User’s Guide
September 2000 Mixed-Signal Products
SLOU075
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Copyright 2000, Texas Instruments Incorporated
Related Documentation From Texas Instruments
THS4081, THS4082 175-MHz LOW-POWER HIGH-SPEED
AMPLIFIERS
for the THS4082 operational amplifier integrated circuit that is
used in the THS4082 evaluation module.
(literature number SLOS274) This is the data sheet
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
tested for compliance with the limits of computing devices pursuant to subpart
J of part 15 of FCC rules, which are designed to provide reasonable protection
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.
Preface
Trademarks
TI is a trademark of Texas Instruments Incorporated.
PowerPAD is a trademark of Texas Instruments Incorporated.
Chapter Title—Attribute Reference
iii
iv
Running Title—Attribute Reference
Contents
1 General 1-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1 Feature Highlights 1-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Description 1-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3 THS4082 EVM Noninverting Operation 1-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.4 Using the THS4082 EVM in the Noninverting Mode 1-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.5 THS4082 EVM Inverting Operation 1-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.6 Using the THS4082 EVM in the Inverting Mode 1-9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.7 THS4082 EVM Differential Input 1-10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.7.1 Differential Input, Noninverting Operation 1-10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.7.2 Differential Input, Inverting Operation 1-11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.8 Using the THS4082 EVM With Differential Inputs 1-14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.9 THS4082 EVM Specifications 1-14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.10 THS4082 EVM Performance 1-15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.11 General High-Speed Amplifier Design Considerations 1-16. . . . . . . . . . . . . . . . . . . . . . . . . .
1.12 General PowerPAD Design Considerations 1-17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 Reference 2-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1 THS4082 EVM Complete Schematic 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 THS4082 Dual High-Speed Operational Amplifier EVM Parts List 2-3. . . . . . . . . . . . . . . . .
2.3 THS4082 EVM Board Layouts 2-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter Title—Attribute Reference
v
Running Title—Attribute Reference
Figures
1–1 THS4082 Evaluation Module 1-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1–2 THS4082 EVM Schematic: Noninverting Operation 1-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1–3 THS4082 EVM Schematic: Inverting Operation 1-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1–4 THS4082 EVM Schematic: Differential Input (Noninverting Operation) 1-10. . . . . . . . . . . . . .
1–5 THS4082 EVM Schematic: Differential Input (Inverting Operation) 1-12. . . . . . . . . . . . . . . . . .
1–6 THS4082 EVM Frequency Response With Gain = 2 1-15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1–7 THS4082 EVM Phase Response With Gain = 2 1-15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1–8 PowerP AD PCB Etch and Via Pattern 1-17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1–9 Maximum Power Dissipation vs Free-Air Temperature 1-18. . . . . . . . . . . . . . . . . . . . . . . . . . . .
2–1 THS4082 EVM Schematic 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2–2 THS4082 EVM Component Placement Silkscreen and Solder Pads 2-4. . . . . . . . . . . . . . . . .
2–3 THS4082 EVM PC Board Layout: Component Side 2-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2–4 THS4082 EVM PC Board Layout: Back Side 2-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
T ables
2–1 THS4082 EVM Parts List 2-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vi
Chapter 1
General
This chapter details the Texas Instruments (TI) THS4082 dual high-speed
operational amplifier evaluation module (EVM), SLOP239. It includes a list of
EVM features, a brief description of the module illustrated with a pictorial and
a schematic diagram, EVM specifications, details on connecting and using the
EVM, and discussions on high-speed amplifier design and thermal
considerations.
Topic Page
1.1 Feature Highlights 1–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Description 1–3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3 THS4082 EVM Noninverting Operation 1–4. . . . . . . . . . . . . . . . . . . . . . . . . .
1.4 Using the THS4082 EVM in the Noninverting Mode 1–6. . . . . . . . . . . . . . .
1.5 THS4082 EVM Inverting Operation 1–7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.6 Using the THS4082 EVM in the Inverting Mode 1–9. . . . . . . . . . . . . . . . . .
1.7 THS4082 EVM Differential Input 1–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.8 Using the THS4082 EVM With Differential Inputs 1–14. . . . . . . . . . . . . .
1.9 THS4082 EVM Specifications 1–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.10 THS4082 EVM Performance 1–15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.11 General High-Speed Amplifier Design Considerations 1–16. . . . . . . . .
