19-1449; Rev 0; 4/99 Direct-Conversion Tuner IC The MAX2108 is a low-cost direct-conversion tuner IC designed for use in digital direct-broadcast satellite (DBS) television set-top box units and microwave links. Its direct-conversion architecture reduces system cost compared to devices with IF-based architectures. The MAX2108 directly tunes L-band signals to baseband using a broadband I/Q downconverter. The operating frequency range spans from 950MHz to 2150MHz. The IC includes a low-noise amplifier (LNA) with gain control, two downconverter mixers with output buffers, a 90° quadrature generator, and a divide-by 32/33 prescaler. Features MAX2108 General Description ♦ Low-Cost Architecture ♦ Operates from Single +5V Supply ♦ On-Chip Quadrature Generator, Dual-Modulus Prescaler (/32, /33) ♦ Input Levels: -20dBm to -70dBm per Carrier ♦ Over 50dB RF Gain-Control Range ♦ 10dB Noise Figure at Maximum Gain ♦ +8dBm IIP3 at Minimum Gain Applications DirecTV, PrimeStar, EchoStar DBS Tuners DVB-Compliant DBS Tuners Ordering Information Cellular Base Stations Wireless Local Loop PART MAX2108CEG Broadband Systems LMDS TEMP. RANGE 0°C to +70°C PIN-PACKAGE 24 QSOP Pin Configuration appears at end of data sheet. Microwave Links Functional Diagram PS_SEL VCC 12 11 GC 10 GND 9 GND RFIN RFIN VCC 8 7 6 5 GND VCC 4 3 IOUT IOUT 2 1 I /32 /33 0 90 MAX2108 Q 13 PSOUT 14 PSOUT 15 GND 16 GND 17 N.C. 18 LO 19 LO 20 N.C. 21 VCC 22 23 GND QOUT 24 QOUT ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. 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MAX2108 Direct-Conversion Tuner IC ABSOLUTE MAXIMUM RATINGS VCC to GND ..............................................................-0.3V to +7V VCC to Any Other VCC ...........................................-0.3V to +0.3V All Other Pins to GND.................................-0.3V to (VCC + 0.3V) RFIN to RFIN ..........................................................................±2V LO to LO ................................................................................±2V Short-Circuit Current IOUT, IOUT, QOUT, QOUT to GND .................................10mA PSOUT, PSOUT to GND...................................................40mA Short-Circuit Duration IOUT to IOUT, QOUT to QOUT, PSOUT to PSOUT ............................................................10sec Continuous Power Dissipation (TA = +70°C) 24 QSOP (derate 10mW/°C above TA = +70°C) ..........800mW Operating Temperature Range...............................0°C to +70°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10sec) .............................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. DC ELECTRICAL CHARACTERISTICS (VCC = +4.75V to +5.25V; VGC = 1.3V; PS_SEL = 0.5V; IOUT, IOUT, QOUT, QOUT = terminated with 2.5kΩ to GND; no input signal applied; TA = 0°C to +70°C; unless otherwise noted. Typical values are at VCC = +5V, TA = +25°C.) PARAMETER Supply Current SYMBOL PS_SEL Logic-High Threshold VTHH PS_SEL Logic-Low Threshold VTHL PS_SEL Input Bias Current CONDITIONS MIN ICC IPS_SEL GC Input Bias Current IGC IOUT, IOUT, QOUT, QOUT Common-Mode Output Voltage VCM TYP MAX UNITS 105 152 mA 2.4 V 0.5 V 0 < VPS_SEL < VCC -30 +10 µA 1V < VGC < 4V -80 +80 µA 3.8 V 2.9 3.35 AC ELECTRICAL CHARACTERISTICS (VCC = +5V; PS_SEL = 0.5V; PRFIN = -20dBm; fLO = fRFIN +125kHz; GC set via servo loop for VIOUT - V IOUT = 