AD9870 Datasheet, PDF (1/20 Pages) Analog Devices – IF Digitizing Subsystem

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FEATURES
10 MHz–300 MHz Input Frequency
Baseband (I/Q) Digital Output
10 kHz–150 kHz Output Signal Bandwidth
12 dB SSB NF
> –1 dBm IIP3 (High IIP3 Mode)
25 dB Continuous AGC Range + 16 dB Gain Step
Support for LO and Sampling Clock Synthesis
Programmable Decimation Rate, Output Format, AAF
Cutoff, AGC and Synthesizer Settings
360 ⍀ Input Impedance
2.7 V–3.6 V Supply Voltage
Low Current: 42 mA Typ (High IIP3 Mode),
30 mA Typ (Low IIP3, Fixed Gain Mode)
48-Lead LQFP Package (1.4 mm Thick)
APPLICATIONS
Portable and Mobile Radio Products
Digital UHF/VHF FDMA Products
TETRA
IF Digitizing Subsystem
AD9870
PRODUCT DESCRIPTION
The AD9870 is a general-purpose IF subsystem that digitizes a
low-level 10 MHz–300 MHz IF input with a bandwidth of up to
150 kHz. The signal chain of the AD9870 consists of a low-noise
amplifier, a mixer, a variable gain amplifier with integral antialias
filter, a bandpass sigma-delta analog-to-digital converter, and a
decimation filter with programmable decimation factor. An auto-
matic gain control (AGC) circuit provides the AD9870 with
25 dB of continuous gain adjustment. The high dynamic range
of the bandpass sigma-delta converter allows the AD9870 to
cope with blocking signals that are as much as 70 dB stronger
than the desired signal. Auxiliary blocks include clock and LO
synthesizers as well as a serial peripheral interface (SPI) port.
The SPI port programs numerous parameters of the AD9870,
including the synthesizer divide ratios, the AGC attack and decay
times, the AGC target signal level, the decimation factor, the
output data format, the 16 dB attenuator, and the bias currents of
several blocks. Reducing bias currents allows the user to reduce
power consumption at the expense of reduced performance.
FUNCTIONAL BLOCK DIAGRAM
AD9870
–16dB
IFIN
LNA
FREF
LO
SYNTH
DAC AGC
VGA /
AAF
⌺-⌬ ADC
f_CLK = 18MHz
DECIMATION
FILTER
FORMATTING/SSI
SAMP CLOCK
SYNTHESIZER
VOLTAGE
REFERENCE
CONTROL LOGIC
SPI
DOUTA
DOUTB
FS
CLKOUT
LO VCO AND
LOOP FILTER
CLK VCO AND
LOOP FILTER
REV. 0
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© Analog Devices, Inc., 2001