BIOPOTENTIAL AMPLIFIERS - Design and Development of Medical Electronic Instrumentation - page 32

generator. Connect the output of the signal generator to the noninverting input (J1-
2) of the biopotential ampli

er.
7. Adjust the signal generator to produce a sinusoidal wave with an amplitude of
1mV p-p at a frequency within the passband of the

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fi filter con fi guration selected.

8. Check that changes in the con guration of JP1 and JP2 cause corresponding

changes in the amplitude of the output signal.
9. Set the gain to 10, and using the second channel of the oscilloscope, check that
there is no phase di

fi

erence between the signal at the output of the ICIA and that at
the noninverting input.
10. Without changing the settings of the instruments, short the noninverting (J1-3) input
terminal of the biopotential ampli

ff

er to the subject ground terminal (J1-1,4), and
connect these to the ground terminal of the signal generator. Connect the output of
the signal generator to the inverting input (J1-2) of the biopotential ampli

fi

fi er.

11. Verify that the output signal is an ampli ed and inverted version (opposite phase)

of the input signal. Verify that the gain remained constant.

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er
while increasing and decreasing the frequency of the signal generator. You can verify your
choice of components used for the

While the signal generator is connected, monitor the output of the biopotential ampli fi

filter stages by observing that the decay in output ampli-
tude indeed occurs at the expected frequencies. The procedure is as follows:

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1. Set the gain of the biopotential ampli er front gain to unity.

2. Adjust the input sine wave to exactly 0.07 V and the frequency to the midpoint of
the bandpass expected. Make this adjustment as accurately as possible.
3. Check that the output signal is of the amplitude expected. Readjust the signal gen-
erator if 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 high-
frequency cutoff

fi

er.
5. Repeat the preceding steps for gain factors of 10, 100, and 1000 using appropriate
settings for the signal generator and the oscilloscope.
6. Reset the gain of the biopotential ampli

ff point of the biopotential ampli fi

fi er front end to unity.

7. Connect a 1- F nonpolar capacitor in series between the signal generator and the

input to the biopotential ampli

µ

er.
8. Slowly sweep the frequency of the input signal starting from dc and measure the
frequency at the two points where the output signal is 0.05 V (70.7% of the
midrange gain). This is the low-frequency cutoff

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ff point of the biopotential ampli fi er.

9. Plot the response of this last con fi guration on a semilogarithmic graph.

er is suitable for applications involving low-level low-frequency signals.
Thus, you may want to measure the ampli

This ampli fi

er's equivalent noise level. To do this you will
need a digital storage oscilloscope or chart recorder. Follow this procedure:

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1. Short both inputs of the biopotential ampli er to the patient ground terminal.

2. Connect the oscilloscope to the output of the biopotential ampli

fi

er.
3. Set the oscilloscope for a 10-second total sweep and dc coupling.
4. Set the overall gain of the biopotential ampli

fi

er to 100,000.
5. Set the gain of the oscilloscope up to a point where the peak events of the wide
fuzzy noise signal can be measured.

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