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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 base-

band using a broadband I/Q downconverter. The oper-

ating 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.

Applications

DirecTV, PrimeStar, EchoStar DBS Tuners

DVB-Compliant DBS Tuners

Cellular Base Stations

Wireless Local Loop

Broadband Systems

LMDS

Microwave Links

Features

♦ 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

MAX2108

Direct-Conversion Tuner IC

________________________________________________________________

Maxim Integrated Products

PS_SEL GC GND GND RFIN

RFIN

GND IOUT

IOUT

PSOUT

PSOUT GND GND N.C. LO LO QOUT QOUT

N.C. GND

1211109 876543 21

13 14 15 16 17 18 19 20 21 22 23 24

MAX2108

/32

/33

Functional Diagram

19-1449; Rev 0; 4/99

PART

MAX2108CEG 0°C to +70°C

TEMP. RANGE PIN-PACKAGE

24 QSOP

Ordering Information

Pin Configuration appears at end of data sheet.

Summary of content (12 pages)

PAGE 1
9-1449; 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.
PAGE 2
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 ................................................................................
PAGE 3
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.
PAGE 4
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.
PAGE 5
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.
PAGE 6
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.
PAGE 7
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.
PAGE 8
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.
PAGE 9
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.
PAGE 10
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.
PAGE 11
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.
PAGE 12
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.