## 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

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June 21, 2017