Datasheet AD8018ARU-REEL7, AD8018ARU-REEL, AD8018ARU, AD8018AR-REEL7, AD8018AR-REEL Datasheet (Analog Devices)

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Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
a
AD8018
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 2000
5 V, Rail-to-Rail, High-Output Current,
xDSL Line Drive Amplifier
FEATURES Ideal xDSL Line Drive Amplifier for USB, PCMCIA, or
PCI-Based Customer Premise Equipment (CPE). The AD8018 provides maximum reach on 5 V supply, driving 16 dBm of power into a back-terminated, transformer-coupled 100 while maintaining –82 dBc of out-of-band SFDR.
Rail-to-Rail Output Voltage and High Output Current
Drive
400 mA Output Current into Differential Load of 10
@ 8 V p-p
Low Single-Tone Distortion
–86 dBc Worst Harmonic, 6 V p-p into Differential 10 @ 100 kHz
Low Noise
4.5 nV/Hz Voltage Noise Density, 100 kHz
Out-of-Band SFDR = –82 dBc, 144 kHz to 500 kHz,
R
LOAD
= 12.5 , P
LINE
= 13 dBm
Low-Power Operation
3.3 V to 8 V Power Supply Range
Two Logic Bits for Standby and Shutdown Low Supply Current of 9 mA/Amplifier (Typ) Current Feedback Amplifiers High Speed
130 MHz Bandwidth (–3 dB)
300 V/s Slew Rate
APPLICATIONS xDSL USB, PCI, PCMCIA Cards Consumer DSL Modems Twisted Pair Line Driver
PRODUCT DESCRIPTION
The AD8018 is intended for use in single-supply (5 V) xDSL modems where high-output current and low distortion are essential to achieve maximum reach. The dual high-speed amplifiers are capable of driving low distortion signals to within
0.5 V of the power supply rail. Each amplifier can drive 400 mA of current into 10 (differential) while maintaining –82 dBc out-of-band SFDR. The AD8018 is available with flexible standby and shutdown modes. Two digital logic bits (PWDN1 and PWDN0) may be used to put the AD8018 into one of three modes: full power, standby (outputs low impedance), and shutdown (outputs high impedance).
Fabricated with ADI’s high-speed XFCB (eXtra Fast Comple­mentary Bipolar) process, the high bandwidth and fast slew rate of the AD8018 keep distortion to a minimum, while dissipat­ing a minimum of power. The quiescent current of the AD8018 is a low 9 mA/amplifier. The AD8018 drive capability comes in compact 8-lead Thermal Coastline SOIC and 14-lead TSSOP packages. Low-distortion, rail-to-rail output voltage, and high­current drive in small packages make the AD8018 ideal for use in low-cost USB, PCMCIA, and PCI Customer Premise Equipment for ADSL, SDSL, VDSL, and proprietary xDSL systems. Both models will operate over the temperature range –40°C to +85°C.
10
1nF
5V
750
V
IN
10
1nF
750
750
0.01␮F
0.01␮F
V
REF
0.01␮F
100
100
10k
10k
P
OUT
16dBm
R1
3.1
R2
3.1
RL = 100
LINE­POWER 13dBm
TRANSFORMER
1:4
10k
10k
Figure 2. Single-Supply Voltage Differential Drive Circuit for xDSL Applications
8-Lead SOIC
(Thermal Coastline)
V
S
–IN2
IN2
6
5
7
8
OUT2
OUT1
–IN1
IN1
–V
S
1
2
3
4
AD8018AR
PIN CONFIGURATIONS
14-Lead TSSOP
OUT1
–IN1
IN1
–V
S
PWDN1
V
S
OUT2
–IN2
IN2
PWDN0
DGND
AD8018ARU
6
5
7
8
1
2
3
4
9
14
13
12
11
10
NC
NC
NC
NC = NO CONNECT
P
LINE
– dBm
SFDR – dBc
70
80
90
60
50
40
30
4186 8 10 12 14 16
N = 4.0
VS = 3.3V
VS = 5V
VS = 8V
Figure 1. Out-of-Band SFDR vs. ADSL Upstream Line Power; V
S
= 5 V, N = 4 Turns, 144 kHz to 500 kHz. See Evaluation
Board Schematics in Figure 11.
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AD8018–SPECIFICATIONS
(@ 25C, VS = 5 V, RL = 100 , RF = RG = 750 unless otherwise noted.)