200mVp-p (differential); TA = +25°C; unless otherwise noted.) PARAMETER SYMBOL RFIN Frequency Range (Note 1) fRFIN CONDITIONS MIN TYP 950 RFIN Maximum Input Power (Note 2) PRFINMAX 950MHz < fRFIN < 2150MHz, PLO = -5dBm RFIN Minimum Input Power (Note 2) PRFINMIN MHz dBm 950MHz < fRFIN < 2150MHz, PLO = -5dBm, VIOUT - V IOUT = 10mVp-p, TA = 0°C +70°C -70 -5 1V < VGC < 4V, PLO = -5dBm UNITS -20 External LO Drive Level (Note 2) Gain-Control Range (Note 2) MAX 2150 50 dBm dBm dB RFIN Input Third-Order Intercept Point (Note 3) IIP3 8 dBm RFIN Input Second-Order Intercept Point (Note 4) IIP2 14 dBm Noise Figure NF 10 dB 2 VGC = 4V, fLO = 1750MHz _______________________________________________________________________________________ Direct-Conversion Tuner IC (VCC = +5V; PS_SEL = 0.5V; PRFIN = -20dBm; fLO = fRFIN +125kHz; GC set via servo loop for VIOUT - V IOUT = 200mVp-p (differential); TA = +25°C; unless otherwise noted.) PARAMETER SYMBOL Prescaler Divide Ratio VPSOUT V PSOUT Differential Prescaler Output Swing CONDITIONS MIN TYP MAX VPS_SEL > 2.4V 32 32 VPS_SEL < 0.5V 33 33 CPSOUT = C PSOUT = 10pF to GND 1.0 UNITS Vp-p I/Q Channel Quadrature Phase Error (Note 2) fIOUT = f IOUT = fQOUT = f QOUT = 125kHz 3 degrees I/Q Amplitude Mismatch (Note 2) fIOUT = f IOUT = fQOUT = f QOUT = 125kHz 1 dB I/Q Channel Clipping Level fIOUT = f IOUT = fQOUT = f QOUT = 10MHz, no output load 1.4 Vp-p Baseband Bandwidth At -3dB attenuation 150 MHz I/Q Channel Differential Output Impedance fIOUT = f IOUT = fQOUT = f QOUT = 20MHz 33 Ω Note 1: AC specifications with minimum/maximum limits are met within this frequency range. Note 2: LO and LO are differentially driven through an AC-coupled matching network. Note 3: PRFIN = -20dBm per tone, GC set via servo loop for VIOUT - V IOUT = 20mVp-p per tone. f1RFIN = 1749MHz, f2RFIN = 1751MHz, fLO = 1740MHz. Note 4: PRFIN = -20dBm per tone, GC set via servo loop for VIOUT - V IOUT = 20mVp-p per tone. f1RFIN = 1200MHz, f2RFIN = 2150MHz, fLO = 951MHz. Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX2108 toc03 8 -20 RF LEVEL (dBm) TA = +70°C 110 105 TA = +25°C fRFIN = 1750 MHz -30 IIP3 (dBm) 115 ICC (mA) GC SET FOR 10mVp-p BASEBAND OUTPUT -10 10 MAX2108 toc02 120 INPUT IP3 vs. FREQUENCY CARRIER LEVEL vs. GAIN CONTROL 0 MAX2108 toc01 125 -40 -50 6 4 TWO-TONE FREQUENCY SPACING EQUALS 2MHz 100 -60 TA = 0°C 95 90 4.75 4.85 4.95 5.05 VCC(V) 2 -70 5.15 5.25 0 -80 1 1.5 2 2.5 GC VOLTAGE (V) 3 3.5 900 1100 1300 1500 1700 RF FREQUENCY (MHz) _______________________________________________________________________________________ 3 MAX2108 AC ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) NOISE FIGURE vs. INSERTION GAIN (RF TO BASEBAND) NOISE FIGURE vs. FREQUENCY 70 14 13 60 25 MAX2108 toc05 15 MAX2108 toc04 80 20 12 40 11 NF (dB) NF (dB) 50 MAX2108 toc06 IM3 vs. CARRIER LEVEL IM3 (dBc) 10 15 9 30 8 20 10 10 7 TWO-TONE FREQUENCY SPACING EQUALS 2MHz VGC = 4V 6 5 0 5 950 -55 -50 -45 -40 -35 -30 -25 -20 -15 -10 1150 RF INPUT LEVEL (dBm) 1350 1550 20 22 26 REAL 10 0 -10 -20 MAX2108 toc08 30 20 SERIES IMPEDANCE (Ω) 20 IMAGINARY REAL 10 0 -10 -20 -30 IMAGINARY -40 -50 -30 -60 VGC = 4V -40 1100 1300 1500 1700 1900 VGC = 1V -70 900 2100 1100 1300 LO PORT SERIES IMPEDANCE vs. FREQUENCY 1700 1900 2100 0 -10 -20 IMAGINARY -40 -50 MAX2108 toc11 REAL 10 NORMALIZED BASEBAND GAIN vs. BASEBAND FREQUENCY 5 NORMALIZED BASEBAND