Introducing the SG390 Series Vector Signal
SG390 Series Vector Signal Generators
SG390 Series —
Introducing the new SG390 Series Vector Signal
The instruments use an ovenized
New Frequency Synthesis Technique
The SG390 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
The SG390 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 SG390 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.
The SG390 series builds upon this performance by adding full support for vector signal modulation on RF carriers between 400 MHz and 6.075 GHz. It features a dual, arbitrary waveform generator operating at 125 MHz for baseband signal generation. The generator has built-in support for the most common vector modulation schemes: ASK, QPSK, DQPSK, π/4 DQPSK, 8PSK, FSK, CPM. QAM (4 to 256), 8VSB, and 16VSB. It also includes built-in support for all the standard pulse shaping filters used in digital communications: raised cosine, root-raised cosine, Gaussian, rectangular, triangular, and more. Lastly, it provides direct support for the controlled injection of additive white Gaussian noise (AWGN) into the signal path.
Internal baseband generators
Using a novel architecture for I/Q modulation, the SG390 series provides quick, user-friendly waveform generation. The baseband generator supports the playback of pure digital data. It automatically maps digital symbols into a selected I/Q constellation at symbol rates of up to 6 MHz and passes the result through the selected pulse shaping filter to generate a final waveform updated in real time at 125 MHz. This baseband signal is then modulated onto an RF carrier using standard IQ modulation techniques.
Preset communications protocols (GSM, GSM EDGE, W-CDMA, APCO-25, DECT, NADC, PDC, TETRA, and ATSC DTV) quickly configure the signal generator to the correct modulation type, symbol data rates, TDMA duty cycles and digital waveform filters. The preset protocols also configure the rear-panel TDMA, START of FRAME, and SYMBOL CLOCK digital outputs. The baseband generators can be configured for these protocols without the use of external computers or third party software.
The I/Q waveforms are computed in real time. Symbols are mapped to constellations, digitally filtered, and up-sampled to 125 Msps to drive the I/Q modulator via dual
External I/Q Modulation
The rear-panel BNC I/Q modulation inputs and outputs enable arbitrary vector modulation via an external source. The external signal path supports more than 300 MHz of bandwidth with a full scale range of ±0.5 V and a 50 Ω input impedance.
Power vs Frequency
All SRS RF signal generators have cascaded stages of amplifiers and digital attenuators to drive the RF output. Five stages can provide up to +25 dB of gain to
This method eliminates the need for precision attenuators and automatic level controls (ALC) without any sacrifice in performance. Eliminating the ALC also removes its unwanted interactions with amplitude, pulse and I/Q modulation.
OCXO or Rubidium Timebase
The SG390 Series come with a oven-controlled crystal oscillator (OCXO) timebase. The timebase uses a third-overtone 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. An external 10 MHz timebase reference may be supplied to the rear-panel timebase input.
Remote operation is supported with GPIB,
Baseband Generator Block Diagram