You have been assigned to interface different sensors (displacement, vibration, pressure,

Question

temperature) to the ADuC847. More specifically, you have been assigned to design the antialiasing
filters for the different analog input channels on the ADuC847 (datasheet posted on Bb
course website).
The following system-level specifications are in place:
• Single-supply operation, with operating voltage = 5 V
• Sampling frequency for the 24-bit ADC on the ADuC847 (fs) = 1 kHz
For each one of the filter “types” listed below (a) – (d), design an appropriate anti-aliasing lowpass
filter that satisfies the following specifications:
• Minimum order necessary to have appropriate attenuation in the “stop band” for 24-bit
accuracy
• 2 ≤ K ≤ 4, where K is the “constant term” associated with the filter’s transfer function
(when expressed in standard form)
• –3 dB corner frequency (fc) = 50 Hz
Note that the value you decide for K should be the same for all designed filter types (a) – (d).
(a) Cascade of identical RC low-pass sections
(b) Butterworth
(c) 1 dB Chebyshev type I
(d) Bessel

In implementing your filters at the circuit-level (verification only being expected at the SPICE
simulation level), you may use Sallen-Key and/or Multi-Feedback topologies (with appropriate
rationale expected to have been provided in your report).
Your circuit-level design should use resistor and capacitor component values that can be
purchased (digikey.com, jameco.com, mouser.com, …). You may NOT use inductors in
realizing your filters.
Your circuit-level design should also use appropriate Analog Devices operational amplifiers that
are capable of single-supply operation (with appropriate rationale expected to have been
provided for your choice(s) in your report). To assist with single-supply operation, your lowpass
filters should be “AC” devices. That is, there should be no “DC” at either the input
(where your filter connects to the sensor) or output (where your filter connects to the
ADuC847).
To provide the names of some Analog Devices single-supply operational amplifiers (there are
many more out there):
OP162/262/462, AD8605/8606/8608, AD8628, AD8656, OP196/296/496, AD8541/8542/8544,
OP777/727/747, OP181/281/481, OP193/293/493, OP196/296/496, OP191/291/491,
AD820/822/824, OP184/284/484, OP113/213/413, AD8031/8032, AD8061/8062,
AD8051/8052/8054, AD8063/823, AD8591/8592/8594, AD8531/8532/8534, AD820/822/824,
AD8551/8552/8554, AD8601/8602/8604
In selecting appropriate operational amplifier(s) for your filter designs, you may find useful the
following documents posted on the Bb course website:
• “Select the right operational amplifier for your filtering circuits,” by Bonnie C. Baker at
Microchip Technology Inc.
• “A single-supply op-amp circuit collection,” by Bruce Carter at Texas Instruments Inc.
Appropriate catalog numbers and bill of materials is expected for each filter design.