GAIN (dB) MAX2108 toc10 30 -30 1500 FREQUENCY (MHz) FREQUENCY (MHz) 20 28 0 -60 SINGLE-ENDED -70 900 1100 1300 1500 1700 FREQUENCY (MHz) 4 1900 2100 30 GAIN (dB) 40 MAX2108 toc07 30 900 24 RF PORT SERIES IMPEDANCE vs. FREQUENCY 40 SERIES IMPEDANCE (Ω) 1750 RF FREQUENCY (MHz) RF PORT SERIES IMPEDANCE vs. FREQUENCY SERIES IMPEDANCE (Ω) MAX2108 Direct-Conversion Tuner IC -5 0.1 1 10 100 1000 BASEBAND FREQUENCY (MHz) _______________________________________________________________________________________ 32 34 36 38 Direct-Conversion Tuner IC PIN NAME FUNCTION 1 IOUT Inverting I-Channel Baseband Output 2 IOUT Noninverting I-Channel Baseband Output 3 VCC Downconverter +5V Supply. Bypass with a 10pF capacitor to GND as close to the IC as possible. Connect an additional 0.1µF capacitor in parallel with the 10pF capacitor. 4 GND Ground. Connect to a low-inductance ground plane. 5 VCC RF +5V Supply. Bypass with a 22pF capacitor to GND as close to the IC as possible. 6 RFIN Inverting RF Input. Connect to a 22pF capacitor in series with a 75Ω resistor to GND. 7 RFIN Noninverting RF Input. Connect via matching network to a 75Ω cable. 8, 9 GND RF Ground. Connect to a low-inductance ground plane. 10 GC 11 PS_SEL 12 VCC 13 PSOUT Inverting Prescaler Output 14 PSOUT Noninverting Prescaler Output 15 GND Prescaler Ground. Connect to a low-inductance ground plane. 16 GND Local Oscillator Ground. Connect to a low-inductance ground plane. 17, 20 N.C. No Connection. Do not make any connection to this pin. 18 LO Inverting LO Input 19 LO Noninverting LO Input 21 VCC Local Oscillator +5V Supply. Bypass with a 22pF capacitor and a 0.1µF capacitor to pin 16. 22 GND Downconverter Ground. Connect to a low-inductance ground plane. 23 QOUT Noninverting Q-Channel Baseband Output 24 QOUT Inverting Q-Channel Baseband Output Gain-Control Input. Apply a voltage between 1V and 4V to control the gain of the RF amplifier. Bypass with a 1000pF capacitor to minimize noise on the control line. Prescaler Modulus Control. Drive PS_SEL <0.5V to operate in divide-by-33 mode. Drive PS_SEL >2.4V to operate in divide-by-32 mode. Prescaler +5V Supply. Bypass with a 1000pF capacitor to GND. _______________________________________________________________________________________ 5 MAX2108 Pin Description MAX2108 Direct-Conversion Tuner IC _______________Detailed Description The MAX2108 downconverts signals in the 950MHz to 2150MHz range directly to baseband in-phase/ quadrature-phase (I/Q) signals. It is designed for digital DBS tuner applications where a direct downconversion provides a cost savings over multiple-conversion approaches. However, the MAX2108 is applicable to any system requiring a broadband I/Q downconversion. Internally, the MAX2108 consists of a broadband frontend variable gain stage, a quadrature downconverter, a 90° quadrature generator, a divide-by 32/33 prescaler, and high-linearity I and Q baseband buffers. The front-end gain-control range is over 50dB. Specifically, when the MAX2108 operates in an automatic gain control (AGC) loop, VGC is adjusted by the loop so that a sine wave at RFIN ranging in power from -70dBm to -20dBm produces a sine wave across IOUT, IOUT and QOUT, QOUT at 10mVp-p differential. The noise figure is at its minimum when GC is at its maximum gain setting. The quadrature downconverter follows the front-end variable-gain