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19-1449; Rev 0; 4/99
Direct-Conversion Tuner IC
General Description
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. o Low-Cost Architecture o Operates from Single +5V Supply o On-Chip Quadrature Generator, Dual-Modulus Prescaler (/32, /33) o Input Levels: -20dBm to -70dBm per Carrier o Over 50dB RF Gain-Control Range o 10dB Noise Figure at Maximum Gain o +8dBm IIP3 at Minimum Gain
Features
MAX2108
Applications
DirecTV, PrimeStar, EchoStar DBS Tuners DVB-Compliant DBS Tuners Cellular Base Stations Wireless Local Loop Broadband Systems LMDS Microwave Links
PART MAX2108CEG
Ordering Information
TEMP. RANGE 0C to +70C PIN-PACKAGE 24 QSOP
Pin Configuration appears at end of data sheet.
Functional Diagram
VCC 12
PS_SEL 11
GC 10
GND 9
GND 8
RFIN 7
RFIN 6
VCC 5
GND 4
VCC 3
IOUT 2
IOUT 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 GND
23 QOUT
24 QOUT
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769.
Direct-Conversion Tuner IC MAX2108
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 = +70C) 24 QSOP (derate 10mW/C above TA = +70C) ..........800mW Operating Temperature Range...............................0C to +70C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10sec) .............................+300C
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 2.5k to GND; no input signal applied; TA = 0C to +70C; unless otherwise noted. Typical values are at VCC = +5V, TA = +25C.) PARAMETER Supply Current PS_SEL Logic-High Threshold PS_SEL Logic-Low Threshold PS_SEL Input Bias Current GC Input Bias Current IOUT, IOUT, QOUT, QOUT Common-Mode Output Voltage SYMBOL ICC VTHH VTHL IPS_SEL IGC VCM 0 < VPS_SEL < VCC 1V < VGC < 4V -30 -80 2.9 3.35 2.4 0.5 +10 +80 3.8 CONDITIONS MIN TYP 105 MAX 152 UNITS mA V V A A V
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 = +25C; unless otherwise noted.) PARAMETER RFIN Frequency Range (Note 1) RFIN Maximum Input Power (Note 2) RFIN Minimum Input Power (Note 2) External LO Drive Level (Note 2) Gain-Control Range (Note 2) RFIN Input Third-Order Intercept Point (Note 3) RFIN Input Second-Order Intercept Point (Note 4) Noise Figure IIP3 IIP2 NF VGC = 4V, fLO = 1750MHz 1V < VGC < 4V, PLO = -5dBm 50 8 14 10 SYMBOL fRFIN PRFINMAX 950MHz < fRFIN < 2150MHz, PLO = -5dBm PRFINMIN 950MHz < fRFIN < 2150MHz, PLO = -5dBm, VIOUT - V IOUT = 10mVp-p, TA = 0C +70C -5 CONDITIONS MIN 950 -20 -70 TYP MAX 2150 UNITS MHz dBm dBm dBm dB dBm dBm dB
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Direct-Conversion Tuner IC
AC ELECTRICAL CHARACTERISTICS (continued)
(VCC = +5V; PS_SEL = 0.5V; PRFIN = -20dBm; fLO = fRFIN +125kHz; GC set via servo loop for VIOUT - V IOUT = 200mVp-p (differential); TA = +25C; unless otherwise noted.) PARAMETER Prescaler Divide Ratio Differential Prescaler Output Swing I/Q Channel Quadrature Phase Error (Note 2) I/Q Amplitude Mismatch (Note 2) I/Q Channel Clipping Level Baseband Bandwidth I/Q Channel Differential Output Impedance VPSOUT V PSOUT SYMBOL VPS_SEL > 2.4V VPS_SEL < 0.5V CPSOUT = C PSOUT = 10pF to GND fIOUT = f IOUT = fQOUT = f QOUT = 125kHz fIOUT = f IOUT = fQOUT = f QOUT = 125kHz fIOUT = f IOUT = fQOUT = f QOUT = 10MHz, no output load At -3dB attenuation fIOUT = f IOUT = fQOUT = f QOUT = 20MHz 1.4 150 33 CONDITIONS MIN 32 33 1.0 3 1 TYP MAX 32 33 Vp-p degrees dB Vp-p MHz UNITS
MAX2108
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 = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX2108 toc01
CARRIER LEVEL vs. GAIN CONTROL
