N Parameter; Cts Parameter; Recommended N And Expected Cts Values; Figure 96: Audio Clock Regeneration - Analog Devices ADV8003 Hardware Manual

f
128 ×
S
VIDEO CLOCK
N
Figure 96 illustrates the overall system architecture model used by HDMI Rxs for audio clock regeneration. The HDMI source determines
the fractional relationship between the video clock and an audio reference clock (128*fs) and passes the numerator and denominator for
that fraction to the sink across the HDMI link. The sink may then recreate the audio clock from the TMDS clock by using a clock divider
and a clock multiplier. The relationship between the two clocks is shown in
The source determines the value of the numerator N as specified in the HDMI specification. Typically, this value N is used in a clock
divider to generate an intermediate clock that is slower than the 128*fs clock by the factor N. The source typically determines the value of
the denominator Cycle Time Stamp (CTS) by counting the number of TMDS clocks in each of the 128*fs/N clocks.
6.11.3.1.

N Parameter

N is an integer number and is calculated using
approximately equals N for coherent audio and video clock sources.
coherent sources or sources where coherency is not known,
6.11.3.2.

CTS Parameter

The CTS value is an integer number that satisfies
6.11.3.3.

Recommended N and Expected CTS Values

The recommended values of N for several standard pixel clocks are given in
The ADV8003 has two modes for CTS generation.
Rev. B, August 2013
SOURCE DEVICE
DIVIDE
CYCLE
BY
TIME
N
COUNTER
REGISTER
N
1
N AND CTS VALUES ARE TRANSMITTED USING THE "AUDIO CLOCK REGENERATION"
PACKET. VIDEO CLOCK IS TRANSMITTED ON TMDS CLOCK CHANNEL.

Figure 96: Audio Clock Regeneration

128
Equation 20: Relationship Between Audio Reference and TMDS Clocks
Equation 21
128*fS/1500Hz ≤N ≤128*fS/300Hz
Equation 21: Restriction for N Value
Equation
CTS
Equation 23: Relationship Between N and CTS
1
CTS
TMDS
CLOCK
1
N
Equation
N
=
f f
s TMDS _ CLK
CTS
with the recommended optimal value shown in
Table 62 to Table
Equation 21, Equation
128*fs/1000Hz
Equation 22: Optimal N Value
23.
f
=
TMDS _ CLK
Average
128 f
s
Table 62
273
SINK DEVICE
DIVIDE MULTIPLY
BY BY
CTS N
20.
64 can be used to determine the value of N. For non
22, and Equation 23 should be used.
N
to Table 64.
ADV8003 Hardware Manual
f
128 ×
S
Equation 22 which