LMX1501 National Semiconductor, LMX1501 Datasheet - Page 13

• Manufacturer Part Number: LMX1501
• Description: PLLatinumTM 1.1 GHz Frequency Synthesizer for RF Personal Communications
• Manufacturer: National Semiconductor

Analog Switch (1511 only)
The analog switch is useful for radio systems that utilize a frequency scanning mode and a narrow band mode The purpose of
the analog switch is to decrease the loop filter time constant allowing the VCO to adjust to its new frequency in a shorter
amount of time This is achieved by adding another filter stage in parallel The output of the charge pump is normally through the
D
second filter stage (LPF-2) is effective only when the switch is closed (in the scanning mode)
Typical Crystal Oscillator Circuit
A typical circuit which can be used to implement a crystal
oscillator is shown below
o
pin but when LE is set HIGH the charge pump output also becomes available at BISW A typical circuit is shown below The
TL W 12340 – 26
13
Typical Lock Detect Circuit
A lock detect circuit is needed in order to provide a steady
LOW signal when the PLL is in the locked state A typical
circuit is shown below
TL W 12340– 25
TL W 12340– 27