OM5156M

Features:

· Low current from 3V supply
· Fully programmable RF divider
· 3-line serial interface bus
· Second synthesizer to control first IF or offset loop frequency
· Independent fully programmable reference dividers for each loop, driven from external crystal oscillator
· Dual phase detector outputs to allow fast frequency switching
· Dual power-down modes.


Application

· 2 GHz mobile telephones
· Portable battery-powered radio equipment.


Pinout




Description

The OM5156M BICMOS device integrates prescalers, programmable dividers, and phase comparators to implement two phase-locked loops. The device is designed to operate from 3 NiCd cells, in pocket phones,with low current and a wide supply voltage range from 2.7 to 5.5 V.

The principal synthesizer of OM5156M operates at RF input frequencies up to 2 GHz the auxiliary synthesizer operates at 300 MHz. The auxiliary loop is intended for the first IF or to transmit offset loop-frequency settings. Each synthesizer has a fully programmable reference divider. All divider ratios are supplied via a 3-wire serial programming bus.

Separate power and ground pins are provided to the analog and digital circuits. The OM5156M ground leads should be externally short-circuited to prevent large currents flowing across the die and thus causing damage. Digital supplies VDD1 and VDD2 must also be at the same potential. V_CC must be equal to or greater than V_DD (i.e. V_DD = 3 V and V_CC = 5 V for wider tuning range).

The principal synthesizer phase detector of OM5156M uses two charge pumps, one provides normal loop feedback, while the other is only active during fast mode to speed-up switching. The auxiliary loop has a separate phase detector. All charge pump currents (gain) are fixed by an external resistance at pin ISET (pin 14). Only passive loop filters are used; the charge-pumps function within a wide voltage compliance range to improve the overall system performance.