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19-2799; Rev 0; 4/03
Digitally Controlled, Variable-Gain, Differential ADC Driver/Amplifier
General Description
The MAX2055 high-performance, digitally controlled, variable-gain, differential analog-to-digital converter (ADC) driver/amplifier (DVGA) is designed for use from 30MHz to 300MHz in base station receivers. The device integrates a digitally controlled attenuator and a high-linearity single-ended-to-differential output amplifier, which can either eliminate an external transformer, or can improve the even-order distortion performance of a transformer-coupled circuit, thus relaxing the requirements of the anti-alias filter preceding an ADC. Targeted for ADC driver applications to adjust gain either dynamically or as a one-time channel gain setting, the MAX2055 is ideal for applications requiring high performance. The attenuator provides 23dB of attenuation range with 0.2dB accuracy. The MAX2055 is available in a thermally enhanced 20pin TSSOP-EP package and operates over the -40C to +85C temperature range. o 30MHz to 300MHz Frequency Range o Single-Ended-to-Differential Conversion o -3dB to +20dB Variable Gain o 40dBm Output IP3 (at All Gain States and 70MHz) o 2nd Harmonic -76dBc o 3rd Harmonic -69dBc o Noise Figure: 5.8dB at Maximum Gain o Digitally Controlled Gain with 1dB Resolution and 0.2dB Accuracy o Adjustable Bias Current
Features
MAX2055
Ordering Information
PART MAX2055EUP-T TEMP RANGE -40C to +85C PIN-PACKAGE 20 TSSOP-EP*
Applications
Cellular Base Stations PHS/PAS Infrastructure Receiver Gain Control Broadband Systems Automatic Test Equipment Terrestrial Links High-Performance ADC Drivers
*EP = Exposed paddle.
Pin Configuration/ Functional Diagram
TOP VIEW
VCC 1 RF_IN 2 GND 3 B4 4 B3 5 B2 6 B1 7 B0 8 VCC 9 RF_OUT- 10 ATTENUATION LOGIC CONTROL
20 GND 19 ATTNOUT
MAX2055
18 GND 17 ISET 16 CC 15 AMPIN 14 LE 13 CBP 12 IBIAS 11 RF_OUT+
TSSOP
________________________________________________________________ Maxim Integrated Products
1
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Digitally Controlled, Variable-Gain, Differential ADC Driver/Amplifier MAX2055
ABSOLUTE MAXIMUM RATINGS
All Pins to GND. .....................................-0.3V to +(VCC + 0.25V) Input Signal (RF_IN).....................................................20dBm Output Power (RF_OUT) ...................................................24dBm Continuous Power Dissipation (TA = +70C) 20-Pin TSSOP (derate 21.7mW/C above +70C) ...........2.1W Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +165C Lead Temperature (soldering, 10s) .................................+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
(Circuit of Figure 1; VCC = +4.75V to +5.25V, GND = 0V. No input signals applied, and input and output ports are terminated with 50. R1 = 1.13k, TA = -40C to +85C. Typical values are at VCC = +5V and TA = +25C, unless otherwise noted.) (Notes 1, 2)
PARAMETER SUPPLY Supply Voltage Supply Current ISET Current CONTROL INPUTS Control Bits Input Logic High Input Logic Low Input Leakage Current -1.2 Parallel 2 0.6 +1.2 5 Bits V V A VCC ICC ISET 4.75 5.0 240 1.1 5.25 290 V mA mA SYMBOL CONDITIONS MIN TYP MAX UNITS
