Serializer IC Options for High Speed Boards

Serializer ICs are one of those often-overlooked components that runs quietly in the background of computer peripherals, networking equipment, high-definition multimedia, and other high speed digital systems. Getting data between different locations on a board quickly is critical to digital system performance, and serializer IC components play an important role in moving data at high speed.

Serializer ICs in High Speed Channels

A high speed digital channel can take many forms, but the most common form is a SerDes channel (serializer/deserializer). Components used in these channels compress a parallel datastream down to a smaller number of channels that run at a high data rate. The common manifestation of a SerDes channel is one where the transmitter component (serializer) takes a parallel data stream and reduces it to a single serial data stream. Some serializer ICs will reduce the input parallel data stream to a smaller number of parallel channels (an example is shown below).

Reducing the number of channels for long links saves board space, and it eliminates or reduces crosstalk. This allows longer links to be routed, and channel losses become dominated by insertion loss. At the receive end, the data is received and compensated with equalization, and then converted back to parallel data at the output interface.

SerDes channel schematic

There are some basic specifications to consider when selecting a serializer IC for a high speed link.

• Input and output interfaces: Input data can be routed into these components as single-ended signals (e.g., LVCMOS/LVTTL) or differential pairs (e.g., LVPECL). The common output interface is LVDS.
• Data rate: Some serializers have configurable data rates, either by adjusting one of the inputs or with an external MCU.
• Clock style: Since system clocks are not ideal for high speed digital systems, source-synchronous or embedded clocking is used to route clock signals around the system.
• Channel pre-emphasis: This is an important point to consider when selecting a serializer IC. At the transmit end, applying pre-emphasis overcomes some of the designed channel losses and provides a longer link.
• Rise time: The rise time for your output signals is important when modeling channel losses and dispersion. This will determine the signal bandwidth, which can be calculated using a knee frequency.
• Input and output channels: Remember that a serializer compresses a large number of parallel channels into a smaller number of serial channels. Check for the number of input and output channels.

The above specifications are also important at the receiver (deserializer) end of the channel. More advanced SerDes transceivers are using multilevel signalling with half-duplex or full-duplex communication. However, simpler serializer ICs provide high data rates and still have their place in many systems, particularly in high-speed networking and high-definition video.

High Speed Serializer IC Options

The components shown below are more application-specific, but you can still find serializers that are closer to general-purpose. This is the starting point for building your high speed serial link. At the receive end, you’ll need a deserializer to convert data back to parallel, which is then output through a standard interface. If you’re working with long channel links, some components provide channel equalization, where effects like skew, insertion loss, and intersymbol interference are compensated at the receiver end. Take a look at the components below for some example serializer ICs.

Texas Instruments, DS32ELX0421SQE

The DS32ELX0421SQE from Texas Instruments is an older component, but it remains useful to this day in lower-speed networking equipment over fiber or copper (e.g., small switches and routers). This component delivers 3.125 Gbps from a 5-bit DDR LVDS parallel interface. It includes integrated LVDS terminations, making it easy to incorporate into a channel. One application involves FPGA-to-FPGA links, where high throughput is required. An example from the DS32ELX0421SQE datasheet is shown below.

Example application diagram from the DS32ELX0421SQE datasheet.

Maxim Integrated, MAX9291GTN+

The MAX9291GTN+ serializer IC from Maxim Integrated is a multigigabit SerDes interface that is ideal for multimedia applications. This is one example of a particular serializer IC designed for a specific application; this component converts an HDMI input to a gigabit multimedia serial link (GMSL) output. Control, audio, and video signals can be sent over at least 15 m of 50Ω coax or 100Ω shielded twisted-pair (STP) cable. This component can also be used to control a peripheral at the remote end via I2C communication.

At the receive end, you can use a MAX9286GTN/V+ deserializer to retrieve parallel data. Data rates for both components can be varied from 9.6 kbps to 1 Mbps in each channel, and both components can be programmed with a microcontroller. Take a look at the MAX9291GTN+ datasheet for more information.

Evaluation board for the MAX9291GTN+ serializer IC.

Texas Instruments, DS90CR485VS

The DS90CR485VS 10 Gbps serializer IC from Texas Instruments is another older component that continues to stand the test of time. It provides 48-in/8-out data transmission (24 LVCMOS/LVTTL double-edge inputs) at 6.384 Gbps via LVDS. This component pairs with the DS90CR486VS deserializer at the receive end. This component incorporates pre-emphasis to overcome long-channel and cable-loading effects. Note that this component uses parallel clocking, making it useful in source-synchronous systems.

Functional block diagram from the DS90CR485VS datasheet.

The serializer IC options shown here are just a few examples, and there are many more general-purpose options for different data rates and signalling standards. Newer serializers are being released periodically for high speed peripherals, and Octopart will be here to help you find the components you need.

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