1.12 General PowerPAD Design Considerations 1–17. . . . . . . . . . . . . . . . . . . .
1-1
Feature Highlights
1.1 Feature Highlights
THS4082 dual high-speed operational amplifier EVM features include:
High Bandwidth: 75 MHz, –3 dB at ±15 V
±5-V to ±15-V Operation
Noninverting Single-Ended Inputs: Inverting-Capable Through Com-
& Gain = 2
CC
ponent Change
Module Gain Set to 2 (Noninverting): Adjustable Through Component
Change
Nominal 50-Ω Impedance Inputs and Outputs
Standard SMA Input and Output Connectors
Good Example of High-Speed Amplifier Design and Layout
1-2
General
1.2 Description
The TI THS4082 dual high-speed operational amplifier evaluation module
(EVM) is a complete dual high-speed amplifier circuit. It consists of the TI
THS4082 dual low-noise high-speed operational amplifier IC, along with a
small number of passive parts, mounted on a small circuit board measuring
approximately 1.9 inch by 2.2 inch (Figure 1–1). The EVM uses standard SMA
miniature RF connectors for inputs and outputs and is completely assembled,
tested, and ready to use—just connect it to power, a signal source, and a load
(if desired).
Figure 1–1.THS4082 Evaluation Module
Description
J1
VIN1
J4
VIN2
C1
R8
–VCC
+
R1
R2R3R4R5R6C3R7
C4
R9
R10
GND
J2
U1
C5
R11
R12
R13
R14C6R15
+VCC
C2
+
J3
VOUT1
TEXAS
INSTRUMENTS
J5
VOUT2
Note: The EVM is shipped with the following component locations empty:
C3, C6, R2, R4, R8, R10, and R12.
Although the THS4082 EVM is shipped with components installed for
dual-channel single-ended noninverting operation, it can also be configured
for single-channel differential and/or inverting operation by moving
components. Noninverting gain is set to 2 with the installed components. The
input of each channel is terminated with a 50-Ω impedance to provide correct
line impedance matching. The amplifier IC outputs are routed through 50-Ω
resistors, both to provide correct line impedance matching and to help isolate
capacitive loading on the outputs of the amplifier. Capacitive loading directly
on the output of the IC decreases the amplifier’s phase margin and can result
in peaking or oscillations.
SLOP239
THS4082 EVM Board
General
1-3
THS4082 EVM Noninverting Operation
1.3 THS4082 EVM Noninverting Operation
The THS4082 EVM is shipped preconfigured for dual-channel noninverting
operation, as shown in Figure 1–2.
Note:
Compensation capacitors C3 and C6 are not installed.
Figure 1–2.THS4082 EVM Schematic: Noninverting Operation
C3
x µF
R6
1 kΩ
C5
0.1 µF
U1:A
THS4082
1
C4
0.1 µF
–VCC
GND
+VCC
J2
1
2
3
C1
6.8 µF
VIN1
J1
C2
6.8 µF
R1
49.9 Ω
–VCC
+VCC
R5
1 kΩ
R3
0 Ω
2
3
+VCC
–
+
8
4
R7
49.9 Ω
J3
VOUT1
VIN2
J4
R9
49.9 Ω
R13
1 kΩ
R11
0 Ω
–VCC
6
–
+
5
x µF
R14
1 kΩ
U1:B
THS4082
7
C6
R15
49.9 Ω
J5
The gain of the EVM can easily be changed to support a particular application
by simply changing the ratio of resistors R6 and R5 (channel 1) and R14 and
R13 (channel 2) as described in the following equation:
Noninverting Gain 1
R
R
F
1
G
R6
R5
and 1
R14
R13
In addition, some applications, such as those for video, may require the use
of a 75-Ω cable and 75-Ω EVM input termination and output isolation resistors.
VOUT2
1-4
General
THS4082 EVM Noninverting Operation
Any of the resistors on the EVM board can be replaced with a resistor of a
different value; however, care must be taken because the surface-mount
solder pads on the board are somewhat fragile and will not survive many
desoldering/soldering operations.
Note:
External factors can significantly affect the effective gain of the EVM. For example, connecting test equipment with 50-Ω input impedance to the EVM
output will divide the output signal level by a factor of 2 (assuming the output
isolation resistor on the EVM board remains 50 Ω). Similar effects can occur
at the input, depending upon how the input signal sources are configured.
The gain equations given above assume no signal loss in either the input or
the output.
Frequency compensation capacitors C3 and C6 may need to be installed to
improve stability at lower gains. The appropriate value depends on the
particular application.
