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PDF AD8018 Data sheet ( Hoja de datos )
| Número de pieza | AD8018 | |
| Descripción | 5 V/ Rail-to-Rail/ High-Output Current/ xDSL Line Drive Amplifier | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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a
5 V, Rail-to-Rail, High-Output Current,
xDSL Line Drive Amplifier
AD8018
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,
RLOAD = 12.5 ⍀, PLINE = 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
–30
–40
–50 VS = 3.3V
–60
–70
VS = 5V
N = 4.0
VS = 8V
–80
–90
4 6 8 10 12 14 16 18
PLINE – dBm
Figure 1. Out-of-Band SFDR vs. ADSL Upstream Line Power;
VS = 5 V, N = 4 Turns, 144 kHz to 500 kHz. See Evaluation
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.
PIN CONFIGURATIONS
8-Lead SOIC
(Thermal Coastline)
14-Lead TSSOP
AD8018AR
OUT1 1
8 ؉VS
–IN1 2
7 OUT2
؉IN1 3
6 –IN2
–VS 4
5 ؉IN2
NC 1
OUT1 2
–IN1 3
؉IN1 4
–VS 5
PWDN1 6
NC 7
AD8018ARU 8 NC
9 ؉VS
10 OUT2
11 –IN2
12 ؉IN2
13 PWDN0
14 DGND
PRODUCT DESCRIPTION
NC = NO CONNECT
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 Ω (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 Comple-
mentary Bipolar) process, the high bandwidth and fast slew rate
of the AD8018 keep distortion to a minimum, while dissipat-
ing 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 high-
current drive in small packages make the AD8018 ideal for use
in low-cost USB, PCMCIA, and PCI Customer Premise Equip-
ment for ADSL, SDSL, VDSL, and proprietary xDSL systems.
Both models will operate over the temperature range –40°C to
+85°C.
0.01F 100⍀
5V
1nF
10⍀
10k⍀
VIN VREF
0.01F
10k⍀
0.01F 100⍀
750⍀
750⍀
750⍀
R1
10k⍀ 3.1⍀
POUT
16dBm
RL = 100⍀
LINE-
POWER
13dBm
R2
3.1⍀
1:4
10⍀
TRANSFORMER
1nF 10k⍀
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
1 page  
5
2 G=2
VS = ؎2.5V
–1 RL = 100⍀
–4
–7
–10
–13
–16
–19
–22
–25
10k
100k
1M 10M
FREQUENCY – Hz
100M
1G
TPC 7. Output Voltage vs. Frequency
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1
؉SWING –SWING
VS = ؎2.5V
10 100 1000
LOAD RESISTANCE – ⍀
TPC 8. Output Swing vs. RLOAD
10k
0
–10
–20
–30
–40
–50 ؊PSRR
–60
–70
؉PSRR
–80
–90
100k
1M 10M
FREQUENCY – Hz
G=2
VS = ؎2.5V
⌬VS = ؎1V
RL = 100⍀
100M
TPC 9. PSRR vs. Frequency
AD8018
5
2 G=2
VS = ؎2.5
–1 RL = 5⍀
–4
–7
–10
–13
–16
–19
–22
–25
10k
100k
1M 10M
FREQUENCY – Hz
100M
1G
TPC 10. Output Voltage vs. Frequency
12
750⍀ 750⍀
9
6 VIN
50⍀
3
VOUT
RL
STANDBY
(1,0) or (0,1)
G=2
VS = ؎2.5V
RL = 100⍀
0
(1,1)
–3 FULL POWER
–6
–9
–12
–15
–18
100k
1M 10M 100M
FREQUENCY – Hz
1G
TPC 11. Small Signal Frequency Response
–10
–20
–30 STANDBY
(1,0) or (0,1)
–40
–50
–60
–70
100k
(1,1)
FULL POWER
G=2
VS = ؎2.5V
RL = 100⍀
1M
10M
100M
FREQUENCY – Hz
1G
TPC 12. CMRR vs. Frequency, Full Power, and Standby
Mode
REV. 0
–5–
5 Page 
AD8018
Following these generic guidelines will improve the performance
of the AD8018 in all applications.
To optimize the AD8018’s 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 cir-
cuits 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 AD8018ARU-
EVAL board will provide the capability to evaluate the
AD8018ARU along with other Analog Devices products in a typi-
cal 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 kΩ 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 Ω 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 trans-
former with a 1:4 turns ratio. R1 and R2 are back-termination
or line-matching resistors, each 3.1 Ω (100 Ω/(2 × 42)), where
100 Ω is the approximate phone line impedance. The total dif-
ferential load for the AD8018, including the termination resistors,
is 12.5 Ω. 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 amplifier’s output and ground. The
recommended values are 10 Ω for the resistor and 1 nF for the
capacitor to create a low impedance path to ground at frequen-
cies 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 tele-
phone 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, Quadra-
ture 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 spe-
cifically 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.
REV. 0
–11–
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet AD8018.PDF ] | |
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