amplifier. The mixer LO ports are fed with the two LO signals, which are 90° apart in phase. These quadrature LO signals are generated internally using the signal from the LO and LO pins. The resulting I/Q baseband signals are fed through separate I-channel and Q-channel baseband buffers. The outputs are capable of driving lowpass filters with 100Ω characteristic impedance (that is, the equivalent of an AC-coupled 100Ω load). The baseband -3dB output bandwidth is approximately 150MHz. Applications Information Front-End Tuner Circuitry for DBS Tuners In a typical application, the signal path ahead of the tuner includes a discrete low-noise amplifier/buffer and a PIN-diode attenuator. Since the MAX2108 satisfies the noise and linearity requirements for DBS, this frontend circuitry is not required. In some very high linearity applications, such as single channel-per-carrier (SCPC), a varactor-tuned preselection bandpass filter is added between a discrete LNA and the MAX2108. The filter provides a means of broadly filtering adjacent interference signals, thus improving the intermodulation performance of the tuner. 6 Additionally, the filter removes RF interference at twice the LO frequency, which otherwise adds to the cochannel interference. The MAX2108 rejects this carrier to approximately 25dBc. LO Port The MAX2108 accepts either a single-ended or differential LO signal. For single-ended drive, AC-couple the LO signal into LO with a 47pF capacitor, and bypass LO to ground with a 47pF capacitor in series with a 25Ω resistor. Drive LO with a 50Ω source at -5dBm. Prescaler The prescaler requires a stable logic level at PS_SEL 4ns before the falling edge of PSOUT, PSOUT to assert the desired modulus. The logic level at PS_SEL must remain static until 2ns after this falling edge. Baseband Buffers The MAX2108 baseband buffers provide at least 10mVp-p differential swing across IOUT, IOUT and QOUT, QOUT, and are capable of driving an AC-coupled 100Ω differential load. In a typical application, IOUT, IOUT, QOUT, and QOUT drive a 5th- or 7th-order lowpass filter for ADC anti-aliasing purposes (see the Filters in Direct-Conversion Tuners section ). In general, additional gain is required, after the filters. This is accomplished with a pair of video-speed op amps, such as the MAX4216 dual video op amp, or a simple transistor circuit. Contact Maxim for more information about the MAX4216. Layout Considerations Observe standard RF layout rules. A ground plane is essential; when connecting areas of ground plane between layers, use vias liberally. If a ground plane is used under the lowpass filters, note that the filter response may be slightly offset due to parasitic capacitance. In a direct-conversion receiver, LO leakage to the RF input connector is a major issue, since filtering of the LO is impossible (the LO operates at the same frequency as the RF input). Observe the power-supply bypass capacitor connections in the Pin Description table, notably pins 3, 5, 12, and 21. Traces from these IC pins to the bypass capacitors must be kept on the top side of the board and as short as possible. _______________________________________________________________________________________ Direct-Conversion Tuner IC Filters in Direct-Conversion Tuners Typically, a 5th- or 7th-order L-C lowpass filter is used for anti-aliasing the ADCs following the