simulation and laboratory

capacitance simulation

how are the impedance and capacitance taken in account in a spice simulation. These are examples of them :

osciloscope input: 1MΩ 13pF
test probe: 10MΩ 15pF

this values are in simulation set in series, parallel or how ?

STOIKOV said:

how are the impedance and capacitance taken in account in a spice simulation. These are examples of them :

osciloscope input: 1MΩ 13pF
test probe: 10MΩ 15pF

this values are in simulation set in series, parallel or how ?

Click to expand...

Fairly correct model with your value and 3 dB roll of around 12 MHz on 1 kOhm source. 15 pF probe-tip must have 135 pF total capacitive load in backend for curve fidility (square wave displays square wave on oscilloscope) - and this fact setting maximum frequency compare to source impedance and make no difference between oscilloscope with 13, 20 and 30 pF capacitive input (tuning cap compensate for difference in ports capacitance...).

Note R4, R5, R6 is important to terminate and attenuate ringing effect (reflex) between probe and oscilloscope port via coax-cable - is not true power matched system ie want high measure impedance, so... , R6 is many case inbuild in oscilloscope.


transmissions line simulate in Microcap needs heavy computing and not work so well (DC-offset can drift away - typical numeric calculate error)

So, for regular simulate of oscilloscope measure in simulator - use simplified model for very little difference to full scale model.