The EVM circuit board is an excellent example of proper board layout for
high-speed amplifier designs and can be used as a guide for user application
board layouts.
General
1-5
Using the THS4082 EVM in the Noninverting Mode
1.4 Using the THS4082 EVM in the Noninverting Mode
The THS4082 EVM operates from power-supply voltages ranging from ±5 V
to ±15 V. As shipped, the EVM is configured for noninverting operation and the
gain is set to 2. Signal inputs on the module are terminated for 50-Ω nominal
source impedance. An oscilloscope is typically used to view and analyze the
EVM output signal.
1) Ensure that all power supplies are set to OFF before making power supply
connections to the THS4082 EVM.
2) Connect the power supply ground to the module terminal block (J2)
location marked GND.
3) Select the operating voltage for the EVM and connect appropriate split
power supplies to the module terminal block (J2) locations marked –VCC
and +VCC.
4) Connect an oscilloscope to the module SMA output connector
through a 50-Ω nominal impedance cable (an oscilloscope having a 50-Ω
input termination is preferred for examining very high frequency signals).
5) Set the power supply to ON.
(J3/J5)
6) Connect the signal input to the module SMA input connector (J1/J4).
Note:
Each EVM input connector is terminated with a 50-Ω impedance to ground.
With a 50-Ω source impedance, the voltage seen by the THS4082 amplifier
IC on the module will be 1/2 the source signal voltage applied to the EVM.
This is due to the voltage division between the source impedance and the
EVM input terminating resistors (R1, R9).
7) Verify the output signal on the oscilloscope.
Note:
The signal shown on an oscilloscope with a 50-Ω input impedance will be 1/2
the actual THS4082 amplifier IC output voltage. This is due to the voltage
division between the output resistor (R7, R15) and the oscilloscope input impedance.
1-6
General
1.5 THS4082 EVM Inverting Operation
Although the THS4082 EVM is shipped preconfigured for dual-channel
noninverting operation, it can be reconfigured for inverting operation by
making the following component changes:
1) Move resistor R3 to the R2 location and R5 to the R4 location on the board.
2) Move resistor R1 1 to the R10 location and R13 to the R12 location on the
board.
This configuration is shown in Figure 1–3.
Note:
Compensation capacitors C3 and C6 are not installed.
Figure 1–3.THS4082 EVM Schematic: Inverting Operation
THS4082 EVM Inverting Operation
–VCC
GND
+VCC
J2
1
2
3
6.8 µF
C1
VIN1
J1
C2
6.8 µF
R1
49.9 Ω
–VCC
+VCC
R4
1 kΩ
2
3
R2
0 Ω
+VCC
–
+
–VCC
8
4
C3
x µF
R6
1 kΩ
C5
0.1 µF
U1:A
THS4082
1
C4
0.1 µF
C6
x µF
R14
1 kΩ
R7
49.9 Ω
J3
VOUT1
J4
VIN2
R9
49.9 Ω
R12
1 kΩ
6
5
R10
0 Ω
–
+
U1:B
THS4082
7
R15
49.9 Ω
General
J5
VOUT2
1-7
THS4082 EVM Inverting Operation
The gain of the EVM can easily be changed to support a particular application
by simply changing the ratio of resistors R6 and R4 (channel 1) and R14 and
R12 (channel 2) as described in the following equation:
Inverting Gain
–R
R
–R6
F
R4
G
and
–R14
R12
In addition, some applications, such as those for video, may require the use
of 75-Ω cable and 75-Ω EVM input termination and output isolation resistors.
Because the noninverting terminals are at ground potential, the inverting
terminal becomes a
virtual ground
and is held to 0 V. This causes the input
impedance to ground at the input terminal to look like two resistors in parallel
(R1 and R4 for channel 1, and R9 and R12 for channel 2). As a result, if the
source termination is changed, R1 and R9 must be adjusted in accordance
with the following equations:
R1
R4 R
R4–R
T
(Channel 1) and R9
T
R12 R
R4–R
T
(Channel 2)
T
where RT is the source impedance.
Any of the resistors on the EVM board can be replaced with a resistor of a
different value; however, care must be taken because the surface-mount
solder pads on the board are somewhat fragile and will not survive many
desoldering/soldering operations.
Note:
External factors can significantly affect the effective gain of the EVM. For example, connecting test equipment with 50-Ω input impedance to the EVM
output will divide the output signal level by a factor of 2 (assuming the output
isolation resistor on the EVM board remains 50 Ω). Similar effects can occur
at the input, depending upon how the input signal sources are configured.
