Texas Instruments THS4131 User manual

THS4131
EVM User's Guide for HighĆSpeed
Full ĆDifferential Amplifier
February 2001 Mixed-Signal Products
User’s Guide
SLOU110

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Copyright 2001, Texas Instruments Incorporated

iii
Read This First
Preface
About This Manual
This manual is written to provide information about the evaluation module of
the fully differential amplifier under test. Additionally, this document provides
a good example of PCB design for high speed applications. The user should
keep in mind the following points.
The design of the high-speed amplifier PCB is an elegant and sensitive
process. Therefore, the user must approach the PCB design with care and
awareness. It is recommend that the user initially review the datasheet of the
device under test. It is also helpful to review the schematic and layout of the
THS4131 EVM to determine the design techniques used in the evaluation
board.In addition, itis recommended thatthe user reviewthe application note
Fully-Differential Amplifiers (literature number SLOA054B) to gain more
insight about differential amplifiers. This application note reviews the
differential amplifiers and presents calculations for various filters.
How to Use This Manual
- Chapter 1—Introduction and Description
- Chapter 2—Using the THS4131 EVM
- Chapter 3—General High-Speed Amplifier Design Considerations

Related Documentation From Texas Instruments
iv
Information About Cautions and Warnings
This book may contain cautions and warnings.
This is an example of a caution statement.
A caution statement describes a situation that could potentially
damage your software or equipment.
This is an example of a warning statement.
A warning statement describes a situation that could potentially
cause harm to you.
The information in a caution or a warning is provided for your protection.
Please read each caution and warning carefully.
Related Documentation From Texas Instruments
- THS4131 data sheet (literature number SLOS318)
- THS4131 application report (literature number SLOA054A),
Fully-Differential Amplifiers
FCC Warning
This equipment is intended for use in a laboratory test environment only. It
generates, uses, and can radiate radio frequency energy and has not been
testedforcompliance withthelimits ofcomputingdevices pursuant tosubpart
Jofpart15ofFCCrules,whicharedesignedtoprovidereasonableprotection
against radio frequency interference. Operation of this equipment in other
environments may cause interference with radio communications, in which
case the user at his own expense will be required to take whatever measures
may be required to correct this interference.
Trademarks
PowerPAD is a trademark of Texas Instruments.

Running Title—Attribute Reference
v
Chapter Title—Attribute Reference
Contents
1 Introduction and Description 1-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1 Description 1-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Evaluation Module Features 1-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3 THS4131 EVM Specifications 1-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.4 Schematic of the Populated Circuit (Default Configuration) 1-3. . . . . . . . . . . . . . . . . . . . . . .
1.5 THS4131 EVM Schematic 1-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.6 Additional Sample Schematics 1-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.7 THS4131 EVM Layout 1-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 Using the THS4131 EVM 2-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1 Required Equipment 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 Power Supply Setup 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 Input and Output Setup 2-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4 Testing the EVM Setup 2-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5 Power Down Verification 2-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.6 Measuring the Frequency Response 2-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.7 Butterworth Filter 2-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.8 THS4131 EVM Bill of Materials 2-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 General High-Speed Amplifier Design Considerations 3-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Running Title—Attribute Reference
vi
Figures
1–1 Schematic of the Populated Circuit on the EVM (Default Configuration) 1-3. . . . . . . . . . . . . .
1–2 Schematic 1-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1–3 Fully-Differential In/Fully-Differential Out, Without Transformer 1-5. . . . . . . . . . . . . . . . . . . . . .
1–4 Fully-Differential In/Fully-Differential Out, Utilizing Transformer 1-5. . . . . . . . . . . . . . . . . . . . . .
1–5 VICR Level Shifter 1-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1–6 Butterworth Filter With Multiple Feedback 1-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1–7 Top Layer (Silkscreen) 1-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1–8 Top (Layer 1) (Signals) 1-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1–9 Internal Plane (Layer 2) (Ground Plane) 1-8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1–10 Internal Plane (Layer 3) (+ VCC Plane) 1-8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1–11 Bottom (Layer 4) (Ground and Signal) 1-9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2–1 Power Supply Connection 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2–2 Signal Connections 2-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2–3 Driver 1 Output Signal 2-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2–4 Multiple Feedback Filter Circuit 2-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2–5 Gain vs Phase 2-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tables
2–1 THS4131 EVM Bill of Materials 2-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-1
Introduction and Description
Introduction and Description
The Texas Instruments THS4131 evaluation module (EVM) helps designers
evaluate the performance of the THS4131 operational amplifier. Also, this
EVM is a good example of high-speed PCB design.
This document details the Texas Instruments THS4131 high-speed
operational amplifier evaluation module (EVM). It includes a list of EVM
features,abriefdescriptionofthemoduleillustratedwithaseriesofschematic
diagrams, EVM specifications, details on connecting and using the EVM, and
a discussion of high-speed amplifier design considerations.
ThisEVMenablestheusertoimplementvariouscircuitstoclarifytheavailable
configurations presented by the schematic of the EVM. In addition, the
schematic of the default circuit has been added to depict the components
mounted on the EVM when it is received by the customer. This configuration
correlates to the single input/differential output signal.
Othersamplecircuitsarepresentedtoshowhowtheusercanimplementother
circuit configurations such as differential input/differential output signal,
transformer utilization on the input and output terminals, VICR level shifter,
and Butterworth filter with multiple feedback. The user may be able to create
and implement circuit configurations in addition to those presented in this
document using the THS4131 EVM.
Topic Page
1.1 Description 1-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Evaluation Module Features 1-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3 THS4131 EVM Specification 1-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.4 Schematic of the Populated Circuit (Default Configuration) 1-3. . . . . . .
1.5 THS4131 EVM Schematic 1-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.6 Additional Sample Schematics 1-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.7 THS4131 EVM Layout 1-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 1

