Broadband Amplifiers Drive OC-768 Modulators

These broadband amplifiers deliver the voltages needed to drive LiNO<sub>3</sub> modulators at rates to 43 Gb/s with input signals as low as +0.25 VDC peak to peak.

Drivers for lithium niobate (LiNO3) or electro-absorptive (EA) modulators used in OC-768 optical-communications systems must provide high-quality output signals over six decades of bandwidth, covering approximately DC to beyond 40 GHz. Through a combination of design techniques refined over years of commercial and military projects, Narda Microwave-East (Hauppauge, NY) has created a family of broadband-modulator driver amplifiers that delivers the flat gain and group-delay responses required to produce wide-open open-eye patterns required in these high-speed optical-communications systems.

In addition to the model FO-MDA-40-00 modulator driver amplifier (see figure), the company also offers 20- and 40-GHz clock-driver amplifiers, 10-, 20-, and 40-GHz clock oscillators, broadband-data amplifiers, and OC-768 clock-recovery circuits.

The FO-MDA-40-00 modulator driver amplifier can be specified with +6.0- or +7.5-VDC outputs from LiNO3 modulators, or with a +4-VDC output from EA modulators. The +7.5-VDC version delivers its rated output level with input signals as low as +0.25 VDC peak to peak. All of the models provide a +3-VDC output-amplitude control range and incorporate eye-crossing symmetry adjustment. A dither voltage can be superimposed onto the output waveform by applying a sinusoidal input to the amplitude-adjustment control pin. An optional output-voltage-level detector can be provided that allows the amplifier's output voltage to be continuously monitored for external amplitude adjustment. The detector is temperature compensated to ensure accuracy over the operating range of 0 to +80°C. The minimum operating frequency of standard units is 80 kHz, although a version with 30-kHz, low-frequency 3-dB roll-off is also available. For all units, the input and output return loss is 10 dB, rise and fall times are 5 ps, and root-mean-square (RMS) jitter is 0.5 ps.

The FO-MDA-40-00 is available as complete unit that includes all the control circuits, as an RF hybrid alone with design information for an external control board, or as a special unit with customer-defined control functionality. The family of amplifiers operates from +9 VDC at 300 mA and −9 VDC at 20 mA, is internally regulated, and has automatic DC bias sequencing. Narda Microwave-East, 435 Moreland Rd., Hauppauge, NY 11787; (631) 231-1700, FAX: (631) 1711, e-mail: [email protected], Internet:

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