/* Comparator and inverting Schmitt trigger */
kill(all)$ display2d:false$ fpprintprec:12$
print("OP-AMP COMPARATORS AND SCHMITT TRIGGER")$
beta:R2/(R1+R2)$
VTp:beta*VOH+(1-beta)*VR$
VTm:beta*VOL+(1-beta)*VR$
VH:ratsimp(VTp-VTm)$
print("Upper threshold =",VTp)$
print("Lower threshold =",VTm)$
print("Hysteresis width =",VH)$

/* Symmetric example. */
symp:ratsimp(subst([VOH=VS,VOL=-VS,VR=0],VTp))$
symm:ratsimp(subst([VOH=VS,VOL=-VS,VR=0],VTm))$
print("Symmetric thresholds =",symp,symm)$

/* Design from measured output levels and desired thresholds. */
VOHn:11.5$ VOLn:-10.8$ VTpn:2.5$ VTmn:-2.0$
betan:float((VTpn-VTmn)/(VOHn-VOLn))$
VRn:float((VTpn-betan*VOHn)/(1-betan))$
ratio:float((1-betan)/betan)$
print("Example beta =",betan)$
print("Required reference V_R (V) =",VRn)$
print("R1/R2 =",ratio)$

/* Zero-crossing timing offset. */
Vos:2e-3$ f:1000$ Vm:2$
dt:float(Vos/(2*%pi*f*Vm))$
print("Timing error for 2 mV offset, 2 V peak, 1 kHz (s) =",dt)$
quit();