Book Analog Interfacing to Embedded Microprocessors
rejecting differential amplification of the differential amplifier. The instrumentation
amplifier provides this capability. Figure A.6 shows an instrumentation amplifier circuit
using three opamps. The input impedance of the instrumentation amplifier is equal
to the input impedance of the two input opamps.
Instrumentation amplifiers do not need to be built from discrete opamps and resis-
tors, but are available as discrete ICs. For example, the AD624 from Analog Devices is
available in a 16-pin package. The AD624 can be programmed for a gain of 1, 100,
200, 500, or 1000 by connecting various pins on the package together. An integrated
instrumentation amplifier uses laser-trimmed resistors, providing very good matching
and excellent accuracy.
Appendix A 243
Figure A.6
Instrumentation amplifier.
244 Appendix A
Appendix B
PWM
annaabi.ee 
