ADA4817-1ARDZ-R7 datasheet(21/28 Pages) AD

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Data Sheet

ADA4817-1/ADA4817-2

Rev. B | Page 21 of 28

HIGH SPEED JFET INPUT INSTRUMENTATION

AMPLIFIER

Figure 53 shows an example of a high speed instrumentation

amplifier with a high input impedance using the ADA4817-1/

ADA4817-2. The dc transfer function is

(

)













−

OUT

(16)

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 by

In-amp−3dB = (fCR × RG)/(2 × RF)

Common-mode rejection of the in-amp is primarily determined by

the match of resistor ratios, R1:R2 to R3:R4. It can be estimated by

(

)

(

) 2

−

(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.

VCC

VEE

10µF

0.1µF

10µF

0.1µF

RS1

350Ω

ADA4817-1

VCC

VEE

VCC

VEE

350Ω

RS2

10µF

0.1µF

10µF

0.1µF

350Ω

RF = 500Ω

10µF

0.1µF

10µF

0.1µF

ADA4817-2

Figure 53. High Speed Instrumentation Amplifier

ADA4817-1ARDZ-R7 Datasheet(PDF) 21 Page - Analog Devices

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