ECE 4760: Homework 2

The DTMF frequencies vary between 697 and 1477 Hz. According the the DTMF spec:

Given these specifications:

  1. what minimum DDS sample frequency is required, based on the above specs?
    You will choose ONE DDS sample frequency for all tones produced.
    A matlab program which computes spectrum versus number of samples/cycle.
    When you run the program, notice that the first large spectral errors are at approximately
    first_error_frequency = steps_per_cycle * frequency - frequency
    Program output examples: 8 samples/cycle, 16 samples/cycle
  2. Should you add a low pass filter to the DAC output? If so, what cutoff frequency?
  3. How accurate is the internal PIC32 oscillator? Does it meet the frequency accuracy spec?
  4. What kind of amplitude modulation will you use and why. Linear ramp? Cosine? Exponential? Hanning?
    A matlab program computes spectrum for different envelopes. Listen to the resulting waveforms.

Copyright Cornell University June 29, 2018