Instrumentation Anthology Circuits from the Lab

216 Pages·2009·7.29 MB·English

by  Analog Devices, Inc.

Circuits from the Lab
Reference Designs
Instrumentation Anthology
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Instrumentation Anthology
Circuits from the Lab
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This instrumentation anthology of circuit notes contains
more than 48 Circuits from the Lab designs specifically • Comprehensive documentation for easier use with a
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Anthology | Page 2 of 215
Instrumentation Anthology Circuits from the Lab Reference Designs
TABLE OF CONTENTS
Introduction ...................................................................................... 2  CN-0102: Precision Weigh Scale Design Using the AD7190
Revision History ............................................................................... 4  24-Bit Sigma-Delta ADC with Internal PGA ............................. 49 
CN-0006: High Accuracy, Bipolar Data Conversion CN-0107: Weigh Scale Design Using the AD7780
(AD5764, ADR02) ............................................................................ 5  24-Bit Sigma-Delta ADC with Internal PGA ............................. 53 
CN-0016: Interface Between I/Q Modulator and High Speed CN-0108: Weigh Scale Design Using the AD7781
DAC (AD9779A, ADL5370) ........................................................... 7  20-Bit Sigma-Delta ADC with Internal PGA ............................. 57 
CN-0021: Interfacing the ADL5375 I/Q Modulator to the CN-0109: Low Jitter Sampling Clock Generator for High
AD9779A Dual-Channel, 1 GSPS High Speed DAC ................... 9  Performance ADCs Using the AD9958/AD9858
CN-0026: Precision, Unipolar, Inverting Conversion Using the 500 MSPS/1 GSPS DDS and AD9515 Clock Distribution IC .. 61 
AD5547/AD5557 DAC .................................................................. 12  CN-0112: Variable Gain Noninverting Amplifier Using the
CN-0027: Precision, Unipolar, Noninverting Configuration for AD5292 Digital Potentiometer and the OP184 Op Amp ......... 64 
the AD5547/AD5557 DAC ............................................................ 14  CN-0114: Low Cost, High Voltage, Programmable Gain
Instrumentation Amplifier Using the AD5292 Digital
CN-0028: Precision, Bipolar, Configuration for the
AD5547/AD5557 DAC .................................................................. 16  Potentiometer and the AD8221 In-Amp ..................................... 67 
CN-0118: Precision Weigh Scale Design Using the AD7191
CN-0030: AD5390/AD5391/AD5392 Channel Monitor
Function ........................................................................................... 18  24-Bit Sigma-Delta ADC with Internal PGA ............................. 70 
CN-0032: Converting a Single-Ended Signal with the AD7982 CN-0119: Precision WEigh Scale Design Using the AD7192 
Differential PulSAR ADC .............................................................. 20  24-Bit Sigma-Delta ADC with Internal PGA ............................. 73 
CN-0041: DC-Coupled, Single-Ended-to-Differential
CN-0123: Automated Calibration Technique that Reduces the
Conversion Using the AD8138 Low Distortion Differential
AD5360 16-Channel, 16-Bit DAC Offset Voltage to
ADC Driver and the AD7356 5 MSPS, 12-Bit SAR ADC ......... 22 
Less Than 1 mV .............................................................................. 77 
CN-0042: Driving the AD7366/AD7367 Bipolar SAR ADC in
CN-0131: 16 Channels of Programmable Output Span Using
Low Distortion, DC-Coupled Applications ................................ 24 
the AD5360 16-Bit Voltage Output DAC ....................................79 
CN-0046: Using the AD8352 as an Ultralow Distortion
CN-0133: Sensing Low-g Acceleration Using the ADXL345
Differential RF/IF Front End for High Speed ADCs ................. 26 
Digital Accelerometer Connected to the ADuC7024 Precision
CN-0050: Stable, Closed-Loop Automatic Power Control for RF Analog Microcontroller ................................................................. 81 
Applicatons ...................................................................................... 29 
CN-0140: High Performance, Dual Channel IF Sampling
CN-0051: Driving the AD9233/AD9246/AD9254 ADCs in Receiver ............................................................................................ 84 
