User’s Guide
May 1999
Mixed-Signal Products
SLOU041
Preface
Related Documentation From Texas Instruments
THS4012 DUAL LOW-NOISE HIGH-SPEED OPERATIONAL
AMPLIFIER (literature number SLOS216) This is the data sheet
for the THS4012 operational amplifier integrated circuit that is
used in the THS4012 evaluation module.
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.
Trademarks
TI is a trademark of Texas Instruments Incorporated.
iii
iv
Contents
1
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
Feature Highlights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
THS4012 EVM Noninverting Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
Using The THS4012 EVM In The Noninverting Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
THS4012 EVM Inverting Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
Using The THS4012 EVM In The Inverting Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9
THS4012 EVM Differential Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10
Using The THS4012 EVM WIth Differential Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14
THS4012 EVM Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14
1.10 THS4012 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
2.1
2.2
THS4012 EVM Complete Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
THS4012 Dual High-Speed Operational Amplifier EVM Parts List . . . . . . . . . . . . . . . . . 2-3
THS4012 EVM Board Layouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
v
Figures
1–1
1–2
1–3
1–4
1–5
1–6
1–7
1–8
1–9
THS4012 Evaluation Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
THS4012 EVM Schematic — Noninverting Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
THS4012 EVM Schematic — Inverting Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
THS4012 EVM Schematic — Differential Input (Noninverting Operation) . . . . . . . . . . . . 1-10
THS4012 EVM Schematic — Differential Input (Inverting Operation) . . . . . . . . . . . . . . . . 1-12
THS4012 EVM Frequency Response with Gain = 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-15
THS4012 EVM Phase Response with Gain = 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-15
PowerPAD PCB Etch and Via Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-17
Maximum Power Dissipation vs Free-Air Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-18
2–1
2–2
2–2
2–3
THS4012 EVM Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
THS4012 EVM Component Placement Silkscreen and Solder Pads . . . . . . . . . . . . . . . . . 2-4
THS4012 EVM PC Board Layout – Component Side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
THS4012 EVM PC Board Layout – Back Side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6
Tables
2–1
THS4012 EVM Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
vi
Chapter 1
General
This chapter details the Texas Instruments (TI ) THS4012 dual high-speed
operational amplifier evaluation module (EVM), SLOP230. It includes a list
ofEVMfeatures, abriefdescriptionofthemoduleillustratedwithapictorialand
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 THS4012 EVM Noninverting Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 1–4
1.4 Using The THS4012 EVM In The Noninverting Mode . . . . . . . . . . . . . 1–6
1.5 THS4012 EVM Inverting Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1–7
1.6 Using The THS4012 EVM In The Inverting Mode . . . . . . . . . . . . . . . . . 1–9
1.7 THS4012 EVM Differential Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1–10
1.8 Using The THS4012 EVM With Differential Inputs . . . . . . . . . . . . . . 1–14
1.9 THS4012 EVM Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1–14
1.10 THS4012 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
THS4012 Dual High-Speed Operational Amplifier EVM features include:
High Bandwidth — 75 MHz, –3 dB at ±15 V
and Gain = 2
CC
±5-V to ±15-V Operation
Noninverting Single-Ended Inputs — Inverting-Capable Through
Component Change
Module Gain Set to 2 (Noninverting) — Adjustable Through Compo-
nent 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
Description
1.2 Description
The TI THS4012 dual high-speed operational amplifier evaluation module
(EVM) is a complete dual high-speed amplifier circuit. It consists of the TI
THS4012 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. THS4012 Evaluation Module
–VCC GND +VCC
+
C1
J2
J3
Vout1
J1
Vin1
+
C2
U1
TEXAS
INSTRUMENTS
J4
J5
Vin2
Vout2
SLOP230
THS4012 EVM Board
Note: The EVM is shipped with the following component locations empty: C3, C6,
R2, R4, R8, R10, R12
Although the THS4012 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.
