ECE 4760: Homework 2
For the cricket calls you are going to generate:
- frequency must be within 1% of specification from 1KHz to 6 KHz.
- All spurous frequencies must be lower than -20 db from main tone.
- All times must be within 1 mSec of specification.
The time shall be measured from the time when the tone reaches 50% of its steady-state value,
until it has dropped to 50% of its steady-state value.
Given these specifications:
- what DDS sample frequency is required, based on the above specs?
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
- Should you add a low pass filter to the DAC output? If so, what cutoff frequency?
- How accurate is the internal PIC32 oscillator? Does it meet the frequency accuracy spec?
- What kind of amplitude modulation will you use and why. Linear ramp? Cosine? Exponential? Hanning?
A matlab program computes spectrum for different envelopes
Copyright Cornell University
June 21, 2017