Parameter Conditions Min Typ Max Unit
DYNAMIC PERFORMANCE
–3 dB Bandwidth G = 1, V
OUT
< 0.4 V p-p, RL = 5 40 50 MHz
G = 1, V
OUT
< 0.4 V p-p, RL = 100 100 130 MHz
G = 2, V
OUT
< 0.4 V p-p, RL = 5 35 40 MHz
G = 2, V
OUT
< 0.4 V p-p, RL = 100 80 100 MHz
0.1 dB Bandwidth V
OUT
< 0.4 V p-p, RL = 100 10 MHz
Large Signal Bandwidth V
OUT
= 4 V p-p, G = +2 80 MHz
Slew Rate Noninverting, V
OUT
= 4 V p-p 300 V/␮s
Rise and Fall Time Noninverting, V
OUT
= 2 V p-p 5.5 ns
Settling Time 0.1%, V
OUT
= 2 V p-p, RL = 100 25 ns
NOISE/HARMONIC PERFORMANCE
Distortion, V
OUT
= 6 V p-p (Differential)
Second Harmonic 100 kHz, R
L
= 10 –89 –94 dBc
500 kHz, RL = 10 –61 –63 dBc
Third Harmonic 100 kHz, R
L
= 10 –86 –89 dBc
500 kHz, RL = 10 –74 –77 dBc
MTPR (In-Band) 25 kHz to 138 kHz, R
L
= 12.5 , P
LINE
= +13 dBm –70 dBc
SFDR (Out-of-Band) 144 kHz to 500 kHz, RL = 12.5 , P
LINE
= +13 dBm –82 dBc
Input Noise Voltage f = 100 kHz 4.5 5 nVHz Input Noise Current f = 100 kHz (+Inputs) 1 pAHz
f = 100 kHz (–Inputs) 10 pAHz
Crosstalk f = 1 MHz, G = +2 –74 dB
DC PERFORMANCE
Input Offset Voltage 115mV
T
MIN
to T
MAX
17 mV Input Offset Voltage Match 0.1 2.6 mV Transimpedance V
OUT
= 2 V p-p, RL = 5 830 2000 kΩ
T
MIN
to T
MAX
700 k
INPUT CHARACTERISTICS
Input Resistance +Input 10 M
–Input 125
Input Capacitance +Input 1 pF Input Bias Current (–) 0.3 8 ␮A
T
MIN
to T
MAX
14 ␮A Input Bias Current (–) Match 0.1 5.5 ␮A
T
MIN
to T
MAX
8 A Input Bias Current (+) 1 1.5 ␮A
T
MIN
to T
MAX
2.5 ␮A
Input Bias Current (+) Match 0.1 0.5 ␮A
T
MIN
to T
MAX
1 A CMRR V
IN
2 V to 4 V 51 54 dB
Input CM Voltage Range 1.2 3.8 V
OUTPUT CHARACTERISTICS
Cap Load 30% Overshoot 1000 pF Output Resistance Frequency = 100 kHz, PWDN1, PWDN0 = 1 0.2 Output Voltage Swing R
L
= 100 0.16 to 4.87 V
RL = 5 0.5 to 4.5 V
Linear Output Current SFDR < –85 dBc, f = 100 kHz, R
L
= 10 , Differential 350 400 mA
Short-Circuit Current 1000 mA
POWER SUPPLY
Supply Current/Amp PWDN1 = 1, PWDN0 = 1 9 10 mA
T
MIN
to T
MAX
11.4 mA
STBY Supply Current/Amp PWDN1 = 0, PWDN0 = 1 or 4.5 5.1 mA
PWDN1 = 1, PWDN0 = 0 4.5 5.1 mA SHUTDOWN Supply Current/Amp PWDN1 = 0, PWDN0 = 0 0.3 0.55 mA Operating Range Single Supply 3.3 8 V +Power Supply Rejection Ratio ⌬V
S
= ⫾1 V 60 66 dB
T
MIN
to T
MAX
56 dB
–Power Supply Rejection Ratio ⌬V
S
= ⫾1 V 52 55 dB
T
MIN
to T
MAX
50 dB
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AD8018
Parameter Conditions Min Typ Max Unit
LOGIC INPUTS (PWDN1, 0)
Logic “1” Voltage 2.0 V Logic “0” Voltage 0.8 V Logic Input Bias Current 240 ␮A Standby Recovery Time RL = 10 , G = +2, IS = 90% of Typical 500 ns
Specifications subject to change without notice.
ORDERING GUIDE
Temperature Package Package
Model Range Description Option
AD8018AR –40°C to +85°C 8-Lead Plastic SO-8
SOIC
AD8018AR–REEL –40°C to +85°C 8-Lead SOIC SO-8 AD8018AR–REEL7 –40°C to +85°C 8-Lead SOIC SO-8 AD8018ARU –40°C to +85°C 14-Lead Plastic RU-14
TSSOP
AD8018ARU–REEL –40°C to +85°C 14-Lead Plastic RU-14
TSSOP
AD8018ARU–REEL7 –40°C to +85°C 14-Lead Plastic RU-14
TSSOP
AD8018ARU–EVAL Evaluatio
n Board RU-14
ABSOLUTE MAXIMUM RATINGS
1
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 V
Internal Power Dissipation
2
Small Outline Package (R) . . . . . . . . . . . . . . . . . . . 650 mW
TSSOP Package (RU) . . . . . . . . . . . . . . . . . . . . . . 565 mW
Input Voltage (Common-Mode) . . . . . . . . . . . . . . . . . . . . ±V
S
Logic Voltage, PWDN0, 1 . . . . . . . . . . . . . . . . . . . . . . . . . ±V
S
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . ± 1.6 V
Output Short Circuit Duration
. . . . . . . . . . . . . . . . . . . . . . Observe Power Derating Curves
Storage Temperature Range RU, R . . . . . . . –65°C to +150°C
Operating Temperature Range . . . . . . . . . . . –40°C to +85°C
Lead Temperature Range (Soldering 10 sec) . . . . . . . . . 300°C
NOTES
1
Stresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
2
Specification is for the device on a 4-layer board in free air at 85°C:
8-Lead SOIC Package: θJA = 100°C/W. 14-Lead TSSOP Package: θJA = 115°C/W.
MAXIMUM POWER DISSIPATION
The maximum power that can be safely dissipated by the AD8018 is limited by the associated rise in junction temperature. The maximum safe junction temperature for plastic encapsulated devices is determined by the glass transition temperature of the plastic, approximately 150°C. Temporarily exceeding this limit may cause a shift in parametric performance due to a change in the stresses exerted on the die by the package. Exceeding a junction temperature of 175°C for an extended period can result in device failure.
While the AD8018 is internally short circuit protected, this may not be sufficient to guarantee that the maximum junction tempera­ture (150°C) is not exceeded under all conditions. To ensure proper operation, it is necessary to observe the maximum power derating curves.
AMBIENT TEMPERATURE – C
2.0
–50
MAXIMUM POWER DISSIPATION – Watts
1.5
1.0
0.5
0
–40 –30 –20 –100 10 2030 4050 6070 8090
TJ = 150ⴗC
14-LEAD TSSOP PACKAGE
8-LEAD SOIC PACKAGE
Figure 3. Plot of Maximum Power Dissipation vs. Temperature
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD8018 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
WARNING!
