LEDC & SigmaDelta documentation (#6330)

* LEDC preripheral doc

* SigmaDelta peripheral doc

* Added missing symbol

* Edited grammar, mistakes

* quick edit

docs/source/api/sigmadelta.rst

@@ -0,0 +1,84 @@
+##########
+SigmaDelta
+##########
+
+About
+-----
+
+ESP32 provides a second-order sigma delta modulation module and 8 (4 for ESP32-C3)
+independent modulation channels. The channels are capable to output 1-bit 
+signals (output index: 100 ~ 107) with sigma delta modulation.
+
+========= =============================
+ESP32 SoC Number of SigmaDelta channels
+========= =============================
+ESP32     8
+ESP32-S2  8
+ESP32-C3  4
+ESP32-S3  8
+========= =============================
+
+Arduino-ESP32 SigmaDelta API
+----------------------------
+
+sigmaDeltaSetup
+***************
+
+This function is used to setup the SigmaDelta channel frequency and resolution.
+
+.. code-block:: arduino
+
+    double ledcSetup(uint8_t channel, double freq, uint8_t resolution_bits);
+
+* ``pin`` select GPIO pin.
+* ``channel`` select SigmaDelta channel.
+* ``freq`` select frequency.
+
+  * range is 1-14 bits (1-20 bits for ESP32).
+  
+This function will return ``frequency`` configured for the SigmaDelta channel.
+If ``0`` is returned, error occurs and the SigmaDelta channel was not configured.
+
+sigmaDeltaWrite
+***************
+
+This function is used to set duty for the SigmaDelta channel.
+
+.. code-block:: arduino
+
+    void sigmaDeltaWrite(uint8_t channel, uint8_t duty);
+
+* ``channel`` select SigmaDelta channel.
+* ``duty`` select duty to be set for selected channel.
+
+sigmaDeltaRead
+**************
+
+This function is used to get configured duty for the SigmaDelta channel.
+
+.. code-block:: arduino
+
+    uint8_t sigmaDeltaRead(uint8_t channel)
+
+* ``channnel`` select SigmaDelta channel.
+
+This function will return ``duty`` configured for the selected SigmaDelta channel.
+
+sigmaDeltaDetachPin
+*******************
+
+This function is used to detach pin from SigmaDelta.
+
+.. code-block:: arduino
+
+    void sigmaDeltaDetachPin(uint8_t pin);
+
+* ``pin`` select GPIO pin.
+
+Example Applications
+********************
+
+Here is example use of SigmaDelta:
+
+.. literalinclude:: ../../../libraries/ESP32/examples/AnalogOut/SigmaDelta/SigmaDelta.ino
+    :language: arduino