Charge injection on PIC10F220

[John Larkin]

That is not always true. The fraction of the charge that is placed on
the signal line during the time that the impedance of the transistor
is still low can be caused to flow to the ground by the existance of
the resistance in series.

Only if it bangs an ESD diode. And Marra specified a "low value
resistance" A series R can help if the injected charge is driving an
opamp nuts, by reducing peak current, but it won't reduce the charge
kicked into a capacitor, barring the esd diode thing.

This is a way that the size of the hold step in a sample and hold
circuit can be reduced at the cost of spreading out the acquire time.
The amount of reduction in charge can be quite a bit if the gate must
move a long way before the device starts to turn off.

I don't understand that. Where do the electrons go?

John

 

[MooseFET]

I don't understand that. Where do the electrons go?

Consider a snap shot of a small part of the turn off process in the
case of the FET going to ground:

Cgd Rx
Gate swing ---!!--+----/\/\/---+-- Vout
! !
\ !
/ Rds --- External
\ --- Capacitor
! !
GND GND


The gate is swinging down and the Rds value is about to start
increasing. If we assume a constant current in Cgd and a huge
external capacitor, we can say that the current splits between the two
paths in the ratio of the resistances.

At each instant in time, Rds has some value. As time goes by, the
Rds value is increasing. When the Rds value becomes more than the Rx,
most of the current will start to charge the capacitor. If the Rx
value is very small, more of the charge ends up in the capacitor than
if it is larger.

In the sample and hold case, the GND end of Rds is driven by a low
impedance voltage source but the added resistor's function remains the
same.

 

[Phil Hobbs]

[.....]

Meanwhile, in baseball,
the last-place NY Yankees pulled ahead on a homer by A-Rod, to
win by one run against the first-place Boston Red Sox. > Sigh.

So did the right or wrong team win?

It's only a game.

John

Yeah, but the Bostonians had--what was it, 83 years?--to get all bent
out of shape about not winning the World Series, and now they're stuck.

Cheers,

Phil Hobbs