DisplayPort multiplexer for bidirectional video in all-in-one computer systems

CBTL12131 is an integrated DisplayPort high-speed path switch/multiplexer that allows all-in-one computer systems to efficiently manage path switching between different display modes of operation. With the CBTL12131, video can be routed either from one DisplayPort source (GPU1) to an integrated DisplayPort panel and simultaneously from a second DisplayPort source (GPU2) to an external DisplayPort sink; or from an external DisplayPort source to the integrated DisplayPort panel.

The device is configured as four main Ports A through D, each providing four high-speed differential lanes for DisplayPort Main Link (ML) channels, one high-speed differential lane for the DisplayPort AUX channel, and one single-ended lane for the HPD (Hot Plug Detect) signal. One port (Port A) provides an additional alternate lane for the AUX channel, in order to allow bypassing of external AC-coupling capacitors for support of the DDC channel in case an external connected sink is a ‘++DP’ type cable adapter.

For the path supporting the ‘external source to integrated DisplayPort panel’ mode, a programmable equalizer is provided which allows compensation for channel loss that the external source or internal sink are unable to adequately compensate for. The equalizer is self-biasing and is programmable to five gain-frequency curves, of which one is a flat response and four are active equalization. The equalizer output can also be set to one of two levels of pre-emphasis (including flat), and also differential swing level can be set to one of two levels. All options (EQ, pre-emphasis, level) are easily programmed using board-strapping (resistor, short or open) of three unique Quinary Input programming pins.

The CBTL12131 includes additional features that support use of the external DisplayPort connector in both directions: either an external sink (monitor or cable adapter) or external source (notebook computer) can be connected, while CBTL12131 configures the direction and termination of the related signals accordingly. The port facing the external DisplayPort connector (Port B) is equipped with dedicated sensing circuitry which detects and reports the status of the HPD and AUX lines, to support the system controller in determining and setting the proper connection status. The AUX channel of Port B also has switchable integrated termination, to allow the system controller to apply the correct DC termination in case an external DisplayPort source is connected. Moreover, it affords the system controller the means to detect the type of system (sink, source or all-in-one computer) connected at Port B, and apply the proper termination required in each scenario.

The CBTL12131 is powered from a single 3.3 V power supply, consumes very little current while providing low insertion loss and low return loss high-speed differential switch channels suitable for use in DisplayPort v1.1a interconnect. All switch and configuration settings can be performed by board-strapping or driving simple CMOS inputs—no software or bus configuration is required. CBTL12131 is available in a 6 mm × 6 mm TFBGA64 package with 0.5 mm ball pitch; owing to its high level of integration and versatility, it is eminently suitable for use in computers employing bidirectional DisplayPort video.