The SP5658 is a single chip frequency synthesiser designed for tuning systems up to 2.7GHz. The RF preamplifer contains a divide by two prescaler which can be disabled for applications up to 2GHz so enabling a step size equal to the comparison frequency up to 2GHz and twice the comparison frequency up to 2.7GHz. Comparison frequencies are obtained either from a crystal controlled on–chip oscillator or from an external source. The device contains two switching ports, in the 14 pin version and four in the 16 pin, together with an ‘‘in–lock” flag output. The device also contains a varactor line disable and charge pump disable facility.