AC-Coupled Baseband Applications ............................................ 32 
CN-0155: Precision Weigh Scale Design Using a 24-Bit Sigma-
CN-0052: Unipolar, Precision DC, Digital-to-Analog Delta ADC with InterNal PGA and AC Excitation .................... 88 
Conversion Using the AD5450/AD5451/AD5452/AD5453 
CN-0185: A Novel Analog-to-Analog Isolator Using an Isolated
8-/10-/12-/14-Bit DACs ................................................................. 35  Sigma-Delta Modulator, Isolated DC-to-DC Converter, and
CN-0053: Precision, Bipolar Configuration for the Active Filter ..................................................................................... 92 
AD5450/AD5451/AD5452/AD5453 8-/10-/12-/14-Bit CN-0187: Crest Factor, Peak, and RMS RF Power Measurement
Multiplying DACs ........................................................................... 38  Circuit Optimized for High Speed, Low power, and
CN-0055: Programmable Gain Element Using the Single 3.3 V Supply ......................................................................... 96 
AD5450/AD5451/AD5452/AD5453 Current Output DAC
CN-0216: Precision Weigh Scale Design Using the AD7791
Family ............................................................................................... 41 
24-Bit Sigma-Delta ADC with External ADA4528-1 Zero-Drift
CN-0073: High Accuracy, Bipolar Voltage Output Digital-to- Amplifiers ...................................................................................... 103 
Analog Conversion Using the AD5765 DAC .............................. 43 
CN-0237: Ultralow Power, 18-Bit, Differential PulSAR ADC
CN-0079: High Precision Digital-to-Analog Conversion Using Driver ............................................................................................. 108 
the 16-Bit AD5542/AD5541 Voltage Output DAC, ADR421
Reference, and AD8628 Auto-Zero Op Amp .............................. 45 
Anthology | Page 3 of 215
Circuits from the Lab Reference Designs Instrumentation Anthology
CN-0241: High-Side Current Sensing with Input Overvoltage CN-0373: Isolated USB to Isolated RS-485/Isolated RS-232
Protection ....................................................................................... 112  Interface .......................................................................................... 161 
CN-0326: Isolated Low Power pH Monitor with Temperature CN-0376: Channel-to-Channel Isolated Temperature Input
Compensation ................................................................................ 118  (Thermocouple/RTD) for PLC/DCS Applications ................... 167 
CN-0357: Low Noise, Single-Supply, Toxic Gas Detector, Using CN-0381: Completely Integrated 4-Wire RTD Measurement
an Electrochemical Sensor with Programmable Gain TIA for System Using a Low Power, Precision, 24-Bit,  
Rapid Prototyping ........................................................................ 125  Sigma-Delta ADC ......................................................................... 174 
CN-0359: Fully Automatic High Performance Conductivity CN-0383: Completely Integrated 3-Wire RTD Measurement
Measurement System ................................................................... 130  System Using a Low Power, Precision, 24-Bit,  
CN-0363: Dual-Channel Colorimeter with Programmable Sigma-Delta ADC ......................................................................... 184 
Gain Transimpedance Amplifiers and Digital Synchronous
CN-0384: Completely Integrated Thermocouple Measurement
Detection ........................................................................................140  System Using a Low Power, Precision, 24-Bit,  
CN-0365: 16-Bit, 600 kSPS, Low Power Data Acquisition Sigma-Delta ADC ......................................................................... 195 
System for High Temperature Environments ...........................148 
CN-0387: Calibration-Free Return Loss Measurement
CN-0370: 16-Bit, Single-Supply LED Current Driver with Less System.............................................................................................. 207 
Than ±1 LSB Integral and Differential Nonlinearity ............... 155 
REVISION HISTORY
2/2017—Revision 0: Initial Version
Anthology | Page 4 of 215
Circuit Note
CN-0006
Devices Connected/Referenced
Circuit Designs Using Analog Devices Products
AD5764 Complete Quad, 16-Bit, High Accuracy DAC
Apply these product pairings quickly and with confidence.
