Datasheet AD8018 Datasheet (Analog Devices)

Page 1
5 V, Rail-to-Rail, High-Output Current,
V
S
–IN2
IN2
6
5
7
8
OUT2
OUT1
–IN1
IN1
–V
S
1
2
3
4
AD8018AR
a
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,
= 12.5 , P
R
LOAD
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
30
40
50
VS = 3.3V
= 13 dBm
LINE
N = 4.0
VS = 5V
xDSL Line Drive Amplifier
AD8018
PIN CONFIGURATIONS
8-Lead SOIC
(Thermal Coastline)
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.
14-Lead TSSOP
NC
2
OUT1
3
–IN1
IN1
4
5
–V
S
6
PWDN1
7
NC
NC = NO CONNECT
AD8018ARU
81
9
10
11
12
13
14
NC
V
S
OUT2
–IN2
IN2
PWDN0
DGND
–60
SFDR – dBc
70
80
90
4186 8 10 12 14 16
P
– dBm
LINE
VS = 8V
Figure 1. Out-of-Band SFDR vs. ADSL Upstream Line Power;
= 5 V, N = 4 Turns, 144 kHz to 500 kHz. See Evaluation
V
S
Board Schematics in Figure 11.
REV. 0
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.
5V
750
1nF
750
750
10
10
1nF
10k
R1
3.1
P
OUT
16dBm
R2
3.1
TRANSFORMER
10k
1:4
RL = 100
LINE­POWER 13dBm
0.01␮F
V
IN
0.01␮F
10k
10k
100
V
REF
0.01␮F
100
Figure 2. Single-Supply Voltage Differential Drive Circuit for xDSL Applications
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
Page 2
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
G = 1, V G = 2, V G = 2, V
0.1 dB Bandwidth V Large Signal Bandwidth V
OUT
OUT
Slew Rate Noninverting, V Rise and Fall Time Noninverting, V Settling Time 0.1%, V
< 0.4 V p-p, RL = 5 40 50 MHz
OUT
< 0.4 V p-p, RL = 100 100 130 MHz
OUT
< 0.4 V p-p, RL = 5 35 40 MHz
OUT
< 0.4 V p-p, RL = 100 80 100 MHz
OUT
< 0.4 V p-p, RL = 100 10 MHz = 4 V p-p, G = +2 80 MHz
= 4 V p-p 300 V/␮s
OUT
= 2 V p-p 5.5 ns
OUT
= 2 V p-p, RL = 100 25 ns
OUT
NOISE/HARMONIC PERFORMANCE
Distortion, V Second Harmonic 100 kHz, R
= 6 V p-p (Differential)
OUT
= 10 –89 –94 dBc
L
500 kHz, RL = 10 –61 –63 dBc
Third Harmonic 100 kHz, R
= 10 –86 –89 dBc
L
500 kHz, RL = 10 –74 –77 dBc MTPR (In-Band) 25 kHz to 138 kHz, R SFDR (Out-of-Band) 144 kHz to 500 kHz, RL = 12.5 , P
= 12.5 , P
L
= +13 dBm –70 dBc
LINE
= +13 dBm –82 dBc
LINE
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
= 2 V p-p, RL = 5 830 2000 kΩ
OUT
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
CMRR V
to T
MIN
IN
MAX
2 V to 4 V 51 54 dB
1 A
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
= 100 0.16 to 4.87 V
L
RL = 5 0.5 to 4.5 V
Linear Output Current SFDR < –85 dBc, f = 100 kHz, R
= 10 350 400 mA
L
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
–Power Supply Rejection Ratio ⌬V
= ⫾1 V 60 66 dB
S
T
to T
MIN
T
MIN
MAX
= ⫾1 V 52 55 dB
S
to T
MAX
56 dB
50 dB
–2–
REV. 0
Page 3
AD8018
WARNING!
ESD SENSITIVE DEVICE
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.
