MAXIM MAX2108

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
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For small orders, phone 1-800-835-8769.
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.
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© 1999 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.