Description
1-2
Introduction and Description
1.1 Description
The THS4131 EVM is a good example of PCB design and layout for
high-speed operational amplifier applications. It is a complete circuit for the
high-speed operational amplifier. The EVM is made of the THS4131
high-speed operational amplifier, a number of passive components, and
various features and footprints that enable the user to experiment, test, and
verify various operational amplifier circuit implementations. The board
measures 4.5 inches in length by 2.5 inches in width. Initially, this board is
populated for a single-ended input amplifier (see Figure 1-2 for populated
circuits). The outputs (VO+ and VO–) can be tested differentially or single
ended. Gain is set to one and can be changed by changing the ratios of the
feedback and gain resistors (see the device datasheet for recommended
resistor values). The user may populate various footprints on the evaluation
moduleboard to verifyfilter designsor perform other experiments. Eachinput
isterminatedwitha50-Ωresistorto provide correctline-impedancematching.
1.2 Evaluation Module Features
THS4131 high-speed operational amplifier EVM features include:
J Voltage supply operation range: 5-V to ±15-V operation (see the
device data sheet)
J Single and differential input and output capability
J Nominal 50-Ωinput and output termination resistors. They can be
configured according to the application requirement.
J VOCM direct input control (see schematic and the device data sheet)
J VOCM pin can be controlled via transformer center-tap (see
schematic)
J Shutdown pin control, JU1 (if applicable to the device, see the device
data sheet)
J Input and output transformer footprints for changing single-ended
signals to differential signals
J Footprint for high-precision, balanced feedback and gain resistors
(0.01% or better)
J Footprints for low-pass filter implementation (see application note
SLOA054A)
J Footprints for antialiasing filter implementation (see application note
SLOA054A)
J Differential probe terminals on input and output nodes for differential
probe insertion
J Various GND and signal test points on the PCB
J Circuit schematic printed on the back of the EVM
J A good example of high-speed amplifier PCB design and layout

THS4131 EVM Specifications
1-3
Introduction and Description
1.3 THS4131 EVM Specifications
Supply voltage range, ±VCC 5 V to ±15 V (see the device data sheet). . . .
Supply current, ICC (see the device data sheet). . . . . . . . . . . . . . . . . . . . . . . .
Output drive, IO, VCC = ±15 (see the device data sheet). . . . . . . . . . . . . . . . .
For complete THS4131 amplifier IC specifications, parameter measurement
information, and additional application information, see the THS4131 data
sheet, TI literature number SLOS318.
1.4 Schematic of the Populated Circuit (Default Configuration)
For verification of jumper locations and other bypass components, see the
complete EVM schematic in Figure 1–2.
Figure 1–1.Schematic of the Populated Circuit on the EVM (Default Configuration)
374 Ω
+
–
THS4131
–
+
VCC
VCC–
402 Ω
0 Ω
0 Ω
VIN
AC 0 Ω
0 Ω
RX1
0 Ω
R1b
R1a 374 Ω
R3b
R3a
R6a
C1 VOCM
C4
C6
R4b
R4a 0 Ω
0 Ω
Rx4
Rx5 49.9 Ω
49.9 Ω
R10
Rx6
50 Ω
Source
NOTE: Default populated footprints on the EVM from the input nodes to the output terminals Gain = 1
402 Ω
R6B
RX3
49.9 Ω
JU4
JU3
Rx0
24.9 Ω

