ADC sampling frequency

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#1

Hi,

I’m reading the RSL10_hardware_reference, i cant’ understand the ADC given information.

I want to use the DIO0 to convert an analog value, but I have trouble understanding the configuration of witch mode to use (Continuous or normal) ? also to choose the ADC prescaler.

If we suppose that SLOWCLK frequency of 1.00 MHz, and the ADC_PRESCALE_40H is used, The sampling frequency is :

  • Continuous mode is 1.00 /40 ?
  • Normal mode is 1.00 /320 ?
    Best regards,
#2

I have trouble understanding the configuration of witch mode to use (Continuous or normal) ?

In “Normal” mode, the ADC converts from all 8 channels so the sample rate of any single channel is 1/8th the base sample rate. In “Continuous” mode the ADC converts only a single channel continuously. The decision to use Continuous vs Normal would be based on whether you want to perform conversions on more than one channel in a round-robin fashion or instead more quickly sample a single channel in your application.

If we suppose that SLOWCLK frequency of 1.00 MHz, and the ADC_PRESCALE_40H is used, The sampling frequency is :

  • Continuous mode is 1.00 /40 ?
  • Normal mode is 1.00 /320 ?

Yes, those are the correct per-channel sample rates for ADC_PRESCALE_40H.

Please note that the ADC_PRESCALE_xH values select the “High-Frequency Mode” of operation resulting in 8-bit resolution. If you need more than 8-bits of resolution, choose the a pre-scale of ADC_PRESCALE_200 to ADC_PRESCALE_6400 (valid settings are listed in Table 22 in the Hardware Reference Manual.)

#3

Thank you Jamie for your explications.

what I understood from reading this from data sheet :

High-Frequency Mode:
SLOWCLK is prescaled by a factor of 2, with sampling rates of up to 25 kHz where ADC
measurement results have a resolution of 14 bits, or up to 50 kHz where ADC measurement
results have a resolution of 8 bits

as long as the frequency does not exceed 25Khz, the result have a 14 bit resolution.

Always in data sheet concernng low frequency mode, i found this :

Low-Frequency Mode
SLOWCLK is first prescaled by a fixed factor of 10, with a maximum sampling rate of 5 kHz.
ADC measurement results have a resolution of 14 bits

This maximum rate sampling is given only when the SLOWCLK=1Mhz ? what about SLOWCLK=8Mhz for example ?

Do you have any schematic about the ADC block of the RSL10 ?

Best regards,

#4

The maximum frequency for the SLOWCLK is 2MHz in High-Frequency mode and1MHz in Low-Frequency mode.

I do not have a schematic available for internal blocks other than what is in the Hardware Reference Manual.

#5

Thank you Jamie.

Just to be clear, can we have 25Khz as sampling rate using high frequency mode and have 14 bit resolution ?

Best regards,

#9

Resolution is typical and not guaranteed, but yes you should see up to 14 bits of resolution at 25kHz in continuous mode of operation in high frequency mode.

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#10

Thank you Jamie for your explanations

Best regards,

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