Nokia 8390 Manuales De Servicio

NSB-8

System Module & UI

PAMS Technical Documentation

Page 32

 

ãNokia Corporation

Issue 1 01/02

PLL is located in HAGAR RF-IC and is controlled via serial RFBus. There is 64/65 (P/P+1)
prescaler, N- and A-divider, reference divider, phase detector and charge pump for the
external loop filter. SHF local signal, generated by a VCO-module (VCO = voltage con-
trolled oscillator), is fed through 180deg balanced phase shifter to prescaler. Prescaler is
a dual modulus divider. Output of the prescaler is fed to N- and A-divider, which produce
the input to phase detector. Phase detector compares this signal to reference signal
(400kHz), which is divided with reference divider from VCTCXO output. Output of the
phase detector is connected into charge pump, which charges or discharges integrator
capacitor in the loop filter depending on the phase of the measured frequency compared
to reference frequency.

Loop filter filters out comparison pulses of phase detector and generates DC control volt-
age to VCO. Loop filter defines step response of the PLL (settling time) and effects to sta-
bility of the loop, that's why integrator capacitor has a resistor for phase compensation.
Other filter components are for sideband rejection. Dividers are controlled via serial bus.
RFBus Data is for data, RFBusClk is serial clock for the bus and RFBusEna1X is a latch
enable, which stores new data into dividers.

LO-signal is generated by SHF VCO module. VCO has double frequency in GSM1900 com-
pared to actual RF channel frequency. LO signal is divided by two in HAGAR.

Receiver is a direct conversion linear receiver. Received RF signal from antenna is fed via
Antenna Switch to the 1st RX SAW filter and a MMIC LNA (Low Noise Amplifier). After
the LNA amplified signal (with low noise level) is fed to a bandpass filter (the 2nd RX
SAW filter). The RX filters define how good are blocking characteristics against spurious
signals outside receive band and protection against spurious responses