AC ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1; VCC = +4.75V to +5.25V, GND = 0V, max gain (B0 = B1 = B2 = B3 = B4 = 0), R1 = 1.13k, POUT = 5dBm, fIN = 70MHz, 50 system impedance. Typical values are at VCC = +5V and TA = +25C, unless otherwise noted.) (Notes 1, 2)
PARAMETER Frequency Range Gain Amplitude Unbalance Phase Unbalance Minimum Reverse Isolation Noise Figure Output 1dB Compression Point 2nd-Order Output Intercept Point 3rd-Order Output Intercept Point 2nd Harmonic 3rd Harmonic RF Gain-Control Range Gain-Control Resolution Attenuation Absolute Accuracy Attenuation Relative Accuracy Gain Drift Over Temperature Compared to the ideal expected attenuation Between adjacent states TA = -40C to +85C NF P1dB OIP2 OIP3 2fIN 3fIN f1 + f2, f1 = 70MHz, f2 = 71MHz, 5dBm/tone at RF_OUT All gain conditions, 5dBm/tone at RF_OUT SYMBOL fR G (Note 3) (Note 3) CONDITIONS MIN 30 19.9 0.06 0.7 29 5.8 25.7 75 40 -76 -69 23 1 0.2 +0.05/ -0.2 0.3 TYP MAX 300 UNITS MHz dB dB Degrees dB dB dBm dBm dBm dBc dBc dB dB dB dB dB
2
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Digitally Controlled, Variable-Gain, Differential ADC Driver/Amplifier
AC ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1; VCC = +4.75V to +5.25V, GND = 0V, max gain (B0 = B1 = B2 = B3 = B4 = 0), R1 = 1.13k, POUT = 5dBm, fIN = 70MHz, 50 system impedance. Typical values are at VCC = +5V and TA = +25C, unless otherwise noted.) (Notes 1, 2)
PARAMETER Gain Flatness Over 50MHz Bandwidth Attenuator Switching Time Input Return Loss Output Return Loss SYMBOL CONDITIONS Peak-to-peak for all settings 50% control to 90% RF fR = 30MHz to 300MHz, all gain conditions fR = 30MHz to 250MHz, all gain conditions fR = 250MHz to 300MHz, all gain conditions MIN TYP 0.5 40 15 15 12 MAX UNITS dB ns dB dB
MAX2055
Note 1: Guaranteed by design and characterization. Note 2: All limits reflect losses of external components. Output measurements are taken at RF_OUT using the application circuit shown in Figure 1. Note 3: The amplitude and phase unbalance are tested with 50 resistors connected from OUT+/OUT- to GND.
Typical Operating Characteristics
(Circuit of Figure 1, VCC = 5.0V, R1 = 1.13k, max gain (B0 = B1 = B2 = B3 = B4 = 0), POUT = 5dBm, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX2055 toc01
INPUT RETURN LOSS vs. RF FREQUENCY (ALL STATES)
MAX2055 toc02
OUTPUT RETURN LOSS vs. RF FREQUENCY (ALL STATES)
5 OUTPUT RETURN LOSS (dB) 10 15 20 25 30 35 40
MAX2055 toc03
270 260 SUPPLY CURRENT (mA) VCC = 5.25V 250 VCC = 5.0V 240 230 VCC = 4.75V 220 210 -40 -15 10 35 60
0 5 INPUT RETURN LOSS (dB) 10 15 20 25 30 35 40 30 60
0
85
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
TEMPERATURE (C)
GAIN vs. RF FREQUENCY (ALL STATES)
MAX2055 toc04
GAIN vs. RF FREQUENCY
MAX2055 toc05
GAIN vs. RF FREQUENCY
MAX2055 toc06
25 20 15 GAIN (dB)
24 22 20 GAIN (dB) 18 16 14 12 10 TA = -40C
24 22 20 GAIN (dB) VCC = 4.75V
10 5 0 -5 -10 30 60 90 120 150 180 210 240 270 300 FREQUENCY (MHz)
TA = +25C TA = +85C
18 VCC = 5.25V 16 14 12 10 VCC = 5.0V
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
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Digitally Controlled, Variable-Gain, Differential ADC Driver/Amplifier MAX2055
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VCC = 5.0V, R1 = 1.13k, max gain (B0 = B1 = B2 = B3 = B4 = 0), POUT = 5dBm, TA = +25C, unless otherwise noted.)
