Datasheet AD8132 (Analog Devices) - 28

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AD8132 +5V +5V + 0.1µF 10µF 1kΩ + 0.1µF 10µF 499Ω 49.9Ω 1 49.9Ω 50Ω AD8132 100Ω SOURCE 0.1µF TWISTED 2 AD830 PAIR 523Ω 49.9Ω 7 3 VOUT 1kΩ 4 10µF 0.1µF + 5 –5V 10µF 0.1µF +
72 0 5- 03
–5V
01 Figure 74. Balanced Line Driver and Receiver Using AD8132 and AD830 Any imbalance in the differential drive signal appears as a
20
common-mode signal on the cable. This is the equivalent of
10
a single wire that is driven with the common-mode signal. In
0
this case, the wire acts as an antenna and radiates. Therefore, to
–10
minimize radiation when driving differential twisted pair cables,
) B –20
make sure the differential drive signal is well balanced.
(d IN –30 /V T
The common-mode feedback loop in the AD8132 helps to
OU –40 V
minimize the amount of common-mode voltage at the output
–50
and can, therefore, be used to create a well-balanced differential
–60
line driver. Figure 74 shows an application that uses an AD8132
–70
as a balanced line driver and an AD830 as a differential receiver configured for unity gain. This circuit was operated with 10 meters
–80
74
1 10 100 1000
0 5- of Category 5 cable.
FREQUENCY (MHz)
03 01 Figure 76. Frequency Response for Transmit Boost Circuit
TRANSMIT EQUALIZER
Any length of transmission line attenuates the signals it carries.
LOW-PASS DIFFERENTIAL FILTER
This effect is worse at higher frequencies than at lower frequencies. Similar to an op amp, various types of active filters can be One way to compensate for this is to provide an equalizer circuit created with the AD8132. These can have single-ended inputs that boosts the higher frequencies in the transmitter circuit, so and differential outputs that can provide an antialias function that at the receive end of the cable, the attenuation effects are when driving a differential ADC. diminished.
2.15kΩ 549Ω
By lowering the impedance of the R
33pF
G component of the feedback
2kΩ 953Ω
network at a higher frequency, the gain can be increased at a
100pF 200pF VIN 49.9Ω VOUT
high frequency. Figure 75 shows the gain of a two-line driver
100pF 953Ω 200pF
that has its R
2kΩ
G resistors shunted by 10 pF capacitors. The effect
24.9Ω 33pF
5
549Ω
07 5- of this is shown in the frequency response plot of Figure 76.
2.15kΩ
03 01
499Ω
Figure 77. 1 MHz, 3-Pole Differential Output,
10pF 49.9Ω
Low-Pass, Multiple Feedback Filter
VIN 249Ω
Figure 77 is a schematic of a low-pass, multiple feedback filter.
49.9Ω 100Ω VOUT 249Ω 49.9Ω
The active section contains two poles, and an additional pole
24.9Ω
3 07 is added at the output. The filter was designed to have a −3 dB 5-
10pF 499Ω
03 frequency of 1 MHz. 01 Figure 75. Frequency Boost Circuit Rev. I | Page 27 of 32 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION CONNECTION DIAGRAM TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ±DIN TO ±OUT SPECIFICATIONS VOCM TO ±OUT SPECIFICATIONS ±DIN TO ±OUT SPECIFICATIONS VOCM TO ±OUT SPECIFICATIONS ±DIN TO ±OUT SPECIFICATIONS VOCM TO ±OUT SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE MAXIMUM POWER DISSIPATION ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS TEST CIRCUITS OPERATIONAL DESCRIPTION DEFINITION OF TERMS Differential Voltage Common-Mode Voltage BASIC CIRCUIT OPERATION THEORY OF OPERATION GENERAL USAGE OF THE AD8132 DIFFERENTIAL AMPLIFIER WITHOUT RESISTORS (HIGH INPUT IMPEDANCE INVERTING AMPLIFIER) OTHER β2 = 1 CIRCUITS VARYING β2 β1 = 0 ESTIMATING THE OUTPUT NOISE VOLTAGE CALCULATING INPUT IMPEDANCE OF THE APPLICATION CIRCUIT INPUT COMMON-MODE VOLTAGE RANGE IN SINGLE-SUPPLY APPLICATIONS SETTING THE OUTPUT COMMON-MODE VOLTAGE DRIVING A CAPACITIVE LOAD OPEN-LOOP GAIN AND PHASE LAYOUT, GROUNDING, AND BYPASSING CIRCUITS APPLICATIONS INFORMATION ANALOG-TO-DIGITAL DRIVER BALANCED CABLE DRIVER TRANSMIT EQUALIZER LOW-PASS DIFFERENTIAL FILTER HIGH COMMON-MODE OUTPUT IMPEDANCE AMPLIFIER FULL-WAVE RECTIFIER AUTOMOTIVE PRODUCTS OUTLINE DIMENSIONS ORDERING GUIDE