The oscillation frequency is determined by the resistor and capacitor values. The following section provides details to calculate these component values.

Figure 8-8 Square-Wave Oscillator Timing Thresholds

First consider the output of figure Figure 8-7 is high, which indicates the inverted input V_C is lower than the noninverting input (V_A). This causes the C₁ to be charged through R₄, and the voltage V_C increases until it is equal to the noninverting input. The value of V_A at the point is calculated by Equation 7.

Equation 7.

If R₁ = R₂= R₃, then V_A1 = 2 V_CC/ 3

At this time the comparator output trips pulling down the output to the negative rail. The value of V_A at this point is calculated by Equation 8.

Equation 8.

If R₁ = R₂ = R₃, then V_A2 = V_CC/3

The C₁ now discharges though the R₄, and the voltage V_CC decreases until it reaches V_A2. At this point, the output switches back to the starting state. The oscillation period equals the time duration from 2 V_CC / 3 to V_CC / 3 then back to 2 V_CC / 3, which is given by R₄C₁ × ln2 for each trip. Therefore, the total time duration is calculated as 2 R₄C₁ × ln2. The oscillation frequency can be obtained by Equation 9:

Equation 9.