0.8 GHz to 2.7 GHz Direct Conversion Quadrature Demodulator AD8347 FEATURES FUNCTIONAL BLOCK DIAGRAM Integrated RF and baseband AGC amplifiers AD8347 LOIN 1 28 LOIP Quadrature phase accuracy 1 typ PHASE VPS1 2 27 COM1 I/Q amplitude balance 0.3 dB typ SPLITTER IOPN 3 26 QOPN Third-order intercept (IIP3) +11.5 dBm min gain IOPP 4 25 QOPP Noise figure 11 dB max gain PHASE VCMO 5 24 QAIN SPLITTER AGC range 69.5 dB IAIN 6 23 COM3 Baseband level control circuit COM3 7 22 QMXO Low LO drive 8 dBm IMXO 8 21 VPS3 COM2 9 20 VDT1 ADC-compatible I/Q outputs 10 DET 19 RFIN VAGC Single supply 2.7 V to 5.5 V 11 18 RFIP VDT2 Power-down mode 12 17 VPS2 VGIN 28-lead TSSOP package 13 16 IOFS QOFS GAIN BIAS 14 15 VREF ENBL CONTROL APPLICATIONS Figure 1. Cellular base stations Radio links Wireless local loop IF broadband demodulators RF instrumentation Satellite modems GENERAL DESCRIPTION 1 Baseband level detectors are included for use in an AGC loop to The AD8347 is a broadband direct quadrature demodulator maintain the output level. The demodulator dc offsets are with RF and baseband automatic gain control (AGC) amplifiers. minimized by an internal loop, whose time constant is It is suitable for use in many communications receivers, performing controlled by external capacitor values. The offset control can quadrature demodulation directly to baseband frequencies. The also be overridden by forcing an external voltage at the offset input frequency range is 800 MHz to 2.7 GHz. The outputs can nulling pins. be connected directly to popular A-to-D converters such as the AD9201 and AD9283. The baseband variable gain amplifier outputs are brought off- chip for filtering before final amplification. By inserting a The RF input signal goes through two stages of variable gain channel selection filter before each output amplifier, high level amplifiers prior to two Gilbert-cell mixers. The LO quadrature out-of-channel interferers are eliminated. Additional internal phase splitter employs polyphase filters to achieve high circuitry also allows the user to set the dc common-mode level quadrature accuracy and amplitude balance over the entire at the baseband outputs. operating frequency range. Separate I and 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. 1 U.S. patents issued and pending. Rev. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. rights of third parties that may result from its use. Specifications subject to change without notice. No Tel: 781.329.4700 www.analog.com license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Fax: 781.461.3113 2005 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. 02675-001AD8347 TABLE OF CONTENTS Features .............................................................................................. 1 LO and Phase Splitters............................................................... 16 Applications....................................................................................... 1 Output Level Detector ............................................................... 17 Functional Block Diagram .............................................................. 1 Bias ............................................................................................... 17 General Description ......................................................................... 1 Applications..................................................................................... 18 Revision History ............................................................................... 2 Basic Connections...................................................................... 18 Specifications..................................................................................... 3 RF Input and Matching ............................................................. 18 Absolute Maximum Ratings............................................................ 5 LO Drive Interface ..................................................................... 18 ESD Caution.................................................................................. 5 Operating the VGA.................................................................... 19 Pin Configuration and Function Descriptions............................. 6 Mixer Output Level and Drive Capability .............................. 19 Typical Performance Characteristics ............................................. 8 Operating the VGA in AGC Mode .......................................... 19 RF Amp and Demodulator ......................................................... 8 Changing the AGC Setpoint ..................................................... 20 Baseband Output Amplifiers .................................................... 11 Baseband Amplifiers.................................................................. 20 RF Amp/Demod and Baseband Output Amplifiers .............. 12 Driving Capacitive Loads.......................................................... 21 Equivalent Circuits..................................................................... 14 External Baseband Amplification ............................................ 21 Theory of Operation ...................................................................... 16 Filter Design Considerations .................................................... 21 RF Variable Gain Amplifiers (VGA)........................................ 16 DC Offset Compensation.......................................................... 22 Mixers .......................................................................................... 16 Evaluation Board ............................................................................ 23 Baseband Variable Gain Amplifiers......................................... 16 Outline Dimensions....................................................................... 26 Output Amplifiers ...................................................................... 16 Ordering Guide .......................................................................... 26 REVISION HISTORY 10/05Rev. 0 to Rev. A Updated Format..................................................................Universal Change VGIN to VVGIN..........................................................Universal Changes to Figure 46...................................................................... 19 Changes to Figure 48 ..................................................................... 21 Changes to Figure 49 and Figure 50............................................. 22 Changes to Ordering Guide .......................................................... 27 10/01Revision 0: Initial Version Rev. A Page 2 of 28