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 onchip 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 ``inlock" flag output. The device also contains a varactor line disable and charge pump disable facility.