Using a negative impedance
converter, the resistance of the coil can be compensated or the circuit can be converted to a Non-Foster circuit which has more bandwidth and a gyrator would allow to replace the capacitor by a second inductor (which would also couple to the magnetic field) [22-24].
1 consists of two operational amplifiers: A1 which is the Wien-bridge oscillator and A2, which acts as a negative impedance
converter (NIC) at higher levels of voltage on the capacitor C3, (see  for the in-depth of the functioning).
converter with reduced nonideal gain and parasitic impedance effects.
From the negative impedance
model, cavity type and DROs to the general feedback type, all oscillators" have one common property.
It uses a negative impedance
drive with powerful driving and damping capabilities to drive the speakers in such a way that the air itself acts as a diaphragm, or "air woofer," allowing even small cabinets to reproduce the same bass range as large speakers.
The equations in Table 1 also consider that the variation of the negative impedance
circuit is small with the frequency; this variation is smaller if the resonant circuit on the left side of the division plane has a high Q.
Note that, for practical purposes, it may be preferable to avoid using a transmission line with a negative impedance
; however, the line with negative impedance
can be easily substituted with a positive impedance line and a dependent voltage source.
To obtain information concerning the oscillator startup reliability, it is useful to simulate the negative impedance
of the circuit.
Therefore, care must be taken when selecting the plane to measure the negative impedance
of the oscillator.
Howes, "A Reflection Coefficient Approach to the Design of One-Port Negative Impedance
Oscillators," IEEE Transactions on Microwave Theory and Techniques, Vol.
Improved elements include OCPL, a model of the end effect of the open end of two coupled microstrip lines; MCPL, to model up to ten coupled transmission lines; CAB, a coaxial cable model; and NIC, a negative impedance
converter element model.
When negative impedances
are involved in design, visualizing the Smith chart as a three-dimensional (3-D) sphere rather than a 2-D circle the Smith chart can perform greater insight .