Rainbow Electronics MAX2108 User Manual

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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 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.

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

1

PS_SEL GC GND GND RFIN

RFIN

GND IOUT

IOUT

PSOUT

V

CC

V

CC

V

CC

V

CC

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

90

Q

0

I

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.

MAX2108

Direct-Conversion Tuner IC

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

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; T

A

= 0°C to +70°C; unless otherwise noted. Typical values are at VCC= +5V, TA= +25°C.)

AC ELECTRICAL CHARACTERISTICS

(VCC= +5V; PS_SEL = 0.5V; P

RFIN

= -20dBm; fLO= f

RFIN

+125kHz; GC set via servo loop for V

IOUT

- V

IOUT

= 200mVp-p (differen-

tial); T

A

= +25°C; unless otherwise noted.)

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.

VCCto GND..............................................................-0.3V to +7V

V

CC

to Any Other VCC...........................................-0.3V to +0.3V

All Other Pins to GND.................................-0.3V to (V

CC

+ 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 (T

A

= +70°C)

24 QSOP (derate 10mW/°C above T

A

= +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

0 < V

PS_SEL

< V

CC

1V < VGC< 4V

CONDITIONS

V0.5V

THL

PS_SEL Logic-Low Threshold

V2.4V

THH

mA105 152I

CC

Supply Current
PS_SEL Logic-High Threshold

µA-30 +10I

PS_SEL

PS_SEL Input Bias Current

µA-80 +80I

GC

GC Input Bias Current

UNITSMIN TYP MAXSYMBOLPARAMETER

V2.9 3.35 3.8V

CM

IOUT, IOUT, QOUT, QOUT
Common-Mode Output Voltage

950MHz < f

RFIN

< 2150MHz, PLO= -5dBm,

V

IOUT

- V

IOUT

= 10mVp-p, TA= 0°C +70°C

950MHz < f

RFIN

< 2150MHz, PLO= -5dBm

1V < VGC< 4V, PLO= -5dBm

CONDITIONS

dBm-70P

RFINMIN

RFIN Minimum Input Power
(Note 2)

dBm-20P

RFINMAX

MHz950 2150f

RFIN

RFIN Frequency Range (Note 1)
RFIN Maximum Input Power

(Note 2)

dBm

-5

External LO Drive Level (Note 2)

dB50Gain-Control Range (Note 2)

UNITSMIN TYP MAXSYMBOLPARAMETER

VGC= 4V, fLO= 1750MHz dB10NFNoise Figure

dBm14IIP

2

dBm8IIP

3

RFIN Input Third-Order
Intercept Point (Note 3)

RFIN Input Second-Order
Intercept Point (Note 4)

MAX2108

Direct-Conversion Tuner IC

_______________________________________________________________________________________ 3

AC ELECTRICAL CHARACTERISTICS (continued)

(VCC= +5V; PS_SEL = 0.5V; P

RFIN

= -20dBm; fLO= f

RFIN

+125kHz; GC set via servo loop for V

IOUT

- V

IOUT

= 200mVp-p (differen-

tial); T

A

= +25°C; unless otherwise noted.)

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: P

RFIN

= -20dBm per tone, GC set via servo loop for V

IOUT

- V

IOUT

= 20mVp-p per tone. f1

RFIN

= 1749MHz, f2

RFIN

=

1751MHz, f

LO

= 1740MHz.

Note 4: P

RFIN

= -20dBm per tone, GC set via servo loop for V

IOUT

- V

IOUT

= 20mVp-p per tone. f1

RFIN

= 1200MHz, f2

RFIN

=

2150MHz, f

LO

= 951MHz.

CONDITIONS UNITSMIN TYP MAXSYMBOLPARAMETER

V

PS_SEL

< 0.5V

C

PSOUT

= C

PSOUT

= 10pF to GND

33 33

V

PS_SEL

> 2.4V

Prescaler Divide Ratio

Vp-p1.0

V

PSOUT -

V

PSOUT

Differential Prescaler Output
Swing

32 32

At -3dB attenuation
f

IOUT

= f

IOUT

= f

QOUT

= f

QOUT

= 20MHz

MHz150

f

IOUT

= f

IOUT

= f

QOUT

= f

QOUT

= 125kHz

Baseband Bandwidth

Ω33

I/Q Channel Differential
Output Impedance

degrees3

I/Q Channel Quadrature
Phase Error (Note 2)

f

IOUT

= f

IOUT

= f

QOUT=fQOUT

= 125kHz dB1

I/Q Amplitude Mismatch
(Note 2)

f

IOUT

= f

IOUT

= f

QOUT

= f

QOUT

= 10MHz,

no output load

Vp-p1.4I/Q Channel Clipping Level

Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

90

100

95

110

105

120

115

125

4.75 4.954.85 5.05 5.15 5.25

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX2108 toc01

VCC(V)

