28
P. K. Muduli et al.
respectively. The figure shows only the presence of a lower sideband; the upper sideband is completely suppressed. This phenomenon of a carrier with one sideband is
known as single sideband (SSB) modulation and is a result of the strong nonlinear
variation of frequency and amplitude with bias current in MTJ-STNOs. The performance of the STNOs as an SSB generator can be tuned with operating parameters
such as in-plane field angle [132] as well as with the field-like torque term present in
MTJ-based devices [131]. The in-plane field angle changes the frequency tunability
with bias current and thus the SSB onset frequency and carrier power for the SSB
transmission [132]. The field-like term also affects the frequency tunability with the
bias current [40, 52, 55]. The observation of lower single side band (LSSB) in the
experimental results of Ref. [131] indicates the presence of smaller field-like torque,
which is consistent with other works on similar devices [40, 133].
Transmission through SSB generation is particularly advantageous for wireless
communication since: (1) less transmission power is required as only one sideband,
carrying the same information as the other one, will be transmitted; (2) there is less
utilization of the available spectrum in comparison with double sideband (DSB)
transmission; (3) there is less selective fading or interference with other signals. Furthermore, SSB generation through MTJ-based STNO devices has an edge over the
existing technology for SSB generation, due to its compact size and fast modulation rate. The traditional method of generating SSB using, for example, a Hartley
modulator [134] or a Weaver modulator [135], requires a number of components for
SSB generation that makes the overall set-up a little bulky. However, STNO uses a
single device for the carrier and sideband generation due to its nonlinearity and is
suitable for chip technology, due to its compatibility with commercialized CMOS
technology.
8.2 Modulation of Parametric Synchronized MTJ-STNOs
Most often, parametric synchronization and modulation are studied in MTJ-STNOs
as a separate study to understand the effect of the external perturbation of the RF signal
on the magnetization dynamics. Recently, an effort has been made to understand the
modulation in a parametrically synchronized STNO in Ref. [136], as shown in Fig. 16.
The major motivation for this study was to take advantage of the high power and low
linewidth due to parametric synchronization and then to determine the data rate of
the synchronized state.
For modulation of the parametrically synchronized STNO, in addition to dc current, two additional RF signals were superimposed. The first RF signal was injected
at twice the frequency of the STNO and serves as the signal for parametric synchronization, while the second RF signal with a frequency range of f mod = 50 MHz–
500 MHz was used for modulation. The synchronization was found to break below
f unlock ∼170 MHz, as shown in Fig. 16a. Figure 16b shows that macrospin simulation performed under similar bias conditions also exhibit similar unlocking behavior.
The value of f unlock increases with the increase in amplitude of the modulation cur-
P. K. Muduli et al.
respectively. The figure shows only the presence of a lower sideband; the upper sideband is completely suppressed. This phenomenon of a carrier with one sideband is
known as single sideband (SSB) modulation and is a result of the strong nonlinear
variation of frequency and amplitude with bias current in MTJ-STNOs. The performance of the STNOs as an SSB generator can be tuned with operating parameters
such as in-plane field angle [132] as well as with the field-like torque term present in
MTJ-based devices [131]. The in-plane field angle changes the frequency tunability
with bias current and thus the SSB onset frequency and carrier power for the SSB
transmission [132]. The field-like term also affects the frequency tunability with the
bias current [40, 52, 55]. The observation of lower single side band (LSSB) in the
experimental results of Ref. [131] indicates the presence of smaller field-like torque,
which is consistent with other works on similar devices [40, 133].
Transmission through SSB generation is particularly advantageous for wireless
communication since: (1) less transmission power is required as only one sideband,
carrying the same information as the other one, will be transmitted; (2) there is less
utilization of the available spectrum in comparison with double sideband (DSB)
transmission; (3) there is less selective fading or interference with other signals. Furthermore, SSB generation through MTJ-based STNO devices has an edge over the
existing technology for SSB generation, due to its compact size and fast modulation rate. The traditional method of generating SSB using, for example, a Hartley
modulator [134] or a Weaver modulator [135], requires a number of components for
SSB generation that makes the overall set-up a little bulky. However, STNO uses a
single device for the carrier and sideband generation due to its nonlinearity and is
suitable for chip technology, due to its compatibility with commercialized CMOS
technology.
8.2 Modulation of Parametric Synchronized MTJ-STNOs
Most often, parametric synchronization and modulation are studied in MTJ-STNOs
as a separate study to understand the effect of the external perturbation of the RF signal
on the magnetization dynamics. Recently, an effort has been made to understand the
modulation in a parametrically synchronized STNO in Ref. [136], as shown in Fig. 16.
The major motivation for this study was to take advantage of the high power and low
linewidth due to parametric synchronization and then to determine the data rate of
the synchronized state.
For modulation of the parametrically synchronized STNO, in addition to dc current, two additional RF signals were superimposed. The first RF signal was injected
at twice the frequency of the STNO and serves as the signal for parametric synchronization, while the second RF signal with a frequency range of f mod = 50 MHz–
500 MHz was used for modulation. The synchronization was found to break below
f unlock ∼170 MHz, as shown in Fig. 16a. Figure 16b shows that macrospin simulation performed under similar bias conditions also exhibit similar unlocking behavior.
The value of f unlock increases with the increase in amplitude of the modulation cur-