Stanford CG635

The CG635 has several clock outputs. The front-panel Q and -Q outputs provide complementary square waves at standard logic levels (ECL, PECL, LVDS or +7 dBm).

The square wave amplitude may also be set from 0.2 V to 1.0 V, with an offset between -2 V and +5 V. These outputs operate from DC to 2.05 GHz, have transition times of 80 ps, a source impedance of 50 Ω, and are intended to drive 50 Ω loads.

Output levels double when these outputs are unterminated.

The front-panel CMOS output provides square waves at standard logic levels. The output may also be set to any amplitude from 0.5 V to 6.0 V. The CMOS output has transition times of less than 1 ns and operates up to 250 MHz.

It has a 50 Ω source impedance and is intended to drive high impedance loads at the end of any length of 50 Ω coax cable.

A rear-panel RJ-45 connector provides differential square wave clocks on twisted pairs at RS-485 levels (up to 105 MHz) and LVDS levels (up to 2.05 GHz).

This output also provides ±5 VDC power for optional line receivers (CG640 to CG649).

The clock outputs have 100 Ω source impedances and are intended to drive shielded CAT-6 cable with 100 Ω terminations.

The differential clocks may be used directly by the target system, or with optional line receivers that provide complementary logic outputs on SMA connectors.

The standard crystal timebase has a stability of better than 5 ppm.

The CG635's 10 MHz timebase input allows the instrument to be phase-locked to an external 10 MHz reference.

The 10 MHz output may be used to lock two CG635s together.

There are two optional timebases.

An oven-controlled crystal oscillator (OCXO) provides about 100 times better frequency stability than the standard crystal oscillator.

A rubidium frequency source provides about 10,000 times better stability.

Either optional timebase will substantially reduce the low-frequency phase noise of the synthesized output.

The clock phase can be adjusted with high precision.

The phase resolution is one degree for frequencies above 200 MHz, and increases by a factor of ten for each decade below 200 MHz, with a maximum resolution of one nano-degree.

This allows clock edges to be positioned with a resolution of better than 14 ps at any frequency between 0.2 Hz and 2.05 GHz.

The timing of clock edges can be modulated over ±5 ns via a rear-panel time-modulation input.

The input has a sensitivity of 1 ns/V and a bandwidth from DC to over 10 kHz, allowing an analog signal to control the phase of the clock output.

This feature is very useful for characterizing a system's susceptibility to clock modulation and jitter.

With its exceptionally low phase noise and high frequency resolution, the CG635 replaces RF signal generators in many applications.

Front-panel outputs provide square waves up to +7 dBm—ideal for driving RF mixers.

Should your application require sine waves, in-line low-pass filters are commercially available to convert the CG635's square wave outputs to low distortion sine wave outputs.

The CG635 can provide a wide range of clean, precise clocks for the most critical timing requirements.

The instrument is an essential tool for demonstrating a system's performance with a nearly ideal clock, and for understanding a system's susceptibility to a compromised clock.

The CG635 has the frequency range, precision, stability, and jitter-free performance needed to fulfill all your clock requirements.