ESD SENSITIVE DEVICE
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AD8018
–4–
AD8018
V
S
V
SIGNAL
50
750
750
–V
S
R
LOAD
V
OUT
10␮F
TANT
10␮F
TANT
0.1␮F
0.1␮F
TPC 1. Single-Ended Test Circuit
TIME – ns
0
OUTPUT VOLTAGE – mV
50
100
150
50
100
0
50
100
150
G = 2 V
S
= 2.5V
R
L
= 5
150 200 250 300 350 400 450 500
TPC 2. Small Signal Step Response
TIME – ns
0
OUTPUT VOLTAGE – V
1
2
3
50
100
0
1
2
3
G = 2 V
S
= 2.5V
R
L
= 5
150 200 250 300 350 400 450 500
TPC 3. Large Signal Step Response
Typical Performance Characteristics
1
FREQUENCY – Hz
10
10
1
100
1000
100 1k 10k 100k 1M
0.1
10
100
VS = ⴞ2.5V R
L
= 100
V
NOISE
I
NOISE
I
NOISE
V
NOISE
– nV/ Hz (RTI)
I
NOISE
– pA/ Hz
TPC 4. I
NOISE
and V
NOISE
vs. Frequency
FREQUENCY – MHz
0.01
OUTPUT IMPEDANCE –
500
0
2k
2.5k
3k
(1,1)
(0,0)
1.5k
1k
0.1 1 10 100
1k
(1,0)
VS=2.5V
TPC 5. Output Impedance vs. Frequency, for Full Power, Standby, and Shutdown Modes
mV
1
2
3
1
2
3
0
G = 2 V
S
= 2.5
V
IN
= 2V p-p
R
L
= 100
0
10 20 30 40 50 60 70 80 10090
TIME – ns
V
OUT
– (VINⴛ2)
(–0.1%)
(+0.1%)
TPC 6. 0.1% Settling Time
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AD8018
–5–
FREQUENCY – Hz
10k
OUTPUT VOLTAGE – dBV
–25
1M
5
10M 100M
1G
100k
22
19
16
13
10
7
4
1
2
G = 2 V
S
= 2.5V
R
L
= 100
TPC 7. Output Voltage vs. Frequency
LOAD RESISTANCE –
1
OUTPUT SWING – Volts
1.9
1.7
1.5 10
2.1
2.5
100 1000 10k
1.6
1.8
2.0
2.2
2.3
2.4
SWING
–SWING
VS = ⴞ2.5V
TPC 8. Output Swing vs. R
LOAD
FREQUENCY – Hz
100k
PSRR – dB
70
90
1M 10M
100M
80
60
50
40
30
20
10
0
G = 2 V
S
= 2.5V
V
S
= 1V
R
L
= 100
PSRR
PSRR
TPC 9. PSRR vs. Frequency
FREQUENCY – Hz
10k
OUTPUT VOLTAGE – dBV
–25
1M
5
10M 100M 1G100k
22
19
16
13
10
7
4
1
2
G = 2 V
S
= 2.5V
R
L
= 5
TPC 10. Output Voltage vs. Frequency
FREQUENCY – Hz
100k
NORMALIZED GAIN – dB
–6
1M
0
4
10M 100M
1G
5
4
3
2
1
1
2
3
(1,1)
(1,0) or (0,1)
G = 2 V
S
= 2.5V
R
L
= 100
FULL POWER
STANDBY
R
L
V
OUT
V
IN
50
750750
TPC 11. Small Signal Frequency Response
FREQUENCY – Hz
100k
CMRR – dB
–70
1M 10M 100M
60
50
40
30
20
10
1G
G = 2 V
S
= 2.5V
R
L
= 100
STANDBY
(1,0) or (0,1)
(1,1)
FULL POWER
TPC 12. CMRR vs. Frequency, Full Power, and Standby Mode
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AD8018
–6–
500
500
500
500
25
AD8138
50
500
750
750
6V
6V
V
S
V
S
10F0.1␮F
220␮F
0.1␮F R
L
VSIG
IN
6V
0.1␮F
6V
0.1␮F
7.96k
7.96k⍀ 402⍀
402
50
OUT
100
100
AD8018
1/2
AD8018
1/2
AD9632
0.1␮F
10F0.1␮F
TPC 13. Differential Test Circuit
FREQUENCY – MHz
DIFFERENTIAL DISTORTION – dBc
–110
0.01 0.1
100
90
80
70
60
1.0
3RD HARMONIC
2ND HARMONIC
V
OUT
= 6V p–p
R
L
= 10
V
S
= 2.5V
PWDN 1,0 = 1,1
TPC 14. Differential Distortion vs. Frequency
PEAK OUTPUT CURRENT – mA
DIFFERENTIAL DISTORTION – dBc
–110
200
2ND HARMONIC
300
400 500 600 700 800
100
90
80
70
60
50
3RD HARMONIC
VS = ⴞ2.5V R
L
= 3
G
= 4
f
O
= 100kHz
PWDN 1,0 = 1,1
TPC 15. Differential Distortion vs. Peak Output Current
LOAD RESISTANCE –
DIFFERENTIAL DISTORTION – dBc
–110
510
100
100
90
80
70
60
3RD HARMONIC
2ND HARMONIC
VS = 2.5V G = 4 f
O
= 100kHz
V
OUT
= 6V p–p
TPC 16. Differential Distortion vs. R
LOAD
OUTPUT VOLTAGE – Volts
DIFFERENTIAL DISTORTION – dBc
–110
3
45 678
100
90
80
70
60
3RD HARMONIC
2ND HARMONIC
VS = 2.5V R
L
= 10 G = 4 f
O
= 100kHz PWDN 1,0 = 1,1
TPC 17. Differential Distortion vs. Peak-to-Peak Output Voltage
OUTPUT VOLTAGE – Volts
DIFFERENTIAL DISTORTION – dBc
–110
3
3RD HARMONIC
45678
100
90
80
70
60
2ND HARMONIC
VS = 2.5V R
L
= 10 G = 4 f
O
= 100kHz PWDN 1,0 = 1,0 or 0,1
TPC 18. Differential Distortion vs. Peak-to-Peak Output Voltage
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AD8018
–7–
TRANSFORMER TURNS RATIO
P
LINE
– dBm
3.0
16
10
11
12
13
14
15
3.2 4.0 4.2 4.4 4.6 4.83.4
3.6
3.8
VS = 5.25
VS = 4.75
VS = 5.00
TPC 19. Line Power vs. Turns Ratio; MTPR = –65 dBc, f = 43 kHz
TRANSFORMER TURNS RATIO – N
MTPR – dBc
3 4
80
70
60
50
40
30
5
–20
P = 13dBm P = 13.5dBm P = 14dBm P = 12.5dBm P = 12dBm
VS = 5V R
LINE
= 100
f = 93kHz
TPC 20. MTPR vs. Turns Ratio
TRANSFORMER TURNS RATIO – N
SFDR – dBc
3
–90
4
80
70
60
50
40
30
5
P = 12dBm
P = 12.5dBm P = 13dBm P = 13.5dBm P = 14dBm
VS = 5V R
LINE
= 100
f = 361kHz
TPC 21. Out-of-Band SFDR vs. Turns Ratio for Various Line Power
TRANSFORMER TURNS RATIO
P
LINE
– dBm
3.0
16
6
8
10
14
3.2 4.0 4.2 4.4 4.63.4 3.6 3.8
18
12
VS = 4.75
VS = 8.00
VS = 5.00
VS = 3.3
VS = 4.50
4.8
TPC 22. Line Power vs. Turns Ratio; –75 dBc Out-of-Band SFDR, f = 361 kHz
FREQUENCY – Hz
1k 10k 100k 1M 10M 100M 1G
0.01
0.1
1
10
100
1k
10k
100k
1M
10M
TRANSIMPEDANCE –
150
100
50
0
50
200
100
150
PHASE – De
g
rees
TRANSIMPEDANCE
PHASE
–200
TPC 23. Open Loop Transimpedance and Phase
POWER-DOWN VOLTAGE – Volts
TOTAL SUPPLY CURRENT – mA
