There are various applications which require the chaos oscillators working with autonomous limited time power supplies. in this connection, there is a problem of increasing efficiency of the oscillators. It is known that many chaos oscillators based on a bipolar transistor as active element have a low efficiency (a few per cent). The fact is that the transistor performs simultaneously two functions in a wide frequency band namely an amplifier and a nonlinear element. The work of the transistor in such conditions leads to low energy efficiency of the oscillator.
Chaos generator model based on active and passive oscillators interaction is discussed in the article. In this case, transistor play the role of an active element while oscillating circuit with nonlinear capacitor performs the function of a basic nonlinear element. The function of the nonlinear capacitor may perform, for example, p-n transition of the transistor or a special diode. In this case, it does not require an additional power supplies. Interaction measure between passive and active oscillators is determined by its interconnection level. Thus, additional conditions as to chaos generation so to increasing efficiency of the oscillator are realized in the system.
The study has been carried out by means of a special software package ADS. This package allows us to perform a simulation in microwave frequency range. Bipolar transistor BFQ621 played the role of the active element of the oscillator. Limiting frequency of this transistor is 7 GHz. On the other hand, oscillating circuit consisting of 5 nH inductor and 1 pF capacity played the role of passive nonlinear oscillator. One of p-n transitions of microwave transistor BFР620F performed the function of nonlinear capacitor (varactor diode). Above transistor has 60 GHz cut off frequency. In addition, the second transition of this transistor may be used as an additional nonlinearity to improve of characteristics of the oscillator output signal.
The model demonstrates a stable generation of chaotic oscillations in the 1-5 GHz range with an average efficiency 16%. In the article, the upper limit of oscillator efficiency for a chaotic mode is analyzed. It is shown, that it can be up to 40 % of maximum efficiency of the oscillator in the harmonic oscillating mode.