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# DSADC input signal's passband frequency

Level 2
Level 2

I am currently working on DSADC in TC37 microcontroller. Here in the user manual, the following info is mentioned regarding passband frequency.

"Related to hardware characteristic for passband frequency ≤ 10 kHz the FIR1 has to be used with a decimation rate of 1:1." [Source: AURIXTC3XX_um_part2_v2.0 (1) (1).pdf (Page : 1366)]

Is the above passband frequency referring to input analog signal's frequency? Also it is mentioned to use FIR1 filter for passband frequency ≤ 10 kHz. Does anyone the reason for the need to enable FIR1 filter here?

1 Solution

# Re: DSADC input signal's passband frequency

Moderator
Moderator

Hi @Bala , Please find the following feedback:

1. “Passband frequency” means the user expected passband frequency of the analog input frequency. It is not the direct analog input frequency. Frequency components outside the selected passband frequency are expected to be filtered out.

1. With both FIR0 and FIR1 enabled, user will have the optimal SNR.

1. UM mentioned for passband ≤ 10kHz, FIR1 decimation rate should be 1:1. This information is obsolete. The main purpose to offer decimation flexibility for FIR1 (it can be 2:1 or 1:1) is, to have the same passband frequency with different output rates. Please see below summary (fd is the DSADC filter output rate). From this table, we can see that, if FIR1 decimation rate 2:1 is chosen, then the OSR is doubled i.e. fd is halved. The fPB = halved fd/3, which is equal to fd/6.

Best Regards,

Meet.

2 Replies

# Re: DSADC input signal's passband frequency

Moderator
Moderator

Hi @Bala , Yes correct,"passband frequency" in UM is the passband frequency of DSADC analog input signal. For the second query I need to check further internally, I will let you know once I find something.

# Re: DSADC input signal's passband frequency

Moderator
Moderator

Hi @Bala , Please find the following feedback:

1. “Passband frequency” means the user expected passband frequency of the analog input frequency. It is not the direct analog input frequency. Frequency components outside the selected passband frequency are expected to be filtered out.

1. With both FIR0 and FIR1 enabled, user will have the optimal SNR.

1. UM mentioned for passband ≤ 10kHz, FIR1 decimation rate should be 1:1. This information is obsolete. The main purpose to offer decimation flexibility for FIR1 (it can be 2:1 or 1:1) is, to have the same passband frequency with different output rates. Please see below summary (fd is the DSADC filter output rate). From this table, we can see that, if FIR1 decimation rate 2:1 is chosen, then the OSR is doubled i.e. fd is halved. The fPB = halved fd/3, which is equal to fd/6.

Best Regards,

Meet.