CX74001(2000) Ver la hoja de datos (PDF) - Conexant Systems
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CX74001 Datasheet PDF : 16 Pages
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CX74001
RF SAW
(CELL)
LNA_CTRL1
LNA_CTRL0
CELL_LNA_IN
FM
CELL/PCS
SLEEP
PCS LNA IN
BYPASS
LNA1
LNA2
BIAS CONTROL
LOD
SIF
BIAS RESISTORS (3)
BYPASS
3
RF SAW
(PCS)
AMPS IF SAW
CDMA IF SAW
PCS IF SAW
Rx ASIC
PLL
I+
I-
÷2
Q+
Q-
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.
Voltage Controlled Oscillators (VCOs). The active cores of
the two VCOs are present on the CX74001, requiring only
differential external LC tanks and a PLL synthesizer. The VCO
core current is automatically adjusted to give a constant VCO
output swing, regardless of the external tank Q.
2
Conexant - Preliminary
101134A
Proprietary Information
October 20, 2000
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