I

CC

(mA)

TA = +70°C

TA = +25°C

TA = 0°C

-80

-70

-60

-50

-40

-30

-20

-10

0

1 1.5 2 2.5 3 3.5

CARRIER LEVEL vs. GAIN CONTROL

MAX2108 toc02

GC VOLTAGE (V)

RF LEVEL (dBm)

GC SET FOR 10mVp-p
BASEBAND OUTPUT

f

RFIN

= 1750 MHz

0

2

4

6

8

10

900 13001100 1500 1700

INPUT IP3 vs. FREQUENCY

MAX2108 toc03

RF FREQUENCY (MHz)

IIP3 (dBm)

TWO-TONE FREQUENCY
SPACING EQUALS 2MHz

MAX2108

Direct-Conversion Tuner IC

4 _______________________________________________________________________________________

Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

0

20
10

30

60

70

50
40

80

-55 -45 -40 -35 -30-50 -25 -20 -15 -10

IM3 vs. CARRIER LEVEL

MAX2108 toc04

RF INPUT LEVEL (dBm)

IM3 (dBc)

TWO-TONE FREQUENCY
SPACING EQUALS 2MHz

5

7
6

9
8

11
10

12

14
13

15

950 1150 1350 1550 1750

NOISE FIGURE vs. FREQUENCY

MAX2108 toc05

RF FREQUENCY (MHz)

NF (dB)

VGC = 4V

5

10

15

20

25

20 26 2822 24 30 32 34 36 38

NOISE FIGURE vs. INSERTION GAIN

(RF TO BASEBAND)

MAX2108 toc06

GAIN (dB)

NF (dB)

-40

-20

-30

20
10

0

-10

40
30

900 1100 1300 1500 1700 1900 2100

RF PORT SERIES IMPEDANCE

vs. FREQUENCY

MAX2108 toc07

FREQUENCY (MHz)

SERIES IMPEDANCE (Ω)

VGC = 4V

REAL

IMAGINARY

-70

-40

-50

-60

-20

-30

20
10

0

-10

40
30

900 1100 1300 1500 1700 1900 2100

RF PORT SERIES IMPEDANCE

vs. FREQUENCY

MAX2108 toc08

FREQUENCY (MHz)

SERIES IMPEDANCE (Ω)

REAL

IMAGINARY

VGC = 1V

-70

-40

-50

-60

-20

-30

20
10

0

-10

30

900 1100 1300 1500 1700 1900 2100

LO PORT SERIES IMPEDANCE

vs. FREQUENCY

MAX2108 toc10

FREQUENCY (MHz)

SERIES IMPEDANCE (Ω)

REAL

IMAGINARY

SINGLE-ENDED

0.1 101 100 1000

NORMALIZED BASEBAND GAIN

vs. BASEBAND FREQUENCY

MAX2108 toc11

BASEBAND FREQUENCY (MHz)

NORMALIZED BASEBAND GAIN (dB)

5

-5

0

MAX2108

Direct-Conversion Tuner IC

_______________________________________________________________________________________ 5

NAME FUNCTION

1

IOUT

Inverting I-Channel Baseband Output

PIN

Pin Description

2 IOUT Noninverting I-Channel Baseband Output

3 V

CC

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 V

CC

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

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.

11 PS_SEL

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.

12 V

CC

Prescaler +5V Supply. Bypass with a 1000pF capacitor to GND.

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 V

CC

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

MAX2108

Direct-Conversion Tuner IC

6 _______________________________________________________________________________________

_______________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, VGCis 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.

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.

MAX2108

Direct-Conversion Tuner IC

_______________________________________________________________________________________ 7

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.

