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PI3HDMI201
PI3HDMI201 in Source Application
by Ada Yip
Table of Contents
1
Introduction ...............................................................................................................................2
2
PI3HDMI201 in Source Application...........................................................................................2
3
Equalization Setting ..................................................................................................................2
4
Swing and Pre-emphasis Settings ............................................................................................2
5
Reference Design for Source Application .................................................................................3
Page 1 of 4
AN245
Pericom Semiconductor Corp.
www.pericom.com
7/8/2011
245
1
Introduction
Switching between two sources, e.g. chipset and graphic card, is a common HDMI source application. A 2:1 active
HDMI switch, PI3HDMI201, supports deep color and up to 25m cable length application. With various selections of
equalization settings, PI3HDMI201 allows user to place the source up to 24 inches away from the switch device on
PCB. It is a suitable device to handle the switching in a notebook.
2
PI3HDMI201 in Source Application
PI3HDMI201 can be employed in HDMI source application to perform re-driver function with optimized pre-emphasis
and equalization settings. Assuming that the PI3HDMI201 is located close to HDMI output connector, optimum output
swing, pre-/de-emphasis and equalization settings are recommended in this application note. Reference designs are
also provided.
3
Equalization Setting
PI3HDMI201 offers various equalization settings for different input trace lengths. EQ_S1 and S0 control pins are used
to select desired EQ setting.
Input PCB Trace Length
Recommended EQ
EQ_S1
EQ_S0
4 – 8 inch
8 – 16 inch
12 – 18 inch
16 – 24 inch
3dB
8dB
Optimized EQ (12dB)
15dB
0
1
1
0
1
0
1
0
Table 1: Recommended EQ Setting for Source Application
As 100kΩ internal pull-up resistors are implemented in EQ pins of PI3HDMI201, only external pull-down resistors are
required to adjust equalization settings.
4
Swing and Pre-emphasis Settings
PI3HDMI201 offers various swing and pre-emphasis settings for source and sink applications through OC_S[2:0]
control pins. If PI3HDMI201 is used in source application, two swing and pre-emphasis settings are recommended in
order to fulfill the swing and VLOW requirements in HDMI Compliance Specification.
Output PCB
Trace Length
Recommended
Swing
Recommended
Pre-emphasis
OC_S2
OC_S1
OC_S0
1 – 2 inch
3 – 4 inch
500mV
500mV
0dB
1.5dB
0
0
1
1
1
0
Table 2: Recommended OC Setting for Source Application
As 100kΩ internal pull-up resistors are also implemented in OC pins of PI3HDMI201, only external pull-down resistors
are required.
Page 2 of 4
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Pericom Semiconductor Corp.
www.pericom.com
7/8/2011
245
5
Reference Design for Source Application
Below is a reference design of PI3HDMI201 in source application.
Figure 1: Reference Design of PI3HDMI201 Source Application
Intel’s 82G45 north bridge and MXM’s graphic card are used as sources in the reference design above. TMDS output
of Intel 82G45 GMCH is SDVO interface but PI3HDMI201 has integrated 50Ω termination resistor at each TMDS input;
AC coupling capacitor has to be added between each TMDS output of 82G45 and TMDS input of PI3HDMI201 to
prevent SDVO from being damaged.
Figure 2: AC Coupling Capacitors between 82G45 TMDS Output and PI3HDMI201 TMDS Input
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7/8/2011
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In addition to AC coupling implementation, VDD of PI3HDMI201 has to be soft started to avoid inrush current charging
up the capacitor and avoid overshoot creation.
Figure 3: Soft Start Circuit of PI3HDMI201 VDD
To level shift the high level of DDC lines from 3.3V to 5V for external connection, 2N7002 FET is implemented in each
DDC line.
Figure 4: DDC Level Shifter of PI3HDMI201
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7/8/2011
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To offer more flexibility to customers, all TMDS+ and – of PI3HDMI201 are swappable. Also, CLOCK and DATA
channels are interchangeable. However, there is a trade off for interchanging CLOCK and DATA channels: the
equalization setting has to be fixed to 3dB as the EQ of TMDS CLK input is fixed to 3dB by design. Below is an
example.
Figure 5: Reference Design of PI3HDMI201 Source Application with Interchanged CLOCK and DATA
Page 5 of 4
AN245
Pericom Semiconductor Corp.
www.pericom.com
7/8/2011