JAJSO88 October 2023 LMK04714-Q1
PRODUCTION DATA
To ensure proper JESD204B/C operation, the timing relationship between the SYSREF and the Device clock must be adjusted for optimum setup and hold time as shown in Figure 8-6. The global SYSREF digital delay (SYSREF_DDLY), local SYSREF digital delay (SCLKX_Y_DDLY), local SYSREF half step (SCLKX_Y_HS), and local SYSREF analog delay (SCLKX_Y_ADLY, SCLK2_3_ADLY_EN) can be adjusted to provide the required setup and hold time between SYSREF and Device Clock. It is also possible to adjust the device clock digital delay (DCLKX_Y_DDLY) and half step (DCLK0_1_HS, DCLK0_1_DCC) to adjust phase with respect to SYSREF.
The delay between clock and SYSREF is the difference between the delays for these paths.
VARIABLE/FIELD | COMMENTS | EXAMPLE (fVCO = 2.5 GHz, DIVIDE = 6) |
---|---|---|
ClockFixed Delay (DCLKX_Y_DDLY) |
ClockFixedDelay = 6000 ps (DCLK0_1_DDLY = 15) |
|
ClockFixedDelayCorrection |
Correction value when divide is less than 8.
|
ClockFixedDelayCorrection = –400 ps (–1 VCO Cycle) |
ClockDutyCycleCorrect (DCLKX_Y_DCC) |
Adds one VCO cycle if enabled |
ClockDutyCycleCorrect = 400 (DCLKX_Y_DCC = 1) |
ClockDynamicDelay (dDLY_STEP_CNT) |
ClockDynamicDelay is the cumulative effect of programming dDLY_STEP_CNT. It is zero if the dynamic delay is disabled for the channel | ClockDynamicDigitalDelay = 0 (DDLYd0_EN = 0) |
ClockHalfStep (DCLKX_Y_HS) |
This would be ½ of a VCO Cycle if enabled |
ClockHalfStep = 200 (DCLKX_Y_DCC = 1) |
SysrefGlobalDelay (SYSREF_DDLY) |
SYSREF_DDLY≥8 for proper operation |
SysRefGlobalDelay = 4800 ps (SYSREF_DDLY = 12) |
SysrefFixedDelay (SCLKX_Y_DDLY) |
This is the number of cycles represented by the delay | SysrefFixedDelay = 2 × 400 = 800 ps (SCLK0_1_DDLY = 1) |
SysrefHalfStep (SCLKX_Y_HS) |
The half step for the SYSREF is not exactly a half step, but rather about 60 ps less. |
SysrefHalfStep = 200 – 60 = 140 ps (SCLK0_1_HS = 1) |
SysrefAnalogDelay (SCLKX_Y_ADLY) |
This is the stated value in ps for the analog delay |
SysrefAnalogDelay = 230 ps (SCLK0_1_ADLY = 5) |
TotalClockDelay = 6000 + (–400) + 400 – 200 + 0 = 5800 ps | ||
TotalSysrefDelay = 80 + 400 + 4800 + 800 – 140 + 230 = 6170 ps | ||
Clock to SYSREF Delay = 6170 – 5800 = 370 ps |