For more information and/or support call 1-800-AnalogD ADR02 Precision 5.0 V Voltage Reference
(1-800-262-5643) or visit www.analog.com/circuit.
High Accuracy, Bipolar Voltage Output Digital-to-Analog Conversion
Using the AD5764 DAC
CIRCUIT FUNCTION AND BENEFITS +15V
ADR02
This circuit provides high accuracy, bipolar data conversion 2 VIN VOUT 6
GND
using the AD5764, a quad, 16-bit, serial input, bipolar voltage 4
output DAC. This circuit utilizes the ADR02 precision reference
+15V –15V
to achieve optimal DAC performance over full operating
10µF 10µF
temperature range. The only external components needed for 100nF 100nF 100nF
this precision 16-bit DAC are a reference voltage source,
BIN/2sCOMP
decoupling capacitors on the supply pins and reference inputs,
32 31 30 29 28 27 26 25
basanovdtih na gcnls o oisnpe tdcioo-lnsotao alp ns hdseo brrvot-oac ricdroc nsuptirato ccleu a.r nTredhn iost p sceeirntct-iulnoigto irpse cswiosentlolt rrso ullei taeddi nfogr t o SYNC +5V 1 SYNC N/2sCOMP AVDDAVSSNC REFGND NC REFCD REFABAGNDA 24
SCLK 2 SCLK BI VOUTA 23 VOUTA
applications.
SDIN 3 SDIN VOUTB 22 VOUTB
CIRCUIT DESCRIPTION SDO 4 SDO AD5764 AGNDB 21
5 CLR AGNDC 20
The AD5764 is a high performance digital-to-analog converter LDAC 6 LDAC VOUTC 19 VOUTC
that offers guaranteed monotonicity, integral nonlinearity (INL) D0 7 D0 VOUTD 18 VOUTD
D1 8 D1 T AGNDD 17
Pofe r±f1o rLmSaBn (cCe -igsr gaudaer danevteiceed) ,o lvoewr wnoidisee o, panerda t1i0n gμ ss useptptlliyn vgo tlitmagee. RSTOU RSTIN DGND DVCCAVDDPGND AVSSISCC
ranges. The AV supply range is +11.4 V to +16.5 V, and the 9 10 11 12 13 14 15 16
DD
AfuVllS-Ss coapleer oatuitnpgu rta rnagneg eis i fsr ±om10 −V1. 1.4 V to −16.5 V. The nominal RSRTSOTUINT 10µF100nF 100nF 10µF
100nF
A precision voltage reference must be used in order for the
NC = NO CONNECT
DAC to achieve the optimum performance over its full 10µF
operating temperature range. The AD5764 incorporates +5V+15V –15V 5303-064
reference buffers, which eliminate the need for both a positive Figure 1. High Accuracy, Bipolar Configuration of the AD5764 DAC Using a
and negative external reference and associated buffers. This Precision Reference
leads to further savings in both cost and board space. Because
the voltages applied to the reference inputs (REFAB, REFCD) In any circuit where accuracy is important, careful considera-
are used to generate the buffered positive and negative internal tion of the power supply and ground return layout helps to
references for the DAC cores, any error in the external voltage ensure the rated performance. The PCB on which the AD5764
reference is reflected in the outputs of the device. is mounted must be designed so that the analog and digital
sections are physically separated and confined to certain areas
There are four possible sources of error to consider when
of the board. If the AD5764 is in a system where multiple
choosing a voltage reference for high accuracy applications:
devices require an AGND-to-DGND connection, the connec-
initial accuracy, temperature coefficient of the output voltage,
tion is to be made at one point only. The star ground point is
long term drift, and output voltage noise. Table 1 lists other 5 V
established as close as possible to the device. The AD5764 must
precision reference candidates from Analog Devices and their
have ample supply bypassing of 10 µF in parallel with 0.1 µF on
respective attributes.