THS4131 EVM Schematic
1-4
Introduction and Description
1.5 THS4131 EVM Schematic
Figure 1–2.Schematic

Additional Sample Schematics
1-5
Introduction and Description
1.6 Additional Sample Schematics
For verification of jumper locations and other bypass components, see the
complete EVM schematic in Figure 1–2.
Figure 1–3.Fully-Differential In/Fully-Differential Out, Without Transformer
+
–
THS4131
–
+
VCC
VCC–
VIN
AC 0 Ω
0 Ω
RX1
0 Ω
RX2
R1b
R1a
R6a
C1 VOCM
C4
C6
R4b
R4a 0 Ω
0 Ω
Rx4
Rx5
R10
Rx6
50 Ω
Source
R3B
0 Ω
0 Ω
0 Ω
R16 Termination
Resistor
R3a
R6b
Note: Fully-differential in / fully-differential out signal path. See the Texas Instruments February 2001 AnalogApplications
Journal for the information on the termination resistors
.
Figure 1–4.Fully-Differential In/Fully-Differential Out, Utilizing Transformer
+
–
THS4131
–
+
VCC
GND
VIN
AC 0 Ω
0 Ω
R1B
R1A
R3b
R3a
R6a
C1 VOCM
C4
C6
R4b
R4a 0 Ω
0 Ω
R14
R15
R10
Rx6
50 Ω
Source
R6b
R5
R9
T1 T2
Note: Utilizingtheinputandoutputtransformerstocreateafully-differentialsignalinput/differentialor singleoutputandisolate
the amplifier from the rest of the front-end and back-end circuits.

Additional Sample Schematics
1-6
Introduction and Description
Figure 1–5.VICR Level Shifter
+
–
THS4131
–
+
VCC
402 Ω
24.9 Ω
0 Ω
VIN
AC 0 Ω
0 Ω
RX1
0 Ω
R1b
Rx0 374 Ω
R3b
R3a
374 Ω
R6a
C1 VOCM
C4
C6
R4b
R4a 0 Ω
0 Ω
Rx4
Rx5 49.9 Ω
49.9 Ω
R10
Rx6
50 Ω
Source
402 Ω
R6B
RX3
49.9 Ω
VCC
RPU1
RPU2
VCC–
Note: ShiftingtheVICRwithinthespecifiedrangeinthedatasheetviaRPU1andRPU2iftheVICRisoutofthespecifiedrange.
See the Application section of the data sheet for the THS4131 for more information.
Figure 1–6.Butterworth Filter With Multiple Feedback.
+
–
THS4131
–
+
VCC
VCC–
1 dBm
AC
RX1
RX2
R1B
R1A
R2A
R10
RX7
R2B
RX3
R7 R3A
C2
R3B
–5 V
5 V
C1B
C1A
Note: Butterworth filter implemented with multiple feedback architecture

THS4131 EVM Layout
1-7
Introduction and Description
1.7 THS4131 EVM Layout
Figure 1–7.Top Layer (Silkscreen)
TEXAS INSTRUMENTS
THS4131 EVM
REV_B
Figure 1–8.Top (Layer 1) (Signals)
TEXAS INSTRUMENTS
THS4131 EVM
REV_B

THS4131 EVM Layout
1-8
Introduction and Description
Figure 1–9.Internal Plane (Layer 2) (Ground Plane)
Figure 1–10. Internal Plane (Layer 3) ( ± V
CC
Plane)

THS4131 EVM Layout
1-9
Introduction and Description
Figure 1–11. Bottom (Layer 4) (Ground and Signal)

