ADA4817-1ARDZ-R7 datasheet(26/29 Pages) AD

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Data Sheet

ADA4817-1/ADA4817-2

APPLICATIONS INFORMATION

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Rev. H | 26 of 29

HIGH SPEED JFET INPUT INSTRUMENTATION

AMPLIFIER

Figure 66 shows an example of a high speed instrumentation ampli-

fier with a high input impedance using the ADA4817-1/ADA4817-2.

The dc transfer function is

VOUT= VN−VP 1+2RFRG

(15)

For G = 1, it is recommended that the feedback resistors for the two

preamps be set to 0 Ω and the gain resistor be open.

The system bandwidth for G = 1 is 400 MHz. For gains higher than

2, the bandwidth is set by the preamp, and it can be approximated

In-amp−3 dB = (fCR × RG)/(2 × RF)

(16)

The match of resistor ratios, R1:R2 to R3:R4, primarily determine

the common-mode rejection of the in-amp and it is estimated by

VOVCM

= δ1−δ21+δ1δ2

(17)

The summing junction impedance for the preamps is equal to RF

|| 0.5(RG). Keep this value relatively low to improve the bandwidth

response like in the previous example.

Figure 66. High Speed Instrumentation Amplifier

ADA4817-1ARDZ-R7 数据表(PDF) 26 Page - Analog Devices