As the name implies, a limiter circuit (sometimes called a “clipper”) prevents a signal from exceeding desired thresholds, which would otherwise cause saturation and overload of the following stage. The circuit in Figure 1 precisely limits the wideband input signal Vi at the VREF level and can be used with both single and dual power supplies.
Output signal Vo1 of the first stage, U1_1 (one-half of an LT1810, a dual 180-MHz, 350-V/µs low-distortion op amp), is precisely limited at the level of VREF , but with inverse polarity compared with the input signal. U1_1 has a gain of ‒1 for the input signal Vi, and a gain of +2 for the reference signal VREF.
Since the positive input of U1_1 is referenced to VREF, the output signal is referenced to 2 × VREF. Thus, while the input signal rises from zero to VREF, the output signal of the first stage decreases from 2 × VREF to VREF. The second stage of limiter U1_2 is an inverting amplifier with the gain of ‒1. It’s referenced to the VREF as well, and restores the original dc level and polarity of the input signal.