The SP5054 is a single-chip frequency synthesiser designed for satellite TV tuning systems. It is a programming variant of the SP5055, allowing the design of one tuner with either I2C bus or 3-wire bus format, depending on which device is inserted. The SP5054, when used with a satellite varactor tuner, forms a complete phase locked loop tuning system. The circuit consists of a divide-by-16 prescaler with its own preamplifier and a 14/15-bit programmable divider controlled by a serially-loaded data register. Four independently programmable open-collector outputs are included. The device has four modes of operation, selected by the Mode Select input; these modes are summarised in Table1. The comparison frequencies are obtained by the division of the output of a 4MHz crystal controlled on-chip oscillator. The phase comparator has a charge pump output with an output amplifier stage around which feedback may be applied. Only one external transistor is required for varactor line driving.