PCM1865 - HPF bypass

Hirotaka Matsumoto

Other Parts Discussed in Thread: PCM1865

Hi all,

Would you mind if we ask PCM1865?

There are two HPFs on PCM1865, one is for Main ADC, the other is for Secondary ADC.
On Page 0 / Register 113 (Hex 0x71), it is possble to switch Enable/Disable of HPF.
So, in order to bypass HPF, is this Enable/Disable effective for Main ADC and Secondary ADC?
Or, only for Main ADC?

Kind regards,

Hirotaka Matsumoto

over 9 years ago

0 Justin Bohr over 9 years ago

TI__Mastermind 27850 points

Hi Hirotaka,

This is for the main ADC high pass filter. When in standby/sleep and energysense is enabled the HPF for the secondary ADC will always be on, but the filter can be moved with the coefficient registers in table 25 of the data sheet.

Justin

0 Ryan Day over 9 years ago in reply to Justin Bohr

Prodigy 70 points

I am struggling with understanding how to do that. As it isn't very well explained in the datasheets. For example what does HPF_A1 and HPF_A2 stand for ?

0 Justin Bohr over 9 years ago in reply to Ryan Day

TI__Mastermind 27850 points

Hi Ryan,

These are biquad coefficients, there are a few calculators out there for these, we have one here: www.ti.com/.../coefficient-calc

There is also a demo video for this tool:

These coefficients are in 1.23 format.

Justin

0 Hirotaka Matsumoto over 9 years ago in reply to Justin Bohr

Guru 27525 points

Justin san,

Thank you for your update!

We have one confirmation, does "the filter can be moved with" mean bypass, doesn't it?

Kind regards,

Hirotaka Matsumoto

0 Justin Bohr over 9 years ago in reply to Hirotaka Matsumoto

TI__Mastermind 27850 points

Hi Hirotaka,

By move I mean change the coefficient values to make it not filter anything, or set it as a HPF that has a corner frequency of 10s of Hz, and passes almost everything. The secondary HPF and LPF will always be enabled but the definition of those filters can be changed.

Justin

0 Ryan Day over 9 years ago in reply to Justin Bohr

Prodigy 70 points

I am still struggling to understand is there an example of programming this anywhere?

0 Hirotaka Matsumoto over 9 years ago in reply to Justin Bohr

Guru 27525 points

Justin san,

Thank you for your prompt reply.
Ok, it means it is not bypass, it is able to change the coefficient values a corner frequency of filter.
Therefore, by the coefficient values, it is able to passes almost everything(frequency), right?
Is our recognition correct?

Kind regards,

Hirotaka Matsumoto

0 Hirotaka Matsumoto over 9 years ago in reply to Hirotaka Matsumoto

Guru 27525 points

Hi team

Could you let us know our last contribution?

Kind regards,

Hirotaka Matsumoto

0 Justin Bohr over 9 years ago in reply to Hirotaka Matsumoto

TI__Mastermind 27850 points

Hi Hirotaka,

I'm going to give an overall explanation of the filters for both the Main and Secondary ADCs.

Main ADC HPF:

This is a 1st order HPF filter with a Fc of 1 Hz. This can be bypassed by changing the HPF_EN bit in register 113.

Secondary ADC HPF and LPF:

These are both modifiable by the user as to its cutoff frequency and shape with coefficients available in the DSP coefficient registers on page 107 of the data sheet. When in DC sens mode, the HPF component of the secondary ADC path with be bypassed and only the LPF will be used.

I hope this clears things up.

Justin

Audio

Audio forum

PCM1865 - HPF bypass