Hello,
I hope you can help me.
We need to use multiplexers in a sensor circuit. The circuit is like the drawing below.
I got a big voltage glitch at every edge of switching on when using ADG608.
Here are 3 questions.
- Q1 Glitch Voltage Calculation
δVout＝QINJ/Cload
Because there is no Cload after MUX in my circuit,
Is it correct to only use Cd for calculation?
For example,QINJ≒2pC @Vsource＝2.5V Cd=40~54pF
So δVout＝QINJ/CD=2/54*1000=37mV
After amplifier δVout will be 37*11=407mV
But what I see is that the voltage glitch is much bigger (about 2V),can you tell me the reason?
- Q2 @Vsource＝2.5V why I got a negative voltage drop?
From the plot of QINJ vs Vsource, I can see the QINJ is always positive during VDD=+5 VSS=0V
I guess that's because the QINJ result got in the test circuit is under the condition of switching off,
and my negative voltage is happening at the switching on. So it is the opposite.
Is my understanding correct?
- Q3
If my understanding is correct, let's get back to Q1
Because the voltage glitch takes place at switching on,
does that mean I need to take the capacitance of input into consideration for δVout calculation?
or the glitch is happening at the just turning of switching on&off ,
the MOS channel is not thoroughly on ,so the input capacitance will not have an effect on the calculation?
After all, I'm now using ADG1208, the voltage glitch issue has improved quite a bit.