1-10
Introduction and Description

2-1
Using the THS4131 EVM
Using the THS4131 EVM
It is recommended that the user perform the following exercises to learn the
usage of the EVM. This practice helps the user learn about the various
terminals on the EVM and their function. In addition, it suggests the
components and equipment needed to operate the EVM.
Topic Page
2.1 Required Equipment 2–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 Power Supply Setup 2–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 Input and Output Setup 2–3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4 Testing the EVM Setup 2–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5 Power Down Verification 2–5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.6 Measuring the Frequency Response 2–5. . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.7 Butterworth Filter 2–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.8 THS4131 EVM Bill of Materials 2–7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 2

2-2
Using the THS4131 EVM
2.1 Required Equipment
- One double-output dc power supply (±5 V, 100 mA output minimum)
- Two dc current meters with resolution to 1 mA and capable of the
maximum current the dc power supply can supply. If available, set the
current limit on the dc power supply to 100 mA.
Note: Some power supplies incorporate current meters which may be
applicable to this test.
- 50-Ωsource impedance function generator (1 MHz, 10 VPP sine wave)
- Oscilloscope (50-MHz bandwidth minimum, 50-Ωinput impedance).
2.2 Power Supply Setup
1) Set the dc power supply to ±5 V.
2) Makesure thedc power supply is turnedoffbefore proceedingto thenext
step.
3) Connect the positive (+) terminal of the power supply to the positive (+)
terminal of the current meter number 1.
4) Connect the negative (–) terminal of the current meter number 1 to the
VCC+ of the EVM (J7).
5) Connect the common ground terminal of the power supply to the ground
GND on the EVM (J9).
6) Connect the negative (–) terminal of the power supply to the negative (–)
terminal of the second current meter.
7) Connectthepositive(+)terminalofthecurrentmeternumber2totheVCC–
of the EVM (J8).
Figure 2–1.Power Supply Connection
POWER SUPPLY
GND–5V +5V
+– +–
CURRENT
METER 2 CURRENT METER 1
J8 VCC– J9 GND
J7 VCC+ J6 VOCM
EVM
THS4131
Figures are not drawn to scale.

2-3
Using the THS4131 EVM
2.3 Input and Output Setup
1) Ensure that JU3, JU4, and JU1 are not installed (open circuit) .
2) Setthe function generatorto generatea 1MHz, ±0.5 V (1 VPP)sine wave
with no dc offset.
3) Turn off the function generator before proceeding to the next step.
4) Using a BNC-to-SMA cable, connect the function generator to J1 (VI+) on
the EVM.
5) Using a BNC-to-SMA cable, connect the oscilloscope to J3 (VO–) on the
EVM.
6) Using a BNC-to-SMA cable, connect the oscilloscope to J4 (VO+) on the
EVM. Set the oscilloscope to 0.5 V/division and a time-base of 0.2
µs/division.
Note: The oscilloscope must be set to use a 50-Ωinput impedance for
proper results.
Figure 2–2.Signal Connections
OUT
1 MHz
1 VPP
0 V Offset
50 ΩSource
Impedance
J1 Vin+ J3 Vout–
J4 Vout+
CH-1 CH-2
THS4131 EVM
FUNCTION
GENERATOR
OSCILLOSCOPE
50 ΩImpedance
Figures are not drawn to scale.

2-4
Using the THS4131 EVM
2.4 Testing the EVM Setup
1) Turn on the dc power supply.
2) Verify that both the +5 V (current meter 1) and the –5 V (current meter 2)
currents are below 20 mA.
Caution:
Currentsabove20mAindicateapossibleshortorawrongresistorvalue
on the PCB. Do not proceed until this situation is corrected.
3) Turn on the function generator.
4) Verify the oscilloscope is showing two 1 MHz sine waves with amplitude
of ±0.125 V. The dc offset of the signal must be below 50 mV.
Note:VOUT+andVOUT–shouldbe180degreesoutofphase.Theinternal
attenuationofthescopeshouldbesetto6dBforagainofone.Otherwise,
theoutputwillshowa gainofone-half duetothevoltagedivisionoccurring
at the 50-Ωtermination resistor.
Use Figure 3 as a reference for the input and output signals.
Figure 2–3.Driver 1 Output Signal
THS4131
C3
C2
C1