The gain equations given above assume no signal loss in either the input or
the output.
Frequency compensation capacitors C3 and C6 may need to be installed to
improve stability at lower gains. The appropriate value depends on the
particular application.
1-8
General
Using the THS4082 EVM in the Inverting Mode
1.6 Using the THS4082 EVM in the Inverting Mode
The THS4082 EVM operates from power-supply voltages ranging from ±5 V
to ±15 V. As shipped, the EVM is configured for noninverting operation. Move
the resistors as detailed above to configure the EVM for noninverting
operation, which sets the gain to –1. Signal inputs on the module are
terminated for 50-Ω nominal source impedance. An oscilloscope is typically
used to view and analyze the EVM output signal.
1) Ensure that all power supplies are set to OFF before making power supply
connections to the THS4082 EVM.
2) Connect the power supply ground to the module terminal block (J2)
location marked GND.
3) Select the operating voltage for the EVM and connect appropriate split
power supplies to the module terminal block (J2) locations marked –VCC
and +VCC.
4) Connect an oscilloscope to the module SMA output connector
through a 50-Ω nominal impedance cable (an oscilloscope having a 50-Ω
input termination is preferred for examining very high frequency signals).
(J3/J5)
5) Set the power supply to ON.
6) Connect the signal input to the module SMA input connector (J1/J2).
Note:
Each EVM input connector is terminated with an equivalent 50-Ω impedance
to ground. With a 50-Ω source impedance, the voltage seen by the THS4082
amplifier IC on the module will be the source signal voltage applied to the
EVM. This is due to the voltage division between the source impedance and
the EVM input terminating resistors (R1||R4 and R9||R12).
7) Verify the output signal on the oscilloscope.
Note:
The signal shown on an oscilloscope with a 50-Ω input impedance will be 1/2
the actual THS4082 amplifier IC output voltage. This is due to the voltage
division between the output resistor (R7, R15) and the oscilloscope input impedance.
General
1-9
THS4082 EVM Differential Input
1.7 THS4082 EVM Differential Input
The THS4082 EVM is shipped preconfigured for dual-channel, single-ended
noninverting operation. It can be reconfigured for single-channel, differential
operation, either noninverting or inverting.
1.7.1 Differential Input, Noninverting Operation
Configure the THS4082 EVM for differential noninverting operation by
removing two resistors and adding a resistor on the board:
1) Remove resistors R1 and R9.
2) Add a 100-Ω resistor to the R8 location on the board.
This configuration (noninverting) is shown in Figure 1–4. For a noninverting
differential input, R8 should be 100 Ω to match 50-Ω source impedances.
Note:
Compensation capacitors C3 and C6 are not installed.
Figure 1–4.THS4082 EVM Schematic: Differential Input (Noninverting Operation)
C3
x µF
R6
1 kΩ
C5
0.1 µF
–VCC
GND
+VCC
J2
1
2
3
C1
6.8 µF
C2
6.8 µF
–VCC
+VCC
R5
1 kΩ
+VCC
VIN1
VIN2
J1
J4
R8
100 Ω
R3
0 Ω
R13
1 kΩ
R11
0 Ω
2
–
THS4082
4
1
C4
0.1 µF
C6
x µF
R14
1 kΩ
U1:B
THS4082
7
+
3
–VCC
6
–
+
5
R7
49.9 Ω
R15
49.9 Ω
J3
VOUT1
J5
VOUT2
U1:A
8
1-10
General
THS4082 EVM Differential Input
The gain of the EVM can easily be changed to support a particular application
by simply changing the ratio of resistors R6 and R5 (channel 1) and R14 and
R13 (channel 2) as described in the following equation:
Noninverting Gain 1
R
R
F
1
G
R6
R5
and 1
R14
R13
In addition, some applications, such as those for video, may require the use
of 75-Ω cable and 75-Ω EVM input termination and output isolation resistors.
Any of the resistors on the EVM board can be replaced with a resistor of a
different value; however, care must be taken because the surface-mount
solder pads on the board are somewhat fragile and will not survive many
desoldering/soldering operations.
Note:
External factors can significantly affect the effective gain of the EVM. For example, connecting test equipment with 50-Ω input impedance to the EVM
output will divide the output signal level by a factor of 2 (assuming the output
isolation resistor on the EVM board remains 50 Ω). Similar effects can occur
at the input, depending upon how the input signal sources are configured.
The gain equations given above assume no signal loss in either the input or
the output.
