TFP403

TI

PanelBus™ DIGITAL RECEIVER

SLDS125B − DECEMBER 2000 − REVISED MAY 2011

12

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

detailed description (continued)

TFP403 clocking and data synchronization

The TFP403 receives a clock reference from the DVI transmitter that has a period equal to the pixel time, Tpix.

The frequency of this clock is also referred to as the pixel rate. Since the TMDS encoded data on Rx[2:0]

contains 10 bits per 8 bit pixel it follows that the Rx[2:0] serial bit rate is 10 times the pixel rate. For example,

the required pixel rate to support an UXGA resolution with 60 Hz refresh rate is 165 MHz. The TMDS serial bit

rate is 10x the pixel rate or 1.65 Gb/s. Due to the transmission of this high-speed digital bit stream, on three

separate channels (or twisted-pair wires) of long distances (3-5 meters), phase synchronization between the

data steams and the input reference clock is not guaranteed. In addition, skew between the three data channels

is common. The TFP403 uses a 4x oversampling scheme of the input data streams to achieve reliable

synchronization with up to 1-Tpix channel-to-channel skew tolerance. Accumulated jitter on the clock and data

lines due to reflections and external noise sources is also typical of high speed serial data transmission, hence

the TFP403s design for high jitter tolerance.

The input clock to the TFP403 is conditioned by a phase-locked-loop (PLL) to remove high frequency jitter from

the clock. The PLL provides four 10x clock outputs of different phase to locate and sync the TMDS data streams

(4x oversampling). During active display the pixel data is encoded to be transition minimized, whereas in blank,

the control data is encoded to be transition maximized. A DVI compliant transmitter is required to transmit in

blank for a minimum period of time, 128-Tpix, to ensure sufficient time for data synchronization when the

receiver sees a transition maximized code. Synchronization during blank, when the data is transition

maximized, ensures reliable data bit boundary detection. Phase synchronization to the data streams is unique

for each of the three input channels and is maintained as long as the link remains active.

TFP403 TMDS input levels and input impedance matching

The TMDS inputs to the TFP403 receiver have a fixed single-ended termination to AVDD The TFP403 is

internally optimized using a laser trim process to precisely fix the impedance at 50 Ω. The device will function

normally with or without a resistor on the EXT_RES pin, so it remains drop-in compatible with current sockets.

The fixed impedance eliminates the need for an external resistor while providing optimum impedance matching

to standard 50-Ω DVI cables.

Figure 12 shows a conceptual schematic of a DVI transmitter and TFP403 receiver connection. A transmitter

drives the twisted pair cable via a current source, usually achieved with an open drain type output driver. The

internal resistor, which is matched to the cable impedance, at the TFP403 input provides a pullup to AVDD.

Naturally, when the transmitter is disconnected and the TFP403 DVI inputs are left unconnected, the TFP403

receiver inputs pullup to AVDD. The single ended differential signal and full differential signal is shown in

Figure 13. The TFP403 is designed to respond to differential signal swings ranging from 150 mV to 1.56 V with

common mode voltages ranging from (AVDD-300 mV) to (AVDD-37 mV).