ATTENUATION ABSOLUTE ACCURACY (ALL STATES)
MAX2055 toc07
ATTENUATION RELATIVE ACCURACY (ALL STATES)
MAX2055 toc08
REVERSE ISOLATION vs. RF FREQUENCY
MAX2055 toc09
1.0 0.8 ABSOLUTE ACCURACY (dB) 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 30 60
1.0 0.8 RELATIVE ACCURACY (dB) 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0
40
REVERSE ISOLATION (dB) 30 60 90 120 150 180 210 240 270 300 FREQUENCY (MHz)
36
32
28
24
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
20 30 60 90 120 150 180 210 240 270 300 FREQUENCY (MHz)
NOISE FIGURE vs. FREQUENCY
MAX2055 toc10
OUTPUT P-1dB vs. FREQUENCY
MAX2055 toc11
OUTPUT P-1dB vs. FREQUENCY
MAX2055 toc12
8.0 7.5 7.0 NOISE FIGURE (dB) 6.5 6.0 5.5 5.0 4.5 4.0 30 60 TA = +25C TA = -40C TA = +85C
27 26 OUTPUT P-1dB (dBm) 25 24 23 22 21 TA = +25C
27 26 OUTPUT P-1dB (dBm) 25 24 23 22 21 VCC = +5V
TA = +85C
VCC = +5.25V
TA = -40C
VCC = +4.75V
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
OUTPUT IP3 vs. FREQUENCY
MAX2055 toc13
OUTPUT IP3 vs. FREQUENCY
MAX2055 toc14
INPUT IP3 vs. ATTENUATION STATE
50 45 IIP3 (dBm) 40 35 30 25 PRF1 = PRF2 = 5dBm AT OUTPUT, f = 1MHz, fIN = 70MHz
MAX2055 toc15
44 42 40 OIP3 (dBm) 38 TA = +85C 36 34 32 30 30 60 PRF1 = PRF2 = 5dBm AT OUTPUT, f = 1MHz TA = +25C TA = -40C
44 42 40 OIP3 (dBm) 38 VCC = +5V 36 34 32 30 PRF1 = PRF2 = 5dBm AT OUTPUT, f = 1MHz 30 60 VCC = +4.75V VCC = +5.25V
55
20 15 0 4 8 12 16 20 24
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
ATTENUATION STATE
4
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Digitally Controlled, Variable-Gain, Differential ADC Driver/Amplifier
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VCC = 5.0V, R1 = 1.13k, max gain (B0 = B1 = B2 = B3 = B4 = 0), POUT = 5dBm, TA = +25C, unless otherwise noted.)
3RD HARMONIC vs. FREQUENCY
MAX2055 toc16
MAX2055
3RD HARMONIC vs. FREQUENCY
MAX2055 toc17
2ND HARMONIC vs. FREQUENCY
TA = -40C TA = +85C
MAX2055 toc18 MAX2055 toc21
-55 TA = -40C -60 HARMONIC (dBc) -65 -70 -75 -80 -85 30 60 TA = +85C TA = +25C
-55 -60 VCC = +5.25V HARMONIC (dBc) -65 -70 VCC = +4.75V -75 -80 -85 VCC = +5V
-60 -65 HARMONIC (dBc) -70 -75 -80 -85 -90 TA = +25C
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
2ND HARMONIC vs. FREQUENCY
MAX2055 toc19
OUTPUT IP2 vs. FREQUENCY (f1 + f2)
MAX2055 toc20
OUTPUT IP2 vs. FREQUENCY (f1 + f2)
85 VCC = +4.75V 80 VCC = +5.0 75 OIP2 (dBm) 70 65 60 55 50 PRF1 = PRF2 = 5dBm AT OUTPUT, f = 1MHz 30 60 90 120 150 180 210 240 270 300 FREQUENCY (MHz) VCC = +5.25V
-60 -65 VCC = +5.25V HARMONIC (dBc) -70
