LISA-U2 series - System integration manual
UBX-13001118 - R27
System description
Page 30 of 183
C1-Public
1.5.3.2
3G connected mode
During a 3G connection, the module can transmit and receive continuously due to the Frequency
Division Duplex (FDD) mode of operation with the Wideband Code Division Multiple Access (WCDMA).
The current consumption depends again on output RF power, which is always regulated by network
commands. These power control commands are logically divided into a slot of 666 µs, thus the rate of
power change can reach a maximum rate of 1.5 kHz. There are no high current peaks as in the 2G
connection, since transmission and reception are continuously enabled due to FDD WCDMA
implemented in the 3G that differs from the TDMA implemented in the 2G case. In the worst case
scenario, corresponding to a continuous transmission and reception at maximum output power
(approximately 250 mW or 24 dBm), the current drawn by the module at the VCC pins is in the order
of continuous 500-800 mA (see LISA-U2 series data sheet
for detailed values). Even at lowest
output RF power (approximately 0.01 µW or -50 dBm), the current still remains in the order of 200 mA
due to module baseband processing and transceiver activity.
An example of current consumption profile of the data module in UMTS/HSxPA continuous
transmission mode is shown in
Time
[ms]
3G frame
10 ms
(1 frame = 15 slots)
Current [mA]
Current consumption
depends on TX power and
actual antenna load
170
mA
1 slot
666
µ
s
850
mA
0
300
200
100
500
400
600
700
800
Figure 13: VCC current consumption profile versus time during a UMTS/HSPA connection
When a packet data connection is established, the actual current profile depends on the volume of
transmitted packets; there might be some periods of inactivity between allocated slots where current
consumption drops about 100 mA. Alternatively, at higher data rates the transmitted power is likely
to increase due to the higher quality signal required by the network to cope with the enhanced data
speed.