-10 -20 RF LEVEL (dBm) GC SET FOR 10mVp-p BASEBAND OUTPUT fRFIN = 1750 MHz -40 -50 -60 IIP3 (dBm) -30 6
MAX2108 toc02
INPUT IP3 vs. FREQUENCY
MAX2108 toc03
125 120 115 ICC (mA) 110 105 TA = +25C 100 95 90 4.75 4.85 4.95 5.05 5.15 TA = 0C TA = +70C
0
10
8
4 TWO-TONE FREQUENCY SPACING EQUALS 2MHz 2
-70 5.25 -80 1 1.5 2 2.5 3 3.5 GC VOLTAGE (V) 0 900 1100 1300 1500 1700 RF FREQUENCY (MHz)
VCC(V)
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Direct-Conversion Tuner IC MAX2108
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
IM3 vs. CARRIER LEVEL
MAX2108 toc04
NOISE FIGURE vs. FREQUENCY
MAX2108 toc05
NOISE FIGURE vs. INSERTION GAIN (RF TO BASEBAND)
MAX2108 toc06
80 70 60 IM3 (dBc)
15 14 13 12 NF (dB)
25
20 NF (dB) VGC = 4V 5 950 1150 1350 1550 1750 20 22 24 26 28 30 32 34 36 38 RF FREQUENCY (MHz) GAIN (dB) 40 30 20 SERIES IMPEDANCE () 10 0 -10 -20 -30 -40 -50 -60 VGC = 4V -70 900 1100 1300 1500 1700 FREQUENCY (MHz) VGC = 1V 1900 2100 IMAGINARY REAL
50 40 30 20 10 0 -55 -50 -45 -40 -35 -30 -25 -20 -15 -10 RF INPUT LEVEL (dBm) TWO-TONE FREQUENCY SPACING EQUALS 2MHz
11 10 9 8 7 6 5
15
10
RF PORT SERIES IMPEDANCE vs. FREQUENCY
30 SERIES IMPEDANCE () 20 10 0 -10 -20 -30 -40 900 1100 1300 1500 1700 FREQUENCY (MHz) 1900 2100 IMAGINARY REAL
MAX2108 toc07
RF PORT SERIES IMPEDANCE vs. FREQUENCY
MAX2108 toc08
40
LO PORT SERIES IMPEDANCE vs. FREQUENCY
MAX2108 toc10
10 SERIES IMPEDANCE () 0 -10 -20 -30 -40 -50 -60 -70 900 1100 1300 1500 SINGLE-ENDED 1700 1900 2100 IMAGINARY
NORMALIZED BASEBAND GAIN (dB)
20
REAL
0
-5 0.1 1 10 100 1000 BASEBAND FREQUENCY (MHz)
FREQUENCY (MHz)
4
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MAX2108 toc11
30
5
NORMALIZED BASEBAND GAIN vs. BASEBAND FREQUENCY
Direct-Conversion Tuner IC
Pin Description
PIN 1 2 3 4 5 6 7 8, 9 10 11 12 13 14 15 16 17, 20 18 19 21 22 23 24 NAME IOUT IOUT VCC GND VCC RFIN RFIN GND GC PS_SEL VCC PSOUT PSOUT GND GND N.C. LO LO VCC GND QOUT QOUT Inverting I-Channel Baseband Output Noninverting I-Channel Baseband Output Downconverter +5V Supply. Bypass with a 10pF capacitor to GND as close to the IC as possible. Connect an additional 0.1F capacitor in parallel with the 10pF capacitor. Ground. Connect to a low-inductance ground plane. RF +5V Supply. Bypass with a 22pF capacitor to GND as close to the IC as possible. Inverting RF Input. Connect to a 22pF capacitor in series with a 75 resistor to GND. Noninverting RF Input. Connect via matching network to a 75 cable. RF Ground. Connect to a low-inductance ground plane. 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. Inverting Prescaler Output Noninverting Prescaler Output Prescaler Ground. Connect to a low-inductance ground plane. Local Oscillator Ground. Connect to a low-inductance ground plane. No Connection. Do not make any connection to this pin. Inverting LO Input Noninverting LO Input Local Oscillator +5V Supply. Bypass with a 22pF capacitor and a 0.1F capacitor to pin 16. Downconverter Ground. Connect to a low-inductance ground plane. Noninverting Q-Channel Baseband Output Inverting Q-Channel Baseband Output FUNCTION
MAX2108
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Direct-Conversion Tuner IC MAX2108
_______________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 100 characteristic impedance (that is, the equivalent of an AC-coupled 100 load). The baseband -3dB output bandwidth is approximately 150MHz. 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 25 resistor. Drive LO with a 50 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 100 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.
