Service manual

RECEIVER NP88 FLEX
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Circuit Description
The following information describes the circuitry specific to the NP88 Flex 900MHz pager with a
synthesizer receiver board. RF circuit structure of NP88 Flex 900MHz is as RF diagram. RF signal is
received by antenna circuit, then get into RF-amplifier circuit which is low noise and high gain, signal
is amplified about 20dB, afterwards pass through band pass filter to filter out noise. After that, to mix
oscillator signal(L01) which characteristic is excellent, it will filter out noise and send IF1 signal to IF IC,
then restore receiving data to connect DECODER circuit.
Antenna Circuit
NP88 Flex 900MHz uses PCB Antenna, add matching circuit VC004, C4 … etc, it makes
amplifier circuit can work in low noise condition, and resonate to receiving frequency.
RF-amplifier & SAW Filter
• RF-amplifier CircuitΚIt amplifies signal which is received by antenna circuit on needed strength in best
noise figure. RF-amplifier Circuit of NP88 Flex 900MHz uses series connection which composed of Q101
and Q102 to amplify structure. The structure can gain the circuit to the max, and improve sensitivity.
• SAW FilterΚIt filter out all signal except carrier, makes receiver to have good sensitivity and image
rejection. Circuit components for the part includes bias with R1, R3, C6 and C412 load and SAW
filter circuit with L1, C10, VC003, L105, F101, L107 will couple RF signal to mixer circuit.
Oscillator Circuit
Feature of NP88 Flex 900MHz receiving circuit is stable and frequency can be changed any time. It uses feedback
and temperature compensation circuit which composed of PLL IC (U2), low-pass filter circuit, Colpitts
oscillators circuit and frequency multiplier circuit to resonate stable oscillator frequency.
•PLLIC(U2) CircuitΚPLL IC is a integrated circuit which handle frequency compound specially,
DECODER board provides data of oscillator frequency to PIN11 (CLK), PIN12 (Data), PIN13 (LE) of PLL
IC ,PIN1 and PIN2 of PLL IC connect to 12.8 MHz Crystal oscillator (X1, C36, C37, VC5) for offering
sequence. PIN5 of PLL IC output to low-pass filter which composed of C731, R732, C733, R700, C735, R741,
C742 and filter out high frequency noise for offering a stable voltage to VCO Oscillator circuit.
• VCO Oscillator CircuitΚThe circuit changes D406 capacitance through voltage which provide by LPF,
resonate programming frequency. Components are composed of D406, C405, C404, VC404, C403, C402, Q401,
R406, C417, C413, C414, R405, C415, L401 provide bias circuit C416 provides a feed back circuit to PLL IC.
• Frequency Multiplier CircuitΚOscillator signal is multiplied by Q501, then take out triple multiplier through
L501, C501. It couples to Buffer by C520
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3-2 June 21, 2004