Frequency compensation capacitors C3 and C6 may need to be installed to
improve stability at lower gains. The appropriate value depends on the
particular application.
The EVM circuit board is an excellent example of proper board layout for
high-speed amplifier designs and can be used as a guide for user application
board layouts.
1.7.2 Differential Input, Inverting Operation
Configure the THS4082 EVM for differential inverting operation by removing
two resistors and adding a resistor on the board:
1) Move resistor R3 to the R2 location and R5 to the R4 location on the board.
2) Move resistor R1 1 to the R10 location and R13 to the R12 location on the
board.
3) Remove resistors R1 and R9.
4) Add a 100-Ω resistor to the R8 location on the board.
This configuration (inverting) is shown in Figure 1–5.
Note:
Compensation capacitors C3 and C6 are not installed.
General
1-1 1
THS4082 EVM Differential Input
Figure 1–5.THS4082 EVM Schematic: Differential Input (Inverting Operation)
C3
x µF
R6
1 kΩ
C5
0.1 µF
–VCC
GND
+VCC
J2
1
2
3
C1
6.8 µF
C2
6.8 µF
–VCC
+VCC
+VCC
VIN1
VIN2
J1
J4
R8
100 Ω
R4
1 kΩ
R12
1 kΩ
2
3
R2
0 Ω
6
5
R10
0 Ω
–
+
–VCC
–
+
8
4
U1:A
THS4082
1
C4
0.1 µF
C6
x µF
R14
1 kΩ
U1:B
THS4082
7
R7
49.9 Ω
R15
49.9 Ω
J3
VOUT1
J5
VOUT2
The gain of the EVM inputs can easily be changed to support a particular
application by simply changing the ratio of resistors R6 and R4 (channel 1) and
R14 and R12 (channel 2) as described in the following equation:
Note that R4 and R12 form part of the input impedance and R8 should be
adjusted in accordance with the following equation:
where RT is the termination resistance and R4 = R12.
In addition, some applications, such as those for video, may require the use
of 75-Ω cable and 75-Ω EVM input termination and output isolation resistors.
1-12
Inverting Gain
R8
2R4 R
R4–R
T
–R
R
T
–R6
F
R4
G
and
–R14
R12
General
THS4082 EVM Differential Input
Any of the resistors on the EVM board can be replaced with a resistor of a
different value; however, care must be taken because the surface-mount
solder pads on the board are somewhat fragile and will not survive many
desoldering/soldering operations.
Note:
External factors can significantly affect the effective gain of the EVM. For example, connecting test equipment with 50-Ω input impedance to the EVM
output will divide the output signal level by a factor of 2 (assuming the output
isolation resistor on the EVM board remains 50 Ω). Similar effects can occur
at the input, depending upon how the input signal sources are configured.
The gain equations given above assume no signal loss in either the input or
the output.
Frequency compensation capacitors C3 and C6 may need to be installed to
improve stability at lower gains. The appropriate value depends on the
particular application.
The EVM circuit board is an excellent example of proper board layout for
high-speed amplifier designs and can be used as a guide for user application
board layouts.
General
1-13
Using the THS4082 EVM With Differential Inputs
1.8 Using the THS4082 EVM With Differential Inputs
The THS4082 EVM operates from power-supply voltages ranging from ±5 V
to ±15 V. Move resistors on the board as detailed above for either noninverting
or inverting operation to configure the EVM for differential input operation.
Signal inputs on the module are terminated for 50-Ω nominal source
impedance. An oscilloscope is typically used to view and analyze the EVM
output signal.
1) Ensure that all power supplies are set to OFF before making power supply
connections to the THS4082 EVM.
2) Connect the power supply ground to the module terminal block (J2)
location marked GND.
3) Select the operating voltage for the EVM and connect appropriate split
power supplies to the module terminal block (J2) locations marked –VCC
and +VCC.
4) Connect an oscilloscope across the module SMA output connectors
(J3
and J5) through a 50-Ω nominal impedance cable (an oscilloscope having
a 50-Ω input termination is preferred for examining very high frequency
signals).
5) Set the power supply to ON.
6) Connect the differential signal input across the module SMA input connectors (J1 and J4).
Note:
The differential EVM input is terminated with an equivalent 50-Ω impedance
for each input. With a 50-Ω source impedance, the voltage seen by the
THS4082 amplifier IC on the module will be 1/2 the source signal voltage applied to the EVM. This is due to the voltage division between the source impedance and the EVM equivalent input resistance.
