CYUSB3014 Rx CTLE Transfer Function data

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tcarlsso
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Hi,

A follow up question to this thread:

https://community.cypress.com/t5/USB-Superspeed-Peripherals/CTLE-settings-for-CYUSB3014/m-p/96123

...where 4dB was stated to be the default CTLE Rx Equalization.

My follow up question is:

What pole and zero frequencies do you use for the CTLE Transfer Function? Refer to Figure 6-27 (from USB3.2 Spec - https://www.usb.org/document-library/usb-32-specification-released-september-22-2017-and-ecns) copied below.

Does CYUSB3014 use characteristics for "Long Channel" or "Short Channel"?

I.e.

Adc 0.667
fz 650MHz 
fp1 1.95GHz 
fp2 5GHz

or

Adc 1.000
fz 650MHz
fp1 650MHz
fp2 10GHz

?

tcarlsso_0-1619621827603.png

And if I want to change these frequencies in the CYUSB3014 device, is that possible? Imagine if I have a "short channel" and your default Rx Equalization is for "Long channel". Then I may want to change to "Short Channel" equalization to avoid over equalization.

Thanks.

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Rashi_Vatsa
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Hello,

Please find my comments below

From you previous post "where 4dB was stated to be the default CTLE Rx Equalization."

>> The RX equalization value set as 4 in FX3 SDK does not mean that it is the gain value (4dB)

So, what pole and zero frequencies does the FX3 chip implement by default? Is there different frequencies for long and short channel or do you use the same?

>> During the tests, we set the frequencies irrespective of the RX equalization value set in FX3 device. We test for both the channels i.e. long and short channel and set the pole  frequencies same as mentioned in Fig 6-7 of  the USB 3 spec (shared by you in the description)

We follow the attached document for the USB3 Compliance tests

Regards,
Rashi

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Rashi_Vatsa
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Hello,

FX3 passes USB compliance tests for both short channel and long channel with the default CTLE RX equalization setting mentioned in the thread 

Regards,
Rashi
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tcarlsso
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Hello,

Yes, I believe so, but that does not help me when I measure on my implementation. 

So, what pole and zero frequencies does the FX3 chip implement by default? Is there different frequencies for long and short channel or do you use the same? I believe you use the same, right? but what are they? I need to know so I can set the oscilloscope to correct CTLE characteristic to see what the FX3 chip sees after Rx equalization. If I use the "Long" channel frequencies I get a lot of eye violations on the high/low side (over equalization) since I have a short channel implementation. 

Ore are these frequencies possible to change through the API? Or do you do some adaptation?

Thanks

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Rashi_Vatsa
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Hello,

Please find my comments below

From you previous post "where 4dB was stated to be the default CTLE Rx Equalization."

>> The RX equalization value set as 4 in FX3 SDK does not mean that it is the gain value (4dB)

So, what pole and zero frequencies does the FX3 chip implement by default? Is there different frequencies for long and short channel or do you use the same?

>> During the tests, we set the frequencies irrespective of the RX equalization value set in FX3 device. We test for both the channels i.e. long and short channel and set the pole  frequencies same as mentioned in Fig 6-7 of  the USB 3 spec (shared by you in the description)

We follow the attached document for the USB3 Compliance tests

Regards,
Rashi
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tcarlsso
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Hi,

>> What is the "RX equalization value 4" then if it is not the gain value (4dB)? Can you link me to a document where this is described?

>> During operation, does the FX3 chip do Rx equalization training to compensate different channels (of different loss) as optimal as possible?

Thanks,

Tomas

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Rashi_Vatsa
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Hello,

Apologies for the delayed response. We understand that you are trying to do CTLE settings on your scope. But we would like to understand the following:

  1. Are you performing receiver electrical compliance test? If yes, with the default CTLE settings (as per USB 3.0 spec) on the scope, do you see JTOL test failing?
  2. OR are you performing transmitter electrical compliance test? If yes, do you see any test failing with default scope CTLE values. In general, CTLE is ON for long channel tests. Please let us know the reason to use CTLE for short channel.
Regards,
Rashi
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tcarlsso
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>> And if link training is done, how is it done? Is it done according to some standard USB 3.2 Gen1 link training sequence?

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tcarlsso
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Hi again,

Another question:

>>From the FX3 API Guide:

CyU3PUsbSetTxDeemphasis() API sets the Tx de-emphasis setting for the USB 3.0 signals. TX De-emphasis value should be less than 0x1F. The default value is 0x11. Please use this API with caution. This API is expected to be called before calling the CyU3PConnectState() API to enable USB connections.

 

What does default 0x11 mean for CyU3PUsbSetTxDeemphasis()? 3dB?

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Rashi_Vatsa
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Hello Tomas,

Please find the formula for calculating corresponding Tx de-emphasis (dB) value 

Tx de-emphasis (dB) = 20 *log10  [(128 − 2 * tx_deemphasis value) /128]

Note:  tx_deemphasis value is the value set using CyU3PUsbSetTxDeemphasis API

Regards,
Rashi
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