DESIGN AND DEVELOPMENT OF MEDICAL ELECTRONIC ...

32 BIOPOTENTIAL AMPLIFIERSgenerator. Connect the output of the signal generator to the noninverting input (J1-2) of the biopotential amplifier.7. Adjust the signal generator to produce a sinusoidal wave with an amplitude of1mV p-p at a frequency within the passband of the filter configuration selected.8. Check that changes in the configuration of JP1 and JP2 cause correspondingchanges in the amplitude of the output signal.9. Set the gain to 10, and using the second channel of the oscilloscope, check thatthere is no phase difference between the signal at the output of the ICIA and that atthe noninverting input.10. Without changing the settings of the instruments, short the noninverting (J1-3) inputterminal of the biopotential amplifier to the subject ground terminal (J1-1,4), andconnect these to the ground terminal of the signal generator. Connect the output ofthe signal generator to the inverting input (J1-2) of the biopotential amplifier.11. Verify that the output signal is an amplified and inverted version (opposite phase)of the input signal. Verify that the gain remained constant.While the signal generator is connected, monitor the output of the biopotential amplifierwhile increasing and decreasing the frequency of the signal generator. You can verify yourchoice of components used for the filter stages by observing that the decay in output amplitudeindeed occurs at the expected frequencies. The procedure is as follows:1. Set the gain of the biopotential amplifier front gain to unity.2. Adjust the input sine wave to exactly 0.07 V and the frequency to the midpoint ofthe bandpass expected. Make this adjustment as accurately as possible.3. Check that the output signal is of the amplitude expected. Readjust the signal generatorif necessary.4. Slowly increase the input frequency until the output amplitude decreases to 0.05 V(70.7% of the midrange gain). Measure the frequency at this point. This is the highfrequencycutoff point of the biopotential amplifier.5. Repeat the preceding steps for gain factors of 10, 100, and 1000 using appropriatesettings for the signal generator and the oscilloscope.6. Reset the gain of the biopotential amplifier front end to unity.7. Connect a 1-µF nonpolar capacitor in series between the signal generator and theinput to the biopotential amplifier.8. Slowly sweep the frequency of the input signal starting from dc and measure thefrequency at the two points where the output signal is 0.05 V (70.7% of themidrange gain). This is the low-frequency cutoff point of the biopotential amplifier.9. Plot the response of this last configuration on a semilogarithmic graph.This amplifier is suitable for applications involving low-level low-frequency signals.Thus, you may want to measure the amplifier’s equivalent noise level. To do this you willneed a digital storage oscilloscope or chart recorder. Follow this procedure:1. Short both inputs of the biopotential amplifier to the patient ground terminal.2. Connect the oscilloscope to the output of the biopotential amplifier.3. Set the oscilloscope for a 10-second total sweep and dc coupling.4. Set the overall gain of the biopotential amplifier to 100,000.5. Set the gain of the oscilloscope up to a point where the peak events of the widefuzzy noise signal can be measured.