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Arjan te Marvelde 2022-01-02 12:02:08 +01:00 zatwierdzone przez GitHub
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@ -3,7 +3,7 @@ Inspired by a description of an [Arbitrary Waveform Generator](https://www.instr
![Prototype](doc/Proto.jpg)
The prototype provides two channels with 8 bit resolution, on which waveforms (sample files) can be played independently. The maximum sample frequency is the system clock, so on a Pico this is by default 125MHz. This obviously sets a limit to the maximum waveform frequency, in the sense that it will be a tradeoff with desired accuracy. If a sample file defining a single waveform has a length of 25 samples, the maximum *waveform frequency* is 125/25 = 5MHz. Of course, the real frequence can be increased by including multiple waves in a waveform buffer. There is a practical minimum buffer size of about 8 32bit words, which is driven by the DMA bus conflicts occurring at the highest sample clock rates. The sample clock can also be lowered, so for a minimum frequency both buffer length and clock divider must be tuned.
The prototype provides two channels with 8 bit resolution, on which waveforms (sample files) can be played independently. The maximum sample frequency is the system clock, so on a Pico this is by default 125MHz. This obviously sets a limit to the maximum waveform frequency, in the sense that it will be a tradeoff with desired accuracy. If a sample file defining a single waveform has a length of 25 samples, the maximum *waveform frequency* is 125/25 = 5MHz. Of course, the real frequence can be increased by including multiple waves in a waveform buffer. There is a practical minimum buffer size of about 8x32bit words, which is driven by the DMA bus conflicts occurring at the highest sample clock rates. The sample clock can also be lowered, so for a minimum frequency both buffer length and clock divider must be tuned.
Still, the performance is quite remarkable, and mostly limited by the implementation of the R-2R ladder network on the digital output. Stray capacitance together with the used resistor values and maybe some inductance will act as a low-pass filter, in case of the prototype maxing output to about 10MHz.