OPA818 datasheet(12/27 Pages) TI1

12 / 27 page

301

±5 V

+5 V

49.9

0.01 …F

0.22 …F

0.01 …F

0.22 …F

49.9

VIN

49.9

Source

Load

OPA818

SBOS940 – MAY 2019

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8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

8.1.1 Wideband, Noninverting Operation

The OPA818 provides a unique combination of high GBWP, low-input voltage noise, and the DC precision of a

trimmed JFET-input stage to provide an exceptional high input impedance for a voltage-feedback amplifier. Its

very high GBWP of 2.7 GHz can be used to either deliver high-signal bandwidths at high gains, or to extend the

achievable bandwidth or gain in photodiode-transimpedance applications. To achieve the full performance of the

OPA818, careful attention to printed circuit board (PCB) layout and component selection is required as discussed

in the following sections of this data sheet.

Figure 12 shows the noninverting gain of +7 V/V circuit used as the basis for most of theTypical Characteristics:

VS = ±5 V. Most of the curves were characterized using signal sources with 50-Ω driving impedance, and with

measurement equipment presenting a 50-Ω load impedance. In Figure 12, the 49.9-Ω shunt resistor at the VIN

terminal matches the source impedance of the test generator, while the 49.9-Ω series resistor at the VO terminal

provides a matching resistor for the measurement equipment load. Generally, data sheet voltage swing

specifications are at the output pin (VO in Figure 12) while output power specifications are at the matched 50-Ω

load. The total 100-Ω load at the output combined with the 350-Ω total feedback network load, presents the

OPA818 with an effective output load of 78 Ω for the circuit of Figure 12.

Figure 12. Noninverting G = +7 V/V Configuration and Test Circuit

Voltage-feedback operational amplifiers, unlike current feedback products, can use a wide range of resistor

values to set their gain. To retain a controlled frequency response for the noninverting voltage amplifier of

Figure 12, the parallel combination of RF || RG should always be less than 50Ω. In the noninverting configuration,

the parallel combination of RF || RG will form a pole with the parasitic input capacitance at the inverting node of

the OPA818 (including layout parasitics). For best performance, this pole should be at a frequency greater than

the closed loop bandwidth for the OPA818.

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