Design an EKG amplifier interface to a 9S12 (Figure 12.64). The biopotential is a ±5 mV signal measured between the left and right arms using silver-silver chloride electrodes. A third electrode is placed on the right leg and is used as a reference. To make the entire system battery-operated, low-power, rail-to-rail TLC2274 op amps will be used, each powered with +5 and ground. Notice that the analog system uses the 2.5 V signal as its reference.
Figure 12.64
a) Design the preamplifier that has the following characteristics: differential input, gain = 10, good CMRR, high Zin, low Zout, bandwidth > 200 Hz. Show resistor values, but not pin numbers.
b) Show the amplifier stage that has the following characteristics: single input, gain = 250, high Zin, low Zout, bandwidth > 200 Hz. Show resistor values, but not pin numbers.
c) The signals of interest are 0.1 to 100 Hz. There is unwanted noise at 120, 240, 360, and 480 Hz. Discuss the trade-offs between the following two options:
c1) Add an active analog low-pass filter with a 100 Hz cutoff, and sample at 200 Hz.
c2) Sample at 1920 Hz and add a digital 120, 240, 360, 480 Hz reject filter.
Which approach would you take and why? Under what conditions would the other choice be better?