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Application Note 87
November 2000
Linear Technology
Magazine Circuit Collection, Volume V
Data Conversion, Interface and Signal Conditioning Products
Richard Markell, Editor
INTRODUCTION
Application Note 87 is the fifth in a series that excerpts
useful circuits from Linear Technology magazine to pre-
serve them for posterity. This application note highlights
data conversion, interface and signal conditioning circuits
from issue VI:1 (February 1996) through issue VIII:4
(November 1998). Like its predecessor, AN67, this Appli-
cation Note includes circuits for high speed video, inter-
face and hot swap circuits, active RC and switched capaci-
tor filter circuitry and a variety of data conversion and
instrumentation circuits. There are also several circuits
that cannot be so neatly categorized. So, without further
ado, I’ll let the authors describe their circuits.
Note: Article Titles appear in this application note exactly
as they originally appeared in
Linear Technology
maga-
zine. This may result in some inconsistency in the usage
of terminology.
TABLE OF CONTENTS
Introduction ......................................................................................................................................................... 1
DATA CONVERTERS
The LTC
®
1446 and LTC1446L: World’s First Dual 12-Bit DACs in SO-8 Packages ............................................... 3
Multichannel A/D Uses a Single Antialiasing Filter................................................................................................ 4
LTC1454/54L and LTC1458/58L: Dual and Quad 12-Bit, Rail-to-Rail, Micropower DACs .................................... 5
Micropower ADC and DAC in SO-8 Give PC 12-Bit Analog Interface .................................................................... 7
The LTC1594 and LTC1598: Micropower 4- and 8-Channel 12-Bit ADCs ........................................................... 10
MUX the LTC1419 Without Software ................................................................................................................. 13
The LTC1590 Dual 12-Bit DAC is Extremely Versatile......................................................................................... 14
New 16-Bit SO-8 DAC Has 1LSB Max INL and DNL Over Industrial Temperature .............................................. 16
LTC1659, LTC1448: Smallest Rail-to-Rail 12-Bit DACs Have Lowest Power ...................................................... 18
An SMBus-Controlled 10-Bit, Current Output, 50µA Full-Scale DAC .................................................................. 19
INTERFACE CIRCUITS
Simple Resistive Surge Protection for Interface Circuits .................................................................................... 20
The LTC1343 and LTC1344 Form a Software-Selectable Multiple-Protocol Interface Port
Using a DB-25 Connector ................................................................................................................................... 22
The LT1328: a Low Cost IrDA Receiver Solution for Data Rates up to 4Mbps ................................................... 34
LTC1387 Single 5V RS232/RS485 Multiprotocol Transceiver ............................................................................ 36
A 10MB/s Multiple-Protocol Chip Set Supports Net1 and Net2 Standards ......................................................... 37
Net1 and Net2 Serial Interface Chip Set Supports Test Mode............................................................................. 44
OPERATIONAL AMPLIFIERS/VIDEO AMPLIFIERS
LT1490/LT1491 Over-the-Top™ Dual and Quad Micropower Rail-to-Rail Op Amps........................................... 46
The LT1210: A 1-Ampere, 35MHz Current Feedback Amplifier........................................................................... 47
The LT1207: An Elegant Dual 60MHz, 250mA Current Feedback Amplifier ........................................................ 50
AN87-1
Application Note 87
Micropower, Dual and Quad JFET Op Amps Feature C-Load™ Capability
and PicoAmpere Input Bias Currents.................................................................................................................. 54
The LT1210: High Power Op Amp Yields Higher Voltage and Current ................................................................ 56
New Rail-to-Rail Amplifiers: Precision Performance from Micropower to High Speed ....................................... 59
LT1256 Voltage-Controlled Amplitude Limiter ................................................................................................... 61
The LT1495/LT1496: 1.5µA Rail-to-Rail Op Amps ............................................................................................. 62
Send Camera Power and Video on the Same Coax Cable ................................................................................... 64
200µA, 1.2MHz Rail-to-Rail Op Amps Have Over-The-Top Inputs ...................................................................... 65
Low Distortion Rail-to-Rail Op Amps Have 0.003% THD with 100kHz Signal .................................................... 66
The LT1167: Precision, Low Cost, Low Power Instrumentation Amplifier Requires
a Single Gain-Set Resistor .................................................................................................................................. 67
Level Shift Allows CFA Video Amplifier to Swing to Ground on a Single Supply ................................................ 70
LT1468: An Operational Amplifier for Fast, 16-Bit Systems ............................................................................... 71
TELECOMMUNICATIONS CIRCUITS
How to Ring a Phone with a Quad Op Amp ........................................................................................................ 73
