Gennum unveils ROSAs with "receiver on a chip"

FEBRUARY 20, 2008 By Stephen Hardy -- Gennum Corp. (search for Gennum), known in the optical communications market for its transceiver ICs, has announced a line of receive optical subassemblies (ROSAs). The devices leverage the company's expertise in TIA technology and manufacturing in the form of what Gennum calls the Rchip, a "receiver on a chip" that integrates the TIA, photodiode, and passives into a single package. The design improves yield and lowers cost, according to company sources.

The four new ROSAs represent Gennum's first foray into optical products for telecommunications applications; the company makes optical modules for video applications. Imran Sherazi, marketing director, optical products, at Gennum, says the 10-Gbit/sec devices -- for 850-nm multimode, 10GBase-LRM, 1310-nm 10-km, and 1550-nm 40-km applications, respectively -- benefit from both a new TIA and the Rchip design.

The Rchip significantly improves both yield and performance, Sherazi asserts. It obviates the need for external capacitors and decreases the number of wire bonds necessary in the receiver assembly from around 20 to 7. The design therefore limits the intrinsic oscillation encountered in conventional designs. Meanwhile, long-wavelength Rchip design enables the InP PIN diode to be flip-chip bonded to the rest of the assembly before the wafer is diced. This enables the assembly to be tested at the wafer level before the package in encapsulated into a ROSA. Wafer-level testing of the short-wavelength versions of the device is limited to the TIA with the decoupling capacitors because of the GaAs materials used in the PIN diodes for such applications.

The four ROSAs are currently available. They include:

• The GN3150 short-wavelength ROSA targets multimode applications from 50 to 300 m. The 850-nm device offers sensitivity of -15 dBm, overload capability of +3.5 dBm, and gain of 10 kOhms.
  
• The GN3050 long-wavelength device is designed for 10-km singlmode fiber applications, such as OC-192 SR-1 and 10-Gigabit Ethernet LR. If offers stress sensitivity of -21 dBm, overload of +0.5 dBm, and 10-kOhm gain.
  
• The GN3250 40-km ROSA operates at 1550 nm. It features optical return loss of greater than 27 dBm, stress sensitivity of -21 dBm, overload of +1.6 dBm, and gain of 10 kOhms.
  
• The GN3052 has automatic gain control for 10GBase-LRM applications. It has shown -12-dBm sensitivity when measured under stress conditions.
  

The ROSAs are targeted at X2, XFP, and SFP+ transceivers. The products will be on display next week during OFC/NFOEC at booth 3049.

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