Interesting idea Nelson. How would you go about it?It would be trivial to turn the second diff pair into a cascode for the first
diff pair. I bet that would improve things.
I suppose one could also bypass the second diff pair all together (now Miller compensation might be required on the VAS though).
I wouldn't go so far as to say that it is an internal resistance or impedance between the plate and grid of a triode. Think of it as an interaction of electric fields, and the influences they have on one another.
Remember, the triode has the benefit of a very high input impedance, and that is one benefit that dies a miserable death as soon as we implement Schade fb around a MOSFET using external resistors.
The feedback in a triode results from the influence of the plate's electric field on the grid's electric field. It is this influence (local nfb) that results in the triode's unique characteristic of output curves.
That is not free . The bill will come due soon enough.I just had a free lunch……. without any negative feedback!
my wife paid the bill!
.You're both right. Since capacitive reactance is, strictly speaking, an impedance, and because an interaction between the charge on two conductors (plate and grid for example) through a common electric field is how capacitance is defined, then they are the something. It just depends on what level of abstraction you find convenient and that is consistent with the underlying assumptions (i.e., the circuit theory approximation). At audio frequencies either modeling abstraction can be used.
I may start playing with a sjep120r100 used as a common source amp but have a question about the bias. Looking at the data sheet it looks like on a warm heat sink i will need about 1.2v or call it 1.5v if I use a small source resistor. But then I see this 220 ma gate current at 3v GS ? Is this something to be worried about or in normal operation ? I was actually hoping to just use a 1.56V carbon battery as the bias supply if the current drain was below 1 ma.
Shouldn't be a problem. The "leakage" current at 3 V is really the forward bias current of the gate-source pn junction. It's like forward biasing any diode, as the forward-bias voltage increases the forward-bias current increases exponentially. But this works the other way, too!. So, the forward bias current at 1.5 V is exponentially smaller than the value quoted at 3 V. I would expect less than 1 mA.
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