docs: provide CN translation for api-reference/peripherals/sdm.rst

docs/en/api-reference/peripherals/sdm.rst

@@ -1,6 +1,8 @@
 Sigma-Delta Modulation (SDM)
 ============================
 
+:link_to_translation:`zh_CN:[中文]`
+
 Introduction
 ------------
 
@@ -8,11 +10,11 @@ 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 the PDM in I2S peripheral and DAC are:
+The main differences comparing to I2S PDM mode and DAC peripheral are:
 
-1. SDM has no clock signal, it just like the DAC mode of PDM;
+1. SDM has no clock signal, it is just like the DAC mode of PDM;
-2. SDM has no DMA, and it can't change its output density continuously. If you have to, you can update the density in a timer's callback;
+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. Base on the former two points, an external active or passive filter is required to restore the analog wave (See :ref:`convert_to_analog_signal`);
+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:
 
@@ -23,34 +25,36 @@ Typically, a Sigma-Delta modulated channel can be used in scenarios like:
 Functional Overview
 -------------------
 
-The following sections of this document cover the typical steps to install and operate a SDM channel:
+The following sections of this document cover the typical steps to install and operate an SDM channel:
 
--  `Resource Allocation <#resource-allocation>`__ - covers which parameters should be set up to get a channel handle and how to recycle the resources when it finishes working.
+- :ref:`sdm-resource-allocation` - covers how to initialize and configure an SDM channel and how to recycle the resources when it finishes working.
--  `Enable and Disable Channel <#enable-and-disable-channel>`__ - covers how to enable and disable the channel.
+- :ref:`sdm-enable-and-disable-channel` - covers how to enable and disable the channel.
--  `Set Equivalent Duty Cycle <#set-equivalent-duty-cycle>`__ - describes how to set the equivalent duty cycle of the PDM pulses.
+- :ref:`sdm-set-equivalent-duty-cycle` - describes how to set the equivalent duty cycle of the PDM pulses.
--  `Power Management <#power-management>`__ - describes how different source clock selections can affect power consumption.
+- :ref:`sdm-power-management` - describes how different source clock selections can affect power consumption.
--  `IRAM Safe <#iram-safe>`__ - lists which functions are supposed to work even when the cache is disabled.
+- :ref:`sdm-iram-safe` - lists which functions are supposed to work even when the cache is disabled.
--  `Thread Safety <#thread-safety>`__ - lists which APIs are guaranteed to be thread safe by the driver.
+- :ref:`sdm-thread-safety` - lists which APIs are guaranteed to be thread-safe by the driver.
--  `Kconfig Options <#kconfig-options>`__ - lists the supported Kconfig options that can be used to make a different effect on driver behavior.
+- :ref:`sdm-kconfig-options` - lists the supported Kconfig options that can be used to make a different effect on driver behavior.
+
+.. _sdm-resource-allocation:
 
 Resource Allocation
 ^^^^^^^^^^^^^^^^^^^
 
-A SDM channel is represented by :cpp:type:`sdm_channel_handle_t`. Each channel is capable to output the binary, hardware generated signal with the sigma-delta modulation. The driver manages all available channels in a pool, so that users don't need to manually assign a fixed channel to a GPIO.
+In ESP-IDF, the information and attributes of SDM channels are managed and accessed through specific data structures, where the data structure is called :cpp:type:`sdm_channel_handle_t`. Each channel is capable to output the binary, hardware-generated signal with the sigma-delta modulation. The driver manages all available channels in a pool so that there is no need to manually assign a fixed channel to a GPIO.
 
-To install a SDM channel, you should call :cpp:func:`sdm_new_channel` to get a channel handle. Channel specific configurations are passed in the :cpp:type:`sdm_config_t` structure:
+To install an SDM channel, you should call :cpp:func:`sdm_new_channel` to get a channel handle. Channel-specific configurations are passed in the :cpp:type:`sdm_config_t` structure:
 
-- :cpp:member:`sdm_config_t::gpio_num` sets the GPIO that the PDM pulses will output from
+- :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::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.
 
