Question regarding ADAU1446 DSP signal detector

Hi S.J.

I have moved this question from the Processors and DSP community to the SigmaDSP Processors and SigmaStudio Development Tool community. Please continue the discussion here.

Regards,

Craig.

Hello,

The number formats for SigmaDSP are described here: https://ez.analog.com/docs/DOC-3168

The numbers you are reading back are in 5.23 format.

Here are some simple examples:

A full-scale 0 dB signal is 0x0800000.

A -6 dB signal is 0x0400000.

A -12 dB signal is 0x0200000.

Keep in mind the relationship between the analog-to-digital / digital-to-analog converters and the signal represented in the digital world. This allows you to determine the signal level (in volts) of a digital signal inside the DSP (in dBFS).

If you are using a dual-supply ADC that has a full scale level of 10 Vpp, ranging from -5 V to +5 V, then 5 V will be represented as linear 1 (0 dBFS peak) in the DSP, 0 V will be represented as linear 0 (or -∞ dBFS) in the DSP, and -5 V will be represented as linear -1 (full scale in the negative direction) in the DSP.

So, in this example...

+5 V input to ADC = 0x0800000 in the DSP

0V input to the ADC = 0x0000000 in the DSP

-5 V input to the ADC = 0xFF00000 in the DSP.

You can also map values in between. -6 dB of +5 V is +2.5 V. So...

+2.5 V input to the ADC = 0x0400000 in the DSP.

That's the case of a dual-supply ADC. Let's imagine the case of a single-supply ADC with a range of 0 V to +3.3 V (centered around the common mode of +1.65 V.

In this case...

+3.3 V input to ADC = 0x0800000 in the DSP

+1.65 V input to the ADC = 0x0000000 in the DSP

0 V input to the ADC = 0xFF00000 in the DSP.

The positive range of the ADC is between 1.65 and 3.3 volts, giving a range of 1.65 volts. -6 dB of that is 3.3 - 1.65(0.5) = 2.475 V.

So, in this case...

+2.475 V input to the ADC = 0x0400000 in the DSP.

Hopefully this is easy to understand.