7) Verify the differential output signal on the oscilloscope.
Note:
The signal shown on an oscilloscope with a 50-Ω input impedance will be 1/4
the actual THS4082 amplifier IC output voltage. This is due to the voltage
division between the output resistors (R7, R15) and the oscilloscope input
impedance.
1.9 THS4082 EVM Specifications
Supply voltage range, ±V
Supply current, I
Input voltage, V
Output drive, I
1-14
CC
I
O
For complete THS4082 amplifier IC specifications, parameter measurement
information, and additional application information, see the THS4082 data
sheet, TI literature number SLOS274.
CC
±5 V to ±15 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 mA typ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
±VCC, max. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
65 mA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
General
1.10 THS4082 EVM Performance
Figure 1–6 shows the typical frequency response of the THS4082 EVM using
the noninverting configuration (G = 2). Typical –0.1 dB bandwidth is 22 MHz
and –3-dB bandwidth is 75 MHz with both a ±15-V power supply and a ±5-V
power supply.
Figure 1–6.THS4082 EVM Frequency Response With Gain = 2
7
6
5
4
3
2
Output Amplitude – dB
1
VCC = ±5 V and ±15 V
0
VI = 0.1 VRMS
RL = 100 Ω
–1
100k 1G1M
f – Frequency – Hz
100M10M
THS4082 EVM Performance
Figure 1–7 shows the typical phase response of the THS4082 EVM using the
noninverting configuration (G = 2).
Figure 1–7.THS4082 EVM Phase Response With Gain = 2
30
0
–30
–60
–90
Output Phase – °
–120
–150
–180
VCC = ±5 V and ±15 V
VI = 0.1 VRMS
RL = 100 Ω
100k 1G1M
f – Frequency – Hz
100M10M
General
1-15
General High-Speed Amplifier Design Considerations
1.11 General High-Speed Amplifier Design Considerations
The THS4082 EVM layout has been designed and optimized for use with
high-speed signals and can be used as an example when designing THS4082
applications. Careful attention has been given to component selection,
grounding, power supply bypassing, and signal path layout. Disregard of these
basic design considerations could result in less than optimum performance of
the THS4082 high-speed, low-power operational amplifier.
Surface-mount components were selected because of the extremely low lead
inductance associated with this technology. Also, because surface-mount
components are physically small, the layout can be very compact. This helps
minimize both stray inductance and capacitance.
T antalum power supply bypass capacitors (C1 and C2) at the power input pads
help supply currents for rapid, large signal changes at the amplifier output. The
0.1-µF power supply bypass capacitors (C4 and C5) were placed as close as
possible to the IC power input pins in order to keep the PCB trace inductance
to a minimum. This improves high-frequency bypassing and reduces
harmonic distortion.
A proper ground plane on both sides of the PCB should always be used with
high-speed circuit design. This provides low-inductive ground connections for
return current paths. In the area of the amplifier IC input pins, however, the
ground plane was removed to minimize stray capacitance and reduce ground
plane noise coupling into these pins. This is especially important for the
inverting pin while the amplifier is operating in the noninverting mode. Because
the voltage at this pin swings directly with the noninverting input voltage, any
stray capacitance would allow currents to flow into the ground plane, causing
possible gain error and/or oscillation. Capacitance variations at the amplifier
IC input pin of less than 1 pF can significantly affect the response of the
amplifier.
In general, it is always best to keep signal lines as short and as straight as
possible. Round corners or a series of 45° bends should be used instead of
sharp 90° corners. Stripline techniques should also be incorporated when
signal lines are greater than 1 inch in length. These traces should be designed
with a characteristic impedance of either 50 Ω or 75 Ω, as required by the
application. Such signal lines should also be properly terminated with an
appropriate resistor.
Finally , proper termination of all inputs and outputs should be incorporated into
the layout. Unterminated lines, such as coaxial cable, can appear to be a
reactive load to the amplifier IC. By terminating a transmission line with its
characteristic impedance, the amplifier’s load then appears to be purely
resistive and reflections are absorbed at each end of the line. Another
advantage of using an output termination resistor is that capacitive loads are
isolated from the amplifier output. This isolation helps minimize the reduction
in amplifier phase-margin and improves the amplifier stability for improved
performance such as reduced peaking and settling times.
