Frequency Synthesisers

Giastar has extensive experience of many types of frequency synthesizer: indirect (phase locked), with both integer and fractional divisors; analogue direct; digital direct (DDS) and hybrid combinations of these technologies.

Frequency synthesiser design can be particularly challenging. It is a discipline requiring a good understanding of RF circuitry, low-frequency analogue circuitry, low-noise design methods, control systems, digital design and EMC. The tradeoffs can be complex. Local oscillator quality frequently limits the performance of a receiver or transmitter, so the correct specification and competent design of a synthesiser can be vital.

Most of the projects featured on this site included integral synthesisers, however the following are of particular interest:

VHF local oscillator for high-performance HF receiver. This LO used a hybrid DDS/PLL design to deliver:
- Excellent (better than -110dBc discrete spurs) spectral purity.
- 1Hz resolution.
- 1ms switching time.
- Phase noise better than -135dBc/Hz at 30kHz offset.
Vibration-resistant UHF frequency synthesiser for use as a Tx/Rx local oscillator in a motorsport communications system. A hybrid DDS/PLL configuration allowed a 6.25kHz channel spacing to be achieved at UHF while maintaining the wide loop bandwidth required for suppression of vibration-induced phase noise.
Low-power fractional-N synthesiser for subminiature satcomms terminal.
AIS1 indirect VHF synthesiser. A general-purpose VHF synthesiser module used in satcomms IF processing and ATE systems.
A low-noise, fast-switching analogue direct synthesiser module for R&D use in an avionics environment.
A low-power L-band synthesiser and modulator for low data-rate FSK applications.
VHF receiver LO with excellent suppression of vibration-induced noise (for use in helicopters).

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