DS90UB953-Q1: Can 953 support spread spectrum under external clock mode

Hi Cindy,

If use a external Oscillator which can support SSC input to 953 CLKIN pin , can this work for SSC? if not ,  why?

Looks like 933 can support this, with a external Oscillator which can support SSC.

Thanks

Best regards,

David

Hi David,

Huang David said:

If use a external Oscillator which can support SSC input to 953 CLKIN pin , can this work for SSC? if not ,  why?

This is not supported. The 953 can only support SSC if it is 1) connected to a partner deserializer such as the 954 and 960 with an SSC REFCLK applied to the DES and 2) is operating in synchronous mode with the DES. This is the way these devices are designed. You will still get SSC on both the forward channel and back channel doing it this way. 

Huang David said:

Looks like 933 can support this, with a external Oscillator which can support SSC.

I am not sure where you got this information, but the 933 cannot support an external oscillator with SSC. The 933 PLL is not designed to track an SSC clock input.

Regards,

Cindy

Hi Cindy,

Thanks for your feedback. 

1: The 953 can only support SSC if it is 1) connected to a partner deserializer such as the 954 and 960 with an SSC REFCLK applied to the DES and 2) is operating in synchronous mode with the DES. This is the way these devices are designed. You will still get SSC on both the forward channel and back channel doing it this way. 

What is the SSC range of the 954 or 960 REFCLK input？  Can below range  be supported?

What is the difference between SSC REFCLK  in 954/960 and SSC REFCLK  in 953? The two side PLL is different?

2: So similar to 953, 933 can not support SSC REFCLK  in 933. How to use SSC with 933, also need to apply the SSC REFCLK in 934 or 933 can not support SSC?  You mentioned "The 933 PLL is not designed to track an SSC clock input.", what is the special requirement of PLL to  track an SSC clock input?

Thanks

Best regards,

David

Hi David,

Huang David said:

What is the SSC range of the 954 or 960 REFCLK input？  Can below range  be supported?

You can refer to Table 7-3 REFCLK Oscillator Specifications in the 954 datasheet for more information. I cannot read the picture you attached, but the SSC range depends on the type of spread spectrum you are using. If using center spread, the SSC modulation percentage can range from -0.5 to +0.5%. If using down spread, the SSC modulation percentage can range from -1 to 0%. The SSC modulation frequency has a max of 33kHz.

Only the 954/960 PLL can support SSC applied to the REFCLK pin. In synchronous mode, the 953 uses the deserializer reference clock extracted from the backchannel, so that is how the 953 spreads the forward channel as well. 

Huang David said:

So similar to 953, 933 can not support SSC REFCLK  in 933. How to use SSC with 933, also need to apply the SSC REFCLK in 934 or 933 can not support SSC?

The 933 does not support SSC. It requires an external clock since it is a DVP device, so it cannot use the deserializer REFCLK as its clocking source. I cannot discuss the detailed design of the 933 - it is just important to know that you cannot apply SSC directly to a 933 or 953.

Regards,

Cindy

Hi Cindy,

Thanks for your feedback. Could you help illustrate the 33kHz and  -0.5 to +0.5% center or  -1 to 0% down relationship?

Best regards,

David

Hi David,

Here is an E2E thread that goes over the relationship between these SSC parameters that you may find helpful: https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1115377/ds90ub960-q1-ssc-clarification?tisearch=e2e-sitesearch&keymatch=spread%20spectrum%20clock#

Regards,

Cindy