85 80 75 OIP2 (dBm) 70 65 60 55 50 TA = -40C TA = +85C PRF1 = PRF2 = 5dBm AT OUTPUT, f = 1MHz 30 60 TA = +25C
-75 -80 VCC = +5V -85 -90 30 60 90 120 150 180 210 240 270 300 FREQUENCY (MHz) VCC = +4.75V
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
OUTPUT-PORT AMPLITUDE UNBALANCE vs. FREQUENCY
MAX2055 toc22
OUTPUT-PORT PHASE UNBALANCE vs. FREQUENCY
MAX2055 toc23
0.25
3.0 PHASE UNBALANCE (DEGREES) 2.5 2.0 1.5 1.0 0.5 0
AMPLITUDE UNBALANCE (dB)
0.20
0.15
0.10
0.05
0 30 60 90 120 150 180 210 240 270 300 FREQUENCY (MHz)
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
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5
Digitally Controlled, Variable-Gain, Differential ADC Driver/Amplifier MAX2055
Typical Operating Characteristics
(Circuit of Figure 2, VCC = 5.0V, R1 = 909, max gain, (B0 = B1 = B2 = B3 = B4 = 0), POUT = 5dBm, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX2055 toc24
INPUT RETURN LOSS vs. RF FREQUENCY (ALL STATES)
MAX2055 toc25
OUTPUT RETURN LOSS vs. FREQUENCY (ALL STATES)
MAX2055 toc26
270 260 SUPPLY CURRENT (mA) 250 VCC = 5.0V 240 230 220 210 -40 -15 10 35 60 VCC = 5.25V
0 10 INPUT RETURN LOSS (dB) 20 30 40 50 60
0 10 OUTPUT RETURN LOSS (dB) 20 30 40 50 60
VCC = 4.75V
85
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
TEMPERATURE (C)
GAIN vs. RF FREQUENCY (ALL STATES)
MAX2055 toc27
GAIN vs. RF FREQUENCY
MAX2055 toc28
GAIN vs. RF FREQUENCY
MAX2055 toc29 MAX2055 toc32
25 20 15 GAIN (dB)
24 22 20 GAIN (dB) 18 TA = +25C 16 TA = +85C 14 12 10 TA = -40C
24 22 20 GAIN (dB) 18 VCC = 5.25V 16 14 12 10 VCC = 5.0V VCC = 4.75V
10 5 0 -5 -10 30 60 90 120 150 180 210 240 270 300 FREQUENCY (MHz)
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
ATTENUATION ABSOLUTE ACCURACY (ALL STATES)
MAX2055 toc30
ATTENUATION RELATIVE ACCURACY (ALL STATES)
0.8 RELATIVE ACCURACY (dB) 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0
MAX2055 toc31
REVERSE ISOLATION vs. RF FREQUENCY
40
1.0 0.8 ABSOLUTE ACCURACY (dB) 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 30 60
1.0
REVERSE ISOLATION (dB) 30 60 90 120 150 180 210 240 270 300 FREQUENCY (MHz)
36
32
28
24
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
20 30 60 90 120 150 180 210 240 270 300 FREQUENCY (MHz)
6
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Digitally Controlled, Variable-Gain, Differential ADC Driver/Amplifier
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VCC = 5.0V, R1 = 909, max gain, (B0 = B1 = B2 = B3 = B4 = 0), POUT = 5dBm, TA = +25C, unless otherwise noted.)
