
CX74001
Rx ASIC for CDMA, AMPS, and PCS Applications
2
Skyworks
101134A
Proprietary Information and Specifications are Subject to Change
March 5, 2002
÷2
CDMA IF SAW
PCS IF SAW
RF SAW
(CELL)
RF SAW
(PCS)
CELL_LNA_IN
PCS LNA IN
V
3
LOD
SIF
BIAS RESISTORS (3)
LNA_CTRL0
V
BYPASS
BYPASS
LNA_CTRL1
LNA1
C
AMPS IF SAW
LNA2
P
BIAS CONTROL
FM
CELL/PCS
SLEEP
I+
I-
Q+
Q-
PLL
Figure 2. CX74001 Rx ASIC Block Diagram
Technical Description
Low Noise Amplifiers (LNAs) _________________________
The cellular band LNA is designed with a low noise figure and
high linearity to achieve receiver sensitivity and single-tone
requirements. The cellular LNA is a three-step gain LNA
designed to meet the inter-modulation distortion specifications in
CDMA per TIA/EIA 98-C.
The PCS band LNA is also designed to provide a low noise
figure and high linearity to achieve receiver sensitivity and
single-tone requirements. At high signal strength, it is preferable
to bypass the LNA completely, and the PCS LNA supports this
feature.
Mixers ____________________________________________
The CX74001 Rx ASIC has three independent mixers, one for
the PCS band and two for the cellular band (AMPS and CDMA).
The mixers are designed to operate with LO powers of –10
dBm, typical.
The cellular and PCS band mixers have a high gain and IIP3,
and a low noise figure that allow them to meet the system
requirements with margin. The cellular CDMA and PCS mixers
have balanced output to drive the IF SAW filters. The differential
outputs of the AMPS mixer are combined externally to mate to a
single-ended input IF SAW filter.
Variable Gain Amplifier (VGA) _________________________
The high dynamic range required by CDMA handsets is
achieved by the VGA, which is common to all modes. It has
three different inputs and the appropriate signal path is switched
inside the chip. The VGA has a dynamic range of 90 dB with a
control voltage of 0.5 to 2.5 volts. It has a low noise figure at
maximum gain, which allows it to meet the system noise figure
requirements. The balanced output is common for all the modes
and is fed directly to the I/Q Demodulator.
I/Q Demodulator_____________________________________
The VGA stage is internally AC coupled to the I/Q demodulator.
The LO signals are derived from one of the on-chip VCOs, then
fed to a divider block that divides the VCO frequency by two.
The differential I and Q outputs are designed specifically with a
low DC output offset and a low phase and amplitude imbalance
when cascaded with the baseband processor.