each supply, located as close to the package as possible, ideally
right up against the device. The 10 µF capacitors are the
Rev. A
“Circuits from the Lab” from Analog Devices have been designed and built by Analog Devices
engineers. Standard engineering practices have been employed in the design and construction of
each circuit, and their function and performance have been tested and verified in a lab environment
at room temperature. However, you are solely responsible for testing the circuit and determining its
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
suitability and applicability for your use and application. Accordingly, in no event shall Analog
Devices be liable for direct, indirect, special, incidental, consequential, or punitive damages due to Tel: [phone] www.analog.com
any cause whatsoever connected to the use of any “Circuit from the Lab”. (Continued on last page) Fax: [phone] ©2009 Analog Devices, Inc. All rights reserved.
Anthology | Page 5 of 215
CN-0006 Circuit Note
Table 1. Precision 5.0 V References
Initial Accuracy Max Long-Term Drift Typ Temp Drift Max 0.1 Hz to 10 Hz Noise
Part Number (mV) (ppm) (ppm/°C) Typ (µV p-p)
ADR435B ±2 40 3 8
ADR425B ±1 50 3 3.4
ADR02B ±3 50 3 10
ADR395B ±5 50 9 8
AD586T ±2.5 15 10 4
tantalum bead type. The 0.1 µF capacitor must have low
LEARN MORE
effective series resistance (ESR) and low effective series
inductance (ESL), such as the common ceramic types, which Kester, Walt. 2005. The Data Conversion Handbook. Analog
provide a low impedance path to ground at high frequencies to Devices. Chapters 3 and 7.
handle transient currents due to internal logic switching. MT-015 Tutorial, Basic DAC Architectures II: Binary DACs.
The power supply traces of the AD5764 must be as wide as Analog Devices.
possible to provide low impedance paths and reduce the effects
MT-031 Tutorial, Grounding Data Converters and Solving the
of glitches on the power supply line. Fast switching signals, such
Mystery of AGND and DGND. Analog Devices.
as clocks, must be shielded with digital ground to avoid
MT-101 Tutorial, Decoupling Techniques. Analog Devices.
radiating noise to other parts of the board, and must never be
run near the reference inputs. A ground line routed between the Voltage Reference Wizard Design Tool.
SDIN and SCLK lines helps reduce crosstalk between them (not
Data Sheets and Evaluation Boards
required on a multilayer board, which has a separate ground
plane; however, it is helpful to separate the lines). It is essential AD5764 Data Sheet.
to minimize noise on the reference inputs because it couples AD5764 Evaluation Board.
through to the DAC output. Avoid crossover of digital and
ADR02 Data Sheet.
analog signals. Traces on opposite sides of the board must run
at right angles to each other. This reduces the effects of
REVISION HISTORY
feedthrough on the board. A microstrip technique is
recommended, but not always possible with a double-sided 5/09—Rev. 0 to Rev. A
board. In this technique, the component side of the board is
Updated Format .................................................................. Universal
dedicated to the ground plane, and signal traces are placed on
the solder side. Best layout and performance are achieved with 10/08—Revision 0: Initial Version
at least a 4-layer multilayer board, where there is a ground plane
layer, a power supply layer, and two signal layers.
(Continued from first page) "Circuits from the Lab" are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors. While you may
use the "Circuits from the Lab" in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual property by application or use
of the "Circuits from the Lab". Information furnished by Analog Devices is believed to be accurate and reliable. However, "Circuits from the Lab" are supplied "as is" and without warranties
of any kind, express, implied, or statutory including, but not limited to, any implied warranty of merchantability, noninfringement or fitness for a particular purpose and no responsibility is
assumed by Analog Devices for their use, nor for any infringements of patents or other rights of third parties that may result from their use. Analog Devices reserves the right to change any
"Circuits from the Lab" at any time without notice, but is under no obligation to do so. Trademarks and registered trademarks are the property of their respective owners.
©2009 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
CN08192-0-5/09(A)
Rev. A | Page 2 of 2
Circuit Note
CN-0016
Devices Connected/Referenced
Circuit Designs Using Analog Devices Products
AD9779A Dual 16-Bit, 1 GSPS DAC
Apply these product pairings quickly and with confidence.
