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CDMA and GPS phones
There are separate mixers for CDMA cellular and GPS modes.
The CDMA mixer has balanced outputs for the IF SAW filters
and can be combined externally to mate to a single-ended
SAW filter. The GPS mixers have a differential output for an
external L-C bandpass filter. After IF filtering, the IF signal is
amplified by a Variable Gain Amplifier (VGA) and fed to an I/Q
demodulator, resulting in baseband I/Q signals at the output.
The CX74076 is also designed with two Local Oscillator (LO)
input ports, one for the CDMA mixer and one for the GPS
mixer. These mixers operate at different RF frequency inputs,
but have the same IF frequency output. This usually refers to a
single IF (SIF) plan at 183.6 MHz.
The CELL_LO signal (pin 30) provides an LO port for the
CDMA-cellular mixer. In the cellular band, the frequency is
divided by two by an internal divider, which provides the LO
input to the cellular mixer. Only one external VCO is required
for the UHF PLL. Additionally, the mixer LO signal is coupled
and amplified internally, which provides another RF signal to
drive the transmtiter upconverter LO port.
The VGA has a minimum dynamic range of 90 dB with a
control voltage range of 0.5 to 2.5 V, which is common to all
modes. A VHF oscillator operates with external tank circuits to
provide LO frequencies for the I/Q demodulator in the cellular,
PCS, and GPS modes.
The noise figure, gain, and third order Input Intercept Point
(IIP3) of each stage in the receiver chip are optimized to meet
the system requirements for CDMA modes according to
TIA/EIA-98-C. The ASIC design employs BiCMOS technology for
low cost, high performance, and a high level of integration.
A block diagram of the CX74076 is shown in Figure 1.
FEATURES
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Three-step gain control cellular LNA
GPS LNA
External resistor to adjust LNA bias current
Independent CDMA and GPS mixers
Buffer LO signal for transmit upconverter
90 dB dynamic range VGA
200 to 600 MHz VHF oscillator
Battery cell operation (2.7 V < Vcc < 3.3 V)
6 x 6 mm 40-pin RFLGA鈩?package with down-set paddle
DESCRIPTION
The CX74076 Application-Specific Integrated Circuit (ASIC) is a
single Intermediate Frequency (IF), multi-mode receiver
intended for use in Code Division Multiple Access (CDMA) and
Global Positioning System (GPS) modes.
The CX74076 is a highly integrated super-heterodyne receiver.
Except for the Surface Acoustic Wave (SAW) filters and
matching components, the device incorporates all the
components required to implement the receiver chain, from
the Low-Noise Amplifier (LNA) to the In-Phase and Quadrature
(I/Q) demodulator stages. Two LNAs are in the front-end
receiver: a three-step gain stage cellular LNA (high, mid, and
bypass) and a high gain GPS LNA.
After RF LNA signal amplification and filtering from the
antenna, the received signal is mixed down from RF to the IF.
Skyworks Solutions, Inc. Proprietary and Confidential
103087A
[781] 376-3000 I FAX [781] 376-3100 I SALES@SKYWORKSINC.COM I WWW.SKYWORKSINC.COM
1
FEBRUARY 5, 2003
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