0.86
16
6
8
10
14
DECREASING
18
12
20
0.88 0.90 0.92 0.94 0.96 0.98 1.00 1.02
INCREASING
LOGIC 1 TO 0
LOGIC 0 TO 1
TPC 24. Power-Up/-Down Threshold Voltage
Page 8
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AD8018
–8–
THEORY OF OPERATION
The AD8018 is composed of two current feedback amplifiers capable of delivering 400 mA of output current while swinging to within 0.5 V of either power supply, and maintaining low distortion. A differential line driver using the AD8018 can provide CPE performance on a single 5 V supply. This performance is enabled by Analog Device’s XFCB process and a novel, two­stage current feedback architecture featuring a patent-pending rail-to-rail output stage.
A simplified schematic is shown in Figure 4. Emitter followers buffer the positive input, V
P
, to provide low input current and current noise. The low impedance current feedback summing junction is at the negative input, V
N
. The output stage is another high-gain amplifier used as an integrator to provide frequency compensation. The complementary common-emitter output provides the extended output swing.
A current feedback amplifier’s dynamic and distortion performance is relatively insensitive to its closed-loop signal gain, which is a distinct advantage over a voltage-feedback architecture. Figure 5 shows a simplified model of a current feedback amplifier. The feedback signal is a current into the inverting node. R
IN
is inversely proportional to the transconductance of the amplifier’s input stage, g
mi
. Circuit analysis of the pictured follower with gain yields:
VV G
T
TRGR
OUT IN
ZS
ZS F IN
/
()
()
++×
where:
GRR
T
R
CR
Rg
FG
ZS
T
S
TT
IN mi
=+
=
+
=≅
1
1
1 125
/
()
/
()
Recognizing that G RIN < RF, and that the –3 dB point is set when T
Z(S)
= RF, one can see that the amplifiers bandwidth depends primarily on the feedback resistor. There is a value of R
F
below which the amplifier will be unstable, as an actual ampli­fier will have additional poles that will contribute excess phase shift. The optimum value for R
F
depends on the gain and the
amount of peaking tolerable in the application.
V
O
BIAS
V
N
V
P
Figure 4. Simplified Schematic
G = 1
IT = IINCTR
T
I
IN
V
OUT
R
G
R
F
R
IN
+
V
IN
V
O
+
Figure 5. Model of Current Feedback Amplifier
FEEDBACK RESISTOR SELECTION
In current feedback amplifiers, selection of the feedback and gain resistors will impact the MTPR performance, bandwidth, noise, and gain flatness. Care should be exercised in the selection of these resistors so that the optimum performance is achieved. Table I shows the recommended resistor values for use in a variety of gain settings for the test circuit in TPC 1. These values are intended to be a starting point when designing for any application.
FREQUENCY – Hz
CROSSTALK – dB
–90
1M 10M
100M
1G
80
70
60
50
40
30
20
10
RL = 5
SIDE A DRIVEN
RL = 5
SIDE B DRIVEN
VIN = 2V p-p G = 2 V
S
= 2.5
100k
RL = 100 SIDE A DRIVEN
RL = 100 SIDE B DRIVEN
100
110
TPC 25. Crosstalk vs. Frequency
Page 9
REV. A
AD8018
–9–
Table I. Resistor Selection Guide
Gain RF ()R
G
(⍀)
–1 681 681 +1 1 k +2 750 750 +3 511 256 +4 340 113 +5 230 59
POWER-DOWN FEATURES
Two digitally programmable logic pins, PWDN1 and PWDN0, are available on the TSSOP-14 package to select among three different modes of operation, full power, standby and shutdown. The DGND pin is the logic ground reference. The logic thresh­old voltage is established 1 V above DGND. In a typical 5 V single-supply application, the DGND pin is connected to analog ground. If PWDN1, PWDN0, and DGND are left unconnected, the AD8018 will operate at full power.
Table II. Power-Down Features and Truth Table
Supply Output
PWDN0 PWDN1 State Current Impedance
High High Full Power 18 mA Low Low High Standby 9 mA Low High Low Standby 9 mA Low Low Low Disabled 300 µA High
POWER SUPPLY AND DECOUPLING
The AD8018 can be powered with a good quality (i.e., low-noise) supply anywhere in the range from 3.3 V to 8 V. However, in order to optimize the ADSL upstream drive capability to +13 dBm and maintain the best Spurious Free Dynamic Range (SFDR), the AD8018 circuit should be supplied with a well regulated 5 V supply. The 5 V supplied at the Universal Serial Bus (USB) port may be poorly regulated. Improving the quality of the 5 V supply will optimize the performance of the AD8018 in a Universal Serial Bus-supplied CPE ADSL modem. This can be accomplished through the use of a step-up dc-to-dc converter or switching power supply followed by a low dropout (LDO) regulator such as the ADP3331 (see Figure 6). Setting R1 to be 953 k and R2 to be 301 k will result in a V
OUT
of 5 V.