Table 1. Suggested Component Values for Discrete Lowpass Filters

0.1dB Chebyshev,
fC= 30MHz

60

0.1dB Chebyshev,
fC= 20MHz

40

FILTER TYPE

ADC

SAMPLING

RATE

(Msps)

50

50

R

S

(Ω)

11

20

C1

(pF)

620

910

L1

(nH)

41

60

C2

(pF)

910

1500

L2

(nH)

50

75

C3

(pF)

1000

1500

L3

(nH)

41

60

C4

(pF)

20

20

R

L

(kΩ)

50 15 680 39 820 33 Short Open 20

0.1dB Chebyshev,
fC= 20MHz

90

50 9 390 28 620 34 680 28 20

0.1dB Chebyshev,
fC= 45MHz

MAX2108

Direct-Conversion Tuner IC

8 _______________________________________________________________________________________

RS

C1 C2 C3 C4

RL

ADCS

DSP

MATCHED

FILTERS

RS

L1

L1

BASEBAND LP FILTER

BASEBAND LP FILTER

L2

L2

L3

L3

0.1µF

0.1µF

RS

C1 C2 C3 C4

RL

RS

L1

L1

L2

L2

L3

L3

0.1µF

0.1µF

IOUT IOUT

MAX2108

QOUT QOUT

FOR POINTS 1, 2, 3, 4, REFER TO THE SIGNAL SPECTRUMS SHOWN IN FIGURE 2

4

3

2

1

Figure 1. In-Phase and Quadrature-Phase Signal Paths

MAX2108

Direct-Conversion Tuner IC

_______________________________________________________________________________________ 9

MHz

DESIRED

CHANNEL

(20Msps)

dBc

AT POINT

0

010

PASSBAND FILTER REQUIREMENTS:
(1) <20% OF BAUD PERIOD DELAY RIPPLE
(2) <0.1dB GAIN RIPPLE

TRANSITION BAND FILTER REQUIREMENTS:
< 2dB GAIN RIPPLE

FILTER CUTOFF

12 20 28 40 MHz17.16

-30

ADC SAMPLING

TRANSPONDER SPACING = 29.16 MHz

LOWPASS FILTER RESPONSE

DESIRED

CHANNEL

(20Msps)

UNDESIRED ADJACENT CHANNEL

TRANSPONDER BW = 24MHz

dBc

AT POINT

0

1

010

DATA NYQUIST

NYQUIST FOR ADC

α = 0.2

12 20 29.16 40 41.1617.16

-30

ADC SAMPLING

MHz

DESIRED
CHANNEL
(20Msps)

ADJ

CHANNEL

FOLDOVER

dBc

AT POINT

0

010

ADC NYQUIST

12 20 4017.16

-30

ADC SAMPLING

MHz

DESIRED
CHANNEL
(20Msps)

FOR POINTS 1, 2, 3, 4, REFER TO FIGURE 1

DIGITAL MATCHED FILTER

dBc

AT POINT

0 10 12 40

-30

ADC SAMPLING

2

3

4

Figure 2. Lowpass Filtering Example

MAX2108

Direct-Conversion Tuner IC

10 ______________________________________________________________________________________

24

23

22

21

20

19

18

17

1

2

3

4

5

6

7

8

16

15

14

13

9

10

MODULUS
CONTROL

GAIN
CONTROL

RFIN

11

12

GND

V

CC

IOUT

IOUT

GND

RFIN

RFIN

V

CC

V

CC

PS_SEL

GC

GND

QOUT

QOUT

GND

V

CC

N.C.

LO

LO

N.C.

GND

GND

PSOUT

PSOUT

V

CC

V

CC

V

CC

V

CC

C12
22pF

C13

0.1µF

25Ω

(75Ω SOURCE) R2

75Ω

R1

75Ω

47pF

LO DRIVE
(-5dBm, 50Ω SOURCE)

50Ω

47pF

C4

22pF

C5

22pF

C6

1000pF

C7

1000pF

C3

22pF

C1

10pF

C2

0.1µF

PRESCALER

OUTPUT

MAX2108

BASEBAND

LP

FILTER

BASEBAND

LP

FILTER

Typical Operating Circuit

MAX2108

Direct-Conversion Tuner IC

______________________________________________________________________________________ 11

24

23

22

21

20

19

18

17

1
2
3
4
5
6
7
8

QOUT
QOUT
GND
V

CC

GND

V

CC

IOUT

IOUT

TOP VIEW

N.C.
LO
LO
N.C.GND

RFIN

RFIN

V

CC

16

15

14

13

9
10
11
12

GND
GND
PSOUT
PSOUTV

CC

PS_SEL

GC

GND

QSOP

MAX2108

Pin Configuration ___________________Chip Information

TRANSISTOR COUNT: 1484

MAX2108

Direct-Conversion Tuner IC

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

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Package Information

QSOP.EPS