Design Articles

SATA¹ has become the ubiquitous connection to hard drives in both laptops and desktop PCs. SATA is available in two basic forms, internal and external (eSATA). Both forms use seven conductor cables with two balanced pairs and grounds between the pairs. In addition, eSATA can be used for runs up to 2m in length and adds shielding to the cable. Many laptops and desktop computers have an eSATA connector to be used with an eSATA drive. Current data rates of 3.0Gbps can transfer data up to 10x the speed of USB 2.0 drives. Unlike the ungainly parallel cables, SATA and eSATA cables are thin and flexible, and relatively easy to handle.

Challenge of Connecting an eSATA Port to a SATA Connection

SATA and eSATA transfer data at 3.0Gbps, or 300Mbps. The eSATA signal is usually derived from a standard internal SATA port. This signal is propagated down a PC board and sent to an eSATA connector. Many hosts do not have the drive capabilities to accommodate the losses of the board, connector, and cable.

The MAX4951BE overcomes the issues of mating an eSATA port to a SATA connection. The MAX4951B drives the eSATA cable and enhances the signals in both directions through equalization. Input equalization (EQ) and output preemphasis (PE) both improve the signal quality. Both board traces and cables exhibit a lowpass filter characteristic; a typical board or cable can exhibit a -3dB point at 600MHz. Since the board or cable losses are frequency dependent, the ideal match would be a device that compensates for the high-frequency losses. With eSATA, the system must deal with signals moving in two directions: one signal goes from the host to the storage device, and one returns from the storage device to the host.