-The function :cpp:func:`sdm_new_channel` can fail due to various errors such as insufficient memory, invalid arguments, etc. Specifically, when there are no more free channels (i.e. all hardware SDM channels have been used up), then :c:macro:`ESP_ERR_NOT_FOUND` will be returned.
+The function :cpp:func:`sdm_new_channel` can fail due to various errors such as insufficient memory, invalid arguments, etc. Specifically, when there are no more free channels (i.e., all hardware SDM channels have been used up), :c:macro:`ESP_ERR_NOT_FOUND` will be returned.
 
-If a previously created SDM channel is no longer required, you should recycle it by calling :cpp:func:`sdm_del_channel`. It allows the underlying HW channel to be used for other purposes. Before deleting a SDM channel handle, you should disable it by :cpp:func:`sdm_channel_disable` in advance or make sure it has not enabled yet by :cpp:func:`sdm_channel_enable`.
+If a previously created SDM channel is no longer required, you should recycle it by calling :cpp:func:`sdm_del_channel`. It allows the underlying HW channel to be used for other purposes. Before deleting an SDM channel handle, you should disable it by :cpp:func:`sdm_channel_disable` in advance or make sure it has not been enabled yet by :cpp:func:`sdm_channel_enable`.
 
-Creating a SDM Channel with Sample Rate of 1MHz
+Creating an SDM Channel with a Sample Rate of 1 MHz
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 .. code:: c
@@ -63,57 +67,70 @@ Creating a SDM Channel with Sample Rate of 1MHz
     };
    ESP_ERROR_CHECK(sdm_new_channel(&config, &chan));
 
+.. _sdm-enable-and-disable-channel:
+
 Enable and Disable Channel
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-Before doing further IO control to the SDM channel, you should enable it first, by calling :cpp:func:`sdm_channel_enable`. Internally, this function will:
+Before doing further IO control to the SDM channel, you should enable it first, by calling :cpp:func:`sdm_channel_enable`. Internally, this function:
 
-* switch the channel state from **init** to **enable**
+* switches the channel state from **init** to **enable**
-* acquire a proper power management lock is a specific clock source (e.g. APB clock) is selected. See also `Power management <#power-management>`__ for more information.
+* acquires a proper power management lock if a specific clock source (e.g., APB clock) is selected. See also :ref:`sdm-power-management` for more information.
 
-On the contrary, calling :cpp:func:`sdm_channel_disable` will do the opposite, that is, put the channel back to the **init** state and release the power management lock.
+On the contrary, calling :cpp:func:`sdm_channel_disable` does the opposite, that is, put the channel back to the **init** state and releases the power management lock.
+
+.. _sdm-set-equivalent-duty-cycle:
 
 Set Pulse Density
 ^^^^^^^^^^^^^^^^^
 
-For the output PDM signals, the pulse density decides the output analog voltage that restored by a low-pass filter. The restored analog voltage from the channel is calculated by ``Vout = VDD_IO / 256 * duty + VDD_IO / 2``. The range of the quantized ``density`` input parameter of :cpp:func:`sdm_channel_set_pulse_density` is from -128 to 127 (eight-bit signed integer). For example, if a zero value is set, then the output signal's duty will be around 50%.
+For the output PDM signals, the pulse density decides the output analog voltage that is restored by a low-pass filter. The restored analog voltage from the channel is calculated by ``Vout = VDD_IO / 256 * duty + VDD_IO / 2``. The range of the quantized ``density`` input parameter of :cpp:func:`sdm_channel_set_pulse_density` is from -128 to 127 (8-bit signed integer). Depending on the value of the ``density`` parameter, the duty cycle of the output signal will be changed accordingly. For example, if a zero value is set, then the output signal's duty will be around 50%.
+
+.. _sdm-power-management:
 
 Power Management
 ^^^^^^^^^^^^^^^^
 
-When power management is enabled (i.e. :ref:`CONFIG_PM_ENABLE` is on), the system will adjust the APB frequency before going into light sleep, thus potentially changing the sample rate of the sigma-delta modulator.
+When power management is enabled (i.e., :ref:`CONFIG_PM_ENABLE` is on), the system will adjust the APB frequency before going into Light-sleep, thus potentially changing the sample rate of the sigma-delta modulator.
 