1-16
General
General PowerPADE Design Considerations
1.12 General PowerPAD Design Considerations
The THS4082DGN IC is mounted in a special package incorporating a thermal
pad that transfers heat from the IC die directly to the PCB. The PowerPAD
package is constructed using a downset leadframe. The die is mounted on the
leadframe but is electrically isolated from it. The bottom surface of the lead
frame is exposed as a metal thermal pad on the underside of the package and
makes physical contact with the PCB. Because this thermal pad is in direct
physical contact with both the die and the PCB, excellent thermal performance
can be achieved by providing a good thermal path away from the thermal pad
mounting point on the PCB.
Although there are many ways to properly heatsink this device, the following
steps illustrate the recommended approach as used on the THS4082 EVM.
1) Prepare the PCB with a top side etch pattern as shown in Figure 1–8.
There should be etch for the leads as well as etch for the thermal pad.
Figure 1–8.PowerPAD PCB Etch and Via Pattern
Thermal pad area (68 mils x 70 mils) with 5 vias
(Via diameter = 13 mils)
2) Place five holes in the area of the thermal pad. These holes should be 13
mils in diameter. They are kept small so that solder wicking through the
holes is not a problem during reflow.
3) Additional vias may be placed anywhere along the thermal plane outside
of the thermal pad area. This helps dissipate the heat generated by the
THS4082DGN IC. These additional vias may be larger than the 13-mil
diameter vias directly under the thermal pad. They can be larger because
they are not in the thermal pad area to be soldered so that wicking is not
a problem.
4) Connect all holes to the internal ground plane.
5) When connecting these holes to the ground plane, do not use the typical
web or spoke via connection methodology . Web connections have a high
thermal resistance connection that is useful for slowing the heat transfer
during soldering operations. This makes the soldering of vias that have
plane connections easier. In this application, however, low thermal
resistance is desired for the most efficient heat transfer. Therefore, the
holes under the THS4082DGN package should make their connection to
the internal ground plane with a complete connection around the entire
circumference of the plated-through hole.
6) The top-side solder mask should leave the terminals of the package and
the thermal pad area with its five holes exposed. The bottom-side solder
mask should cover the five holes of the thermal pad area. This prevents
solder from being pulled away from the thermal pad area during the reflow
process.
7) Apply solder paste to the exposed thermal pad area and all of the IC
terminals.
General
1-17
General PowerPADE Design Considerations
8) With these preparatory steps in place, the THS4082DGN IC is simply
placed in position and run through the solder reflow operation as any
standard surface-mount component. This results in a part that is properly
installed.
The actual thermal performance achieved with the THS4082DGN in its
PowerPAD package depends on the application. In the example above, if the
size of the internal ground plane is approximately 3 inches × 3 inches, then the
expected thermal coefficient, θ
non-PowerPAD version of the THS4082 IC (D-package in SOIC) is shown.
For a given θ
JA
is calculated by the following formula:
P
D
Where:
P
D
T
MAX
T
A
θ
JA
, is about 58.4C/W. For comparison, the
JA
, the maximum power dissipation is shown in Figure 1–9 and
T
MAX–TA
JA
= Maximum power dissipation of THS4082 IC (watts)
= Absolute maximum junction temperature (150°C)
= Free-ambient air temperature (°C)
= θ
+ θ
JC
CA
θJC= Thermal coefficient from junction to case (4.7°C/W)
for THS4082DGN (PowerPAD)
θJC= Thermal coefficient from junction to case (38.3°C/W)
for THS4082D (SOIC)
θCA= Thermal coefficient from case to ambient air (°C/W)
Figure 1–9.Maximum Power Dissipation vs Free-Air Temperature
3.5
TJ = 150°C
3
2.5
2
1.5
1
Maximum Power Dissipation – W
.5
0
DGN Package
θJA = 158°C/W
2 oz Trace and
Copper Pad
without Solder
THS4082
SOIC – Package
θJA = 166.7°C/W
–20 80
0–40
TA – Free-Air Temperature – °C
Even though the THS4082 EVM PCB is smaller than the one in the example
above, the results should give an idea of how much power can be dissipated
by the PowerPAD IC package. The THS4082 EVM is a good example of
proper thermal management when using PowerPAD-mounted devices.
No Air Flow
DGN Package
θJA = 58.4°C/W
2 oz Trace and
Copper Pad
with Solder
6020 40
100
1-18
General
General PowerPADE Design Considerations
Correct PCB layout and manufacturing techniques are critical for achieving
adequate transfer of heat away from the PowerPAD IC package. More
details on proper board layout can be found in the
175-MHz Low-Power High-Speed Amplifiers
data sheet (literature number
THS4081, THS4082
SLOS274). For more general information on the PowerP AD package and its
thermal characteristics, see the Texas Instruments Technical Brief,
PowerPAD Thermally Enhanced Package
PowerPad Made Easy
the
application brief (literature number SLMA004).
