Data Sheet

ADA4870

APPLICATIONS INFORMATION

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Rev. B | 23 of 24

COMPOSITE AMPLIFIER

When dc precision and high output current are required, the

ADA4870 can be combined with a precision amplifier such as the

ADA4637-1 to form a composite amplifier as shown in Figure 77.

By placing the ADA4870 inside the feedback loop of the

ADA4637-1, the composite amplifier provides the high output cur-

rent of the ADA4870 while preserving the dc precision of the

ADA4637-1.

Figure 77. Composite Amplifier

Figure 78 shows the bandwidth of the composite amplifier at a gain

of 10. The offset voltage at the output is <500 μV.

The circuit can be tailored for different gains as desired. Depend-

ing on the board parasitics, the 6 pF capacitor may need to be

empirically adjusted to optimize performance. Minimize PCB stray

capacitance as much as possible, particularly in the feedback path.

The small signal and large signal pulse response is shown in Figure

79 and Figure 80, respectively.

Figure 78. Composite Amplifier Frequency Response

Figure 79. Composite Amplifier Small Signal Pulse Response

Figure 80. Composite Amplifier Large Signal Pulse Response