Datasheet AD648 (Analog Devices) - 10

AD648 INSTRUMENTATION AMPLIFIER
the common-mode range, with a common-mode impedance of The AD648J’s maximum input current of 20 pA per amplifier over 1 × 1012 Ω. The capacitors C1, C2, C3 and C4 compensate makes it an excellent building block for the high input impedance for peaking in the gain over frequency which is caused by input instrumentation amplifier shown in Figure 29. Total current capacitance. drain for this circuit is under 600 µA. This configuration is To calibrate this circuit, first adjust trimmer R1 for common- optimal for conditioning differential voltages from high imped- mode rejection with 10 V dc applied to the input pins. Next, ance sources. adjust R2 for zero offset at VOUT with both inputs grounded. The overall gain of the circuit is controlled by RG, resulting in Trim the circuit a second time for optimal the following transfer function: performance. V The –3 dB small signal bandwidth for this low power instru- OUT = 1+ (R3 + R4) mentation amplifier is 700 kHz for a gain of 1 and 10 kHz for a VIN RG gain of 100. The typical output slew rate is 1.8 V/µs. Gains of 1 to 100 can be accommodated with gain nonlinearities of less than 0.01%. The maximum input current is 30 pA over Figure 29. Low Power Instrumentation Amplifier –10– REV. E