SIGNAL CONDITIONING, DATA ACQUISITION, AND SPECTRAL ANALYSIS - Design and Development of Medical Electronic Instrumentation - page 231

Figure 5.14 cial ECG test signal generated by an Agilent 33120A ARB was acquired using the circuit of Figure 5.13 and a soft-

ware FM demodulator. Note that the demodulated signal faithfully reproduces the dc of

An arti fi

ff set and low-frequency components of the ECG.

channel needs. For example, Table 5.4 shows some of the IRIG subcarrier frequencies and
FM deviations used to yield channels whose bandwidths are constant and independent of
their carrier frequency. On the other hand, Table 5.5 shows some choices for subcarrier fre-
quencies and deviations which result in channels where their bandwidth is proportional to
their carrier frequency. For a consumer-grade sound card, the maximum sampling rate is
44.1 kHz, which imposes an absolute maximum tone frequency limit of around 18 kHz,
which ultimately constrains the number of channels that can be sampled simultaneously
with the FM carrier technique.
IRIG publications can be ordered from:

Defense Technical Information Center
Attn: DTIC-OCP
John J. Kingman Road, Suite 0944
Fort Belvoir, VA 22060-6218
[phone]
[phone] (fax)

The complete VCO circuit of Figure 5.13 (one channel) can be built for under $10. How-
ever, if you have a cost-sensitive application that can tolerate somewhat lower precision and