Careful attention must be paid to decoupling the power supply pins at the output of the dc-to-dc converter, the output of the LDO regulator and the supply pins of the AD8018. High-quality capacitors with low equivalent series resistance (ESR) such as multilayer ceramic capacitors (MLCCs) should be used to mini­mize supply voltage ripple and power dissipation. A large, usually tantalum, 10 µF to 47 µF capacitor located in proximity to the AD8018 is required to provide good decoupling for lower fre­quency signals. In addition, 0.1 µF MLCC decoupling capacitors should be located as close to each of the power supply pins as is physically possible, no more than 1/8 inch away. An additional large (4.7 µF to 10 µF) tantalum capacitor should be placed on the board near the supply terminals to supply current for fast, large­signal changes at the AD8018 outputs.
ADP3331
C1
0.47␮F
V
IN
ON
OFF
V
OUT
E
OUT
C2
0.47␮F
R3
330k
IN
SD GND
OUT
FB
ERR
R1
953k
R2
301k
Figure 6. ADP3331 LDO
METHOD FOR GENERATING A MIDSUPPLY VOLTAGE
To operate an amplifier on a single voltage supply, a voltage midway between the supply and ground must be generated to properly bias the inputs and the outputs.
A voltage divider can be created with two equal value resistors (Figure 7). There is a trade-off between the power consumed by the divider and the voltage drop across these resistors due to the positive input bias currents. Selecting 2.5 k for R1 and R2 will create a voltage divider that draws only 1 mA from a 5 V supply. The voltage generated with this topology can vary due to the temperature coefficient (TC) of resistance. Resistors that are closely matched and have a low TC will minimize variations in the voltage reference due to temperature. One should also be sure to use a decoupling capacitor (0.1 µF) at the node where V
REF
is generated.
5V
R1
2.5k
R2
2.5k
V
REF
0.1␮F
Figure 7. Midsupply Reference
DIFFERENTIAL TESTING
The test circuit shown in TPC 13 is used for measuring the dif­ferential distortion of the AD8018. A single-ended test signal is applied to the inverting input of the AD8138 differential driver with the noninverting input grounded. Applying the differential output of the AD8138 through 100 resistors serves to isolate the inputs of the AD8018 differential driver and provide a well­balanced low-distortion input signal. The differential load (R
L
) of the AD8018 can be set to the equivalent of the line imped­ance reflected through a transformer. The AD9632 converts the differential output voltage back to a single-ended signal. The differential-to- single-ended converter using the AD9632 has an attenuation of –26 dB and is wired with precision resis­tors to optimize the balance of differential input signal. The resulting smaller output signal can be easily measured using a 50 spectrum analyzer.
Page 10
REV. A
AD8018
–10–
P V rmsV V rms
R
IV P
TOT O S O
L
Q S OUT
++408
1
2
2
(. ) α
For the AD8018, operating on a single 5 V supply and deliver­ing a total of 16 dBm (13 dBm to the line and 3 dBm to the matching network) into 12.5 (100 reflected back through a 1:4.0 transformer plus back termination), the power is:
= 261 mW + 40 mW
= 301 mW
Using these calculations, and a θ
JA
of 115°C/W for the TSSOP
package and 100°C/W for the SOIC, Tables III and IV show junction temperature versus power delivered to the line for sev­eral supply voltages.
Table III. Junction Temperature vs. Line Power and Operating Voltage for TSSOP, T
AMB
= 85ⴗC
V
SUPPLY
P
LINE,
dBm 5 6 7 8
13 115 122 129 136 14 117 125 132 140 15 119 127 136 144 16 121 130 139 148 17 123 133 143 153 18 125 136 147 158
Table IV. Junction Temperature vs. Line Power and Operating Voltage for SOIC, T
AMB
= 85ⴗC
V
SUPPLY
P
LINE,
dBm 5 6 7 8
13 111 117 123 129 14 113 119 126 133 15 115 122 129 136 16 116 124 132 140 17 118 127 136 144 18 120 130 139 149
Running the AD8018 at voltages near 8 V can produce junction temperatures that exceed the thermal rating of the TSSOP pack­ages and should be avoided. The shaded areas indicate junction temperatures greater than 150°C.
LAYOUT CONSIDERATIONS
As is the case with all high-speed applications, careful attention to printed circuit board layout details will prevent associated board parasitics from becoming problematic. Proper RF design technique is mandatory. The PCB should have a ground plane covering all unused portions of the component side of the board to provide a low-impedance return path. Removing the ground plane on all layers from the area near the input and output pins will reduce stray capacitance, particularly in the area of the inverting inputs. Signal lines connecting the feedback and gain resistors should be as short as possible to minimize the inductance and stray capacitance associated with these traces. Termination resistors and loads should be located as close as possible to their respective inputs and outputs. Input and output traces should be kept as far apart as possible to minimize coupling (crosstalk) though the board. Adherence to stripline design techniques for long signal traces (greater than about 1 inch) is recommended.
This circuit requires significant power supply bypassing. The AD8018 operates on a split supply in this circuit. The bypassing technique shown in TPC 13 utilizes a 220 µF tantalum capacitor and a 0.1 µF ceramic chip capacitor in parallel, connected from the positive to negative supply, and a 10 µF tantalum and 0.1 µF ceramic chip capacitor in parallel, connected from each supply to ground. The capacitors connected between the power supplies serve to minimize any voltage ripples that might appear at the supplies while sourcing or sinking any large differential current. The large capacitor has a pool of charge instantly available for the AD8018 to draw from, thus preventing any erroneous dis­tortion results.