1-3
General
THS4012 EVM Noninverting Operation
1.3 THS4012 EVM Noninverting Operation
The THS4012 EVM is shipped preconfigured for dual-channel noninverting
operation, as shown in Figure 1–2. Note that compensation capacitors C3 and
C6 are not installed.
Figure 1–2. THS4012 EVM Schematic — Noninverting Operation
C3
J2
x µF
1
2
3
–VCC
GND
–VCC
+VCC
+VCC
R5
1 kΩ
R6
1 kΩ
C2
6.8 µF
C1
6.8 µF
C5
0.1 µF
+VCC
8
U1:A
2
3
R7
49.9 Ω
–
THS4012
J3
J1
Vout1
1
Vin1
+
C4
0.1 µF
4
R3
0 Ω
R1
49.9 Ω
–VCC
C6
x µF
R13
R14
1 kΩ
1 kΩ
U1:B
THS4012
6
5
R15
49.9 Ω
–
+
J5
J4
Vout2
7
Vin2
R11
0 Ω
R9
49.9 Ω
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:
R
R6
R5
F
R14
R13
Noninverting Gain
1
1
and 1
R
G
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.
1-4
General
THS4012 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.
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.
1-5
General
Using the THS4012 EVM In The Noninverting Mode
1.4 Using the THS4012 EVM In The Noninverting Mode
The THS4012 EVM operates from power-supply voltages ranging from ±5 V
to ±15 V. As shipped, the EVM is configured for inverting operation and the
gain is set to 4. 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 toOFF before making power supply
connections to the THS4012 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 (J3/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 signal input to the module SMA input connector (J1/J4).
Each EVM input connector is terminated with a 50-Ω impedance to ground.
With a 50-Ω source impedance, the voltage seen by the THS4012 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, R9).
7) Verify the output signal on the oscilloscope.
The signal shown on an oscilloscope with a 50-Ω input impedance will be
the actual THS4012 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
THS4012 EVM Inverting Operation
1.5 THS4012 EVM Inverting Operation
Although the THS4012 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 R11 to the R10 location and R13 to the R12 location on the
board.
This configuration is shown in Figure 1–3. Note that compensation capacitors
C3 and C6 are not installed.
Figure 1–3. THS4012 EVM Schematic — Inverting Operation
C3
x µF
J2
1
2
3
–VCC
GND
–VCC
+VCC
+VCC
R6
1 kΩ
C2
6.8 µF
C1
6.8 µF
C5
0.1 µF
+VCC
8
R4
1 kΩ
J1
U1:A
2
3
R7
49.9 Ω
Vin1
–
+
THS4012
J3
R1
49.9 Ω
Vout1
1
C4
0.1 µF
4
R2
0 Ω
C6
x µF
–VCC
R14
1 kΩ
R12
1 kΩ
J4
U1:B
THS4012
6
5
R15
49.9 Ω
Vin2
–
+
J5
R9
Vout2
7
49.9 Ω
R10
0 Ω
1-7
General
THS4012 EVM Inverting Operation
The gain of the EVM can easily be changed to support a particular application
by changing the ratio of resistors R6 and R4 (channel 1) and R14 and R12
(channel 2) as described in the following equation:
–R
–R6
R4
F
–R14
R12
Inverting Gain
and
R
G
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:
R4 RT
R4–RT
R12 RT
R4–RT
R1
(Channel 1)
and
R9
(Channel 2)
where R is the source impedance.
T
Any resistor 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.
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.
1-8
General
Using the THS4012 EVM In The Inverting Mode
1.6 Using the THS4012 EVM In The Inverting Mode
The THS4012 EVM operates from power-supply voltages ranging from ±5 V
to ±15 V. As shipped, the EVM is configured for inverting operation. Move the
resistors as detailed above to configure the EVM for noninverting operation,
which sets the gain to –3. 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 toOFF before making power supply
connections to the THS4012 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 (J3/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 signal input to the module SMA input connector (J1/J2).
