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PSoC™ 5, 3 & 1

rg
New Contributor II

What is the effective analog BW of the SAR in a PSoC 5LP when using an AMux on the front end? I found someone online claiming 70KHz but I seem to be getting much lower. I'm looking for what it is before it drops 1 or 2 dBV, so a frequency plot would be nice. The specific chip is CY8C5868AXI-LP35.

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Len_CONSULTRON
Honored Contributor II

rg,

What bandwidth are you trying to achieve?

If the bandwidth is as Rashith suggests (> 26MHz) than <70KHz should be near 0dBV.

There may be other factors contributing to the appearance of lower bandwidth.

As Rashith indicates, the analog routing may have a factor (albeit a smaller one).  Each analog switch used in the routing may be 30 to 500 ohms of series resistance.  Along with each switch comes a tiny amount of capacitance (< 1pF).

Is your AMUX setup set up with maximum isolation?  If not, you might be seeing some cross-talk with one or more of the other channel on the MUX.

What is your SAR update rate?  If the update rate is 10Ksps, then effectively the BW is about 10KHz.  You effectively lower the BW with the lower sample rate.

Len
"Engineering is an Art. The Art of Compromise."

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Rakshith
Moderator
Moderator

Hi @rg

Unfortunately, we do not have a frequency plot for the SAR or AMUX operations. The Analog Global resource 3 dB bandwidth is typically 26 MHz and you can find this information in Table 11-31 Analog Globals AC Specifications in PSoC 5LP Datasheet.  
The bandwidth can be affected by your design and routing implemented in your application. Please refer to the AMUX component datasheet to understand about the analog routing and AMUX configurations. Additionally, the bandwidth also can be limited by reconfiguring the analog switches in firmware. The Performance section on Page 8 of the AMUX component datasheet should be able to provide some details regarding the performance of software-controlled AMUX. Also, please have a look at the Analog Hardware MUX component which might help with your design.

Thanks and Regards,
Rakshith M B
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Len_CONSULTRON
Honored Contributor II

rg,

What bandwidth are you trying to achieve?

If the bandwidth is as Rashith suggests (> 26MHz) than <70KHz should be near 0dBV.

There may be other factors contributing to the appearance of lower bandwidth.

As Rashith indicates, the analog routing may have a factor (albeit a smaller one).  Each analog switch used in the routing may be 30 to 500 ohms of series resistance.  Along with each switch comes a tiny amount of capacitance (< 1pF).

Is your AMUX setup set up with maximum isolation?  If not, you might be seeing some cross-talk with one or more of the other channel on the MUX.

What is your SAR update rate?  If the update rate is 10Ksps, then effectively the BW is about 10KHz.  You effectively lower the BW with the lower sample rate.

Len
"Engineering is an Art. The Art of Compromise."

View solution in original post

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odissey1
Honored Contributor II

rg,

you didn't mention if AMux is being scanned. If that is the case, then you should expect about 1% cross-talk between channels at 100kHz scan rate.

If AMux is static, then analog bandwidth is limited by the path resistance ~1k and capacitance ~10p, which is negligible: dF = 1/(2Pi RC)~10MHz

 

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