Optical and Electrical Dual-Channel Plug-In Modules in Waveform Analysis

Dual-channel plug-in modules integrate optical-to-electrical (O/E) converters and electrical samplers within a single physical module. This co-location is essential for minimizing physical path length differences between the optical receiver and the electrical sampling path. By reducing skew, engineers can perform highly accurate time-domain waveform analysis, including jitter and eye-diagram characterization, without introducing external cable delays that distort relative timing.\n\nFor example, modules like the Keysight 86105C utilize a single DCA slot to house both a 9 GHz optical channel and a selectable 12.4 GHz or 20 GHz electrical channel. At the upper limit of high-speed digital design, the Keysight 86116C scales this architecture to handle ultra-high-speed signals, offering up to a 70 GHz optical channel alongside a 93 GHz electrical channel.

To comply with industry standards such as SONET/SDH, Fibre Channel, and Ethernet, optical channels must employ specific reference receiver filtering. These filters shape the frequency response of the optical channel (typically a fourth-order Bessel-Thomson response) to match a specified data rate. This ensures standard-compliant eye-mask testing.\n\nDepending on the target application, modules provide fixed or selectable filtering. The Keysight 86105D, for example, integrates an unfiltered 20 GHz optical channel but supports selectable compliant reference receiver filters for rates up to 14.025 Gb/s, including standard rates like 8.5 Gb/s, 10.3 Gb/s, and 11.3 Gb/s. Software-based corrections can also play a role; the 86105D offers Option IRC (system impulse response correction) to provide measured system impulse response correction for optical reference receiver compliance. For ultra-high-speed NRZ testing, the Keysight 86116C supports reference receiver rates at 39.8 and 43.0 Gb/s NRZ (Option 040) or 17, 25.8, and 27.7 Gb/s NRZ (Option 025).

High-bandwidth electrical channels require specialized RF input connectors to prevent signal attenuation and reflections. As electrical bandwidth rises, the connector geometry must shrink:\n\n* 20 GHz Bandwidth: The Keysight 86105C utilizes a 3.5 mm male electrical connector, achieving an RMS electrical noise of 0.25 mV at 12.4 GHz bandwidth and 0.5 mV at 20 GHz bandwidth.\n* 40 GHz Bandwidth: The Keysight 86109A utilizes a 2.4 mm female RF connector for its 40 GHz electrical channel.\n* 93 GHz Bandwidth: The Keysight 86116C uses a 1.0 mm male connector to sustain a nominal 50 Ω input impedance across its selectable 93 GHz, 55 GHz, and 30 GHz settings.\n\nProper nominal impedance matching and adhering to the maximum safe input voltage limits—such as ±2 V for the Keysight 86105D and Keysight 86105C—are critical to protecting the sensitive sampling bridges from ESD and overvoltage damage.