POWER DISSIPATION
It is important to consider the total power dissipation of the AD8018 in order to properly size the heat sink area of an application. Figure 8 is a simple representation of a differential driver. With some simplifying assumptions we can estimate the total power dissipated in this circuit. If the output current is large compared to the quiescent current, computing the dissipa­tion in the output devices and adding it to the quiescent power dissipation will give a close approximation of the total power dissipation in the package. A factor α (~0.6-1) corrects for the slight error due to the Class A/B operation of the output stage. It can be estimated by subtracting the quiescent current in the output stage from the total quiescent current and ratioing that to the total quiescent current. For the AD8018, α = 0.833.
+V
S
–V
S
+V
O
+V
S
–V
S
–V
O
R
L
Figure 8. Simplified Differential Driver
Remembering that each output device dissipates for only half the time gives a simple integral that computes the power for each device:
1 2
2
×
 
 
( )VV
V
R
SO
O
L
The total supply power can then be computed as:
PVVV
R
IV P
TOT S O O
L
Q S OUT
=
 
 
×+ +4
1
2
2
|| α
In this differential driver, VO is the voltage at the output of one amplifier, so 2 V
O
is the voltage across RL, which is the total impedance seen by the differential driver, including back termina- tion. Now, with two observations, the integrals are easily evaluated. First, the integral of V
O
2
is simply the square of the rms value of
V
O
. Second, the integral of |VO| is equal to the average recti-
fied value of V
O
, sometimes called the Mean Average Deviation, or MAD. It can be shown that for a Discrete MultiTone (DMT) signal, the MAD value is equal to 0.8 times the rms value.
Page 11
REV. A
AD8018
–11–
Following these generic guidelines will improve the performance of the AD8018 in all applications.
To optimize the AD8018s performance as an ADSL differential line driver, locate the transformer hybrid near the AD8018 drivers and as close to the RJ11 jack as possible. Maintain differential circuit symmetry into the differential driver and from the output of the drivers through the transformer-coupled output of the bridge circuit as much as possible.
CPE ADSL Application
The low-cost, high-output current dual AD8018 xDSL driver amplifiers have been specifically designed to drive high fidelity xDSL signals to within 0.5 V of the power rails, the performance needed to provide CPE ADSL on a single 5 V supply. The AD8018 may be used in transformer-coupled bridge hybrid cir­cuits to drive modulated signals including Discrete MultiTone (DMT) upstream to the central office.
Evaluation Board
The AD8018ARU-EVAL evaluation board circuit in Figure 12 offers the ability to evaluate the AD8018 in a typical xDSL bridge hybrid circuit.
The receiver circuit on these boards is typically unpopulated. Requesting samples of the AD8022AR with the AD8018ARU­EVAL board will provide the capability to evaluate the AD8018ARU along with other Analog Devices products in a typi­cal transceiver circuit. The evaluation circuits have been designed to replicate the CPE side analog transceiver hybrid circuits.
The circuit mentioned above is designed using a one-transformer transceiver topology including a line receiver, line driver, line matching network, an RJ11 jack for interfacing to line simulators, and transformer-coupled inputs for single-ended-to-differential input conversion.
AC-coupling capacitors of 0.01 µF, C8, and C10, in combina- tion with 10 k resistors R24 and R25, will form a zero frequency at 1.6 kHz.
Transformer Selection
Customer premise ADSL requires the transmission of a +13 dBm (20 mW) DMT signal. The DMT signal can have a crest factor as high as 5.3, requiring the line driver to provide peak line power of 27.5 dBm (560 mW). 27.5 dBm peak line power translates into a 7.5 V peak voltage on the 100 telephone line. Assuming that the maximum low-distortion output swing available from the AD8018 line driver on a 5 V supply is 4 V and, taking into account the power lost due to the termination resistance, a step-up transformer with turns ratio of 4.0 or greater is needed.
In the simplified differential drive circuit shown in Figure 2, the AD8018 is coupled to the phone line through a step-up trans­former with a 1:4 turns ratio. R1 and R2 are back-termination or line-matching resistors, each 3.1 Ω (100 Ω/(2 × 4
2
)), where
100 is the approximate phone line impedance. The total dif­ferential load for the AD8018, including the termination resistors, is 12.5 . Even under these conditions the AD8018 provides low distortion signals to within 0.5 V of the power rails.
Stability Enhancements
The CPE bridge hybrid circuit presents a complex impedance to the drive amplifiers, particularly when transformer parasitics are factored in. To ensure stable operation under the full range of load conditions, a series R-C network (Zoebel Network) should be connected between each amplifiers output and ground. The recommended values are 10 for the resistor and 1 nF for the capacitor to create a low impedance path to ground at frequen­cies above 16 MHz (see Figure 2). R33 and R34 are added to improve common-mode stability.
Receive Channel Considerations
A transformer used at the output of the differential line driver to step up the differential output voltage to the line has the inverse effect on signals received from the line. A voltage reduction or attenuation equal to the inverse of the turns ratio is realized in the receive channel of a typical bridge hybrid. The turns ratio of the transformer may also be dictated by the ability of the receive circuitry to resolve low-level signals in the noisy twisted pair tele­phone plant. Higher turns ratio transformers effectively reduce the received signal-to-noise ratio due to the reduction in the received signal strength.
The AD8022, a dual amplifier with typical RTI voltage noise of only 2.5 nV/Hz and a low supply current of 4 mA/amplifier, is recommended for the receive channel.
DMT Modulation, MultiTone Power Ratio (MTPR), and Out-of-Band SFDR
ADSL systems rely on DMT modulation to carry digital data over phone lines. DMT modulation appears in the frequency domain as power contained in several individual frequency subbands, sometimes referred to as tones or bins, each of which is uniformly separated in frequency. A uniquely encoded, Quadra­ture Amplitude Modulation (QAM)-like signal occurs at the center frequency of each subband or tone. See Figure 9 for an example of a DMT waveform in the frequency domain, and Figure 10 for a time domain waveform. Difficulties will exist when decoding these subbands if a QAM signal from one subband is corrupted by the QAM signal(s) from other subbands, regardless of whether the corruption comes from an adjacent subband or harmonics of other subbands.
