Signal Generator
Understanding Signal Generators
Signal generators are one of the three essential RF test instruments (along with spectrum analyzers and VNAs). They provide the stimulus signal for testing receiver sensitivity, amplifier gain compression, filter response, and modulation quality.
Signal Generator Types
- Analog/CW: Provides continuous-wave or simple analog modulation (AM, FM, PM). Used for basic receiver and component testing.
- Vector signal generator (VSG): Provides complex digital modulation (QAM, OFDM, 5G NR, Wi-Fi). Uses I/Q modulation with arbitrary waveform generation.
- Microwave signal generator: Extends to 40-70+ GHz for mmWave testing.
Key Specifications
- Frequency range: 9 kHz to 6/20/40/67 GHz depending on model.
- Phase noise: -110 to -140 dBc/Hz at 10 kHz offset. Critical for receiver testing.
- Output power: -130 to +20 dBm. Flatness +/- 0.5 dB typical.
- Modulation bandwidth: Up to 2 GHz for wideband vector generators.
Frequently Asked Questions
What is a signal generator?
A signal generator produces RF signals with precise frequency, amplitude, and modulation. Essential for testing receivers, amplifiers, and systems. Modern generators provide sub-Hz frequency resolution, low phase noise, and complex digital modulation.
What is the difference between CW and vector signal generators?
CW generators provide simple tones for basic testing. Vector signal generators produce complex digitally modulated signals (5G NR, Wi-Fi, LTE) by independently controlling I and Q signal components with arbitrary waveforms.
What phase noise does a signal generator need?
The signal generator phase noise must be 10-20 dB below the DUT's phase noise contribution. For testing a receiver with -100 dBc/Hz phase noise floor, the generator needs -110 to -120 dBc/Hz. Higher-performance testing requires lower phase noise generators.