The THS3491 is designed to produce better than 40 dB SFDR while driving a 100-MHz, 20-V_pp signal into a 100-Ω load. To accomplish this, the geometries of certain signal path transistors must be limited. As a result of this limitation, some internal devices begin to saturate when large signal levels are input at frequencies greater than 100 MHz. When these devices saturate, the loop opens and the amplifier is no longer in linear operation. This appears as a gain step-up in the frequency response curve. To avoid this phenomenon, applications must comply with the recommended linear operating region shown in Figure 9-4. Figure 9-4 shows the maximum output voltage vs frequency that is permitted to keep the amplifier in linear operation.

Figure 9-4 Maximum Recommended Output Voltage vs Frequency