A Low Distortion, Low Power, Single-Pair HDSL Driver Using the LT1497 ........................................................ 79
COMPARATORS
Ultralow Power Comparators Include Reference ................................................................................................ 80
A 4.5ns, 4mA, Single-Supply, Dual Comparator Optimized for 3V/5V Operation ................................................ 82
INSTRUMENTATION CIRCUITS
LTC1441-Based Micropower Voltage-to-Frequency Converter ........................................................................... 86
Bridge Measures Small Capacitance in Presence of Large Strays ...................................................................... 87
Water Tank Pressure Sensing, a Fluid Solution .................................................................................................. 89
0.05µV/°C Chopped Amplifier Requires Only 5µA Supply Current ..................................................................... 92
4.5ns Dual-Comparator-Based Crystal Oscillator has 50% Duty Cycle and Complementary Outputs ................. 93
LTC1531 Isolated Comparator............................................................................................................................ 94
FILTERS
The LTC1560-1: A 1MHz/500kHz Continuous-Time, Low Noise, Elliptic Lowpass Filter .................................... 96
The LTC1067 and LTC1067-50: Universal 4th Order Low Noise, Rail-to-Rail Switched Capacitor Filters ........... 98
Universal Continuous-Time Filter Challenges Discrete Designs ........................................................................ 102
High Clock-to-Center Frequency Ratio LTC1068-200 Extends Capabilities of Switched Capacitor
Highpass Filter ................................................................................................................................................. 104
Clock-Tunable, High Accuracy, Quad 2nd Order, Analog Filter Building Blocks................................................ 106
MISCELLEANEOUS
Biased Detector Yields High Sensitivity with Ultralow Power Consumption ..................................................... 110
Zero-Bias Detector Yields High Sensitivity with Nanopower Consumption....................................................... 111
Transparent Class-D Amplifiers Featuring the LT1336 ..................................................................................... 112
Single-Supply Random Code Generator ........................................................................................................... 118
APPENDIX A: COMPONENT VENDOR CONTACTS ......................................................................... 120
INDEX ............................................................................................................................ 123
, LTC, and LT are registered trademarks of Linear Technology Corporation; Adaptive Power, Burst Mode, C-Load, FilterCAD, No R
SENSE
, Operational Filter, Over-The-Top, PolyPhase, PowerPath
and UltraFast are trademarks of Linear Technology Corporation. Gelcell is a trademark of Johnson Controls, Inc.; Kool Mµ is a registered trademark of Magnetics, Inc.; Pentium is a registered
trademark of Intel Corp.; VERSA-PAC is a trademark of Coiltronics, Inc.
AN87-2
Application Note 87
Data Converters
THE LTC1446 AND LTC1446L: WORLD’S FIRST
DUAL 12-BIT DACS IN SO-8 PACKAGES
by Hassan Malik and Jim Brubaker
Dual 12-Bit Rail-to-Rail Performance in a Tiny SO-8
The LTC1446 and LTC1446L are dual 12-bit, single-sup-
ply, rail-to-rail voltage output digital-to-analog convert-
ers. Both of these parts include an internal reference and
two DACs with rail-to-rail output buffer amplifiers, packed
in a small, space-saving 8-pin SO or PDIP package. A
power-on reset initializes the outputs to zero-scale at
power-up.
The LTC1446 has an output swing of 0V to 4.095V, making
each LSB equal to 1mV. It operates from a single 4.5V to
5.5V supply, dissipating 3.5mW (I
CC
typical = 700µA). The
22µF
LTC1446L has an output swing of 0V to 2.5V. It can
operate on a single supply with a wide range of 2.7V to
5.5V. It dissipates 1.35mW (I
CC
typical = 450µA) at a 3V
supply.
An Autoranging 8-Channel ADC with Shutdown
Figure 1 shows how to use an LTC1446 to make an
autoranging ADC. The microprocessor sets the reference
span and the common pin for the analog input by loading
the appropriate digital code into the LTC1446. V
OUTA
controls the common pin for the analog inputs to the
LTC1296 and V
OUTB
controls the reference span by setting
the REF+ pin on the LTC1296. The LTC1296 has a shut-
down pin that goes low in shutdown mode. This will turn
off the PNP transistor supplying power to the LTC1446.
The resistor and capacitor on the LTC1446 outputs act as
a lowpass filter for noise.
+
V
CC
CS
D
OUT
µP
CLK
D
IN
LTC1296
SSO
CLK
D
IN
CS/LD
LTC1446
D
OUT
5V
CH0
8 ANALOG
INPUT CHANNELS
CH7
COM
REF +
–
REF
74HC04
47k
47k
5V
0.1µF
2N3906
V
OUTB
100Ω
0.1µF
V
CC
GND
100Ω
V
OUTA
0.1µF
Figure 1. An Autoranging 8-Channel ADC with Shutdown
AN87-3
Application Note 87
A Wide-Swing, Bipolar-Output DAC with
Digitally Controlled Offset
Figure 2 shows how to use an LTC1446 and an LT1077 to
make a wide bipolar-output-swing 12-bit DAC with an
offset that can be digitally programmed. V
OUTA
, which can
5V
8.192
0.1µF
CLK
V
OUTB
4.99k
1%
D
IN
µP
CS/LD
LTC1446
GND
10k
1%
V
CC
15V
V
OUT
4.096
V
OUTA
=
2.048V
(MID SCALE)
LT1077
V
OUT
= 2 { V
OUTB
–V
OUTA
}
0
D
IN
V
OUTA
=
4.096V
(FULL SCALE)
–4.096
–15V
49.9k
1%
TO D
IN
OF NEXT DAC
100k
1%
–8.192
V
OUTA
=
0V
(ZERO SCALE)
be set by loading the appropriate digital code for DAC A,
sets the offset. As this value changes, the transfer curve
for the output moves up and down, as shown in the figure.
