Electronic Design

Digitally Controlled Potentiometer Controls And Monitors Laser Diode's Bias Current

Combining its nonvolatile memory technology with analog and mixed-signal functions, Xicor Inc. has created a new line of digitally controlled potentiometers (DCPs). This series offers major control and monitoring functions required for driving laser diodes used in fiber-optic communications.

In essence, the X952x integrates proven DCP technology, nonvolatile memory, and basic control functions onto a single chip. This simplifies the design of fiber-optic modules targeting Fibre Channel and Gigabit Ethernet applications. Plus, it cuts manufacturing costs. The X9520, the flagship member of this family, provides three nonvolatile DCPs, power-on reset control, and two programmable threshold-voltage monitor inputs. The device combines these features with software and hardware output flags, and 2-kbit EEPROM with write protect and block-lock protection. These functions are accessed by a standard two-wire serial interface that complies with the gigabit interface converter (GBIC) protocol.

To control the bias and modulation currents of the laser diode in a fiber-optic module, 256 tap 100 kΩ and 100 tap 10 kΩ DCPs may be used. Other reference parameters can be set by the third low-resolution DCP (64 tap 10 kΩ). With the on-chip EEPROM, users can store fiber-optic manufacturing data, serial numbers, or other system parameters. The programmable voltage monitor keeps a tab on the supply voltages. Similarly, the power-on reset ensures that VCC is stable before power is applied to the laser diode.

Other members of the new DCP family include the X9521, X9522, and X9523. They provide combinations that are subsets of the X9520. For instance, the X9521 offers two DCPs and 2-kbit EEPROM, but omits voltage monitors and power-on reset. While the X9522 contains three DCPs and two programmable voltage monitors, it excludes memory and power-on rest. the X9523 includes two DCPs, two programmable monitors and power-on rest, but has no EEPROM.

Sampling now, the X952x series is slated for production in the fourth quarter. Available in 1000-piece quantities, the X9520 is priced at $4.19 in a 20-pin TSSOP and $5.07 for 20-ball BGA packaging.

Xicor Inc., 1511 Buckeye Dr., Milpitas, CA 95035; (408) 546-3492; Internet: www.xicor.com.

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