amplifier for promising Magnetic Tunnel Junction (MTJ) STO devices. The motional resistance of different MTJ STO devices varies from several Ohms to hundreds Ohms, which makes the design challenging. This thesis focuses first on extracting the amplifier requirements using the state-of-the-art MTJ STO devices. The operation frequency of MTJ STO is in the range of 4-8GHzwith a -40～-60 dBm output power. Therefore, a wideband amplifier with 45-65 dB gain is required.
Then based on the amplifier requirements, an amplifier topology is proposed, which is composed of two types of input balun-LNA stages depending onthe motional resistance of the STO, a broadband limiting amplifier and an outputbuffer. CG-CS architecture is suitable for the input balun-LNA in the small motional resistance case and cascoded-CS architecture is suitable for the large motional resistance case. The limiting amplifier and the output buffer are the common circuits shared by two cases via switches.
The wideband amplifier for STO is implemented using a 65nm CMOS process with 1.2 V supply and it exhibits 52.36 dB gain with 1.34-11.8 GHz bandwidth in small motional resistance case and 59.29 dB gain with 1.171-8.178 GHz bandwidth in large motional resistance case. The simulation results show that the amplifier has very low power consumption and meets the linearity and noise performance requirements.
Source: KTH
Author: Chen, Tingsu