A.low Noise Amplifiers; B.down-Converting Mixers; C.baseband Amplifiers / Low Pass Filters - LG KG110 Service Manual

EGSM/GSM850 In
TX RF Input
Vmod_en
Vramp
Logic
&
Vbatt
Power
Vtx
Control
Vbs2
Vbs1
DCS/PCS In
TX RF Input
A. Low Noise Amplifiers
The AD6548 includes four fully integrated Low Noise Amplifiers (LNAs), to support quad band
applications without further external active components. The LNAs have differential inputs
which minimize the effect of unwanted interferers. The inputs are easily matched to industry
standard FEMs or discrete Rx SAW filters. The outputs of the LNAs are directly coupled to the
down-converting mixers. The voltage gain of the LNAs are typically 24 dB. Each LNA can be
switch to a low gain mode when receiving large input signals as part of the AGC system.
B. Down-Converting Mixers
Two quadrature mixers are used to mix down the signals from the LNAs, one for the
high bands (1800 and 1900 MHz) and one for the low bands (850 and 900 MHz).
The outputs of the mixers are connected to the baseband section through an integrated
single pole filter with nominal cut-off frequency of 800kHz. This acts as a "roofing filter"
for the largest blocking signals (i.e. those 3MHz) and prevents the baseband amplifiers
from being overloaded.
C. Baseband Amplifiers / Low Pass Filters
The baseband amplifiers provide the majority of the analog receiver gain.
The filtering is provided by an integrated 5th order Chebyshev filter giving the necessary adja-
cent channel and blocking filtering, it is also acting as an anti-alias filtering for Baseband IC's
converters. A final low pass pole is possible at each of the baseband outputs via internal series
resistor along with an external shunt capacitor.
ANT
TXOP_HI
ANT
TXOP_LO
TX RF Output
RX RF Input
VCC_FE
ESD-
RX850
Diode
RX850B
RX900
RX900B
RX1800
RX1800B
RX1900
RX1900B
LNA Gain Reduction
V1 Vcc1 Vcc2
(Internal Voltage)
TX_LO
TX_LO1
2 Generator
SDATA
Serial
SCLK
Interface
SEN
VDD
Figure 3-2: The RF Receiver Block
9
VCC_TXVC
O
TX Loop filter
PHD
/2
Band
Tx_LO1
Control
DC Offset
Correction
DC Offset
Correction
RX LO
Generator
Frac-N Synth
TX LO
TX circuits
LO VCO General
Supply
Supply Supply
LDO LDO LDO
Reg 3 Reg 2 Reg 1
3. TECHNICAL BRIEF
TXIB
TXI
I
IB
RX
I
RXIB
/4
VCC_BBI
Tx_LO2
VCC_BBQ
TX
Q
B
Q
TXQ
A
B
S
QB
RX
E
Q
B
RXQB
A
N
D
VAFC
AFC
REFINB
VCTCXO
REFIN
Supply
REF_OP
CLK
REF_OP
Ref
VCC_REF