Stanford Research Systems SG386 datasheet

RF Signal Generators

SG380 Series — DC to 2 GHz, 4 GHz and 6 GHz analog signal generators

· DC to 2 GHz, 4 GHz or 6 GHz

· 1 µHz resolution

· AM, FM, ΦM, PM and sweeps

· OCXO timebase (std.)

· −116 dBc/Hz SSB phase noise
(20 kHz offset, f = 1 GHz)

· Rubidium timebase (opt.)

· Square wave clock outputs (opt.)

· Analog I/Q inputs (opt.)

· Ethernet, GPIB, and RS-232

· SG382 ... $3,900 (U.S. list)

· SG384 ... $4,600 (U.S. list)

· SG386 ... $5,900 (U.S. list)

SG380 Series RF Signal Generators

Introducing the new SG380 Series RF Signal Generators —
finally, high performance, affordable RF sources.

The SG380 Series RF Signal Generators use a unique,
innovative architecture (Rational Approximation Frequency
Synthesis) to deliver ultra-high frequency resolution (1 µHz),
excellent phase noise, and versatile modulation capabilities
(AM, FM, ΦM, pulse modulation and sweeps) at a fraction of
the cost of competing designs.

The standard models produce sine waves from DC to

2.025 GHz (SG382), 4.05 GHz (SG384) and 6.075 GHz
(SG386). There is an optional frequency doubler (Opt. 02)
that extends the frequency range of the SG384 and SG386 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 SG380 Series
can be ordered with a rubidium timebase (Opt. 04).

On the Front Panel

The SG380 Series Signal Generators have two front-panel
outputs with overlapping frequency ranges. A BNC provides
outputs from DC to 62.5 MHz with adjustable offsets and
amplitudes from 1 mV to 1 Vrms into a 50 Ω load. An
N-type

output supplies frequencies from 950 kHz to the upper

frequency limit of each model, with power from +16.5 dBm to

–110 dBm (1 Vrms to 0.707 µVrms) into a 50 Ω load.

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SG380 Series RF Signal Generators

Modulation

The SG380 Signal Generators offer a wide variety of
modulation capabilities. Modes include amplitude modulation
(AM), frequency modulation (FM), phase modulation (ΦM),
and pulse modulation. There is an internal modulation
source as well as an external modulation input. The internal
modulation source produces sine, ramp, saw, square, and noise
waveforms. An external modulation signal may be applied to
the rear-panel modulation input. The internal modulation
generator is available as an output on the rear panel.

Unlike traditional analog signal generators, the SG380 Series
can sweep continuously from DC to 62.5 MHz. And for
frequencies above 62.5 MHz, each sweep range covers more
than an octave.

OCXO or Rubidium Timebase

The SG380 Series come with a oven-controlled crystal
oscillator (OCXO) timebase. The timebase uses a third­overtone stress-compensated 10 MHz resonator in a
thermostatically controlled oven. The timebase provides very
low phase noise and very low aging. An optional rubidium
oscillator (Opt. 04) may be ordered to substantially reduce
frequency aging and improve temperature stability.

The internal 10 MHz timebase (either the standard OCXO or
the optional rubidium reference) is available on a rear-

panel
output. An external 10 MHz timebase reference may be
supplied to the rear-panel timebase input.

Square Wave Clock Outputs

Optional differential clock outputs (Opt. 01) are available on
the rear panel which makes your SG380 a precision clock

SG380 Series Phase Noise vs. Offset Frequency

-40

-50

-60

-70

-80

-90

-100

-110

Phase Noise (dBc/Hz)

-120

-130

-140

-150

10 100 1,000 10,000 100,000 1,000,00 0 10,000,0 00

100 MHz

10 MHz

Frequency Offset (Hz)

4 GHz

1 GHz

The SG380 Series always synthesizes a frequency in
the top octave and digitally divides to generate outputs
at lower frequencies. Doing so creates phase noise
characteristics which scale with output frequency by
6

dB/octave or 20 dB/decade.

The low phase noise at small offsets (for
example, –80

dBc/Hz at 10 Hz offset from 1 GHz)
is attributable to the low phase noise OCXO timebase
reference oscillator. An important figure of merit for
communications applications is the phase noise at
20

kHz offset, which is about –116 dBc/Hz at 1 GHz.

Differential Clock Outputs

Option 01 provides differential clock outputs in
addition to sine outputs. The clocks have transition
times of about 35 ps. Both the offset and amplitude of
the clock outputs can be adjusted for compliance with
standard logic levels. Shown here at 2 ns/division:
100 MHz front-panel sine wave output (top trace)
and differential clock outputs (bottom traces). The
displayed transition times are limited by the 1.5 GHz
bandwidth of the oscilloscope.

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Amplitude Modulation (100 %)

The frequency range of the SG380 Series extends from
DC to 2 GHz, 4 GHz or 6 GHz (depending on model).
All of the analog modulation modes also extend to DC
allowing your SG380 to perform function generator
tasks. Shown here is a 20 kHz carrier being amplitude
modulated by a 1 kHz sine.

Top trace: Modulation output
Bottom trace: Front-panel BNC output

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SG380 Series RF Signal Generators

generator in addition to a signal generator. Transition times
are typically 35 ps, and both the offset and amplitude of the
clock outputs can be adjusted for compliance with PECL,
ECL, RSECL, LVDS, CML, and NIM levels.

I/Q Inputs

Optional I/Q inputs (Opt. 03) allow I & Q baseband signals to
modulate carriers from 400 MHz to the upper frequency limit
of your instrument. This option also allows the I/Q modulator
to be driven by an internal noise generator with adjustable
bandwidth. Rear-panel outputs allow the noise source to be
viewed or used for other purposes.

I/Q Modulation of 1 GHz Carrier by

Internal Noise Generator

Option 03 allows I/Q modulation of carriers
from 400 MHz to the upper frequency limit of your
instrument. Two signal sources may be used for I/Q
modulation: external I & Q inputs or an internal
noise generator. The external I & Q BNC inputs are
on the rear panel. The internal noise generator
has adjustable noise bandwidth. Shown here is a
1

GHz carrier being modulated by the internal noise

generator with 1 kHz noise bandwidth.

Output Frequency Doubler

The SG384 and SG386 can be ordered with a frequency doubler
(Opt. 02) that extends the frequency range to 8.10 GHz.
amplitude of the rear-panel RF output can be adjusted from
–10 dBm to +13 dBm. This option also comes with a bias
source output which can be set with 5 mV resolution over
±10 VDC.

Easy Communication

Remote operation is supported with GPIB, RS-232 and
Ethernet interfaces. All instrument functions can be controlled
and read over any of the interfaces. Up to nine instrument
configurations can be saved in non-volatile memory.

A New Frequency Synthesis Technique

The SG380 Series Signal Generators are 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.

The

Unmodulated Spectrum of a 1 GHz Output

The SG380 Series outputs exhibit low phase noise and
low spurious content. In this direct measurement taken
with 100 Hz RBW, the noise floor of the spectrum
analyzer dominates over most of the 200 kHz span.

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Spectrum of Frequency Modulated 50 MHz Carrier

Outputs below 62.5 MHz are generated by direct­digital synthesis with a sample frequency of 1 GHz.
this example, a 50 MHz carrier is frequency modulated
at a rate of 10 kHz and a deviation of 24.0477 kHz,

for a modulation index β = 2.40477. The carrier

amplitude is proportional to the Bessel function J0(β),
which has its first zero at 2.40477.

In

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