Add a 0.5 pF load capacitor from the output to ground to the integrator in Fig. 7.50. When this capacitor is added, the circuit has a loop of three capacitors. Direct application of the short-circuit time constant method here gives zero for each short-circuit time-constant. The problem here is that three short-circuit time constants are being calculated for the three capacitors, and the sum of the reciprocal of these time constants equals the sum of three poles, as shown in (7.146). However, this circuit has only two poles because only two of the capacitor voltages are independent. An alternative approach to estimating the nondominant pole is to calculate the zero-value time constants and determine if one zero-value time constant is much larger than the others. If so, the capacitor associated with the largest zero-value time constant is shorted, and one time constant for the remaining capacitors, which are in parallel, is the short-circuit time constant. Carry out these steps, and compare the estimated nondominant pole with a SPICE simulation.

Figure 7.50:

R, Cn Vo V Vx