-However, the driver can prevent the system from changing APB frequency by acquiring a power management lock of type :cpp:enumerator:`ESP_PM_APB_FREQ_MAX`. Whenever the driver creates a SDM channel instance that has selected :cpp:enumerator:`SDM_CLK_SRC_APB` as its clock source, the driver will guarantee that the power management lock is acquired when enable the channel by :cpp:func:`sdm_channel_enable`. Likewise, the driver releases the lock when :cpp:func:`sdm_channel_disable` is called for that channel.
+However, the driver can prevent the system from changing APB frequency by acquiring a power management lock of type :cpp:enumerator:`ESP_PM_APB_FREQ_MAX`. Whenever the driver creates an SDM channel instance that has selected :cpp:enumerator:`SDM_CLK_SRC_APB` as its clock source, the driver guarantees that the power management lock is acquired when enabling the channel by :cpp:func:`sdm_channel_enable`. Likewise, the driver releases the lock when :cpp:func:`sdm_channel_disable` is called for that channel.
+
+.. _sdm-iram-safe:
 
 IRAM Safe
 ^^^^^^^^^
 
-There's a Kconfig option :ref:`CONFIG_SDM_CTRL_FUNC_IN_IRAM` that can put commonly used IO control functions into IRAM as well. So that these functions can also be executable when the cache is disabled. These IO control functions are listed as follows:
+There is a Kconfig option :ref:`CONFIG_SDM_CTRL_FUNC_IN_IRAM` that can put commonly-used IO control functions into IRAM as well. So that these functions can also be executable when the cache is disabled. These IO control functions are listed as follows:
 
 - :cpp:func:`sdm_channel_set_pulse_density`
 
+.. _sdm-thread-safety:
+
 Thread Safety
 ^^^^^^^^^^^^^
 
-The factory function :cpp:func:`sdm_new_channel` is guaranteed to be thread safe by the driver, which means, user can call it from different RTOS tasks without protection by extra locks.
+The factory function :cpp:func:`sdm_new_channel` is guaranteed to be thread-safe by the driver, which means, the user can call it from different RTOS tasks without protection by extra locks.
+
 The following functions are allowed to run under ISR context, the driver uses a critical section to prevent them being called concurrently in both task and ISR.
 
 - :cpp:func:`sdm_channel_set_pulse_density`
 
-Other functions that take the :cpp:type:`sdm_channel_handle_t` as the first positional parameter, are not treated as thread safe. Which means the user should avoid calling them from multiple tasks.
+Other functions that take the :cpp:type:`sdm_channel_handle_t` as the first positional parameter, are not treated as thread-safe. This means the user should avoid calling them from multiple tasks.
+
+.. _sdm-kconfig-options:
 
 Kconfig Options
 ^^^^^^^^^^^^^^^
 
-- :ref:`CONFIG_SDM_CTRL_FUNC_IN_IRAM` controls where to place the SDM channel control functions (IRAM or Flash), see `IRAM Safe <#iram-safe>`__ for more information.
+- :ref:`CONFIG_SDM_CTRL_FUNC_IN_IRAM` controls where to place the SDM channel control functions (IRAM or Flash), see :ref:`sdm-iram-safe` for more information.
-- :ref:`CONFIG_SDM_ENABLE_DEBUG_LOG` is used to enabled the debug log output. Enable this option will increase the firmware binary size.
+- :ref:`CONFIG_SDM_ENABLE_DEBUG_LOG` is used to enable the debug log output. Enabling this option increases the firmware binary size.
 
 .. _convert_to_analog_signal:
 
-Convert to analog signal (Optional)
+Convert to an analog signal (Optional)
------------------------------------
+--------------------------------------
 
-Typically, if the sigma-delta signal is connected to an LED, you don't have to add any filter between them (because our eyes are a low pass filter naturally). However, if you want to check the real voltage or watch the analog waveform, you need to design an analog low pass filter. Also, it is recommended to use an active filter instead of a passive filter to gain better isolation and not lose too much voltage.
+Typically, if a Sigma-Delta signal is connected to an LED to adjust the brightness, you do not have to add any filter between them, because our eyes have their own low-pass filters for changes in light intensity. However, if you want to check the real voltage or watch the analog waveform, you need to design an analog low-pass filter. Also, it is recommended to use an active filter instead of a passive filter to gain better isolation and not lose too much voltage.
 