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.
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Direct-Conversion Tuner IC
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.
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.
MAX2108
Table 1. Suggested Component Values for Discrete Lowpass Filters
ADC SAMPLING RATE (Msps) 40 60 FILTER TYPE RS () C1 (pF) L1 (nH) C2 (pF) L2 (nH) C3 (pF) L3 (nH) C4 (pF) RL (k)
0.1dB Chebyshev, fC = 20MHz 0.1dB Chebyshev, fC = 30MHz 0.1dB Chebyshev, fC = 20MHz 0.1dB Chebyshev, fC = 45MHz
50 50 50 50
20 11 15 9
910 620 680 390
60 41 39 28
1500 910 820 620
75 50 33 34
1500 1000 Short 680
60 41 Open 28
20 20 20 20
90
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Direct-Conversion Tuner IC MAX2108
0.1F
RS
L1
L2
L3
C1 0.1F RS L1
C2 L2 BASEBAND LP FILTER
C3 L3
C4
RL
DSP IOUT IOUT
MAX2108
4 QOUT QOUT
MATCHED FILTERS 3
ADCS
0.1F
RS
L1
L2
L3
C1 0.1F 1 RS L1
C2 L2 BASEBAND LP FILTER
C3 L3
C4
RL 2
FOR POINTS 1, 2, 3, 4, REFER TO THE SIGNAL SPECTRUMS SHOWN IN FIGURE 2
Figure 1. In-Phase and Quadrature-Phase Signal Paths
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Direct-Conversion Tuner IC MAX2108
TRANSPONDER BW = 24MHz 0
AT POINT
1
dBc -30 0
DESIRED CHANNEL (20Msps) 10 12 DATA NYQUIST 17.16 = 0.2 NYQUIST FOR ADC 20
UNDESIRED ADJACENT CHANNEL
29.16
40 41.16
MHz
ADC SAMPLING
TRANSPONDER SPACING = 29.16 MHz
LOWPASS FILTER RESPONSE 0
AT POINT
2
dBc -30 0
DESIRED CHANNEL (20Msps) 10 12 17.16 20 28 FILTER CUTOFF ADC SAMPLING 40 MHz
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
3
dBc -30 0
DESIRED CHANNEL (20Msps) 10 12
ADJ CHANNEL FOLDOVER 17.16 20 40 MHz
ADC NYQUIST
ADC SAMPLING
DIGITAL MATCHED FILTER
AT POINT
4
dBc -30 0
DESIRED CHANNEL (20Msps) 10 12 40 MHz
ADC SAMPLING FOR POINTS 1, 2, 3, 4, REFER TO FIGURE 1
Figure 2. Lowpass Filtering Example
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Direct-Conversion Tuner IC MAX2108
Typical Operating Circuit
1 BASEBAND LP FILTER VCC 3 C2 0.1F C1 10pF 4
IOUT
QOUT
24 BASEBAND LP FILTER
2
IOUT
QOUT
23
VCC
GND
22 VCC
GND
VCC
21 C12 22pF C13 0.1F
VCC 5 C3 22pF 6 C4 22pF 7 C5 22pF 8 RFIN VCC
MAX2108
N.C. 20
R1 75
LO
19 47pF 50
LO DRIVE (-5dBm, 50 SOURCE)
RFIN (75 SOURCE) R2 75
RFIN
LO
18 47pF 25
GND
N.C.
17
9
GND
GND
16
GAIN CONTROL
10 C6 1000pF 11 VCC 12
GC
GND
15
MODULUS CONTROL
PS_SEL
PSOUT
14 PRESCALER OUTPUT
VCC
PSOUT
13
C7 1000pF
10
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Direct-Conversion Tuner IC
Pin Configuration
TOP VIEW
IOUT 1 IOUT 2 VCC 3 GND 4 VCC 5 RFIN 6 RFIN 7 GND 8 GND 9 GC 10 PS_SEL 11 VCC 12 24 QOUT 23 QOUT 22 GND 21 VCC
___________________Chip Information
TRANSISTOR COUNT: 1484
MAX2108
MAX2108
20 N.C. 19 LO 18 LO 17 N.C. 16 GND 15 GND 14 PSOUT 13 PSOUT
QSOP
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11
Direct-Conversion Tuner IC MAX2108
Package Information
QSOP.EPS
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 (c) 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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