About SPICE |
SPICE Basics |
Running SPICE |
CIRCUIT COLLECTION
SPICE Commands |
SPICE Downloads |
About |
Contact Us |
Home
Schematic: Op_Amp_cstray.asc
Open Loop Sch: Op_Amp_cstray - OL.asc
Op Amp Symbol: Opamp_2.asy
Op Amp Shematic: Opamp_2.asc
Right Click on filename, select "Save link as...",
Back to Design Series
Intro You can't avoid these unwanted effects in your op amp circuit:
• stray capacitance on PCB traces from R1, R2 junction to the op amp's negative input.
• parasitic capacitance internal to op amp device at input pins.
So, how does it effect your design?
These capacitances form a low-pass filter which can lead to ringing and oscillations!Definitions Cstray - the total capacitance due to PCB traces and active/passive devices on that node.
Ccomp - A physical cap added by the designer to compensate for Cstray.Design Goal A stable amplifier output (minimial overshoot and ringing). Design Spec Overshoot < 10% given Cstray = 10pF and a 0.1V step voltage input.
Step Response Phase (deg) Oscillations - UNSTABLE -360 (or 0) 40% Overshoot -330 (or +30) 25% Overshoot -315 (or +45) 10% Overshoot -300 (or +60) No Overshoot - Optimal Response --270 (or +90)
Back to Design Series...