The transmitter consists of a PLL frequency synthesizer and a power amplifier. The frequency synthesizer consists of a voltage-controlled oscillator (VCO), a crystal oscillator, dualmodulus prescaler, programmable frequency dividers and a phase-detector. The loop filter is external for flexibility and can be a simple passive circuit. The VCO is a Colpitts oscillator which requires an external resonator and varactor. FSK modulation can be applied externally to the VCO or the crystal oscillator. The synthesizer has two different N, M and A frequency dividers. FSK modulation can also be implemented by switching between these dividers (max. 2400bps). The lengths of the N and M and A registers are 12, 10 and 6 bits respectively. For all types of FSK modulation, data is entered at the DATAIXO pin (see application circuit). The output power of the power amplifier can be programmed to eight levels. A lock-detect circuit detects when the PLL is in lock.