SAMSUNG SCH-570
Instrukcja Serwisowa

5-2 Receiver Section
LOW NOISE AMPLIFIER (LNA, Q302)
The low noise amplifier amplifies a weak signal received from the base station to obtain the optimum level (Noise figure = 1.5 dB, Gain = 16 dB).

IF SAW BAND PASS FILTER (FOR CDMA)
IF SAW BPF (F303) is used for CDMA system having 1.23 MHz wideband and 630 kHz bandwidth. The filter also attenuates the image product generated at the mixer.

RADIO FREQUENCY BAND PASS FILTER (RF BPF, F302)
The RF BPF accepts only a specific frequency (881 12.5 MHz) from the signal received from the base station. The band width is 25 MHz.

BUFFER AMP (Q304)
Buffer (Q304) amplifiers signal to be applied to the local input of the down converter (U301) when a phase is locked between VCO (U341) and PLL IC (U342).

DOWN CONVERTER (MIXER, U301)
First local signal is applied to this down converter. The down converter transfers the signal amplified at the LNA into 85.38 MHz IF signal. 85.38 MHz IF signal is made by subtracting 881 12.5 MHz RF signal from 966 12.5 MHz first local signal.

AUTOMATIC GAIN CONTROLLER (AGC) AMP (Q302)
85.38 MHz IF signal is applied to IF AGC amp, the IF AGC output level is applied to BBA (Baseband Analog ASIC). The IF AGC amp (Q302) keeps the signal at a constant level by controlling the gain. Dynamic range is 90dB, up gain +45dB, and down gain -45dB.

5-4