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 THS4012
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.
The signal shown on an oscilloscope with a 50-Ω input impedance will be
the actual THS4012 amplifier IC output voltage. This is due to the voltage
division between the output resistor (R7, R15) and the oscilloscope input
impedance.
1-9
General
THS4012 EVM Differential Input
1.7 THS4012 EVM Differential Input
The THS4012 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 THS4012 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
that compensation capacitors C3 and C6 are not installed.
Figure 1–4. THS4012 EVM Schematic — Differential Input (Noninverting Operation)
C3
J2
x µF
1
2
3
–VCC
GND
–VCC
+VCC
+VCC
R5
1 kΩ
R6
1 kΩ
C2
6.8 µF
C1
6.8 µF
C5
0.1 µF
+VCC
8
U1:A
2
3
R7
49.9 Ω
–
+
THS4012
J3
R3
0 Ω
J1
Vout1
1
Vin1
C4
0.1 µF
4
C6
x µF
–VCC
R8
100 Ω
R13
1 kΩ
R14
1 kΩ
U1:B
THS4012
6
5
R15
49.9 Ω
–
+
J5
R11
0 Ω
J4
Vout2
7
Vin2
1-10
General
THS4012 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:
R
R6
R5
F
R14
R13
Noninverting Gain
1
1
and 1
R
G
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.
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 THS4012 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 R11 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. For a inverting differential
input, R8 should be 200 Ω to match a 50-Ω source impedance. Note that
compensation capacitors C3 and C6 are not installed.
1-11
General
THS4012 EVM Differential Input
Figure 1–5. THS4012 EVM Schematic — Differential Input (Inverting Operation)
C3
J2
x µF
1
2
3
–VCC
GND
–VCC
+VCC
+VCC
R6
1 kΩ
C2
6.8 µF
C1
6.8 µF
C5
0.1 µF
+VCC
8
R4
1 kΩ
J1
U1:A
2
3
R7
49.9 Ω
Vin1
–
+
THS4012
J3
Vout1
1
C4
0.1 µF
4
R2
0 Ω
C6
x µF
–VCC
R8
100 Ω
R14
1 kΩ
R12
1 kΩ
J4
U1:B
THS4012
6
5
R15
49.9 Ω
Vin2
–
+
J5
Vout2
7
R10
0 Ω
The gain of the EVM inputs can easily be changed to support a particular
application by changing the ratio of resistors R6 and R4 (channel 1) and R14
and R12 (channel 2) as described in the following equation:
–R
–R6
R4
F
–R14
R12
Inverting Gain
and
R
G
R4 and R12 form part of the input impedance and R8 should be adjusted in
accordance with the following equation:
2 R4
R4–R
R
T
R8
T
where R is the termination resistance and R4 = R12.
T
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
General
THS4012 EVM Differential Input
Any resistor 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.
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.
1-13
General
Using the THS4012 EVM With Differential Inputs
1.8 Using the THS4012 EVM With Differential Inputs
The THS4012 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 toOFF before making power supply
connections to the THS4012 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 con-
nectors (J1 and J4)
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
THS4012 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 equivalent input resistance.
7) Verify the differential output signal on the oscilloscope.
The signal shown on an oscilloscope with a 50-Ω input impedance will be
the actual THS4012 amplifier IC output voltage. This is due to the voltage
division between the output resistors (R7, R15) and the oscilloscope input
impedance.
1.9 THS4012 EVM Specifications
Supply voltage range, ±V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . ±5 V to ±15 V
CC
Supply current, I
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 mA typ
CC
Input voltage, V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±VCC, max
I
Output drive, I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 mA
O
For complete THS4012 amplifier IC specifications and parameter
measurement information, and additional application information, see the
THS4012 data sheet, TI Literature Number SLOS216.
