The integer-N phase-locked loop (PLL) constitutes an efficient method for phase noise reduction of high frequencies by multiplying the reference frequency by N times to produce the voltage-controlled oscillator (VCO) output frequency. The VCO and subsequent pre-scaler are required to operate in the highest possible speed. Therefore, it is beneficial to implement these devices using tunnel devices including tunnel diodes (TDs) or resonant tunneling diodes, because these types of diodes avoid the use of speed-limiting CMOS circuits. A review of published literature reveals that several schemes have been proposed for frequency division. Recently, a frequency divider, which utilizes a nonlinear solitary wave developed in a one-dimensional (1D) TD oscillator lattice, was proposed for use in pre-scaler applications. Research has shown that by employing quasi-continuous approximation, a unique equilibrium point can become a saddle point with a homoclinic orbit. This way, the solitary pulse obtained experimentally can be well explained qualitatively. Homoclinic pulses exhibit attractive interactions to form n-homoclinics. Moreover, counter-propagating self-sustained pulses (including homoclinic ones) tend to annihilate during a head-on collision. This property can be straightforwardly utilized for frequency division, which can be successfully observed experimentally.
In general, it is well known that self-sustained solitary waves, which propagate in a one-dimensional lattice of tunnel diode oscillators, can be effectively applied to frequency division. To further investigate this, Professor Koichi Narahara from the Kanagawa Institute of Technology proposed to experimentally characterize solitary waves are, for the first time. His work is currently published in the International Journal of Circuit theory and Applications.
In his approach, several experimental observations of a self-sustained solitary wave in a tunnel diodes oscillator lattice were conducted. The results obtained from bifurcation analysis were summarized for the lattice’s quasi-continuous model to confirm that the system supports a homoclinic pulse. Experimental results directly confirmed the annihilation of counter-propagating self-sustained pulses.
The author reported that the self-sustained waves annihilate during a head-on collision. In addition, he reported that owing to this phenomenon, a tunnel diodes oscillator lattice acts as an efficient frequency divider through its simple connection to an ordinary LC ladder circuit.
In summary, the study presented a frequency division scheme, which utilizes the annihilation of solitary pulses in a tunnel diodes oscillator lattice. This study experimentally validated this scheme. Based on the outlined workflow, it was established that in principle, the division ratio can be increased to 2m:1 when properly designed lattice networks are cascaded m times. In a statement to Advances in Engineering, Professor Koichi Narahara mentioned that the proposed frequency division scheme was compatible with voltage-controlled oscillation and can be efficiently introduced in integer-N phase-locked loop. He further added that by replacing tunnel diodes with state-of-the-art resonant tunneling diodes, the proposed scheme can be possibly applied to frequency division in submillimeter wave frequencies.
Koichi Narahara. Self-sustained solitary waves in a tunnel diode oscillator lattice and their applications in frequency division. International Journal of Circuit theory and Applications 2021; Volume 49: page 505–512.