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楼主 |
发表于 2016-11-8 18:05:03
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It also sets the frequency to 100.0Mhz (provided from PLLD@500Mhz, divided by 5), which provides a carrier. At this point, radios will stop making a "fuzz" noise, and become silent.
Modulation is done by adjusting the frequency using the fractional divider between 100.025Mhz and 99.975Mhz, which makes the audio signal. The fractional divider doesn't have enough resolution to produce more than ~6 bit audio, but since the PI is very fast, we can do oversampling to provide about 9.5 bit audio by using 128 subsamples per real audio sample.
有用的话就是这几句
这玩意有个PLL从500分频到100M, 还可以小数分频可以实现在100M左右随便设定频点(更低更加可以)，再把音频也调制到小数分频上，小数分辨率依然不够，好在音频只有44K，可以加快速度去修改分频寄存器做抖动实现过采样。
看来真的都是纯硬件功劳，这个分频输出也是直接类似单片机的频率输出脚？ 好奇这个处理器怎么会搞了个带小数分频的模块，原来是用在什么上的？ |
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发表于 2016-11-8 16:11:12