NOISE FIGURE vs. FREQUENCY
MAX2055 toc33
MAX2055
OUTPUT P-1dB vs. FREQUENCY
MAX2055 toc34
OUTPUT P-1dB vs. FREQUENCY
MAX2055 toc35
8.0 7.5 7.0 NOISE FIGURE (dB) 6.5 6.0 5.5 5.0 4.5 4.0 30 60 TA = -40C TA = +25C TA = +85C
27 26 OUTPUT P-1dB (dBm) 25 24 TA = -40C 23 22 21 TA = +85C
27 26 OUTPUT P-1dB (dBm) 25 24 23 22 21 VCC = +4.75V VCC = +5V
VCC = +5.25V
TA = +25C
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
OUTPUT IP3 vs. FREQUENCY
MAX2055 toc36
OUTPUT IP3 vs. FREQUENCY
MAX2055 toc37
INPUT IP3 vs. ATTENUATION STATE
50 45 PRF1 = PRF2 = 5dBm AT OUTPUT, f = 1MHz, fIN = 70MHz
MAX2055 toc38
44 42 TA = +25C 40 OIP3 (dBm)
44 42 40 OIP3 (dBm) VCC = +5.25V VCC = +4.75V VCC = +5V
55
38 36 34 32 30 30
TA = +85C
38 36 34 32 30
IIP3 (dBm) PRF1 = PRF2 = 5dBm AT OUTPUT, f = 1MHz
40 35 30
TA = -40C PRF1 = PRF2 = 5dBm AT OUTPUT, f = 1MHz 60 90 120 150 180 210 240 270 300 FREQUENCY (MHz)
25 20 15 30 60 90 120 150 180 210 240 270 300 FREQUENCY (MHz) 0 4 8 12 16 20 24 ATTENUATION STATE
3RD HARMONIC vs. FREQUENCY
MAX2055 toc39
3RD HARMONIC vs. FREQUENCY
MAX2055 toc40
2ND HARMONIC vs. FREQUENCY
-55 -60 TA = -40C TA = +25C
MAX2055 toc41
-55 -60 HARMONIC (dBc) -65 -70 -75 -80 -85 30 60 TA = +85C TA = +25C TA = -40C
-55 -60 HARMONIC (dBc) -65 -70 -75 -80 VCC = +4.75V -85 VCC = +5.25V VCC = +5V
-50
HARMONIC (dBc)
-65 -70 -75 -80 -85 -90 TA = +85C
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
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Digitally Controlled, Variable-Gain, Differential ADC Driver/Amplifier MAX2055
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VCC = 5.0V, R1 = 909, max gain, (B0 = B1 = B2 = B3 = B4 = 0), POUT = 5dBm, TA = +25C, unless otherwise noted.)
2ND HARMONIC vs. FREQUENCY
MAX2055 toc42
OUTPUT IP2 vs. FREQUENCY (f1 + f2)
MAX2055 toc43
OUTPUT IP2 vs. FREQUENCY (f1 + f2)
MAX2055 toc44
-50 -55 -60 HARMONIC (dBc)
85 80 75 OIP2 (dBm) 70 65 TA = +25C 60 55 50 TA = -40C PRF1 = PRF2 = 5dBm AT OUTPUT, f = 1MHz 30 60 TA = +85C
80 75 70 OIP2 (dBm) 65 60 55 50 VCC = +5.25V
VCC = +5.0V VCC = +4.75V
-65 -70 -75 -80 -85 -90 30 60 VCC = +5V
VCC = +5.25V
VCC = +4.75V
PRF1 = PRF2 = 5dBm AT OUTPUT, f = 1MHz 30 60 90 120 150 180 210 240 270 300 FREQUENCY (MHz)
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
OUTPUT-PORT AMPLITUDE UNBALANCE vs. FREQUENCY
MAX2055 toc45
OUTPUT-PORT PHASE UNBALANCE vs. FREQUENCY
MAX2055 toc46
0.25
3.0 PHASE UNBALANCE (DEGREES) 2.5 2.0 1.5 1.0 0.5 0
AMPLITUDE UNBALANCE (dB)
0.20
0.15
0.10
0.05
0 30 60 90 120 150 180 210 240 270 300 FREQUENCY (MHz)
30
60
90 120 150 180 210 240 270 300 FREQUENCY (MHz)
8
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Digitally Controlled, Variable-Gain, Differential ADC Driver/Amplifier
Pin Description
