Comments on "Accurate Determination of Threshold Voltage levels of a Schmitt Trigger

It is shown that for an accurate determination of the two threshold voltages of a Schmitt trigger, the influence of the forward current amplification\betaand the internal ohmic base and emitter resistorsR_BandR_Eof the transistorsT_1andT_2may not be neglected. The hysteresis width of a real Schmitt trigger is smaller than calculated with the formula of Roy [1], because neither\betais infinite norR_BandR_Eare zero. A very accurate but simple formula for the threshold voltages is given, using an analysis similar to that of Roy.