The OPA817 features a unique combination of high GBWP, low-input voltage noise, and the DC precision of a trimmed JFET-input stage to provide a high input impedance for a voltage-feedback amplifier. Figure 9-2 shows how its very high GBWP of 400 MHz and high large signal bandwidth of 250 Mhz can be used to either deliver wide signal bandwidths at high gains or to extend the achievable bandwidth or gain in typical high-speed, high-input impedance data acquisition front-end applications. To achieve the full performance of the OPA817, careful attention to the printed circuit board (PCB) layout and component selection is required as discussed in the following sections of this data sheet. OPA817 also features a wider supply range thereby enabling a wider common-mode input range to support higher input signal swings.

Figure 9-1 shows the noninverting gain of +2 V/V circuit used as the basis for most of the Typical Characteristics. Most of the curves were characterized using signal sources with 50-Ω driving impedance, and with measurement equipment presenting a 50-Ω load impedance. As Figure 9-1 shows, the 49.9-Ω shunt resistor at the V_IN terminal matches the source impedance of the test generator, while the 49.9-Ω series resistor at the V_O terminal provides a matching resistor for the measurement equipment load. Generally, data sheet voltage swing specifications are at the output pin (V_O in Figure 9-1) while output power specifications are at the matched 50-Ω load. As shown in Figure 9-1, the total 100-Ω load at the output combined with the 250-Ω total feedback network load presents the OPA817 with an effective output load of 83.3 Ω for the circuit.

Voltage-feedback operational amplifiers, unlike current feedback amplifiers, can use a wide range of resistor values to set their gain. As Figure 9-1 shows, the parallel combination of R_F || R_G should always be kept to a lower value to retain a controlled frequency response for the noninverting voltage amplifier. In the noninverting configuration, the parallel combination of R_F || R_G will form a pole with the parasitic input capacitance at the inverting node of the OPA817 (including layout parasitic capacitance). For best performance, this pole should be at a frequency greater than the closed loop bandwidth for the OPA817.