Figure 2 shows the recommended test circuit. When using SPICE simulation for audio applications or circuits where large-signal input steps are common (such as those with multiplexers or switches), I recommend verifying the slew rate behavior of your op amp model. In audio applications, for example, slew limiting distorts sine waves into triangle waves, causing visible (and audible) distortion, as shown in Figure 1.įigure 1: Triangular distortion caused by slew rate limit One of the most common ways to force an op amp into slew rate limit is to apply a large-signal input step of 100mV or greater, but slew limiting can also occur when trying to output high-amplitude signals at high frequencies. For a more detailed look at slew rate, watch our TI Precision Labs – Op Amps video series on slew rate. This continues until the op amp corrects the difference at its input pins and the amplifier returns to a linear or small-signal operating state. Instead, the op amp output voltage changes with a constant slope.

An amplifier in this condition is not behaving linearly where the output voltage equals the input voltage multiplied by the closed-loop gain. Slew rate is a type of output distortion, or nonlinearity. Slew rate is defined as the maximum rate of change of an op amp’s output voltage and is typically given in volts per microsecond (V/µs). In part 3, I’ll continue by explaining how to verify an operational amplifier (op amp) model’s slew rate, which is a large-signal output response. Previous installments of this blog post series discussed the need to verify SPICE model accuracy and how to measure common-mode rejection ratio (CMRR) and offset voltage versus common-mode voltage (V OS vs. Other Parts Discussed in Post: OPA196, OPA1678

Ltspice two stage op amp