ABSOLUTE MAXIMUM RATINGS
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 V
Internal Power Dissipation
2
1
Small Outline Package (R) . . . . . . . . . . . . . . . . . . . 650 mW
TSSOP Package (RU) . . . . . . . . . . . . . . . . . . . . . . 565 mW
Input Voltage (Common-Mode) . . . . . . . . . . . . . . . . . . . . ±V
Logic Voltage, PWDN0, 1 . . . . . . . . . . . . . . . . . . . . . . . . . ±V
S
S
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . ± 1.6 V
Output Short Circuit Duration
. . . . . . . . . . . . . . . . . . . . . . Observe Power Derating Curves
Storage Temperature Range RU, R . . . . . . . –65°C to +125°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 in free air:
8-Lead SOIC Package: θJA = 100°C/W. 8-Lead TSSOP Package: θJA = 115°C/W.
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 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–EVAL Evaluation Board RU-14
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.
2.0
1.5
8-LEAD SOIC PACKAGE
1.0
14-LEAD TSSOP PACKAGE
0.5
MAXIMUM POWER DISSIPATION – Watts
0
40 30 20 100 10 2030 4050 6070 8090
50
AMBIENT TEMPERATURE – C
TJ = 150ⴗC
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.
REV. 0
–3–
Page 4
AD8018
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
Typical Performance Characteristics
V
750
S
750
AD8018
V
SIGNAL
50
–V
S
TPC 1. Single-Ended Test Circuit
150
100
50
0
–50
OUTPUT VOLTAGE – mV
–100
10␮F
10␮F
TANT
0.1␮F
0.1␮F
TANT
G = 2 V
= 2.5V
S
R
= 5
L
R
LOAD
V
OUT
TPC 4. I
3k
2.5k
2k
1.5k
1k
OUTPUT IMPEDANCE –
500
NOISE
and V
vs. Frequency
NOISE
(0,0)
VS=2.5V
(1,0)
(1,1)
–150
50
0
150 200 250 300 350 400 450 500
100
TIME – ns
TPC 2. Small Signal Step Response
TPC 5. Output Impedance vs. Frequency, for Full Power,
0
0.01
0.1 1 10 100 FREQUENCY – MHz
1k
Standby, and Shutdown Modes
(+0.1%)
(–0.1%)
3
2
1
0
mV
V
– (VINⴛ2)
1
2
3
10 20 30 40 50 60 70 80 10090
0
OUT
TIME – ns
TPC 6. 0.1% Settling Time
G = 2 V
= 2.5
S
V
IN
R
L
= 100
= 2V p-p
3
G = 2 V
= 2.5V
S
= 5
R
L
2
1
0
–1
OUTPUT VOLTAGE – V
2
3
0
100
50
150 200 250 300 350 400 450 500
TIME – ns
TPC 3. Large Signal Step Response
–4–
REV. 0
Page 5
5
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
= 2.5
R
L
= 5
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
2
1
4
7
10
13
16
OUTPUT VOLTAGE dBv
19
22
25
10k
100k
1M
FREQUENCY – Hz
10M 100M
TPC 7. Output Voltage vs. Frequency
G = 2 V
= 2.5V
S
R
= 100
L
AD8018
1G
TPC 10. Output Voltage vs. Frequency
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
OUTPUT SWING – Volts
1.7
1.6
1.5 1
10
TPC 8. Output Swing vs. R
0
10
20
30
40
PSRR
–50
PSRR – dB
60
70
80
90
100k
TPC 9. PSRR vs. Frequency
REV. 0
SWING
LOAD RESISTANCE –
PSRR
100 1000 10k
1M 10M
FREQUENCY – Hz
–SWING
VS = ⴞ2.5V
LOAD
G = 2 V V R
= 2.5V
S
= 1V
S
= 100
L
100M
12
750750
NORMALIZED GAIN – dB
12
15
18
3
6
9
9
6
3
0
100k
STANDBY
V
1M
R
L
OUT
(1,0) or (0,1)
(1,1)
FULL POWER
10M 100M
FREQUENCY – Hz
V
IN
50
G = 2
= 2.5V
V
S
= 100
R
L
TPC 11. Small Signal Frequency Response
TPC 12. CMRR vs. Frequency, Full Power, and Standby Mode
–5–
1G
Page 6
AD8018
VSIG
50
V
S
100
1/2
500
500
500
25
6V
AD8138
6V
500
IN
100
AD8018
750
0.1␮F
500
750
AD8018
1/2
V
S
10F0.1␮F
220␮F
AD9632
R
L
10F0.1␮F
7.96k⍀ 402⍀
0.1␮F
6V
0.1␮F
0.1␮F
6V
7.96k
50
OUT
402
TPC 13. Differential Test Circuit
60
70
80
3RD HARMONIC
V
= 6V p–p
OUT
R
= 10
L
V
= 2.5V
S
