Circuit Stability Precautions: Power Supply Decoupling – Feedback along supply lines is another source of op-amp circuit instability. This can be minimized by connecting 0.01 μF high-frequency capacitors from each supply terminal to ground (see Fig. 15-23). The capacitors must be connected as close as possible to the IC terminals. Sometimes larger values capacitors are …
Load Capacitance Effect: Capacitance connected at the output of an operational amplifier is termed Load Capacitance Effect (CL). Figure 15-20 shows that CL is in series with the op-amp output resistance (ro), so CL and ro constitute a phase-lag circuit in the feedback network. As in the case of stray capacitance, another 10° of phase lag …
Stray Capacitance Effects: Stray Capacitance Effects (Cs) at the input terminals of an operational amplifier effectively introduces an additional phase-lag network in the feedback loop, (see Fig. 15-17), thus making the op-amp circuit unstable. Stray capacitance problems can be avoided by good circuit construction techniques that keep the stray to a minimum. The effects of …
Op Amp Circuit Bandwidth and Slew Rate Test: Low Cutoff Frequency – Op Amp Circuit Bandwidth and Slew Rate Test are direct-coupled internally, so where they are employed in direct-coupled applications, the circuit lower cutoff frequency (f1) is zero. In capacitor-coupled circuits, the lower cutoff frequency is determined by the selection of coupling capacitors. The …
Frequency Compensation Methods: Phase-Lag and Phase-Lead Compensation – Lag compensation and lead compensation are two Frequency Compensation Methods often employed to stabilize op-amp circuits. The phase-lag network in Fig. 15-7(a) introduces additional phase lag at some low frequency where the op-amp phase shift is still so small that additional phase lag has no effect. It …
Operational Amplifier Circuit Stability: Loop Gain and Loop Phase Shift – Consider the inverting amplifier circuit and waveforms in Fig. 15-1(a). The signal voltage voltage (vs) is amplified by a factor R2/R1, and phase shifted through -180°. The Operational Amplifier Circuit Stability is redrawn in Fig. 15-1(b) to illustrate the fact that the output voltage …