For more information and/or support call 1-800-AnalogD ADL5370 300 MHz to 1000 MHz I/Q Modulator
(1-800-262-5643) or visit www.analog.com/circuit.
Interfacing the ADL5370 I/Q Modulator to the AD9779A
Dual-Channel, 1 GSPS High Speed DAC
CIRCUIT FUNCTION AND BENEFITS a single 50 Ω resistor to ground from each of the DAC outputs
provides the desired 500 mV dc bias. With just the four 50 Ω
This circuit provides a simple, elegant interface between the
resistors in place, the voltage swing on each pin is 1 V p-p.
ADL5370 I/Q modulator and the AD9779A high speed DAC.
This results in a differential voltage swing of 2 V p-p on each
The ADL5370 and the AD9779A are well-matched devices
input pair.
because they have the same bias levels and similarly high
signal-to-noise ratios (SNR). The matched bias levels of 500 mV By adding resistors RSLI and RSLQ to the interface, the output
allow for a “glueless” interface—there is no requirement for a swing of the DAC can be reduced without any loss of DAC
level shifting network that would add noise and insertion loss resolution. The resistor is placed as a shunt between each side of
along with extra components. The addition of the swing- the differential pair, as shown in Figure 1. It has the effect of
limiting resistors (RSLI, RSLQ) allows the DAC swing to be reducing the ac swing without changing the dc bias already
scaled appropriately without loss of resolution or of the 0.5 V established by the 50 Ω resistors and the DAC output current.
bias level. The high SNR of each device preserves a high SNR
The value of this ac swing-limiting resistor is chosen based on
through the circuit.
the desired ac voltage swing. Figure 2 shows the relationship
CIRCUIT DESCRIPTION between the swing-limiting resistor and the peak-to-peak ac
The ADL5370 is designed to interface with minimal swing that it produces when 50 Ω bias-setting resistors are used.
components to members of Analog Devices family of Note that all Analog Devices I/Q modulators present a relatively
TxDAC® converters (AD97xx). The baseband inputs of the high input impedance on their baseband inputs (typically >1 kΩ).
ADL5370 require a dc common-mode bias voltage of 500 mV. As a result, the input impedance of the I/Q modulator will have
With each AD9779A output swinging from 0 mA to 20 mA, no effect on the scaling of the DAC output signal.
2.0
AD9779A ADL5370 1.8
OUT1_P 93 19 IBBP p) 1.6
92 RR55BB00IIΩΩNP 1R0S0LΩI 20 SWING (V p- 11..42
OUT1_N IBBN L 1.0
A
TI
N 0.8
E
R
84 23 FFE 0.6
OUT2_N QBBN DI 0.4
RBQN
50Ω RSLQ 0.2
RBQP 100Ω
OUT2_P 83 50Ω 24 QBBP 08209-001 010 100 RL (Ω) 1k 10k 08209-002
Figure 1. Interface Between the AD9779A and ADL5370 with 50 Ω Resistors Figure 2. Relationship Between the AC Swing-Limiting Resistor and the
to Ground to Establish the 500 mV DC Bias for the ADL5370 Baseband Inputs Peak-to-Peak Voltage Swing with 50 Ω Bias-Setting Resistors
(Simplified Schematic)
Rev. A
“Circuits from the Lab” from Analog Devices have been designed and built by Analog Devices
engineers. Standard engineering practices have been employed in the design and construction of
each circuit, and their function and performance have been tested and verified in a lab environment
at room temperature. However, you are solely responsible for testing the circuit and determining its
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
suitability and applicability for your use and application. Accordingly, in no event shall Analog
Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due to Tel: [phone] www.analog.com
any cause whatsoever connected to the use of any “Circuit from the Lab”. (Continued on last page) Fax: [phone] ©2008–2009 Analog Devices, Inc. All rights reserved.