Conventional methods of expressing the output signal integrity of line drivers, such as single-tone harmonic distortion or THD, two-tone InterModulation Distortion (IMD), and third order intercept (IP3), become significantly less meaningful when amplifiers are required to process DMT and other heavily modulated waveforms. A typical ADSL upstream DMT signal can contain as many as 27 carriers (subbands or tones) of QAM signals. MultiTone Power Ratio (MTPR) is the relative difference between the measured power in a typical subband (at one tone or carrier) versus the power at another subband spe­cifically selected to contain no QAM data. In other words, a selected subband (or tone) remains open or void of intentional power (without a QAM signal), yielding an empty frequency bin. MTPR, sometimes referred to as the empty bin test, is typically expressed in dBc, similar to expressing the relative difference between single-tone fundamentals and second or third harmonic distortion components. Measurements of MTPR are typically made on the line side or secondary side of the transformer.
Page 12
REV. A
AD8018
–12–
FREQUENCY – kHz
20
–80
0 150
50
POWER – dBm
100
60
40
20
0
Figure 9. DMT Waveform in the Frequency Domain
MTPR versus transformer turns ratio is depicted in TPC 21 and covers a variety of line power ranging from +12 dBm to +14 dBm. As the turns ratio increases, the driver hybrid can deliver more undistorted power due to higher output current capability. Significant degradation of MTPR will occur if the output of the driver swings to the rails, causing clipping at the DMT voltage peaks. Driving DMT signals to such extremes not only compro­mises in-band MTPR, but will also produce spurs that exist outside of the frequency spectrum containing the desired DMT power. Out-of-band spurious free dynamic range (SFDR) can be defined as the relative difference in amplitude between these spurs and a tone in one of the upstream bins. Compromising out-of-band SFDR is equivalent to increasing near end cross­talk (NEXT). Regardless of terminology, maintaining out-of-band SFDR while reducing NEXT will improve the overall performance of the modems connected at either end of the twisted pair.
TPC 21 shows how SFDR varies versus transformer turns ratio for line power ranging from +12 dBm to +14 dBm. As line power increases, or turns ratio decreases, SFDR degrades. The power contained in the spurs can be measured relative to the power contained in a typical upstream carrier and is expressed in dBc as SFDR, similar to MTPR.
The supply voltage of the driver can also affect SFDR. As the supply voltage is increased, voltage swing is increased as well, resulting in the ability to deliver more power to the line with­out sacrificing performance. This can be seen in TPC 22. Less undistorted power is available when lower turns ratio transform­ers are used due to voltage clipping of the signal.
TxDAC is a trademark of Analog Devices, Inc.
TIME – ms
4
–0.25
VOLTS
0
3
1
0
2
0.2 1.5 1.0
0.05
0.05 1.0
1.5
0.2
3
2
1
Figure 10. DMT Signal in the Time Domain
Generating DMT Signals
At this time, DMT-modulated waveforms are not typically menu-selectable items contained within AWGs. Even using AWG software to generate DMT signals, AWGs that are available today may not deliver DMT signals sufficient in performance with regard to MTPR due to limitations in the D/A converters and output drivers used by AWG manufacturers. Similar to evaluating single-tone distortion performance of an amplifier, MTPR evaluation requires a DMT signal generator capable of delivering MTPR performance better than that of the driver under evaluation. Generating DMT signals can be accom­plished using a Tektronics AWG 2021 equipped with Option 4, (12-/24-bit, TTL Digital Data Out), digitally coupled to Analog Devices AD9754, a 14-bit TxDAC
®
, buffered by an AD8002 amplifier configured as a differential driver. Note that the DMT waveforms (available on the Analog Devices website, http://www.analog.com), or similar .WFM files are needed to produce the digital data required to drive the TxDAC from the optional TTL Digital Data output of the TEK AWG2021.
Page 13
REV. A
AD8018
–13–
U1
AD8018
+V
R18
750
TP6
R8
100
R3
10
R19
750
R4
10
C22
1000pF
C27
1000pF
U1
AD8018
+V
TP8
R21 DNI
C12 DNI
TP9
PR2
R1 10 1WATT
R2 750
VCC-T
U2
AD8022
DNI
R6
DNI
TP17
R7
DNI
VCC-R
AGND;4
V
CC
;8
AGND;4
TP18
R13
DNI
C16 DNI
C3
DNI
TP5
R12 DNI
C1
DNI
C2
DNI
TP4
R9 DNI
R10 DNI
C5
0.1␮F
R29
10k
R24
10k
C8
0.1␮F
TP10
C10
0.1␮F
R14
100
TP11
C28 DNI
R30
0
V
CC
R11 50
R15
50
V
CC
P4 2
P4 1
P4 3
55
53
P3 2
P3 3
P3 1
54
56
R5
DNI
V
CC
R17
2.49k
JP4
A
B
3
2
JP3
1
1
2
3
B
A
C4
DNI
CAPPOLY
C7
DNI
CAPPOLY
NC = 5,6
T1
3
2
1
4
8
9
7
10
1
2
3
4
5
6
TP1
78
TP2
C9
DNI
CAPPOLY
CAPPOLY C6 DNI
TB1 1
C18 DNI
VCC-T
TP19
C17 10␮F 25V
C15
0.01␮F
C26
0.1␮F
C14 10␮F
L5
BEAD
2TB1
C19 DNI 25V
C23 DNI
U2 DECOUPLING
TP23 TP24 TP25 TP26
R32 DNI
1
2
R20 DNI
C11 DNI
TP7
PR1
R31
0
V
CC
-R
VCC-R
DNI: DO NOT INSTALL
V
CC
2
V
CC
2
VCC-T
R33
10k
R34
10k
R16
2.49k
C20
0.1␮F
U2
AD8022
DNI
V
CC
2
Figure 11. EVAL Board Schematic
JP1
NC1 NC2 NC3
PDN0
PDN1
DGND
U1
AD8018
0.1␮F C25
0.1␮F C24
100
R25
100
R26
R28 DNI
R27 DNI
V
CC
JP2
Figure 12. Input Control Circuit
Page 14
REV. A
AD8018
–14–
Figure 13. Assembly—Primary Side
Figure 14. Silk Screen—Primary Side
Page 15
REV. A
AD8018
–15–
Figure 15. Layer 1—Primary Side
Figure 16. Layer 2—Ground Plane
Page 16
REV. A
AD8018
–16–
Figure 17. Layer 3—Power Plane
Figure 18. Layer 4—Secondary Side
Page 17
REV. A
AD8018
–17–
Figure 19. Assembly—Secondary Side
Page 18
REV. A
AD8018
–18–
EVALUATION BOARD—BILL OF MATERIALS
Qty. Description Vendor Ref Desc.
