Resonant frequency and maximum signal width
Using the term &quot;resonance&quot;, one should - at first - know what it means and how it is defined.
I am pretty sure that &quot;resonance&quot; is commonly understood as the state of a frequency-dependent part or network when there is no phase shift between voltage and current.
In many cases, this is identical with the voltage maximum at the ouput node of the network. But this is not always the case. When there is no frequency that can fulfill this &quot;resonant condition&quot;, the corresponding network has no resonant point.
Classical networks: Bandpass and band stop filters.
However, lowpass and highpass netwoks can produce resonant points when they are combined with inverting amplifiers. This is the working principle for phase-shift oscillators: A third-order network produces (at one single frequency) a phase shift of 180deg, which - together with the inverting property of the amplifier - results in zero deg phase shift (resonance)  .