0dB attenuaton (ADC_ATTEN_DB_0)

mbalci
Posts: 15
Joined: Fri May 13, 2016 11:54 am

0dB attenuaton (ADC_ATTEN_DB_0)

Postby mbalci » Tue Oct 02, 2018 2:57 pm

Hello,
In adc.h file there is such notes ;

Code: Select all

The default ADC full-scale voltage is 1.1V. To read higher voltages (up to the pin maximum voltage,
 * usually 3.3V) requires setting >0dB signal attenuation for that ADC channel.
 *
 * When VDD_A is 3.3V:
 *
 * - 0dB attenuaton (ADC_ATTEN_DB_0) gives full-scale voltage 1.1V
 * - 2.5dB attenuation (ADC_ATTEN_DB_2_5) gives full-scale voltage 1.5V
 * - 6dB attenuation (ADC_ATTEN_DB_6) gives full-scale voltage 2.2V
 * - 11dB attenuation (ADC_ATTEN_DB_11) gives full-scale voltage 3.9V (see note below)
 *
 * @note The full-scale voltage is the voltage corresponding to a maximum reading (depending on ADC1 configured
 * bit width, this value is: 4095 for 12-bits, 2047 for 11-bits, 1023 for 10-bits, 511 for 9 bits.)
 *
 * @note At 11dB attenuation the maximum voltage is limited by VDD_A, not the full scale voltage.
 *
 * Due to ADC characteristics, most accurate results are obtained within the following approximate voltage ranges:
 *
 * - 0dB attenuaton (ADC_ATTEN_DB_0) between 100 and 950mV
 * - 2.5dB attenuation (ADC_ATTEN_DB_2_5) between 100 and 1250mV
 * - 6dB attenuation (ADC_ATTEN_DB_6) between 150 to 1750mV
 * - 11dB attenuation (ADC_ATTEN_DB_11) between 150 to 2450mV
 *
 * For maximum accuracy, use the ADC calibration APIs and measure voltages within these recommended ranges.


So what is attenuation ? i can not see any attenuation in datasheet if i am not wrong. There is pga unit in datasheet so attenuation 0 means maximum pga gain ? is there any relation these attenuation and pga ?if yes why did you do such confusion , if no what is this attenuation and where pga defined in adc.h file for configuration?

ESP_Dazz
Posts: 38
Joined: Fri Jun 02, 2017 6:50 am

Re: 0dB attenuaton (ADC_ATTEN_DB_0)

Postby ESP_Dazz » Tue Oct 09, 2018 3:22 pm

Attenuation refers to the amount an voltage signal is scaled down before being input into the ADC. The ADC's can ideally only measure voltages between 0 to 1100mV. Therefore to measure voltages larger than 1100mV, an input voltage can be scaled down such that it is within the 0 to 1100mV range hence giving the ADC a larger effective voltage range.

mbalci
Posts: 15
Joined: Fri May 13, 2016 11:54 am

Re: 0dB attenuaton (ADC_ATTEN_DB_0)

Postby mbalci » Sat Oct 13, 2018 11:20 am

ESP_Dazz wrote:Attenuation refers to the amount an voltage signal is scaled down before being input into the ADC. The ADC's can ideally only measure voltages between 0 to 1100mV. Therefore to measure voltages larger than 1100mV, an input voltage can be scaled down such that it is within the 0 to 1100mV range hence giving the ADC a larger effective voltage range.

Did you read my whole message ? Where is Attenuation in data sheet or reference files ? There is pga in datasheet but there is no any info in idf about pga ...

davepl
Posts: 17
Joined: Wed Jun 27, 2018 5:29 pm

Re: 0dB attenuaton (ADC_ATTEN_DB_0)

Postby davepl » Mon Oct 15, 2018 1:57 pm

Can you rephase your question? You're asking about attenuation but seem interested only in answers about pga, so perhaps rephase your question from that perspective?

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