 For example, you can take the following `Sallen-Key topology Low Pass Filter`_ as a reference.
 
@@ -138,7 +155,7 @@ API Reference
 .. include-build-file:: inc/sdm_types.inc
 
 .. [1]
-   Different ESP chip series might have different numbers of SDM channels. Please refer to Chapter `GPIO and IOMUX <{IDF_TARGET_TRM_EN_URL}#iomuxgpio>`__ in {IDF_TARGET_NAME} Technical Reference Manual for more details. The driver won't forbid you from applying for more channels, but it will return error when all available hardware resources are used up. Please always check the return value when doing resource allocation (e.g. :cpp:func:`sdm_new_channel`).
+   Different ESP chip series might have different numbers of SDM channels. Please refer to Chapter `GPIO and IOMUX <{IDF_TARGET_TRM_EN_URL}#iomuxgpio>`__ in {IDF_TARGET_NAME} Technical Reference Manual for more details. The driver does not forbid you from applying for more channels, but it will return an error when all available hardware resources are used up. Please always check the return value when doing resource allocation (e.g., :cpp:func:`sdm_new_channel`).
 
 .. _Sallen-Key topology Low Pass Filter: https://en.wikipedia.org/wiki/Sallen%E2%80%93Key_topology
 

docs/zh_CN/api-reference/peripherals/sdm.rst

@@ -1 +1,163 @@
-.. include:: ../../../en/api-reference/peripherals/sdm.rst
+Sigma-Delta 调制器 (SDM)
+===========================
+
+:link_to_translation:`en:[English]`
+
+简介
+----
+
+{IDF_TARGET_NAME} 具备二阶 Sigma-Delta 调制器，可以为多个通道生成独立的脉冲密度调制 (PDM) 脉冲。请参阅技术参考手册，查看可用的硬件通道数量。[1]_
+
+Sigma-Delta 调制器可以将模拟电压信号转换为脉冲频率或脉冲密度，该过程称为脉冲密度调制 (PDM)（请参阅 |wiki_ref|_）。
+
+与 I2S 外设中的 PDM 模式和和数模转换器 (DAC) 相比，SDM 中的 PDM 主要有以下特点：
+
+1. SDM 没有时钟信号，类似于 PDM 的 DAC 模式；
+2. SDM 没有 DMA 支持，无法持续改变其输出密度。如果需要改变 SDM 的输出密度，可以在定时器的回调函数中进行操作；
+3. 基于以上两点，不同于 DAC，要还原模拟波形，还必须使用外部的有源或无源低通滤波器，详情请参阅 :ref:`convert_to_analog_signal`。
+
+Sigma-Delta 调制通道通常应用于以下场景：
+
+-  LED 调光
+-  使用有源 RC 低通滤波器，实现简单的数模转换（8 位分辨率）
+-  结合半桥或全桥回路，以及 LC 低通滤波器，实现 D 级功率放大
+
+功能概述
+--------
+
+下文将分节概述安装和操作 SDM 通道的一般步骤：
+
+- :ref:`sdm-resource-allocation` - 介绍如何初始化和配置 SDM 通道，以及在通道完成任务后如何回收相关资源。
+- :ref:`sdm-enable-and-disable-channel` - 介绍如何启用和禁用 SDM 通道。
+- :ref:`sdm-set-equivalent-duty-cycle` - 介绍如何设置 PDM 脉冲的等效占空比。
+- :ref:`sdm-power-management` - 介绍不同时钟源对功耗的影响。
