AFE5401-Q1: Question about FIR setting.

Hi,

Let me review this request with team and I will try to get back to you by Wednesday this week.

Regards,

Shabbir 

Hi Shabbir,

Thank you very much for your reply.

I'm looking forward to receiving your next reply.

Thank you again and best regards,
Kazuya.

Thanks for your understanding. 

Regards,

Shabbir

Hi,

I discussed about it team. They use matlab fir1 command to generate filter coefficients as described below

https://www.mathworks.com/help/signal/ref/fir1.html

You will get the coefficients which you can represent using 8-bit 2's complement code and program it in the device. Can you try this approach to design filter of your choice? Let me know if need any further help.

Thanks!

Regards,

Shabbir

Hi Shabbir,

Thank you very much for your reply.

The customer wants to get the answer to the following questions as additional.
Could you please give me your reply?

Q.
I thought AFE5401 internal signal path was the following in case of 12.5Msps and Decimate-by-4 FIR.

>> 12.5Msps data -> 11 tap FIR ->  Decimate-by-4 (3.125Msps).

But I think this may be wrong. I think correct signal path may be follow.

>> 12.5Msps data -> Decimate-by-4 (3.125Msps) -> 11 tap FIR.

I realized this when I compared FIR coefficient calculation result and set 2 case. Is my thought correct?
And in case of this, is decimated data not used?

Thank you again and best regards,
Kazuya.      

Hi,

Before decimating the data, we need to apply filter to avoid noise aliasing. So it is implemented as 

12.5Msps data -> 11 tap FIR ->  Decimate-by-4 (3.125Msps).

When you decimate the data, then yes data is dropped and not used.

Regards,

Shabbir

Hi Shabbir,

Thank you very much for the prompt reply.

Could I ask you a few additional questions?

Q1.
Do you have any newer device which has similar function to AFE5401-Q1?

Q2.
Do you have any plan of this device EOL?

Thank you again and best regards,
Kazuya.

Hi Shabbir,

Thank you very much for your reply and I'm sorry to be late my response.

I told them your reply. They still have the following question. Could you please give me your answer?

Q.
What are calculation parameters of FIR filter for "set1" and "set2" in Figure 50 on page 19 of AFE5401-Q datasheet?

Your reply would be much appreciated.

Thank you again and best regards,
Kazuya.

Hi Shabbir,

I'm sorry I forgot to write the parameters they want to know.

[FIR calculation parameters]
Sample Freq.(12.5MHz/3.125MHz)
Cutoff   Freq. 
Window Type(Hanning / Hamming / etc)
Gain pass band (dB)
Gain stop band(dB)

Thank you and best regards,
Kazuya.

Hi,

Sorry for late reply as I was on leave. I am back from vacation and will review above one. Allow me couple of days to get back to you.

Thanks!

Regards,

Shabbir

Hi,

To know the frequency response of set1 and set2 filter, they can use below command in matlab:

For set 1:

----

set1=[5 2 -13 -2 38 66 38 -2 -13 2 5]

freqz(set1)

----

For set2:

----

set2=[-5 -2 7 19 30 34 30 19 7 -2 -5]

freqz(set2)

----

Cut off frequency for set1 is Fs/4 and for set2, it is Fs/8.

Regards,

Shabbir

Hi Shabbir,

Thank you very much for your strong supports.

The customer wants to know what values should be input to AFE5401-q1 resisters for set1 and set2 filter setting.
Could you tell me the values?

Thank you again and best regards,
Kazuya.

These are the values:

set1=[5 2 -13 -2 38 66 38 -2 -13 2 5]

set2=[-5 -2 7 19 30 34 30 19 7 -2 -5]

Are you looking something else?

Regards,

Shabbir

Hi Shabbir,

Thank you for your reply.

I may misunderstood.
Could I ask you an additional question?
Are these values for MATLAB input?
Or for registers of AFE5401-Q1?

Could you please give me your reply?

Thank you again and best regards,
Kazuya.

Hi,

These set1 and set2 are example filter coefficients which has to be programmed in C1 to C6 registers as shows in below register maps. These example set1 and set2 are optimized coefficients generated by TI design team through other internal approach to get optimum filter response.

If you want your own coefficients, then you can generate fir1 command in Matlab to generate coefficients. 

Thanks!

Regards,
Shabbir

Hi Shabbir,

Thank you very much for your strong supports.

If the following values are for AFE5401 internal registers, are the parameters for set1 and set2, Are these value input to the registers like are followings?
For Set1
1. Register 8
DIG_GAIN_C1_FIR＝5, C2_FIR=2

2. Register 9
C3_FIR = -13, C4_FIR = -2

3. Register 10
C5_FIR = 38, C6_FIR = 66
Are remain values, 38 -2 -13 2 5 ignored?

For Set2
1. Register 8
DIG_GAIN_C1_FIR＝-5, C2_FIR=-2

2. Register 9
C3_FIR = 7, C4_FIR = 19

3. Register 10
C5_FIR = 30, C6_FIR = 34

Are remain values, 30 19 7 -2 -5 ignored?

Could you please give me your reply?

Thank you again and best regards,
Kazuya.

Hi,

Since this is symmetric filter (C1=C11, C2=C10, C3=C9, C4=C8, C5=C7), hence you just need to program half of the coefficients and device will automatically pick up the rest as the values are same.

Thanks!

Regards,
Shabbir

Hi Shabbir,

Thank you very much for your reply.

I understood well.

Could I ask you one additional question for our customer?

Q. The customer has the following question.
What values are input for the following parameters when you calculate these coefficients of Set1/2 with MATLAB's FIR design? 

Parameter 

"n"          = 6? 
"Wn"       = ? 
"ftype"     = ?  
"window  = ?
"scaleopt = ?

Thank you again and best regards,
Kazuya.

Hi,

These coefficients are generated by design team using own optimized tool. So we can show only filter response. As mentioned earlier, customer can generate their own set of coefficients as per their filter response requirement using FIR1 command in matlab.

Thanks!

Regards,

Shabbir

Hi Shabbir,

Thank you very for your reply.

I understood the filter calculation tool is your team original.
Can you disclose the tool to our customer?

If the answer is no, could  you tell us what the following parameter were input to the calculation tool?

Parameter 
Input argument

"n"          = 6?  (Filter order）
"Wn"       = ?   (Frequency constraints)
"ftype"     = ?   (Filter type)
"window  = ?  (Window(Vector))
"scaleopt = ?  (Normalization option)

Thank you again and best regards,
Kazuya.

Hi,

We wont be able to provide tools.  Below are closest parameter in matlab command.

"n"          = 6?  (Filter order）-> 11
"Wn"       = ?   (Frequency constraints) -> Corner frequency for Set 1 coefficient is Fs/4 and for set2 coefficients, it is Fs/8
"ftype"     = ?   (Filter type) -> Internal but closest one is Butterworth 
"window  = ?  (Window(Vector)) -> Internal but closest one in maltab available window in hamming window
"scaleopt = ?  (Normalization option) -> Normalized to get filter response 0dB.

You can consider below command in FIR to get coef:

%You can adjust 0.25 (For Fs/8) in below to change the filter corner

filter_param = round((fir1(10,0.25)).*128);

freqz(filter_param)

Regards,

Shabbir