CX74005 Просмотр технического описания (PDF) - Skyworks Solutions
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CX74005 Datasheet PDF : 14 Pages
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CX74005
Rx ASIC
VGA_CDMA
19,20
2
VGA_PCS
21,22
2
VGA_AMPS
24
CX74005
Rx ASIC
2
6,7
÷ 2,4
29
I
30
11 D I V 2 / D I V 4
16
2 3 17
9,10
2
12,13
2
PLL
27
Q
28
C1431
Figure 2. CX74005 Rx ASIC Block Diagram
Technical Description
Variable Gain Amplifier (VGA). The high dynamic range
required by CDMA handsets is achieved by the VGA, which is
common to all modes. The VGA has a minimum dynamic range
of 90 dB with a control voltage of 0.5 to 2.5 volts. The
appropriate signal path is switched internal to the device. This
eliminates off-chip switching needed to operate this common
VGA in cellular AMPS, CDMA, and PCS modes.
I/Q Demodulator. The local oscillator signals are generated on-
chip. The I/Q demodulator is internally connected to the VGA
output. It is designed to have a very low amplitude and phase
imbalance. The I and Q outputs are differential. The DC offsets
between the differential outputs and between I and Q channels
are designed to be extremely low to facilitate compatibility with
baseband interfaces.
VHF Oscillators. There are two on-chip oscillators, one for the
cellular and one for the PCS bands. These Voltage Controlled
Oscillators (VCOs) work with external tank circuits and varactor
diodes. The outputs of the differential oscillators are buffered
and the output is used to drive the prescaler of an external
Phase Locked Loop (PLL). The VCOs typically operate at twice
the IF frequency and can operate at up to four times the IF
frequency.
The local oscillators for the I/Q demodulators are derived by an
on-chip frequency divider. The logic signal to select the divider
ratio (2 or 4) is available on Pin 11 (DIV2/DIV4).
Mode Control. The operation of the chip is controlled by signals
at Pin 3 (CELL/PCS), Pin 2 (FM/CDMA), Pin 16 (SLEEP), and
the DIV2/DIV4 select commands at Pin 11. All the switching is
done internally. The supply voltage should be present at all the
VCC pins for normal operation. The signals needed to select
each mode is shown in Table 1.
Electrical and Mechanical Specifications
Signal pin assignments and functional pin descriptions are
described in Table 2. The absolute maximum ratings of the
CX74005 are provided in Table 3. The recommended operating
conditions are specified in Table 4. Electrical specifications are
provided in Table 5.
Typical performance characteristics are illustrated in Figures 3
through 32. Figure 33 provides the package dimensions for the
32-pin LGA and tape and reel dimensions are shown in
Figure 34.
2
Conexant - Preliminary
101252A
Proprietary Information and Specifications Are Subject to Change
March 13, 2001
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