1-14
General
THS4012 EVM Performance
1.10 THS4012 EVM Performance
Figure 1–6 shows the typical frequency response of the THS4012 EVM using
the noninverting configuration (G = 2). Typical –0.1 dB bandwidth is 25 MHz
and –3-dB bandwidth is 75 MHz with both a ±15-V power supply and a ±5-V
power supply.
Figure 1–6. THS4012 EVM Frequency Response with Gain = 2
7
6
5
4
3
2
1
0
V
V
R
= ±5 V and ± 15 V
CC
O
L
= 0.2 VRMS
= 150 Ω
–1
100k
1M
10M
100M
500M
f – Frequency – Hz
Figure 1–7 shows the typical phase response of the THS4012 EVM using the
noninverting configuration (G = 2). This shows a 75° phase margin for both
±15-V and ±5-V power supplies on both channels.
Figure 1–7. THS4012 EVM Phase Response with Gain = 2
45
0
–45
–90
–135
V
V
R
= ±5 V and ± 15 V
CC
–180
= 0.2 VRMS
O
= 150 Ω
L
–225
100k
1M
10M
100M
500M
f – Frequency – Hz
1-15
General
General High-Speed Amplifier Design Considerations
1.11 General High-Speed Amplifier Design Considerations
The THS4012 EVM layout has been designed and optimized for use with
high-speed signals and can be used as an example when designing THS4012
applications. Careful attention has been given to component selection,
grounding, powersupplybypassing, andsignalpathlayout. Disregardofthese
basic design considerations could result in less than optimum performance of
the THS4012 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.
Tantalumpowersupplybypasscapacitors(C1andC2)atthepowerinputpads
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
invertingpinwhiletheamplifierisoperatinginthenoninvertingmode. 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 PowerPAD Design Considerations
1.12 General PowerPAD Design Considerations
TheTHS4012DGNICismountedinaspecialpackageincorporatingathermal
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 THS4012 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
THS4012DGN 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 THS4012DGN 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.
1-17
General
General PowerPAD Design Considerations
8) With these preparatory steps in place, the THS4012DGN 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 THS4012DGN 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 , is about 58.4 C/W. For comparison, the
JA
non-PowerPAD version of the THS4012 IC (D-package in SOIC) is shown. For
a given θ , the maximum power dissipation is shown in Figure 1–9 and is
JA
calculated by the following formula:
T
–T
MAX
A
P
D
JA
Where:
P
= Maximum power dissipation of THS4012 IC (watts)
= Absolute maximum junction temperature (150°C)
= Free-ambient air temperature (°C)
D
T
MAX
T
A
θ
= θ + θ
JC CA
JA
θ
= Thermal coefficient from junction to case (4.7°C/W) for
JC
THS4012DGN (PowerPAD)
θ
= Thermal coefficient from junction to case (38.3°C/W) for
THS4012D (SOIC)
JC
θ
= Thermal coefficient from case to ambient air (°C/W)
CA
Figure 1–9. Maximum Power Dissipation vs Free-Air Temperature
3.5
T
J
= 150°C
No Air Flow
3
2.5
2
DGN Package
θ
JA
= 58.4°C/W
2 oz Trace and
Copper Pad
with Solder
DGN Package
= 158°C/W
2 oz Trace and
Copper Pad
θ
JA
1.5
1
without Solder
THS4012
SOIC – Package
.5
θ
= 166.7°C/W
JA
0
–40 –20
0
20
40
60
80
100
T
A
– Free-Air Temperature – °C
Even though the THS4012 EVM PCB is smaller than the one in the example
above, the results should give an idea of how much power can be dissipated
bythePowerPADICpackage. TheTHS4012EVMisagoodexampleofproper
thermal management when using PowerPAD-mounted devices.
