The SP5659 is a single chip frequency synthesiser designed for tuning systems up to 27GHz. The RF preamplifier drives a divide-by two prescaler which can be disabled for applications up to 2GHz, allowing direct interfacing with the programmable divider, resulting in a step size equal to the comparison frequency. For applications up to 27GHz the divide-by two is enabled to give a step size of twice the comparison frequency. The comparison frequency is obtained either from an onchip crystal controlled oscillator or from an external source. The oscillator frequency FREF or the comparison frequency FCOMP may be switched to the REF/COMP output; this feature is ideally suited to providing the reference frequency for a second synthesiser such as in a double conversion tuner (see Fig. 5).