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© Analog Devices, Inc., 2001

0.8 GHz–2.7 GHz

Direct Conversion Quadrature Demodulator

FUNCTIONAL BLOCK DIAGRAM

RFIN

VREF

RFIP

VPS2

IMXO

COM3

IOPP

IOFS

IOPN

VCMO

VPS1

LOIN

IAIN

COM2

VDT2

QMXO

QOPP

QOFS

QOPN

VAGC

COM3

VGIN

ENBL

LOIP

COM1

VDT1

QAIN

VPS3

28

27

26

25

24

23

22

21

20

19

18

17

16

15

1

2

3

4

5

6

7

8

9

10

11

12

13

14

AD8347

PHASE

SPLITTER

PHASE

SPLITTER

GAIN

CONTROL

BIAS

DET

FEATURES

Integrated RF and Baseband AGC Amplifiers

Quadrature Phase Accuracy 1 Typ

I/Q Amplitude Balance 0.3 dB Typ

Third Order Intercept (IIP3) +11.5 dBm @ Min Gain

Noise Figure 11 dB @ Max Gain

AGC Range 69.5 dB

Baseband Level Control Circuit

Low LO Drive –8 dBm

ADC Compatible I/Q Outputs

Single Supply 2.7 V–5.5 V

Power-Down Mode

Package 28-Lead TSSOP

APPLICATIONS

Cellular Basestations

Radio Links

Wireless Local Loop

IF Broadband Demodulator

RF Instrumentation

Satellite Modems

GENERAL DESCRIPTION

The AD8347 is a broadband Direct Quadrature Demodulator

with RF and baseband Automatic Gain Control (AGC) amplifiers.

It is suitable for use in many communications receivers,

performing Quadrature demodulation directly to baseband

frequencies. The input frequency range is 800 MHz to 2.7 GHz.

The outputs can be connected directly to popular A-to-D converters

such as the AD9201 and AD9283.

The RF input signal goes through two stages of variable gain

amplifiers prior to two Gilbert-cell Mixers. The LO quadrature

phase splitter employs polyphase filters to achieve high quadra-

ture accuracy and amplitude balance over the entire operating

frequency range. Separate I & Q channel variable-gain amplifiers

follow the baseband outputs of the mixers. The RF and baseband

amplifiers together provide 69.5 dB of gain control. A precision

control circuit sets the Linear-in-dB RF gain response to the gain

control voltage.

Baseband level detectors are included for use in an AGC loop to

maintain the output level. The demodulator dc offsets are

minimized by an internal loop, whose time constant is controlled

by external capacitor values. The offset control can also be

overridden by forcing an external voltage at the offset nulling pins.

The baseband variable gain amplifier outputs are brought off-chip

for filtering before final amplification. By inserting a channel

selection filter before each output amplifier high-level out-of-

channel interferers can be eliminated. Additional internal circuitry

also allows the user to set the dc common-mode level at the

baseband outputs.

*U.S. Patents Issued and Pending