2 1,000 pF 50 V. 1206 ceramic chip capacitor ADS # 4-5-20 C22, 27 2 0.01 µF 50 V. 1206 ceramic chip capacitor ADS # 4-5-19 C15, 23 5 0.1 µF 50 V. 1206 size ceramic chip capacitor ADS # 4-5-18 C5, 20, 24 -26 2 1.0 µF 16 V. 1206 size ceramic chip capacitor Newark # 83F6841 C8, 10 4 # 26 red (solid) wire jumper ADS # 10-14-3 C4, 6, 7, 9 3 10 µF 16 V. ‘C’ size Tantalum chip capacitor ADS # 4-7-6 C14, 17, 19 1 Ferrite bead (with # 22 wire) ADS # 48-1-1 L5 1 10 5% 3.0 W. metal oxide power resistor D-K # P10W-3BK-ND R1 60 Ω 5% 1/8 W. 1206 size chip resistor ADS # 3-18-88 C11, 12, R20, 21, 30, 31 2 10.0 1% 1/8 W. 1206 size chip resistor ADS # 3-18-120 R3, 4 2 49.9 1% 1/8 W. 1206 size chip resistor ADS # 3-14-26 R11, 15 5 100 1% 1/8 W. 1206 size chip resistor ADS # 3-18-40 R8, 14, 25, 26, 32 2 2.49 k 1% 1/8 W. 1206 size chip resistor ADS # 3-18-71 R16, 17 3 750 1% 1/8 W. 1206 size chip resistor ADS # 3-18-8 R2, 18, 19 2 10.0 k 0.1% 0805 size chip resistor ADS # 3-36-5 R33, 34 2 10.0 k 1% 1/8 W. 1206 size chip resistor ADS # 3-18-119 R24 and 29 4 Test Point (Black) [GND] ADS # 12-18-44 TP23–26 (GND.) 2 Test Point (Brown) ADS # 12-18-59 TP4, 5 3 Test Point (Red) ADS # 12-18-43 TP17–19 4 Test Point (Orange) ADS # 12-18-60 TP1, 2, 10, 11 1 Test Point (Yellow) ADS # 12-18-32 TP3 2 Test Point (Blue) ADS # 12-18-62 TP6, 8 2 Test Point (Green) ADS # 12-18-61 TP7, 9 12 × 5-pin strips (1/4 of a 20-pin Samtek ‘SIP’ strip socket) ADS # 11-2-14 (T1) 1 2 Pos. GRAY term. blk. # 25.161.0253 (Newark # 51F4106) ADS# 12-19-10 TB1, 2 4 0.1 inch ctr. shunt Berg # 65474 -001 ADS # 11-2-38 JP1–4 2 2 pin gold male header 0.1 inch ctr. Berg # 69157 -102 ADS # 11-2-37 JP1, 2 4 50 Ω BNC pc mount Telegartner # J01001A1944 ADS # 12-6-22 S3–6 1 AMP# 555154 -1 MOD. JACK (SHIELDED) 6 –6 ADS # 12-20-5 P1 2 3-pin gold male header Waldom D-K # WM 2723 -ND ADS # 12-3-80 JP3, 4 2 3-pin gold male locking header Waldom # WM 2701 -ND ADS # 12-3-79 P3, 4 1 AD8018ARU ADSL Driver hybrid ADS # AD8018ARU U1 (D.U.T.) 1 AD8018 TSSOP1T Non-Inverting REV. A Evaluation PC board D C S Eval. PC Board 4# 4 –40 × 1/4" panhead ss machine screw ADS # 30-1-1 4# 4 –40 × 1/2" threaded alum. standoffs ADS # 30-16-2
Page 19
REV. A
AD8018
–19–
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8 Lead SOIC
(SO-8)
0.0098 (0.25)
0.0075 (0.19)
0.050 (1.27)
0.016 (0.40)
8 0
0.0196 (0.50)
0.0099 (0.25)
45
85
1
0.1968 (5.00)
0.1890 (4.80)
0.2440 (6.20)
0.2284 (5.80)
PIN 1
0.1574 (4.00)
0.1497 (3.80)
0.0500 (1.27) BSC
0.0688 (1.75)
0.0532 (1.35)
SEATING
PLANE
0.0098 (0.25)
0.0040 (0.10)
0.020 (0.51)
0.013 (0.33)
CONTROLLING DIMENSIONS ARE IN MILLIMETERS
ALL DIMENSIONS PER JEDEC STANDARDS MS-012 AA
14 Lead TSSOP
(RU-14)
0.177 (4.50)
0.173 (4.40)
0.169 (4.30)
14
8
71
0.252
(6.40)
BSC
PIN 1
0.201 (5.10)
0.197 (5.00)
0.193 (4.90)
0.0256 (0.65) BSC
SEATING PLANE
0.006 (0.15)
0.002 (0.05)
0.0118 (0.30)
0.0075 (0.19)
0.047 (1.2) MAX
0.059 (1.50)
0.093 (1.00)
0.031 (0.80)
0.008 (0.20)
0.004 (0.09)
8 0
0.030 (0.75)
0.024 (0.60)
0.018 (0.45)
CONTROLLING DIMENSIONS ARE IN MILLIMETERS
C01519a–.5–11/00 (rev. A)
PRINTED IN U.S.A.
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