MAX2108. Table 1 offers suggested component values for these lowpass filters. Figures 1 and 2 describe typical filtering requirements. Table 1. Suggested Component Values for Discrete Lowpass Filters ADC SAMPLING RATE (Msps) FILTER TYPE RS (Ω) C1 (pF) L1 (nH) C2 (pF) L2 (nH) C3 (pF) L3 (nH) C4 (pF) RL (kΩ) 40 0.1dB Chebyshev, fC = 20MHz 50 20 910 60 1500 75 1500 60 20 60 0.1dB Chebyshev, fC = 30MHz 50 11 620 41 910 50 1000 41 20 0.1dB Chebyshev, fC = 20MHz 50 15 680 39 820 33 Short Open 20 0.1dB Chebyshev, fC = 45MHz 50 9 390 28 620 34 680 28 20 90 _______________________________________________________________________________________ 7 MAX2108 Power-Supply Sequencing The MAX2108 has several +5V supply pins. Configure the supply layout in a star format, with a bypass capacitor that dominates the rise time of the supply at the center of the star to ensure that all pins see approximately the same voltage during power-up. MAX2108 Direct-Conversion Tuner IC 0.1µF RS 0.1µF RS L1 C1 L2 C2 L1 L3 C3 L2 C4 RL L3 BASEBAND LP FILTER DSP IOUT IOUT MATCHED FILTERS MAX2108 ADCS 4 QOUT 3 QOUT 0.1µF RS 0.1µF RS L1 C1 L2 C2 L1 1 L3 C3 L2 C4 RL L3 BASEBAND LP FILTER FOR POINTS 1, 2, 3, 4, REFER TO THE SIGNAL SPECTRUMS SHOWN IN FIGURE 2 Figure 1. In-Phase and Quadrature-Phase Signal Paths 8 _______________________________________________________________________________________ 2 Direct-Conversion Tuner IC MAX2108 TRANSPONDER BW = 24MHz 0 AT POINT 1 DESIRED CHANNEL (20Msps) dBc UNDESIRED ADJACENT CHANNEL -30 0 10 12 17.16 20 29.16 40 41.16 MHz α = 0.2 DATA NYQUIST ADC SAMPLING NYQUIST FOR ADC TRANSPONDER SPACING = 29.16 MHz LOWPASS FILTER RESPONSE 0 AT POINT 2 DESIRED CHANNEL (20Msps) dBc -30 0 10 12 17.16 20 28 FILTER CUTOFF 40 MHz ADC SAMPLING PASSBAND FILTER REQUIREMENTS: (1) <20% OF BAUD PERIOD DELAY RIPPLE (2) <0.1dB GAIN RIPPLE TRANSITION BAND FILTER REQUIREMENTS: < 2dB GAIN RIPPLE 0 AT POINT DESIRED CHANNEL (20Msps) dBc 3 ADJ CHANNEL FOLDOVER -30 0 10 12 17.16 20 40 ADC NYQUIST MHz ADC SAMPLING DIGITAL MATCHED FILTER AT POINT 4 DESIRED CHANNEL (20Msps) dBc -30 0 10 12 40 MHz ADC SAMPLING FOR POINTS 1, 2, 3, 4, REFER TO FIGURE 1 Figure 2. Lowpass Filtering Example _______________________________________________________________________________________ 9 Direct-Conversion Tuner IC MAX2108 Typical Operating Circuit 1 BASEBAND LP FILTER 2 IOUT QOUT IOUT QOUT VCC GND 24 23 BASEBAND LP FILTER VCC 3 C2 0.1µF 22 VCC C1 10pF 4 GND VCC 21 C12 22pF VCC N.C. RFIN LO 20 C3 22pF 6 47pF 7 RFIN LO RFIN 50Ω 18 C5 22pF 47pF 25Ω 8 9 GAIN CONTROL LO DRIVE (-5dBm, 50Ω SOURCE) 19 C4 22pF (75Ω SOURCE) R2 75Ω C13 0.1µF MAX2108 5 R1 75Ω VCC 10 C6 1000pF MODULUS CONTROL 11 GND N.C. GND GND GC GND PS_SEL PSOUT 17 16 15 14 VCC PRESCALER OUTPUT 12 PSOUT VCC 13 C7 1000pF 10 ______________________________________________________________________________________ Direct-Conversion Tuner IC ___________________Chip Information TRANSISTOR COUNT: 1484 TOP VIEW IOUT 1 24 QOUT IOUT 2 23 QOUT VCC 3 22 GND 21 VCC GND 4 VCC 5 MAX2108 20 N.C. RFIN 6 19 LO RFIN 7 18 LO GND 8 17 N.C. GND 9 16 GND GC 10 15 GND PS_SEL 11 14 PSOUT VCC 12 13 PSOUT QSOP ______________________________________________________________________________________ 11 MAX2108 Pin Configuration Direct-Conversion Tuner IC QSOP.EPS MAX2108 Package Information Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.