Texas Instruments Musical Instrument Amplifier THS4012 User Manual

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-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-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-cable and 75-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-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 ). 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-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-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-impedance to ground.  
With a 50-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-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-cable and 75-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-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 ). 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-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-impedance  
to ground. With a 50-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-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-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 to match 50-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-cable and 75-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-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 ). 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-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 to match a 50-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-cable and 75-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-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 ). 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-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-nominal impedance cable (an oscilloscope having  
a 50-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-impedance  
for each input. With a 50-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-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 or 75 , 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-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  
 

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