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The frequency synthesizer consists of a VCO, crystal oscilla- tor, dual-modulus prescaler, programmable frequency divid- ers, phase-detector, charge pump, lock detector and an external loop filter. The dual-modulus prescaler divides the VCO-frequency by 64/65. This mode is controlled by the A- divider. There are two sets of M, N and A-frequency dividers. Using both sets in transmit mode, FSK can be implemented by switching between those two sets. The phase-detector is a frequency/phase detector with back slash pulses to mini- mize phase noise. The VCO, crystal oscillator, charge pump, lock detector and the loop filter will be described in detail below.
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