PWDN 1,0 = 1,1
60
70
80
90
100
DIFFERENTIAL DISTORTION dBc
110
510
2ND HARMONIC
3RD HARMONIC
LOAD RESISTANCE –
TPC 16. Differential Distortion vs. R
60
70
80
2ND HARMONIC
VS = 2.5V G = 4 f
= 100kHz
O
V
= 6V p–p
OUT
LOAD
VS = 2.5V R
= 10
L
G = 4 f
= 100kHz
O
PWDN 1,0 = 1,1
100
90
100
DIFFERENTIAL DISTORTION dBc
110
0.01 0.1 FREQUENCY – MHz
2ND HARMONIC
1.0
TPC 14. Differential Distortion vs. Frequency
–50
VS = ⴞ2.5V R
= 3
L
G
= 4
–60
f
= 100kHz
DIFFERENTIAL DISTORTION – dBc
100
110
70
80
90
O
PWDN 1,0 = 1,1
200
300
PEAK OUTPUT CURRENT – mA
3RD HARMONIC
2ND HARMONIC
400 500 600 700 800
TPC 15. Differential Distortion vs. Peak Output Current
–90
3RD HARMONIC
–100
DIFFERENTIAL DISTORTION – dBc
–110
3
45 678
OUTPUT VOLTAGE – Volts
TPC 17. Differential Distortion vs. Peak-to-Peak Output Voltage
DIFFERENTIAL DISTORTION dBc
60
70
80
90
100
110
2ND HARMONIC
3
45678
OUTPUT VOLTAGE – Volts
VS = 2.5V R
= 10
L
G = 4 f
= 100kHz
O
PWDN 1,0 = 1,0 or 0,1
3RD HARMONIC
TPC 18. Differential Distortion vs. Peak-to-Peak Output Voltage
–6–
REV. 0
Page 7
AD8018
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 = 3.33
VS = 4.50
4.8
g
16
15
14
13
– dBm
LINE
P
12
11
10
3.0
VS = 5.25
3.2 4.0 4.2 4.4 4.6 4.83.4
3.6
TRANSFORMER TURNS RATIO
VS = 4.75
3.8
VS = 5.00
TPC 19. Line Power vs. Turns Ratio; MTPR = –65 dBc, f = 43 kHz
20
30
40
50
MTPR dBc
60
70
80
3 4
TRANSFORMER TURNS RATIO – N
VS = 5V R
LINE
f = 93kHz
P = 13dBm P = 13.5dBm P = 14dBm P = 12.5dBm P = 12dBm
= 100
5
TPC 20. MTPR vs. Turns Ratio
TPC 22. Line Power vs. Turns Ratio; –75 dBc Out-of-Band SFDR, f = 361 kHz
10M
1M
100k
10k
1k
100
10
TRANSIMPEDANCE –
1
0.1
0.01 1k 10k 100k 1M 10M 100M 1G
TRANSIMPEDANCE
FREQUENCY – Hz
PHASE
200
150
100
50
0
50
100
150
200
TPC 23. Open Loop Transimpedance and Phase
rees
PHASE – De
30
40
50
60
SFDR dBc
70
80
P = 12dBm
–90
3
TRANSFORMER TURNS RATIO – N
4
TPC 21. Out-of-Band SFDR vs. Turns Ratio for Various
VS = 5V R
LINE
f = 361kHz
P = 12.5dBm P = 13dBm P = 13.5dBm P = 14dBm
= 100
Line Power
REV. 0
20
18
DECREASING
16
14
12
10
TOTAL SUPPLY CURRENT – mA
8
5
6
0.86
0.88 0.90 0.92 0.94 0.96 0.98 1.00 1.02
LOGIC 0 TO 1
POWER-DOWN VOLTAGE – Volts
LOGIC 1 TO 0
INCREASING
TPC 24. Power-Up/-Down Threshold Voltage
–7–
Page 8
AD8018
–10
VIN = 2V p-p G = 2
–20
V
= ⴞ2.5
S
30
40
50
60
70
CROSSTALK dB
80
90
100
110
RL = 5
SIDE B DRIVEN
100k
TPC 25. Crosstalk vs. Frequency
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
, to provide low input current and
P
current noise. The low impedance current feedback summing junction is at the negative input, V
. The output stage is another
N
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
is inversely
IN
proportional to the transconductance of the amplifier’s input stage, g
. Circuit analysis of the pictured follower with gain yields:
mi
T
ZS
VV G
/
OUT IN
TRGR
ZS F IN
()
()
++×
where:
GRR
=+
1
/
FG
R
/
1
S
CR
+
T
()
TT
T
=
ZS
()
Rg
=≅
1 125
IN mi
Recognizing that G RIN < RF, and that the –3 dB point is set when T
= RF, one can see that the amplifiers bandwidth
Z(S)
depends primarily on the feedback resistor. There is a value of R
below which the amplifier will be unstable, as an actual ampli-
F
fier will have additional poles that will contribute excess phase shift. The optimum value for R
depends on the gain and the
F
amount of peaking tolerable in the application.
