Good on you Mr Al; As usual you bring a beautifully simple way of expressing the subject.
There was a couple of comments posted about the National circuit and the diagram seemed to come from some location and NOT a NS databook and did not include the comment. I happened to have the original Application Note and thought it may be of interest; so I opened up. Also, Mr. Nigel in post 9 asked about the bootstrapping to the drain and what was it for.
We 'did' the cathode follower in my engineering school in 1962, and I had not seen the adaptation to actually boot strap the grid (inphase) AND the anode (antiphase) to bootstrap out the anode to cathode impedance effects due to the anode to grid (drain to gate) capacitance. These effects are present in the FET as well. The whole mechanism is analogous to guarding in bridge arrangements. The beauty of the NS circuit is the 'guarding' of both the real part and the imaginary part of the input admittance.
My TEK 564 has the small RCA subminiature triodes as input buffers and the input admittance is just swamped with extra capacitance rather than the NS trick of bootstrapping it. The bandwidth of the TEK is only 10 mHz, so when you say the effect has some time delay, this puts an upper limit to the ultimate bandwidth achievable with this technique.
There was a couple of comments posted about the National circuit and the diagram seemed to come from some location and NOT a NS databook and did not include the comment. I happened to have the original Application Note and thought it may be of interest; so I opened up. Also, Mr. Nigel in post 9 asked about the bootstrapping to the drain and what was it for.
We 'did' the cathode follower in my engineering school in 1962, and I had not seen the adaptation to actually boot strap the grid (inphase) AND the anode (antiphase) to bootstrap out the anode to cathode impedance effects due to the anode to grid (drain to gate) capacitance. These effects are present in the FET as well. The whole mechanism is analogous to guarding in bridge arrangements. The beauty of the NS circuit is the 'guarding' of both the real part and the imaginary part of the input admittance.
My TEK 564 has the small RCA subminiature triodes as input buffers and the input admittance is just swamped with extra capacitance rather than the NS trick of bootstrapping it. The bandwidth of the TEK is only 10 mHz, so when you say the effect has some time delay, this puts an upper limit to the ultimate bandwidth achievable with this technique.