Design and manufacture a digitally displayed periodic rectangular pulse signal parameter measuring instrument with an input impedance of 50Ω. At the same time, a standard rectangular pulse signal generator is designed and produced as an additional function of the tester. Specific requirements are as follows:
(1) Measure the pulse signal frequency, the frequency range is 10Hz ~ 2MHz, and the absolute value of the measurement error is not more than 0.1%.
(2) Measure the duty ratio D of the pulse signal, the measurement range is 10% to 90%, and the absolute value of the measurement error is not greater than 2%.
(3) Measure the pulse signal amplitude, the amplitude range is 0.1 ~ 10V, and the absolute value of the measurement error is not more than 2%.
(4) Measure the rise time of the pulse signal, the measurement range is 50.0~999ns, and the absolute value of the measurement error is not more than 5%.
(5) Provide a standard rectangular pulse signal generator, requiring:
a) The frequency is 1MHz, and the absolute value of the error is not greater than 0.1%;
b) The pulse width is 100ns, and the absolute value of the error is not greater than 1%;
c) The amplitude is 5±0.1V (the load resistance is 50);
d) The rise time is not greater than 30ns, and the overshoot is not greater than 5%.
Seeing the overall topic, it is obvious that we can only do it with fpga, because this kind of precision requirement cannot be achieved with other platforms, so EDA technology must be used.
1) Frequency measurement is a very classic problem. Frequency meters have also appeared alone in electronic competitions. There are three main methods for frequency measurement, direct method, equal period method, and equal accuracy, which will be described in detail later.
2) Measure the duty cycle, the duty cycle is evolved from the problem of the frequency meter, the duty cycle = high level time / (high level time + low level time).
3) Amplitude measurement is also a very common problem. The difficulty lies in the fact that the amplitude span is too large, from 0.1v to 10v, signal conditioning must be required.
4) Measure the rising edge time. The rising edge time of the square wave in the digital textbook is defined as: the time of the square wave amplitude from 10% to 90% is the rising edge time. Based on this, I think of making a comparator, and the threshold is 10% of the amplitude. and 90%, the high level time after comparison is the rising edge time of the square wave, and the measurement of the high level time of the square wave returns to the second question.
The difficulty of this question lies in the external analog circuit, not in the fpga code.