+- :ref:`sdm-iram-safe` - 介绍禁用 cache 时仍可使用的功能。
+- :ref:`sdm-thread-safety` - 介绍由驱动程序认证为线程安全的 API。
+- :ref:`sdm-kconfig-options` - 介绍 SDM 驱动程序支持的各种 Kconfig 选项，这些选项可以给驱动程序的行为造成不同影响。
+
+.. _sdm-resource-allocation:
+
+资源分配
+^^^^^^^^
+
+在 ESP-IDF 中，SDM 通道的信息和属性通过特定的数据结构进行管理和访问，该数据结构表示为 :cpp:type:`sdm_channel_handle_t`。每个通道都可以输出由硬件生成的二进制信号，且这些信号都经过 Sigma-Delta 调制。所有可用通道均存放在资源池中，由驱动程序管理，无需手动将固定通道分配给 GPIO。
+
+要安装 SDM 通道，请调用 :cpp:func:`sdm_new_channel` 获取通道句柄。通道的具体配置信息由结构体 :cpp:type:`sdm_config_t` 传递。
+
+- :cpp:member:`sdm_config_t::gpio_num` 设置 PDM 脉冲输出的 GPIO 管脚号。
+- :cpp:member:`sdm_config_t::clk_src` 选择 SDM 模块的时钟源。注意，所有通道选择的时钟源应保持一致。
+- :cpp:member:`sdm_config_t::sample_rate_hz` 设置 SDM 模块的采样率。
+- :cpp:member:`sdm_config_t::invert_out` 设置是否反转输出信号。
+- :cpp:member:`sdm_config_t::io_loop_back` 通过 GPIO 矩阵外设，启用 GPIO 的输入和输出功能。注意，该字段仅供调试使用。
+
+函数 :cpp:func:`sdm_new_channel` 可能因为各种原因失败，如内存不足、参数无效等。当缺少空闲通道（即所有的硬件 SDM 通道均在使用中）时，将返回 :c:macro:`ESP_ERR_NOT_FOUND`。
+
+SDM 通道完成任务后，请调用 :cpp:func:`sdm_del_channel` 回收相应资源，以便底层硬件通道用于其他目的。在删除 SDM 通道句柄前，请通过 :cpp:func:`sdm_channel_disable` 禁用要删除的通道，或确保该通道尚未由 :cpp:func:`sdm_channel_enable` 启用，再继续删除操作。
+
+创建采样率为 1 MHz 的 SDM 通道
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. code:: c
+
+    sdm_channel_handle_t chan = NULL;
+    sdm_config_t config = {
+        .clk_src = SDM_CLK_SRC_DEFAULT,
+        .sample_rate_hz = 1 * 1000 * 1000,
+        .gpio_num = 0,
+    };
+   ESP_ERROR_CHECK(sdm_new_channel(&config, &chan));
+
+.. _sdm-enable-and-disable-channel:
+
+启用和禁用通道
+^^^^^^^^^^^^^^
+
+在对 SDM 通道进行进一步的 IO 控制之前，需要先调用 :cpp:func:`sdm_channel_enable` 启用通道。在内部，该函数实现了以下操作：
+
+* 将通道状态从 **init** 切换到 **enable**
+* 如果选择了特定时钟源（如 APB 锁），则会获取合适的电源管理锁。要了解更多有关信息，请参阅 :ref:`sdm-power-management`。
+
+调用 :cpp:func:`sdm_channel_disable` 则执行相反操作，即将通道恢复到 **init** 状态，并释放电源管理锁。
+
+.. _sdm-set-equivalent-duty-cycle:
+
+设置脉冲密度
+^^^^^^^^^^^^
+
+在 PDM 中，脉冲密度决定了低通滤波器转换后的输出模拟电压，该模拟电压可以通过公式 ``Vout = VDD_IO / 256 * duty + VDD_IO / 2`` 计算。使用函数 :cpp:func:`sdm_channel_set_pulse_density` 时，需要传入一个名为 ``density`` 的参数。这个参数是一个整数值，范围在 -128 到 127 之间，表示一个 8 位有符号整数。根据 ``density`` 参数的不同取值，输出信号的占空比也会相应改变。例如，如果将 ``density`` 参数设置为零，输出信号的占空比约为 50%。
+
+.. _sdm-power-management:
+
+电源管理
+^^^^^^^^
+