(literature number SLMA002) and
General
1-19
1-20
General
Chapter 2
Reference
This chapter includes a complete schematic, parts list, and PCB layout
illustrations for the THS4082 EVM.
Topic Page
2.1 THS4082 EVM Complete Schematic 2–2. . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 THS4082 Dual High-Speed Operational Amplifier EVM Parts List 2–3. .
2.3 THS4082 EVM Board Layouts 2–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reference
2-1
THS4082 EVM Complete Schematic
2.1 THS4082 EVM Complete Schematic
Figure 2–1 shows the complete THS4082 EVM schematic. The EVM is
shipped preconfigured for dual-channel, single-ended inverting operation.
Components showing a value of X are not supplied on the board, but can be
installed by the user to reconfigure the EVM for noninverting and/or differential
operation.
Figure 2–1.THS4082 EVM Schematic
J2
–VCC
GND
+VCC
1
2
3
C1
6.8 µF
VIN1
J1
C2
6.8 µF
R1
49.9 Ω
–VCC
+VCC
R5
1 kΩ
R4
x Ω
R3
0 Ω
2
3
R2
x Ω
+VCC
–
+
8
4
x µF
R6
1 kΩ
C5
0.1 µF
U1:A
THS4082
1
C4
0.1 µF
C3
R7
49.9 Ω
J3
VOUT1
VIN2
J4
R8
x Ω
R9
49.9 Ω
R13
1 kΩ
R12
x Ω
R11
0 Ω
6
5
R10
x Ω
–VCC
–
+
x µF
R14
1 kΩ
U1:B
THS4082
7
C6
R15
49.9 Ω
J5
VOUT2
2-2
Reference
THS4082 Dual High-Speed Operational Amplifier EVM Parts List
2.2 THS4082 Dual High-Speed Operational Amplifier EVM Parts List
Table 2–1.THS4082 EVM Parts List
Reference Description Size
C1, C2 Capacitor, 6.8 µF, 35 V, Tantalum, SM Sprague 293D685X9035D2T
C4, C5 Capacitor, 0.1 µF, Ceramic, 10%, SM 1206 Murata GRM42X7R104K50
J2 3-Pin terminal block (On Shore Tech.) Digi-Key ED1515–ND
J1, J3, J4,J5Connector, SMA 50-Ω vertical PC mount,
through-hole
R1, R7, R9,
R15
R5, R6,
R13, R14
R3, R11 Resistor, 0 Ω, 1/8 W, SM 1206
U1 IC, THS4082 amplifier SOIC-8 TI THS4082DGN
R2, R4,
R10, R12
C3, C6 Capacitor, X µF, 10%, Ceramic, SM
PCB1 PCB, THS4082 EVM SLOP239
†
These components are NOT supplied on the EVM and are to be determined and installed by the user to reconfigure the EVM
in accordance with application requirements.
Resistor, 49.9 Ω, 1%, 1/8 W, SM 1206
Resistor, 1 kΩ, 1%, 1/8 W, SM 1206
Resistor, X Ω, 1%, 1/8 W, SM
4–40 Hex Standoffs, 0.625” length, 0.25” O.D.
4–40 Screws
†
†
1206
Manufacturer/Supplier
Part Number
Amphenol ARF1205–ND
Reference
2-3
THS4082 EVM Board Layouts
2.3 THS4082 EVM Board Layouts
Board layout examples of the THS4082 EVM PCB are shown in the following
illustrations. They are not to scale and appear here only as a reference.
Figure 2–2.THS4082 EVM Component Placement Silkscreen and Solder Pads
J1
VIN1
J4
VIN2
C1
R8
–VCC
+
R1
R2R3R4R5R6C3R7
C4
R9
R10
GND
J2
U1
C5
R11
R12
R13
R14C6R15
+VCC
+
J3
VOUT1
C2
TEXAS
INSTRUMENTS
J5
VOUT2
SLOP239
THS4082 EVM Board
2-4
Reference
Figure 2–3.THS4082 EVM PC Board Layout: Component Side
THS4082 EVM Board Layouts
Reference
2-5
THS4082 EVM Board Layouts
Figure 2–4.THS4082 EVM PC Board Layout: Back Side
2-6
Reference
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