Sigma-delta Modulation¶

Introduction¶

ESP32 has a second-order sigma-delta modulation module. This driver configures the channels of the sigma-delta module.

Functionality Overview¶

There are eight independent sigma-delta modulation channels identified with sigmadelta_channel_t. Each channel is capable to output the binary, hardware generated signal with the sigma-delta modulation.

Selected channel should be set up by providing configuration parameters in sigmadelta_config_t and then applying this configuration with sigmadelta_config().

Another option is to call individual functions, that will configure all required parameters one by one:

Prescaler of the sigma-delta generator - sigmadelta_set_prescale()
Duty of the output signal - sigmadelta_set_duty()
GPIO pin to output modulated signal - sigmadelta_set_pin()

The range of the ‘duty’ input parameter of sigmadelta_set_duty() is from -128 to 127 (eight bit signed integer). If zero value is set, then the output signal’s duty will be about 50%, see description of sigmadelta_set_duty().

Application Example¶

Sigma-delta Modulation example: peripherals/sigmadelta.

API Reference¶

Header File¶

driver/include/driver/sigmadelta.h

Functions¶

esp_err_t sigmadelta_config(const sigmadelta_config_t *config)¶

Configure Sigma-delta channel.

Return

ESP_OK Success
ESP_ERR_INVALID_STATE sigmadelta driver already initialized
ESP_ERR_INVALID_ARG Parameter error

Parameters

config: Pointer of Sigma-delta channel configuration struct

esp_err_t sigmadelta_set_duty(sigmadelta_channel_t channel, int8_t duty)¶

Set Sigma-delta channel duty.

   This function is used to set Sigma-delta channel duty,
   If you add a capacitor between the output pin and ground,
   the average output voltage will be Vdc = VDDIO / 256 * duty + VDDIO/2,
   where VDDIO is the power supply voltage.

Return

ESP_OK Success
ESP_ERR_INVALID_STATE sigmadelta driver has not been initialized
ESP_ERR_INVALID_ARG Parameter error

Parameters

channel: Sigma-delta channel number
duty: Sigma-delta duty of one channel, the value ranges from -128 to 127, recommended range is -90 ~ 90. The waveform is more like a random one in this range.

esp_err_t sigmadelta_set_prescale(sigmadelta_channel_t channel, uint8_t prescale)¶

Set Sigma-delta channel’s clock pre-scale value. The source clock is APP_CLK, 80MHz. The clock frequency of the sigma-delta channel is APP_CLK / pre_scale.

Return

ESP_OK Success
ESP_ERR_INVALID_STATE sigmadelta driver has not been initialized
ESP_ERR_INVALID_ARG Parameter error

Parameters

channel: Sigma-delta channel number
prescale: The divider of source clock, ranges from 0 to 255

esp_err_t sigmadelta_set_pin(sigmadelta_channel_t channel, gpio_num_t gpio_num)¶

Set Sigma-delta signal output pin.

Return

ESP_OK Success
ESP_ERR_INVALID_STATE sigmadelta driver has not been initialized
ESP_ERR_INVALID_ARG Parameter error

Parameters

channel: Sigma-delta channel number
gpio_num: GPIO number of output pin.

Header File¶

soc/include/hal/sigmadelta_types.h

Structures¶

struct sigmadelta_config_t¶

Sigma-delta configure struct.

Public Members

sigmadelta_channel_t channel¶: Sigma-delta channel number

int8_t sigmadelta_duty¶: Sigma-delta duty, duty ranges from -128 to 127.

uint8_t sigmadelta_prescale¶: Sigma-delta prescale, prescale ranges from 0 to 255.

uint8_t sigmadelta_gpio¶: Sigma-delta output io number, refer to gpio.h for more details.

Type Definitions¶

typedef int sigmadelta_port_t¶: SIGMADELTA port number, the max port number is (SIGMADELTA_NUM_MAX -1).

typedef int sigmadelta_channel_t¶: Sigma-delta channel list.

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