Part Number: DS90UB935-Q1
Hi, Team!
We are considering the configuration shown in the figure below.
Since the sensor clock requires 45Mhz, the serializer OUTCLK cannot be used.
The CSI-2 clock and the SerDes REF clock are asynchronous.
Is this okay?
Please let me know if you have any notes.
Hello,
It is possible for the CLK_OUT pin on the 935 device to reach 45MHz. You can use the following equation defined in the 935 device datasheet to configure the CLK_OUT frequency.
Also use Table 7-6. Clocking Modes in the datasheet to calculate the FC line rate, depending on the MODE of operation and the REFCLK used.
Also keep in mind that HS_CLK_DIV defaults to 4 and should not be set lower, since we need to meet this equation:
If the connected 935/936 devices are in Synchronous MODE, the REFCLK is 25MHz, and all of the M, N, and HS_CLK_DIV values are in their default values, then CLK_OUT on the 953 will output 25MHz.
Since you want CLK_OUT to be 45MHz, you could set M=9 and N=200, but that will lead to increased jitter on the CLK_OUT signal since N/M is not an integer. Jitter will be about 1ns (HS_CLK_DIV/FC).
If the designer wants less jitter and is fine with 1% deviation from the target 45MHz frequency (CLK_OUT = 45.45MHz), then you can use these settings:
M=9, N=198, HS_CLK_DIV=4
You can check the camera datasheet to see if any of these configurations are possible. Or you can adjust the register settings on the 935 or the REFCLK used in the system, to see if it is possible to reach your desired 45MHz signal output on the CLK_OUT pin.
And getting back to your original question, you could also use a separate 45MHz oscillator as a reference clock for your imager. The CSI clock and the 25MHz REFCLK on the 936 device do not need to be synchronized. The imager can use any reference frequency to drive its MIPI CLK output. You just need to make sure that the MIPI CLK output meets the 935's datasheet specs:
The max frequency of the Mipi CLK that is being inputted into the 935 serializer should be up to 416MHz and only up to 832Mbps of data should be transferred on the CSI-2 data lanes. Also keep in mind that if you are using the 935 device, the total Mipi data rate should be 2.5Gbps or less. For example, you could have x2 CSI-2 data lanes active operating at the max 832Mbps, which will have a total Mipi data rate of 1.664Gbps. Or you could have x4 CSI-2 data lanes active, with each transferring up to around 600Mbps per lane, which will have a total Mipi data rate of about 2.4Gbps.
Best,
Justin Phan