PIN 1, 9 2 3, 18, 20, EP 4-8 10 11 12 13 14 15 16 17 19 NAME VCC RF_IN GND B4-B0 RF_OUTRF_OUT+ IBIAS CBP LE AMPIN CC ISET ATTNOUT FUNCTION Power Supply. Bypass to GND with capacitors as close to the pin as possible as shown in the typical application circuits (Figures 1 and 2). Signal Input. Internally matched to 50 over the operating frequency. See the typical application circuit for recommended component values. Ground. Use low-inductance layout techniques on the PC board. Solder the exposed paddle to the board ground plane. Attenuation Control Bits. Digital input for attenuation control. See Table 3 for attenuation setting. Inverted Differential Signal Output. Requires an external pullup choke inductor (120mA typical current) to VCC along with a DC-blocking capacitor; see Figures 1 and 2. Noninverted Differential Signal Output. Requires an external pullup choke inductor (120mA typical current) to VCC along with a DC-blocking capacitor; see Figures 1 and 2. Amplifier Bias Input. See Figures 1 and 2 for detailed connection. Bypass Capacitor. See Figures 1 and 2 for detailed connection. Amplifier DC Ground. Requires choke inductor that can handle supply current. DC resistance of inductor should be less than 0.2. Amplifier Input. Requires DC-coupling to allow biasing. Compensation Capacitor. Requires connection to AMPIN (pin 15) for stability. Connect R1 from ISET to GND (see Table 1 or Table 2 for values). Attenuator Output. Requires external DC-blocking capacitor.
MAX2055
Table 1. Suggested Components of Circuit of Figure 1
COMPONENT C1, C3-C6, C8, C9, C10, C12 C2, C11 L1, L3 L2 L4, L5 R1 R7 T1, T2 VALUE 1nF 100pF 330nH 100nH 680nH 1.13k 10 1:1 SIZE 0603 0603 0603 0603 1008 0603 0603 --
Table 2. Suggested Components of Circuit of Figure 2
COMPONENT C1, C3, C4, C5, C7-C10, C12 C2, C11 L1, L2, L3 L4, L5 R1 R7 T2 VALUE 1nF 100pF 330nH 680nH 909 10 1:1 SIZE 0603 0603 0603 1008 0603 0603 --
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9
Digitally Controlled, Variable-Gain, Differential ADC Driver/Amplifier MAX2055
VCC
C3
C2 1 RF_IN C1 20 GND ATTNOUT 19 18 GND ISET 17 ATTENUATION LOGIC CONTROL 16 CC AMPIN 15 LE 14 L2
C4 VCC 2 RF_IN 3 GND
C6
T1 R1 C5 1
4 B4 5 B3 CONTROL INPUTS 6 B2 7 B1 8 B0 R7 VCC C12 C11 10 RF_OUTL5 VCC C10 1 9V CC
CBP 13
L1
MAX2055
IBIAS RF_OUT+ L4
12 11 L3
C8
C9
T2
RF_OUT
Figure 1. Typical Application Circuit
Detailed Description
The MAX2055 is a high-dynamic-range, digitally controlled, variable-gain differential ADC driver/amplifier (DVGA) for use in applications from 30MHz to 300MHz. The amplifier is designed for 50 single-ended input and 50 differential output systems. The MAX2055 integrates a digital attenuator with a 23dB selectable attenuation range and a high-linearity, single-ended-to-differential output amplifier. The attenuator is digitally controlled through five logic lines: B0-B4. The on-chip attenuator provides up to 23dB of attenuation with 0.2dB accuracy. The single-ended input to differential output amplifier utilizes negative
feedback to achieve high gain and linearity over a wide bandwidth.
