Baseband Design
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WM_PRJ_Q24NG_PTS_002-001 June
2006
0
5
10
15
20
25
30
35
40
45
50
200
400
600
800
1000
1200
1400
1600
1800
Input Frequency (kHz)
Ur
ipp (
m
V
p
p
)
for f<100kHz U
ripp
Max = 50mVpp
for f> 1800kHz U
ripp
Max = 40 mVpp
Figure 2: Maximal voltage ripple (Uripp) vs Frequency in GSM & DCS,
To be confirmed
3.1.2 Design
Requirements
3.1.2.1 Risk
VBATT directly supplies the RF components with 3.6 V. It is essential to
keep a minimum voltage ripple at this connection in order to avoid any
phase error. Insufficient power supply voltage could dramatically affect
some RF performance factors:
•
TX power of course and modulation spectrum,
•
EMC performances (spurious emission),
•
Emissions spectrum,
•
Phase error and frequency error.
3.1.2.2 General design rules
Careful attention should be paid to:
•
Quality of the power supply: capacity to deliver high peak current in
a short time (bursted radio emission), low ripple and low
impedance.
•
The battery charger line must support 800 mA to comply with the
voltage level required for the product.
•
The VBATT lines on the PCB must support peak currents with a
voltage drop below the specified limit.
In order to test the supply tracks, a burst simulation circuit is shown
hereafter. This circuit simulates burst emissions, equivalent to bursts
generated when transmitting at full power.
