IF Digitizing Subsystem
AD9874*
FEATURES
GENERAL DESCRIPTION
10 MHz to 300 MHz Input Frequency
7.2 kHz to 270 kHz Output Signal Bandwidth
8.1 dB SSB NF
The AD9874 is a general-purpose IF subsystem that digitizes a
low level 10 MHz to 300 MHz IF input with a signal bandwidth
ranging from 6.8 kHz to 270 kHz. The signal chain of the AD9874
consists of a low noise amplifier, a mixer, a band-pass sigma-delta
analog-to-digital converter, and a decimation filter with program-
mable decimation factor. An automatic gain control (AGC) circuit
gives the AD9874 12 dB of continuous gain adjustment. Auxil-
iary blocks include both clock and LO synthesizers.
0 dBm IIP3
AGC Free Range up to –34 dBm
12 dB Continuous AGC Range
16 dB Front End Attenuator
Baseband I/Q 16-Bit (or 24-Bit) Serial Digital Output
LO and Sampling Clock Synthesizers
Programmable Decimation Factor, Output Format,
AGC, and Synthesizer Settings
370 ⍀ Input Impedance
The AD9874’s high dynamic range and inherent antialiasing
provided by the band-pass sigma-delta converter allow the
AD9874 to cope with blocking signals up to 95 dB stronger
than the desired signal. This attribute can often reduce the cost of
2.7 V to 3.6 V Supply Voltage
Low Current Consumption: 20 mA
48-Lead LQFP Package (1.4 mm Thick)
a
radio by reducing its IF filtering requirements. Also, it enables
multimode radios of varying channel bandwidths, allowing the
IF filter to be specified for the largest channel bandwidth.
APPLICATIONS
The SPI port programs numerous parameters of the AD9874,
thus allowing the device to be optimized for any given application.
Programmable parameters include synthesizer divide ratios, AGC
attenuation and attack/decay time, received signal strength level,
decimation factor, output data format, 16 dB attenuator, and the
selected bias currents. The bias currents of the LNA and mixer
can be further reduced at the expense of degraded performance
for battery-powered applications.
Multimode Narrow-Band Radio Products
Analog/Digital UHF/VHF FDMA Receivers
TETRA, APCO25, GSM/EDGE
Portable and Mobile Radio Products
Base Station Applications
SATCOM Terminals
FUNCTIONAL BLOCK DIAGRAM
MXOP MXON IF2P IF2N
GCP GCN
DAC
AGC
AD9874
–16dB
LNA
DECIMATION
FILTER
IFIN
⌺-⌬ ADC
FORMATTING/SSI
DOUTA
DOUTB
FS
CLKOUT
FREF
CONTROL LOGIC
LO
SYN
VOLTAGE
REFERENCE
CLK SYN
SPI
IOUTL
LOP LON
IOUTC CLKP
LOOP FILTER
CLKN VREFP VCM VREFN PC PD PE
SYNCB
LO VCO AND
LOOP FILTER
*Protected by U.S. Patent No. 5,969,657;
REV. A
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