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Stanford Research has developed a DC to 4 GHz high performance, affordable RF source, the SG384 4 GHz RF signal generator. The SG384 uses a unique, innovative architecture (Rational Approximation Frequency Synthesis) to deliver ultra-high frequency resolution (1 μHz), excellent phase noise (-116 dBc/Hz SSB phase noise at 20 kHz offset at 1 GHz), versatile modulation capabilities (AM, FM, ΦM, pulse modulation and sweeps) at a fraction of the cost of competing designs. The standard model SG384 produces sine waves from DC to 4.05 GHz. There is an optional frequency doubler (Opt. 02) that extends the frequency range to 8.10 GHz. Low-jitter differential clock outputs (Opt. 01) are available, and an external I/Q modulation input (Opt. 03) is also offered. For demanding applications, the SG384 can be ordered with a rubidium timebase (Opt. 04).
The SG384 is based on a new frequency synthesis technique called Rational Approximation Frequency Synthesis (RAFS). RAFS uses small integer divisors in a conventional phase-locked loop (PLL) to synthesize a frequency that would be close to the desired frequency (typically within ±100 ppm) using the nominal PLL reference frequency. The PLL reference frequency, which is sourced by a voltage-controlled crystal oscillator that is phase-locked to a dithered direct digital synthesizer, is adjusted so that the PLL generates the exact frequency. Doing so provides a high phase comparison frequency (typically 25 MHz) yielding low phase noise while moving the PLL reference spurs far from the carrier where they can be easily removed. The end result is an agile RF source with low phase noise, essentially infinite frequency resolution, without the spurs of fractional-N synthesis or the cost of a YIG oscillator.
Stanford Research Systems
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