RL = 5
SIDE A DRIVEN
RL = 100 SIDE A DRIVEN
1M 10M
FREQUENCY – Hz
RL = 100
SIDE B DRIVEN
100M
V
P
V
N
1G
V
O
BIAS
Figure 4. Simplified Schematic
+
V
IN
G = 1
V
I
IN
IT = IINCTR
R
F
R
IN
R
G
O
T
+
V
OUT
Figure 5. Model of Current Feedback Amplifier
FEEDBACK RESISTOR SELECTION
In current feedback amplifiers, selection of the feedback and gain resistors will impact on 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.
–8–
REV. 0
Page 9
AD8018
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
V
IN
0.47␮F
ERR
ADP3331
C1
IN
SD GND
OUT
FB
ON
OFF
330k
953k
301k
R3
R1
R2
C2
0.47␮F
E
OUT
V
OUT
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
is generated.
V
REF
5V
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 USB port may be poorly regu­lated. Improving the quality of the 5 V supply will optimize the performance of the AD8018 in a USB-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
of 5 V.
V
OUT
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.
R1
2.5k
2.5k
R2
0.1␮F
V
REF
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.
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Page 10
AD8018
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.
1
P V rms V V rms
++408
TOT O S O
(. ) α
2
R
L
IV P
2
Q S OUT
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
of 115°C/W for the TSSOP
JA
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
V
SUPPLY
AMB
= 85ⴗC
Operating Voltage for TSSOP, T
P
LINE
56 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
+V
S
+V
O
R
L
–V
S
–V
+V
S
O
–V
S
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
( )VV
SO
V
2
O
×
R
L
The total supply power can then be computed as:
2
PVVV
TOT S O O
=
|| α
1
×+ +4
2
IV P
R
L
Q S OUT
In this differential driver, VO is the voltage at the output of one amplifier, so 2 V
is the voltage across RL, which is the total
O
impedance seen by the differential driver, including back ter­mination. Now, with two observations, the integrals are easily
evaluated. First, the integral of V rms value of V
. Second, the integral of |VO| is equal to the
O
average rectified value of V
2
is simply the square of the
O
, sometimes called the Mean Aver-
O
age Deviation, or MAD. It can be shown that for a DMT signal, the MAD value is equal to 0.8 times the rms value.
–10–
Table IV. Junction Temperature vs. Line Power and Operating Voltage for SOIC, T
P
dBm 5 6 7 8
LINE,
AMB
V
SUPPLY
= 85ⴗC
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.
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AD8018
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 × 4 100 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.
2
)), where
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.
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Page 12
AD8018
20
0
20
40
POWER dBm
60
80
0 150
50
FREQUENCY – kHz
100
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.
4
3
2
1
VOLTS
0
1
2
3
0.25
0.2 1.5 1.0
0.05
TIME – ms
0
0.05 1.0
1.5
0.2
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.
TxDAC is a trademark of Analog Devices, Inc.