1-18
General
General PowerPAD 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 THS4012 Low-noise Dual
Differential Receiver data sheet (SLOS216). For more general information on
the PowerPAD package and its thermal characteristics, see the Texas
Instruments Technical Brief, PowerPAD Thermally Enhanced Package
(SLMA002).
1-19
General
1-20
General
Chapter 2
Reference
This chapter includes a complete schematic, parts list, and PCB layout
illustrations for the THS4012 EVM.
Topic
Page
2.1 THS4012 EVM Complete Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2–2
2.1 THS4012 Dual High-Speed Operational Amplifier EVM Parts List . . 2–3
2.2 THS4012 EVM Board Layouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2–4
2-1
THS4012 EVM Complete Schematic
2.1 THS4012 EVM Complete Schematic
Figure 2–1 shows the complete THS4012 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. THS4012 EVM Schematic
C3
J2
x µF
1
2
3
–VCC
GND
–VCC
+VCC
+VCC
R5
1 kΩ
R6
1 kΩ
C1
6.8 µF
C2
6.8 µF
C5
0.1 µF
+VCC
8
R4
x Ω
U1:A
2
3
R7
49.9 Ω
–
J1
THS4012
J3
VIN1
VOUT1
1
R1
49.9 Ω
+
C4
0.1 µF
4
R3
0 Ω
R2
x Ω
–VCC
R8
C6
x µF
x Ω
R13
R14
1 kΩ
1 kΩ
R12
x Ω
U1:B
THS4012
6
5
R15
49.9 Ω
–
+
J4
J5
VIN2
VOUT2
7
R9
49.9 Ω
R11
0 Ω
R10
x Ω
2-2
Reference
THS4012 Dual High-Speed Operational Amplifier EVM Parts List
2.2 THS4012 Dual High-Speed Operational Amplifier EVM Parts List
Table 2–1.THS4012 EVM Parts List
Manufacturer/Supplier
Reference
Description
Size
Part Number
C1, C2
C4, C5
J2
Capacitor, 6.8 µF, 35 V, Tantalum, SM
Capacitor, 0.1 µF, Ceramic, 10%, SM
3-Pin Terminal Block (On Shore Tech.)
Sprague 293D685X9035D2T
MuRata GRM42X7R104K50
Digi-Key ED1515–ND
1206
J1, J3, J4,
J5
Connector, SMA 50-Ω vertical PC mount, through-
hole
Amphenol ARF1205–ND
R1, R7, R9, Resistor, 49.9 Ω, 1%, 1/8 W, SM
1206
1206
1206
R15
R5, R6,
R13, R14
Resistor, 1 kΩ, 1%, 1/8 W, SM
R3, R11
U1
Resistor, 0 Ω, 1/8 W, SM
IC, THS4012 amplifier
SOIC-8 TI THS4012DGN
1206
†
R2, R4,
R10, R12
Resistor, X Ω, 1%, 1/8 W, SM
†
C3, C6
Capacitor, X µF, 10%, Ceramic, SM
4–40 Hex Standoffs, 0.625′′ length, 0.25′′ O.D.
4–40 Screws
PCB1
PCB, THS4012 EVM
SLOP230
†
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.
2-3
Reference
THS4012 EVM Board Layouts
2.3 THS4012 EVM Board Layouts
Board layout examples of the THS4012 EVM PCB are shown in the following
illustrations. They are not to scale and appear here only as a reference.
Figure 2–2. THS4012 EVM Component Placement Silkscreen and Solder Pads
–VCC GND +VCC
+
C1
J3
Vout1
J1
Vin1
J2
+
C2
U1
TEXAS
INSTRUMENTS
J5
J4
Vout2
Vin2
SLOP230
THS4012 EVM Board
2-4
Reference
THS4012 EVM Board Layouts
Figure 2–3. THS4012 EVM PC Board Layout – Component Side
2-5
Reference
THS4012 EVM Board Layouts
Figure 2–4. THS4012 EVM PC Board Layout – Back Side
2-6
Reference
|