Applications Information
Digitally Controlled Attenuator
The digital attenuator is controlled through five logic lines: B0, B1, B2, B3, and B4. Table 3 lists the attenuation settings. The input and output of this attenuator require external DC blocking capacitors. The attenuator's insertion loss is approximately 2dB, when the control bits are set to 0dB (B0 = B1 = B2 = B3 = B4 = 0).
Single-Ended-to-Differential Amplifier
The MAX2055 integrates a single-ended-to-differential amplifier with a nominal gain of 22dB in a negative
10
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Digitally Controlled, Variable-Gain, Differential ADC Driver/Amplifier MAX2055
VCC
C3
C2 1V CC RF_IN C1 2 RF_IN 3 GND GND 20 ATTNOUT 19 GND 18 ISET 17 CC 16 ATTENUATION LOGIC CONTROL AMPIN 15 LE 14 CBP 13 L2 L1 C7 L3 R1 C5 C4
4 B4 5 B3 CONTROL INPUTS 6 B2 7 B1 8 B0 VCC R7 C12 C11 9V CC 10 RF_OUTL5 VCC C10 1
MAX2055
IBIAS RF_OUT+ L4
12 11
C8
C9
T2
RF_OUT
Figure 2. Low-Cost Application Circuit
feedback topology. This amplifier is optimized for a frequency range of operation from 30MHz to 300MHz with a high-output third-order intercept point (OIP3). The bias current is chosen to optimize the IP3 of the amplifier. When R 1 is 1.13k (909 if using the circuit of Figure 2), the current consumption is 240mA while exhibiting a 40dBm typical output IP3 at 70MHz. The common-mode inductor, L2, provides a high commonmode rejection with excellent amplitude and phase balance at the output. L2 must handle the supply current and have DC resistance less than 0.2.
Choke Inductor
The single-ended amplifier input and differential output ports require external choke inductors. At the input, connect a 330nH bias inductor from AMPIN (pin 15) to IBIAS (pin 12). Connect 680nH choke inductors from RF_OUT+ (pin 11) and RF_OUT- (pin 10) to VCC. These connections provide bias current to the amplifier.
Layout Considerations
A properly designed PC board is an essential part of any RF/microwave circuit. Keep RF signal lines as short as possible to reduce losses, radiation, and inductance. For best performance, route the ground-pin traces directly to the exposed pad underneath the
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11
Digitally Controlled, Variable-Gain, Differential ADC Driver/Amplifier MAX2055
package. This pad should be connected to the ground plane of the board by using multiple vias under the device to provide the best RF/thermal conduction path. Solder the exposed pad on the bottom of the device package to a PC board exposed pad. The MAX2055 Evaluation Kit can be used as a reference for board layout. Gerber files are available upon request at www.maxim-ic.com.
Table 3. Attenuation Setting vs. GainControl Bits
ATTENUATION 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 B4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 B3* 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 X X X X X X X X B2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 B1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 B0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
Power-Supply Bypassing
Proper voltage-supply bypassing is essential for highfrequency circuit stability. Bypass each VCC pin with a 1000pF and 100pF capacitor. Connect the 100pF capacitor as close to the device as possible. Resistor R7 helps reduce switching transients. If switching transients are not a concern, R7 is not required. Therefore, connect pin 9 directly to VCC.
Exposed Paddle RF Thermal Considerations
The EP of the MAX2055's 20-pin TSSOP-EP package provides a low thermal-resistance path to the die. It is important that the PC board on which the IC is mounted be designed to conduct heat from this contact. In addition, the EP provides a low-inductance RF ground path for the device. It is recommended that the EP be soldered to a ground plane on the PC board, either directly or through an array of plated via holes. Soldering the pad to ground is also critical for efficient heat transfer. Use a solid ground plane wherever possible.
Chip Information
TRANSISTOR COUNT: 325 PROCESS: BiCMOS
*Enabling B4 disables B3 and the minimum attenuation is 16dB.
12
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Digitally Controlled, Variable-Gain, Differential ADC Driver/Amplifier
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
TSSOP4.40mm.EPS
MAX2055
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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