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Page 13
AD8018
55
P4 1
P4 2
P4 3
56
R17
2.49k
R16
2.49k
R30
0
V
B
A
B
A
V
R31
0
C20
0.1␮F
TP10
C8
0.1␮F
R11
CC
50
C10
0.1␮F
53
P3 3
P3 2
P3 1
54
R24
10k
R29
10k
3
2
JP4
1
C28 DNI
3 2
JP3
1
R15
50
CC
TP11
V
CC
V
CC
2
0.1␮F
C5
R8
100
V
CC
2
R14
100
TP17
TP18
R2 750
VCC-R
AGND;4
V
AGND;4
VCC-T
U1
AD8018
R18
750
R19
750
U1
AD8018
VCC-T
VCC-R
;8
CC
+V
10k
10k
+V
U2
AD8022
DNI
R6
DNI
R7
DNI
U2
AD8022
DNI
R33
R34
DNI
TP6
R20 DNI
R3
10
1
R1 10 1WATT
2
R4
10
R21 DNI
TP8
R12 DNI
C1
DNI
R9 DNI
V
CC
2
R5
R10 DNI
C16 DNI
C11 DNI
C22
1000pF
C27
1000pF
C12 DNI
C2
DNI
C18 DNI
C3
DNI
TP7
TP9
TP4
TP5
PR1
PR2
TB1 1
CAPPOLY
CAPPOLY
2TB1
C4
DNI
NC = 5,6
4
2
3
1
C7
DNI
TP23 TP24 TP25 TP26
L5
BEAD
C14 10␮F
T1
C9
DNI
7
CAPPOLY
9
8
10
C26
0.1␮F
U2 DECOUPLING
CAPPOLY C6 DNI
TP1
TP2
C15
0.01␮F
C23 DNI
R32 DNI
1
2
3
4
5
6
TP19
C17 10␮F 25V
C19 DNI 25V
78
VCC-T
V
CC
-R
DNI: DO NOT INSTALL
R27 DNI
JP1
R13
DNI
Figure 11. EVAL Board Schematic
V
CC
R28 DNI
100
JP2
R26
100
R25
0.1␮F C24
0.1␮F C25
PDN0
PDN1
DGND
Figure 12. Input Control Circuit
U1
AD8018
NC1 NC2 NC3
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–13–
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AD8018
Figure 13. Assembly—Primary Side
Figure 14. Silk Screen—Primary Side
–14–
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Figure 15. Layer 1—Primary Side
AD8018
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Figure 16. Layer 2—Ground Plane
–15–
Page 16
AD8018
Figure 17. Layer 3—Power Plane
Figure 18. Layer 4—Secondary Side
–16–
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AD8018
Figure 19. Assembly—Secondary Side
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–17–
Page 18
AD8018
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 R 8, 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 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
–18–
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Page 19
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
AD8018
0.1574 (4.00)
0.1497 (3.80)
PIN 1
0.0098 (0.25)
0.0040 (0.10)
SEATING
8 Lead SOIC
(SO-8)
0.1968 (5.00)
0.1890 (4.80)
85
1
0.0500 (1.27)
PLANE
CONTROLLING DIMENSIONS ARE IN MILLIMETERS
ALL DIMENSIONS PER JEDEC STANDARDS MS-012 AA
BSC
0.020 (0.51)
0.013 (0.33)
0.2440 (6.20)
0.2284 (5.80)
0.0688 (1.75)
0.0532 (1.35)
0.0098 (0.25)
0.0075 (0.19)
0.0196 (0.50)
0.0099 (0.25)
8
0.050 (1.27)
0
0.016 (0.40)
45
0.177 (4.50)
0.173 (4.40)
0.169 (4.30)
0.059 (1.50)
0.093 (1.00)
0.031 (0.80)
14 Lead TSSOP
(RU-14)
0.201 (5.10)
0.197 (5.00)
0.193 (4.90)
14
PIN 1
0.0256 (0.65) BSC
0.006 (0.15)
0.002 (0.05)
CONTROLLING DIMENSIONS ARE IN MILLIMETERS
0.047 (1.2)
0.0118 (0.30)
0.0075 (0.19)
8
71
MAX
SEATING PLANE
0.252
(6.40)
BSC
0.008 (0.20)
0.004 (0.09)
C01519–4.5–7/00 (rev. 0)
8 0
0.030 (0.75)
0.024 (0.60)
0.018 (0.45)
REV. 0
PRINTED IN U.S.A.
–19–
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