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A dual-channel, DSP-based FM arbitrary waveform generator
By NARDA Microwave-EAST
The Model 10512 programmable signal source employs Narda’s advanced MIC fabrication techniques to deliver dense functional integration along with extremely low power consumption. The compact module digitally creates frequency-modulated “noise” waveforms and applies them to a carrier whose center frequency can be varied +/-50 MHz in less than 100 ns. Its unique characteristics make it well suited for use as a fast-hopping signal generator, programmable noise source, or arbitrary signal generator.
Characteristics of the waveforms generated by the Model 10512, such as video bandwidth, dispersion bandwidth (to 400 MHz), and power level, can be programmed by the user or remotely by a host system. The waveforms include ramp, sinusoidal, triangle, square wave, and random, among others. The standard model operates at 3 GHz but much higher frequency ranges are available. It consumes only 11 W, measures 4 in. L x 4 in. W x 0.6 in. T, weighs less than 11 oz., and is rugged enough to meet military specifications for shock and vibration.
The Model 10512 employs two VCOs and a high-speed, PIN-diode-based single-pole, double-throw switch that allows it to change from one frequency to another at extremely high speed. One VCO can operate at one frequency in a band while the other is “staged” to operate at a higher frequency. By “ping-ponging” the two VCOs, it is possible to hop between frequencies much faster than by retuning a single VCO. While the tuning time for a single VCO is less than 100 ns, switching time between two retuned VCOs via the high-speed switch is less than 15 ns.
For adjusting signal amplitude, each channel utilizes a digitally-controlled attenuator (DCA) with 63 dB range that is controllable in 1-dB steps. The DCAs settle between any two states in less than 100 ns. The Model 10512 delivers +16 dBm RF output power with a 1-dB gain compression point of +21 dBm. The module exerts real-time control over all signal parameters, maintaining them within tight tolerances over a broad range of operating conditions.
The Model 10512 uses an FPGA to enable real-time temperature compensation and linearization. A linearization calibration table is stored for each of eight temperatures over the unit’s operating range and a temperature sensor is read once per second. The FPGA performs tune count updates at 60 Msamples/s. The results are interpolated and applied to a digital-to-analog converter (DAC). This approach achieves high-speed frequency modulation along with ovenized-type temperature stability without the size and power consumption of an oven.
Generating the required modulation bandwidth typically requires a video filter whose output is scaled to achieve the required RF bandwidth. To accommodate numerous bandwidths, a switchable bank of filters is required, the output of each filter shaped to obtain uniform power spectral density. The Model 10512 uses a digital implementation of this approach. A pseudo-random number generator and linear feedback shift register (LFSR) generate a digital random sequence. The long LFSR output is passed through a digital low-pass filter bank and shaping is applied to create uniform distribution with a high-speed look-up table. A digital multiplier block provides programmable frequency excursions.
The standard Model 10512 has a frequency range of 2.8 to 3.2 GHz, but other frequencies can be accommodated well into the millimeter-wave region. Many other electrical and mechanical parameters can also be customized to meet customer requirements. More information is available at our website.
NARDA Microwave-EAST
www.nardamicrowave.com/east
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