S1M8656A Samsung Semiconductor, Inc., S1M8656A Datasheet - Page 15

• Manufacturer Part Number: S1M8656A
• Description: Cdma/amps Dual Mode If/ Baseband Ic
• Manufacturer: Samsung Semiconductor, Inc.

RX IF/BBA WITH AGC
Rx Low-Pass Filters
The CDMA baseband signal frequency can range between 1kHz – 630kHz. Normally, the range between 1kHz –
615kHz is called the In-band, between 630kHz – 750kHz Band-edge, and anything outside of these ranges out
band. Very precise characteristics are required in the in-band range. The ripple, I/Q gain-phase error are critical
factors that lead to noise in the in-band. FM Baseband signal ranges between 100Hz – 15kHz. Normally, the
frequency range between 100Hz –12kHz is called the in-band, between 12kHz – 18kHz the band-edge, and
anything outside of these ranges the out-band. As for the CDMA, the ripple, I/Q gain-phase error are critical
factors that lead to noise in the in-band.
The LPF characteristic required by these two systems are shown in Figures 7 and 8 below.
CHIPx8 Clock Generator
CHIPx8 CLOCK is a digital division that divides the 19.68MHz TCXO by 512/1025. It holds the TCXO clock by
half cycle every 512th TCXO cycle and strictly speaking it does not generate 9,8304 MHz precisely. The
9.8304MHz is the mean on the 1025TCXO cycle, where 9.84MHz of 50% duty is obtained from 1 – 512 and 513
– 1024. The timing diagram in Figure 9 explains this. The CHIPx8 CLOCK output is held at low when the CDMA
is asleep and FM is idle. Moreover, it can use three division ratios(19.68MHz, 9.84MHz, 9.8304MHz) through the
serial I/F. Various external chip clocks can be used by converting them to inputs.
Figure 7. CDMA Rx Low-Pass Filter Masks
-46.0dB
-48.0dB
+1.5dB
+0.5dB
-1.5dB
-4.0dB
0
1kHz
Frequency
CHIPx8
TCXO
600kHz
630kHz
750kHz
Figure 9. CHIPx8 Clock form
1
2
900kHz
1.2MHz
Figure 8. FM Rx Low-Pass Filter Masks
-60.0dB
+0.5dB
-0.5dB
-3.0dB
1023
2/ftcxo
1024
100hz
1025
1026
1027
Frequency
12.2khz
18khz
60khz
S1M8656A
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