+
–
D
OUT
V
OUTA
Figure 2. A Wide-Swing, Bipolar Output DAC with Digitally Controlled Offset
MULTICHANNEL A/D USES
A SINGLE ANTIALIASING FILTER
by LTC Applications Staff
The circuit in Figure 3 demonstrates how the LTC1594’s
independent analog multiplexer can simplify the design of
a 12-bit data acquisition system. All four channels are
MUXed into a single 1kHz, fourth-order Sallen-Key anti-
aliasing filter, which is designed for single-supply opera-
tion. Since the LTC1594’s data converter accepts inputs
from ground to the positive supply, rail-to-rail op amps
were chosen for the filter to maximize dynamic range. The
LT1368 dual rail-to-rail op amp is compensated for the
0.1µF load capacitors (C1 and C2) that help reduce the
amplifier’s output impedance and improve supply rejec-
tion at high frequencies. The filter contributes less than
1LSB of error due to offsets and bias currents. The filter’s
noise and distortion are less than
−72dB
for a 100Hz,
2V
P-P
offset sine input.
The combined MUX and A/D errors result in an integral
nonlinearity error of
±3LSB
(maximum) and a differential
nonlinearity error of
±0.75LSB
(maximum). The typical
signal-to-noise plus distortion ratio is 68dB, with approxi-
mately
−78dB
of total harmonic distortion. The LTC1594
is programmed through a 4-wire serial interface that
allows efficient data transfer to a wide variety of micro-
processors and microcontrollers. Maximum serial clock
speed is 200kHz, which corresponds to a 10.5kHz sam-
pling rate.
The complete circuit consumes approximately 800µA
from a single 5V supply. For ratiometric measurements,
the A/D’s reference can also be taken from the 5V supply.
Otherwise, an external reference should be used.
AN87-4
Application Note 87
5V
0.015µF
0.1µF
+
5V
1/2
LT1368
7.5k
7.5k
0.03µF
C2
0.1µF
–
1µF
CH0
ANALOG
INPUTS
CH1
CH2
LTC1594
CH3
SHA IN
V
REF
0.1µF
COM
GND
V
CC
7.5k
MUX OUT
7.5k
D
IN
CS
CLK
V
CC
D
OUT
CS
DATA IN
CLOCK
DATA OUT
CHIP SELECT
0.015µF
+
1/2
LT1368
–
0.03µF
C1
0.1µF
Figure 3. Simple Data Acquisition System Takes Advantage of the LTC1594’s
MUX OUT/SHA IN Loop to Filter Analog Signals Prior to A/D Conversion
LTC1454/54L AND LTC1458/58L: DUAL AND QUAD
12-BIT, RAIL-TO-RAIL, MICROPOWER DACS
by Hassan Malik and Jim Brubaker
Dual and Quad Rail-to-Rail DACs Offer
Flexibility and Performance
The LTC1454 and LTC1454L are dual 12-bit, single sup-
ply, rail-to-rail voltage-output digital-to-analog convert-
ers. The LTC1458 and LTC1458L are quad versions of this
family. These DACs have an easy-to-use, SPI-compatible
interface. A CLR pin and power-on-reset both reset the
DAC outputs to zero scale. DNL is guaranteed to be less
than 0.5LSB. Each DAC has its own rail-to-rail voltage
output buffer amplifier. The onboard reference is brought
out to a separate pin and can be connected to the REFHI
pins of the DACs. There is also a REFLO pin that can be
used to offset the DAC range. For further flexibility the
×1/×2
pin for each DAC allows the user to select a gain of
either 1 or 2. The LTC1454/54L are available in 16-pin
PDIP and SO packages, and the LTC1458/58L are available
in 28-pin SO or SSOP packages.
5V and 3V Single Supply and Micropower
The LTC1454 and LTC1458 operate from a single 4.5V to
5.5V supply. The LTC1454 dissipates 3.5mW (I
CC
typical
= 700µA), whereas the LTC1458 dissipates 6.5mW (I
CC
typical = 1.3mA). There is an onboard reference of 2.048V
and a nominal full scale of 4.095V when using the onboard
reference and a gain-of-2 configuration.
The LTC1454L and LTC1458L operate on a single supply
with a wide range of 2.7V to 5.5V. The LTC1454L dissi-
pates 1.35mW (I
CC
typical = 450µA), whereas the LTC1458L
dissipates 2.4mW (I
CC
typical = 800µA) from a 3V supply.
There is a 1.22V onboard reference and a convenient full
scale of 2.5V when using the onboard reference and a
gain-of-2 configuration.
Flexibility Allows a Host of Applications
These products can be used in a wide range of applica-
tions, including digital calibration, industrial process con-
trol, automatic test equipment, cellular telephones and
portable, battery-powered systems.
AN87-5

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