The Stanford Research CG648 is a high-performance ECL clock generator producing stable signals from DC to 2.05 GHz with random jitter below 1 ps rms. Built for demanding applications in research, high-speed digital systems, and communications networks, it delivers precise frequency control with 16-digit resolution and adjustable phase positioning to ±5 ns across its full operating range. Front-panel SMA outputs provide complementary square waves in ECL, PECL, LVDS, or CMOS logic levels, while a rear-panel RJ-45 connector offers differential clock distribution via RS-485 (to 105 MHz) or LVDS (to 2.05 GHz). The CG648 features a crystal-controlled 10 MHz timebase with 5 ppm stability, upgradable to OCXO or Rubidium references for applications demanding superior frequency accuracy. Output amplitude is adjustable from 0.2 V to 1.0 V into 50 Ω loads, with offset control from −2 V to +5 V. Rise and fall times of 80 ps minimize signal degradation in time-critical applications. Phase resolution reaches 1 degree above 200 MHz, with edge positioning better than 14 ps at any frequency between 0.2 Hz and 2.05 GHz. An optional PRBS generator supports eye-pattern testing of high-speed data channels up to 1.55 Gb/s. Fast settling time under 30 ms ensures rapid frequency transitions. Remote control via RS-232 and IEEE-488/GPIB enables automated test sequences and system integration.
Technical Specifications
• Frequency Range: DC to 2.05 GHz
• Output Logic Levels: ECL, PECL, LVDS, CMOS, RS-485
• Jitter: Random jitter 200 MHz); 1 nanodegree (finest)
• Edge Positioning Resolution: Better than 14 ps (0.2 Hz to 2.05 GHz)
• Time Modulation Range: ±5 ns
• Timebase Stability: 5 ppm (crystal); upgradable to OCXO or Rubidium
• Settling Time: < 30 ms
• RS-485 Rear Output: Up to 105 MHz
• LVDS Rear Output: Up to 2.05 GHz
• PRBS Generator (Optional): Up to 1.55 Gb/s
– Key Features
• Complementary Q and −Q front-panel outputs on SMA connectors
• Differential clock distribution via RJ-45 on twisted pairs
• Rear-panel ±5 VDC power for optional line receivers
• Adjustable phase and edge timing for precision synchronization
• Dual timebase options for stability-critical measurements
– Typical Applications
• High-speed digital system clocking and synchronization
• Data acquisition and transmission systems
• Communication network testing and development
• Eye-pattern analysis for serial data channels
• Phase-coherent measurement systems
– Compatibility & Integration
• Designed to work with optional line receivers (CG640 to CG649)
• Interfaces via RS-232 and IEEE-488/GPIB for remote control
• Supports CAT-6 cable termination at 100 Ω (rear RJ-45 output)
