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change(sdm): delete the confusing part in sdm programming guide

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laokaiyao
2024-09-09 15:10:34 +08:00
committed by Kevin (Lao Kaiyao)
parent d9d316b97d
commit c6e7e82524
10 changed files with 20 additions and 22 deletions
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docs/en/api-reference/peripherals/sdm.rst
+2 -7
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@@ -10,12 +10,6 @@ Introduction
Delta-sigma modulation converts an analog voltage signal into a pulse frequency, or pulse density, which can be understood as pulse-density modulation (PDM) (refer to |wiki_ref|_).
The main differences comparing to I2S PDM mode and DAC peripheral are:
1. SDM has no clock signal, it is just like the DAC mode of PDM;
2. SDM has no DMA, and it can not change its output density continuously. If you have to, you can update the density in a timer's callback;
3. Based on the former two points, unlike the DAC peripheral, an external active or passive low-pass filter is required additionally to restore the analog wave (See :ref:`convert_to_analog_signal`).
Typically, a Sigma-Delta modulated channel can be used in scenarios like:
- LED dimming
@@ -46,7 +40,7 @@ To install an SDM channel, you should call :cpp:func:`sdm_new_channel` to get a
- :cpp:member:`sdm_config_t::gpio_num` sets the GPIO that the PDM pulses output from.
- :cpp:member:`sdm_config_t::clk_src` selects the source clock for the SDM module. Note that, all channels should select the same clock source.
- :cpp:member:`sdm_config_t::sample_rate_hz` sets the sample rate of the SDM module.
- :cpp:member:`sdm_config_t::sample_rate_hz` sets the sample rate of the SDM module. A higher sample rate can help to output signals with higher SNR (Signal to Noise Ratio), and easier to restore the original signal after the filter.
- :cpp:member:`sdm_config_t::invert_out` sets whether to invert the output signal.
- :cpp:member:`sdm_config_t::io_loop_back` is for debugging purposes only. It enables both the GPIO's input and output ability through the GPIO matrix peripheral.
@@ -141,6 +135,7 @@ For example, you can take the following `Sallen-Key topology Low Pass Filter`_ a
Sallen-Key Low Pass Filter
(Refer to :example_file:`peripherals/sigma_delta/sdm_dac/README.md` to see the waveforms before and after filtering.)
Application Examples
--------------------