Concept of Bootstrapping in Electronics

Question

I was trying to study about bootstrapping in electronic circuits.

When I checked in Internet Wiki says it is a method to improve the input impedance of an amplifier.

In the power electronics context, it has another definition.(https://techweb.rohm.com/knowledge/dcdc/dcdc_sr/dcdc_sr01/829). Here it has another meaning (https://m.eet.com/media/1152270/24127-45890.pdf).

Could you please clarify bootstrapping?

See an early post of mine from years ago at bootstrapping to increase input impedance and a more recent one using bootstrapping to create a current source for two examples. — jonk, Aug 07 '20 at 07:18
I also found this one where I spent more time discussing details of the bootstrap loop used to create a current source. — jonk, Aug 07 '20 at 07:24
Is it bad that there are so many meanings? There is nothing in the English language that suggests that the same word must mean similar meanings in different contexts. Here is another one, the word boot (as in boot your computer) comes from the shortened form of the word bootstrap (a computer), which comes from a phrase "pull oneself up by their own bootstraps" which is impossible, yet computers do it all the time. — Voltage Spike, Aug 07 '20 at 23:29

score 4 · Accepted Answer · edited May 09 '23 at 06:19

Bootstrapping, in both usages, means the arrangement of TWO nodes of the circuit that are coupled in such a way that one (controlled) node will closely follow the (controller) node.

If an emitter-follower uses the emitter output voltage to drive the collector voltage, then the Cob is removed from the Cin computation. This requires a large resistor in the collector to VDD, otherwise the emitter would not be able to move the collector voltage. A bipolar with Cob of 5pF, and a bootstrap cap from emitter to collector of only 5pF, will not optimally minimize the input capacitance; notice this is positive feedback, and some configurations of this are called "oscillators".
Another use is in high_side switching, using N-Channel FETs; a special capacitor Cboot must be charged up, and then charge is stolen from Cboot to control the Cgate of the FET during each switching cycle.
Also, the standard OpAmp non_inverting gain configuration is "bootstrapping" in that differential input capacitance is largely ignorable, as is differential input current. Thus the primary Rin (aka Zin) becomes the common_mode behavior. Note the Miller Multiplication (by non_cascoded input diffpairs) remains a problem; and during slewing, there is no Miller Multiplication, making the Cin become highly NON_LINEAR and upsetting the settling behavior.

Please read the comments by "jonk" and examine his links.

I still keep encountering novel bootstrapping ideas. And the creativity of others in finding novel ways to use the basic idea will outstrip my ability to accumulate them. So I continue to be amazed, at times, the new ways this old idea gets applied. So for the OP I'd want to say that this is more of a creative tool -- an idea that you carry in your mind and make sure to remind and ask yourself to consider when facing some circuit problem. Something might pop to mind. Mental concepts like this are hard to box up, but great when you see one and super if you manage to do something new with it! — jonk, Aug 07 '20 at 18:43

Concept of Bootstrapping in Electronics

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