+启用电源管理（即启用 :ref:`CONFIG_PM_ENABLE`）时，在进入 Light-sleep 模式前，系统会调整 APB 频率，这可能会改变 Sigma-Delta 调制器的采样率。
+
+但是，通过获取类型为 :cpp:enumerator:`ESP_PM_APB_FREQ_MAX` 的电源管理锁，驱动程序可以防止系统改变 APB 频率。每当驱动程序创建 SDM 通道，且该通道选择 :cpp:enumerator:`SDM_CLK_SRC_APB` 作为其时钟源时，在通过 :cpp:func:`sdm_channel_enable` 启用通道的过程中，驱动程序会确保获取类型为 :cpp:enumerator:`ESP_PM_APB_FREQ_MAX` 的电源管理锁。反之，调用 :cpp:func:`sdm_channel_disable` 禁用通道时，驱动程序释放该锁。
+
+.. _sdm-iram-safe:
+
+IRAM 安全
+^^^^^^^^^
+
+Kconfig 选项 :ref:`CONFIG_SDM_CTRL_FUNC_IN_IRAM` 支持将常用的 IO 控制函数存放在 IRAM 中，以保证在禁用 cache 时可以正常使用函数。IO 控制函数如下所示：
+
+- :cpp:func:`sdm_channel_set_pulse_density`
+
+.. _sdm-thread-safety:
+
+线程安全
+^^^^^^^^
+
+驱动程序会确保工厂函数 :cpp:func:`sdm_new_channel` 的线程安全，使用时，可以直接从不同的 RTOS 任务中调用此类函数，无需额外锁保护。
+
+驱动程序设置了临界区，以防函数同时在任务和 ISR 中调用。因此，以下函数支持在 ISR 上下文运行：
+
+- :cpp:func:`sdm_channel_set_pulse_density`
+
+其他以 :cpp:type:`sdm_channel_handle_t` 作为第一个位置参数的函数均非线程安全，因此应避免从多个任务中调用这类函数。
+
+.. _sdm-kconfig-options:
+
+Kconfig 选项
+^^^^^^^^^^^^
+
+- :ref:`CONFIG_SDM_CTRL_FUNC_IN_IRAM` 控制 SDM 通道控制函数的存放位置（IRAM 或 flash）。更多信息请参阅 :ref:`sdm-iram-safe`。
+- :ref:`CONFIG_SDM_ENABLE_DEBUG_LOG` 用于启用调试日志输出。启用此选项将增加固件的二进制文件大小。
+
+.. _convert_to_analog_signal:
+
+转换为模拟信号（可选）
+----------------------
+
+一般而言，Sigma-Delta 信号连接到 LED 用来调节明暗时，无需在信号和 LED 之间添加滤波器，因为人眼本身对光强变化有低通滤波作用。但是，如果你想测量实际电压，或观察模拟波形，就需要设计一个模拟低通滤波器。此外，建议使用有源滤波器，相较于无源滤波器，有源滤波器在处理信号时具有更强的抗干扰性，且损失的电压较少。
+
+请参阅如下示例 `Sallen-Key 拓扑低通滤波器`_，了解滤波器的相关知识。
+
+.. figure:: ../../../_static/typical_sallenkey_LP_filter.png
+    :align: center
+    :alt: Sallen-Key 拓扑低通滤波器
+    :figclass: align-center
+
+    Sallen-Key 拓扑低通滤波器
+
+
+应用示例
+--------
+
+* 使用 Sigma-Delta 调制的 100 Hz 正弦波：:example:`peripherals/sigma_delta/sdm_dac`。
+* 使用 Sigma-Delta 调制、并由 GPIO 驱动的 LED：:example:`peripherals/sigma_delta/sdm_led`。
+
+API 参考
+--------
+
+.. include-build-file:: inc/sdm.inc
+.. include-build-file:: inc/sdm_types.inc
+
+.. [1]
+   不同的 ESP 芯片系列可能具有不同数量的 SDM 通道，请参阅 {IDF_TARGET_NAME} 技术参考手册中的 `GPIO 和 IOMUX <{IDF_TARGET_TRM_EN_URL}#iomuxgpio>`__ 章节，了解更多详情。驱动程序对通道申请数量不做限制，但当硬件资源用尽时，驱动程序将返回错误。因此，每次进行通道分配（如调用 :cpp:func:`sdm_new_channel`）时，请注意检查返回值。
+
+.. _Sallen-Key 拓扑低通滤波器: https://en.wikipedia.org/wiki/Sallen%E2%80%93Key_topology
+
+.. |wiki_ref| replace:: 维基百科上有关 Sigma-Delta 调制的介绍
+.. _wiki_ref: https://en.wikipedia.org/wiki/Delta-sigma_modulation