LMH1982SQ-NOPB Datasheet, PDF (20/43 Pages) Texas Instruments – Multi-Rate Video Clock Generator with Genlock

LMH1982
SNLS289C – APRIL 2008 – REVISED MARCH 2013
www.ti.com
• TOF_LPFM = 1125
(5)
Option 2) 1080p/59.94 TOF generation using 27 MHz
TOF rate = 27 MHz / 2002 x 225) = 60/1.001 Hz
where
• f_{TOF_CLK} = 27 MHz (TOF_CLK = 0, SD_FREQ = 0)
• TOF_PPL = 2002
• TOF_LPFM = 225
(6)
As an example, Figure 10 shows a timing illustration for 1080p/59 TOF and clock outputs for . Once the outputs
are initialized, the SD clock and TOF pulse will have a fixed delay, and the SD clock and HD clock will have a
fixed timing offset relative to each other. Therefore, the timing offset between the TOF pulse and HD clock, or
t_TOF-HD, will also be fixed and can be determined by:
t_TOF-HD = t_{D_TOF} + t_{D_SD} - t_{D_HD}
where
• t_{D_TOF} = TOF Output Delay Time referenced to SD_CLK
• t_{D_SD} = SD_CLK Output Delay Time
• t_{D_HD} = HD_CLK Output Delay Time
(7)
VCXO
27 MHz
3.3 V_PP
SD_CLK
27 MHz
350 mV_PP
HD_CLK
148.35 MHz
350 mV_PP
TOF
59.94 Hz
3.3 V_PP
t_{D_SD} = 4 ns
t_{D_HD} = 1.5 ns
t_{D_TOF} = 2 ns
t_TOF-HD = 4.5 ns
Figure 10. Timing Illustration Showing 1080p/59.94 TOF and CLK Output Delays Using Option 2
Reference Frame Timing
The reference format frame timing is generated internally and used for resetting the internal counters for output
initialization. The reference frame rate should be specified by programming the reference format total lines per
frame to REF_LPFM (register 0Fh-10h) as well as the PLL 1 dividers. See Table 1 for programming the
parameter values according to each reference format. The reference frame rate is determined by:
REF rate = (f_VCXO x R_DIV) / (FB_DIV x REF_LPFM)
where
• f_VCXO = 27 MHz Nominal VCXO Clock Frequency
• R_DIV = Reference Divider (not REF_DIV_SEL)
• FB_DIV = Feedback Divider
• REF_LPFM = Reference Format Total Lines per Frame
(8)
Input-Output Frame Rate Ratio
The input-output frame rate ratio is also used for resetting the internal counters for output initialization. The ratio
is the Input Frame Rate / Output Frame Rate, in which the numerator and denominator values are reduced to
lowest integer factors. The numerator value of this reduced ratio should be programmed to TOF_RST (register
09h-0Ah), and the denominator value is discarded.
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