Anthology | Page 7 of 215
CN-0016 Circuit Note
It is generally necessary to low-pass filter the DAC outputs to COMMON VARIATIONS
remove image frequencies when driving a modulator. The
The interface described here can be used to interface
above interface lends itself well to the introduction of such a
any TxDAC converter with ground referenced 0 mA to 20 mA
filter. The filter can be inserted between the dc bias setting
output currents to any I/Q modulator with a 0.5 V input bias
resistors and the ac swing-limiting resistor. Doing so establishes
level. For zero-IF applications, the AD9783 dual DAC provides
the input and output impedances for the filter.
an LVDS interface, while the CMOS-driven AD9788 dual DAC
A simulated filter example is shown in Figure 3 with a third-order can generate a fine resolution complex IF input to the I/Q
elliptical filter with a 3 dB frequency of 3 MHz. Matching input modulator. The ADL5370/ADL5371/ADL5372/ADL5373/
and output impedances makes the filter design easier, so the ADL5374 family of I/Q modulators provides narrow-band
shunt resistor chosen is 100 Ω, producing an ac swing of 1 V p-p operation with high output 1 dB compression point and OIP3,
differential for a 0 mA to 20 mA DAC full-scale output current. whereas the ADL5375 provides broadband high performance
In a practical application, the use of standard value components, operation from 400 MHz to 6 GHz. The ADL5385 I/Q modula-
along with the input impedance of the I/Q modulator (2900 kΩ tor uses a 2 × LO and operates from 50 MHz to 2.2 GHz.
in parallel with a few picofarads of input capacitance), will slightly
change the frequency response of this circuit.
LEARN MORE
AN-772 Application Note, A Design and Manufacturing Guide
AD9779A LPI ADL5370 for the Lead Frame Chip Scale Package (LFCSP). Analog
93 2.7nH 19
OUT1_P IBBP Devices.
RBIP
50Ω 1.1nF 1.1nF RSLI MT-016 Tutorial, Basic DAC Architectures III: Segmented DACs.
RBIN C1I C2I 100Ω
92 50Ω 20 Analog Devices.
OUT1_N IBBN
LNI MT-017 Tutorial, Oversampling Interpolating DACs. Analog
2.7nH
Devices.
LNQ
OUT2_N 84 2.7nH 23 QBBN MT-031 Tutorial, Grounding Data Converters and Solving the
RBQN Mystery of 'AGND' and 'DGND'. Analog Devices.
50Ω 1.1nF 1.1nF RSLQ
RBQP C1Q C2Q 100Ω MT-080 Tutorial, Mixers and Modulators. Analog Devices.
OUT2_P 83 50Ω 2L.7PnQH 24 QBBP 08209-003 MT-101 Tutorial, Decoupling Techniques. Analog Devices.
Figure 3. DAC Modulator Interface with 3 MHz Third-Order, Low-Pass Filter Zumbahlen, Hank. 2006. Basic Linear Design. Analog Devices.
(Calculated Component Values) ISBN 0915550281. Chapters 4 and 11. Also available as
Linear Circuit Design Handbook. Elsevier-Newnes, 2008,
All the power supply pins of the ADL5370 must be connected to ISBN 0750687037, Chapters 4 and 11.
the same 5 V source. Adjacent pins of the same name can be
Data Sheets
tied together and decoupled to a large area ground plane with a
0.1 µF capacitor. These capacitors should be located as close as AD9779A Data Sheet.
possible to the device. The power supply can range between
ADL5370 Data Sheet.
4.75 V and 5.25 V.
The COM1 pin, COM2 pin, COM3 pin, and COM4 pin should
REVISION HISTORY
be tied to the same ground plane through low impedance paths.
The exposed paddle on the underside of the package should 5/09—Rev. 0 to Rev. A
also be soldered to a low thermal and electrical impedance Updated Format .................................................................. Universal
ground plane. If the ground plane spans multiple layers on the
10/08—Revision 0: Initial Version
circuit board, they should be stitched together with nine vias
under the exposed paddle. The AN-772 application note
discusses the thermal and electrical grounding of the
LFCSP_VQ in greater detail.
