Wideband RF Signal Synthesizer

Can a capable RF signal generator be built entirely from off-the-shelf components? This team project set out to find out, and to measure how well such a design performs.

The result covers 150 kHz to 3 GHz in 0.1-Hz steps, with output power adjustable from −130 dBm to +20 dBm in 0.1-dB steps. It is a complete instrument: RF hardware, a microcontroller and a CPLD to run it, and a control program on a PC.

Team projectHardware and software

Frequency range: 150 kHz – 3 GHz, 0.1-Hz steps
Output power: −130 to +20 dBm, 0.1-dB steps
Phase noise at 2.2 GHz: −84 dBc/Hz at 1 kHz offset
−93 dBc/Hz at 10 kHz offset

Photo of the signal synthesizer prototype — **Fig. 1**The prototype

3 GHztop frequency, from 150 kHz

0.1 Hzfrequency step

150 dBoutput power range

−93dBc/Hz at 10 kHz offset, 2.2 GHz

Hardware

Synthesizer, filters, modulation, power control

System block diagram of the signal synthesizer — **Fig. 2**System block diagram

The signal chain (Fig. 2) starts with a frequency synthesizer, followed by a filter array, a modulation circuit, and a power controller, all managed by a microcontroller. The microstrip filters were designed in Agilent ADS, and the schematics and PCB layout in Cadence Capture and OrCAD.

Software

Three layers of control

MicrocontrollerAtmel ATmega88PAWritten in C with AVR Studio.

CPLDXilinx XC95144XLWritten in Verilog with the Xilinx ISE Design Suite.

PCControl interfaceWritten in C# with Microsoft Visual Studio.

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