(Continued from first page) "Circuits from the Lab" are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors. While you may
use the "Circuits from the Lab" in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual property by application or use of
the "Circuits from the Lab". Information furnished by Analog Devices is believed to be accurate and reliable. However, "Circuits from the Lab" are supplied "as is" and without warranties of any
kind, express, implied, or statutory including, but not limited to, any implied warranty of merchantability, noninfringement or fitness for a particular purpose and no responsibility is assumed
by Analog Devices for their use, nor for any infringements of patents or other rights of third parties that may result from their use. Analog Devices reserves the right to change any "Circuits
from the Lab" at any time without notice, but is under no obligation to do so. Trademarks and registered trademarks are the property of their respective owners.
©2008–2009 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
CN08209-0-5/09(A)
Rev. A | Page 2 of 2
Circuit Note
CN-0021
Devices Connected/Referenced
Circuit Designs Using Analog Devices Products
AD9779A Dual 16-Bit, 1 GSPS DAC
Apply these product pairings quickly and with confidence.
For more information and/or support call 1-800-AnalogD ADL5375-05 400 MHz to 6000 MHz I/Q Modulator
(1-800-262-5643) or visit www.analog.com/circuit.
Interfacing the ADL5375 I/Q Modulator to the AD9779A
Dual-Channel, 1 GSPS High Speed DAC
CIRCUIT FUNCTION AND BENEFITS CIRCUIT DESCRIPTION
This circuit provides a simple, elegant interface between the The ADL5375 is designed to interface with minimal
ADL5375 I/Q modulator and the AD9779A high speed DAC. components to members of Analog Devices family of
The ADL5375 and the AD9779A are well-matched devices TxDAC® converters (AD97xx). The baseband inputs of the
because they have the same bias levels and similarly high ADL5375 require a dc common-mode bias voltage of 500 mV.
signal-to-noise ratios (SNR). The matched bias levels of 500 mV With each AD9779A output swinging from 0 mA to 20 mA, a
allow for a “glueless” interface—there is no requirement for a single 50 Ω resistor to ground from each of the DAC outputs
level shifting network that would add noise and insertion loss provides the desired 500 mV dc bias. With just the four 50 Ω
along with extra components. The addition of the swing- resistors in place, the voltage swing on each pin is 1 V p-p.
limiting resistors (RSLI, RSLQ) allows the DAC swing to be This results in a differential voltage swing of 2 V p-p on each
scaled appropriately without loss of resolution or of the 0.5 V input pair.
bias level. The high SNR of each device preserves a high SNR By adding resistors RSLI and RSLQ to the interface, the output
through the circuit. swing of the DAC can be reduced without any loss of DAC
resolution. The resistor is placed as a shunt between each side of
AD9779A ADL5375-05
93 21
OUT1_P IBBP
RBIP
50Ω RSLI
100Ω
RBIN
92 50Ω 22
OUT1_N IBBN
84 9
OUT2_N QBBN
RBQN
50Ω RSLQ
100Ω
RBQP
83 50Ω 10 1
OUT2_P QBBP 5-00
2
2
8
0
Figure 1. Interface Between the AD9779A and ADL5375 with 50 Ω Resistors to Ground to Establish the
500 mV DC Bias for the ADL5375-05 Baseband Inputs (Simplified Schematic)
Rev. A
“Circuits from the Lab” from Analog Devices have been designed and built by Analog Devices
engineers. Standard engineering practices have been employed in the design and construction of
each circuit, and their function and performance have been tested and verified in a lab environment
at room temperature. However, you are solely responsible for testing the circuit and determining its
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
suitability and applicability for your use and application. Accordingly, in no event shall Analog
Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due to Tel: [phone] www.analog.com
any cause whatsoever connected to the use of any “Circuit from the Lab”. (Continued on last page) Fax: [phone] ©2008–2009 Analog Devices, Inc. All rights reserved.
Anthology | Page 9 of 215
CN-0021 Circuit Note
2.0 A simulated filter example is shown in Figure 3 with a third-
1.8 order elliptical filter with a 3 dB frequency of 10 MHz.
Matching input and output impedances makes the filter design
p) 1.6
p- easier, so the shunt resistor chosen is 100 Ω, producing an ac
V 1.4
G ( swing of 1 V p-p differential for a 0 mA to 20 mA DAC full-
WIN 1.2 scale output current. The simulated frequency response of this
S
AL 1.0 filter is shown in Figure 4. In a practical application, the use of
TI
N 0.8 standard value components along with the input impedance of
E
R
FE 0.6 the I/Q modulator (2900 kΩ in parallel with a few picofarads of
F
DI 0.4 input capacitance), will slightly change the frequency response.
All the power supply pins of the ADL5375 must be connected to
0.2
the same 5 V source. Adjacent pins of the same name can be
010 100 RL (Ω) 1k 10k 08225-002 t0i.e1d μ tFo gceatphaecri taonr.d T dheecsoeu cpalpedac tioto ar sla srhgoeu alrde ab eg rloocuantded p alasn cel owseit has a
Figure 2. Relationship Between the AC Swing-Limiting Resistor and the
possible to the device. The power supply can range between
Peak-to-Peak Voltage Swing with 50 Ω Bias-Setting Resistors
4.75 V and 5.25 V.
The COM1 pin, COM2 pin, COM3 pin, and COM4 pin should
the differential pair, as shown in Figure 1. It has the effect of
be tied to the same ground plane through low impedance paths.
reducing the ac swing without changing the dc bias already
The exposed paddle on the underside of the package should
established by the 50 Ω resistors.
also be soldered to a low thermal and electrical impedance
The value of this ac swing-limiting resistor is chosen based on ground plane. If the ground plane spans multiple layers on the
the desired ac voltage swing. Figure 2 shows the relationship circuit board, they should be stitched together with nine vias
between the swing-limiting resistor and the peak-to-peak ac under the exposed paddle. The AN-772 application note
swing that it produces when 50 Ω bias-setting resistors are used. discusses the thermal and electrical grounding of the
Note that all Analog Devices I/Q modulators present a relatively LFCSP_VQ in greater detail.
high input impedance on their baseband inputs (typically >1 kΩ).
COMMON VARIATIONS
As a result, the input impedance of the I/Q modulator will have
The interface described here can be used to interface
no effect on the scaling of the DAC output signal.
any TxDAC converter with ground referenced 0 mA to 20 mA
It is generally necessary to low-pass filter the DAC outputs to
output currents to any I/Q modulator with a 0.5 V input bias
remove image frequencies when driving a modulator. The
level. For zero-IF applications, the AD9783 dual DAC provides
above interface lends itself well to the introduction of such a
an LVDS interface, while the CMOS-driven AD9788 dual DAC
filter. The filter can be inserted between the dc bias setting
can generate a fine resolution complex IF input to the I/Q
resistors and the ac swing-limiting resistor. Doing so establishes
modulator. The ADL5370/ADL5371/ADL5372/ADL5373/
the input and output impedances for the filter.
0 36
AD9779A LPI ADL5375-05 MAGNITUDE
93 771.1nH 21 –10 30
OUT1_P IBBP
RBIP
OUT1_N 9824R55B00IΩΩN 53.62Cn1FI 773775L11L0N..N.111QCnInp2HHFI 1R0S0LΩI 229 IBBN MAGNITUDE (dB) –––432000 GROUP DELAY 112284 GROUP DELAY (ns)
OUT2_N QBBN
RBQN
50Ω 53.62nF 350.1pF RSLQ –50 6
RBQP C1Q C2Q 100Ω
OUT2_P 83 50Ω 77L1P.1QnH 10 QBBP 08225-003 –601 FREQUE1N0CY (MHz) 1000 08225-004
Figure 3. DAC Modulator Interface with 10 MHz Third-Order, Low-Pass Filter Figure 4. Simulated Frequency Response for DAC Modulator Interface with
(Calculated Component Values) 10 MHz Third-Order Bessel Filter
Rev. A | Page 2 of 3