LMH6554 [TI]
2.8GHz 超线性全差分放大器;
| 型号： | LMH6554 |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | 2.8GHz 超线性全差分放大器 放大器 运算放大器 放大器电路 |
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LMH6554
www.ti.com
SNOSB30O –OCTOBER 2008–REVISED MARCH 2013
LMH6554 2.8 GHz Ultra Linear Fully Differential Amplifier
Check for Samples: LMH6554
1
FEATURES
DESCRIPTION
The LMH6554 is a high performance fully differential
amplifier designed to provide the exceptional signal
fidelity and wide large-signal bandwidth necessary for
driving 8 to 16 bit high speed data acquisition
systems. Using TI’s proprietary differential current
mode input stage architecture, the LMH6554 has
unity gain, small-signal bandwidth of 2.8 GHz and
allows operation at gains greater than unity without
sacrificing response flatness, bandwidth, harmonic
distortion, or output noise performance.
2
•
•
•
•
•
•
•
•
•
•
•
Small Signal Bandwidth 2.8 GHz
2 VPP Large Signal Bandwidth 1.8 GHz
0.1 dB Gain Flatness 830 MHz
OIP3 @ 150 MHz 46.5 dBm
HD2/HD3 @ 75 MHz -96 / -97 dBc
Input Noise Voltage 0.9 nV/√Hz
Input Noise Current 11 pA/√Hz
Slew Rate 6200 V/μs
The device's low impedance differential output is
designed to drive ADC inputs and any intermediate
filter stage. The LMH6554 delivers 16-bit linearity up
to 75 MHz when driving 2V peak-to-peak into loads
as low as 200Ω.
Power 260mW
Typical Supply Current 52 mA
Package 14 Lead UQFN
APPLICATIONS
The LMH6554 is fabricated in Texas Instruments'
advanced complementary BiCMOS process and is
available in a space saving 14 lead UQFN package
for higher performance.
•
•
•
•
•
•
•
•
•
Differential ADC Driver
Single-Ended to Differential Converter
High Speed Differential Signaling
IF/RF and Baseband Gain Blocks
SAW Filter Buffer/Driver
Oscilloscope Probes
Automotive Safety Applications
Video Over Twisted Pair
Differential Line Driver
Typical Application
200W
91W
R
= 50W
S
V
S
+
C
V
~
76.8W
0.1 mF
50W
AC-Coupled
Source
ADC
+
-
LMH6554
V
CM
Up To 16-Bit
Data Converter
+
-
50W
91W
0.1 mF
-
30W
0.1 mF
V
V
CMO
V
EN
200W
Figure 1. Single to Differential ADC Driver
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
2
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2008–2013, Texas Instruments Incorporated
LMH6554
SNOSB30O –OCTOBER 2008–REVISED MARCH 2013
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
(1)(2)
Absolute Maximum Ratings
ESD Tolerance
(3)
Human Body Model
Machine Model
2000V
250V
Charge Device Model
750V
Supply Voltage (VS = V+ - V−)
Common Mode Input Voltage
Maximum Input Current
5.5V
From V-to V+
30mA
(4)
Maximum Output Current (pins 12, 13)
Soldering Information
Infrared or Convection (30 sec)
For soldering specifications see SNOA549
260°C
(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is intended to be functional, but specific performance is not ensured. For ensured specifications, see the Electrical
Characteristics tables.
(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
(3) Human Body Model, applicable std. MIL-STD-883, Method 30157. Machine Model, applicable std. JESD22-A115-A (ESD MM std. of
JEDEC). Field-Induced Charge-Device Model, applicable std. JESD22-C101-C (ESD FICDM std. of JEDEC).
(4) The maximum output current (IOUT) is determined by device power dissipation limitations. See the Power Dissipation section of
Application Information for more details.
(1)
Operating Ratings
Operating Temperature Range
−40°C to +125°C
−65°C to +150°C
4.7V to 5.25V
Storage Temperature Range
Total Supply Voltage Temperature Range
(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is intended to be functional, but specific performance is not ensured. For ensured specifications, see the Electrical
Characteristics tables.
Thermal Properties
Junction-to-Ambient Thermal Resistance (θJA
)
60°C/W
150°C
Maximum Operating Junction Temperature
2
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(1)
+5V Electrical Characteristics
Unless otherwise specified, all limits are ensured for TA = +25°C, AV = +2, V+ = +2.5V, V− = −2.5V, RL = 200Ω, VCM = (V++V-
)/2, RF = 200Ω, for single-ended in, differential out. Boldface Limits apply at the temperature extremes.
(2)
(3)
(2)
Symbol
Parameter
Conditions
Min
Typ
Max
Units
MHz
MHz
AC Performance (Differential)
AV = 1, VOUT = 0.2 VPP
2800
2500
1600
1800
1500
1900
830
6200
290
150
4
(2)
SSBW
LSBW
Small Signal −3 dB Bandwidth
AV = 2, VOUT = 0.2 VPP
AV = 4, VOUT = 0.2 VPP
AV = 1, VOUT = 2 VPP
AV = 2, VOUT = 2 VPP
AV = 2, VOUT = 1.5 VPP
AV = 2, VOUT = 0.2 VPP, RF = 250Ω
4V Step
Large Signal Bandwidth
0.1 dBBW 0.1 dB Bandwidth
MHz
SR
Slew Rate
V/μs
2V Step, 10–90%
tr/tf
Rise/Fall Time
ps
0.4V Step, 10–90%
2V Step, RL = 200Ω
VIN = 2V, AV = 5 V/V
Ts_0.1
0.1% Settling Time
ns
ns
Overdrive Recovery Time
6
Distortion and Noise Response
VOUT = 2 VPP, f = 20 MHz
VOUT = 2 VPP, f = 75 MHz
VOUT = 2 VPP, f = 125 MHz
VOUT = 2 VPP, f = 250 MHz
VOUT = 1.5 VPP, f = 250 MHz
VOUT = 2 VPP, f = 20 MHz
VOUT = 2 VPP, f = 75 MHz
VOUT = 2 VPP, f = 125 MHz
VOUT = 2 VPP, f = 250 MHz
VOUT = 1.5 VPP, f = 250 MHz
f = 150 MHz, VOUT = 2VPP Composite
f = 150 MHz, VOUT = 2VPP Composite
f = 10 MHz
-102
-96
HD2
HD3
2nd Harmonic Distortion
-87
dBc
dBc
−79
−81
−110
−97
−87
−70
−75
46.5
−97
0.9
3rd Harmonic Distortion
OIP3
IMD3
en
Output 3rd-Order Intercept
Two-Tone Intermodulation
Input Voltage Noise Density
Input Noise Current
dBm
dBc
nV/√Hz
pA/√Hz
pA/√Hz
dB
in+
f = 10 MHz
11
in-
Input Noise Current
f = 10 MHz
11
(4)
NF
Noise Figure
50Ω System, AV = 7.3, 100 MHz
7.7
Input Characteristics
IBI+ / IBI-
−75
−29
20
10
µA
TCIbi
Input Bias Current Temperature Drift
8
µA/°C
VCM = 0V, VID = 0V,
IBOFFSET = (IB-- IB+)/2
(5)
IBID
Input Bias Current
−10
1
μA
Input Bias Current Diff Offset
Temperature Drift
TCIbo
0.006
83
µA/°C
dB
(3)
CMRR
Common Mode Rejection Ratio
DC, VCM = 0V, VID = 0V
(1) Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very
limited self-heating of the device such that TJ = TA. No specification of parametric performance is indicated in the electrical tables under
conditions of internal self-heating where TJ > TA. See Application Information for information on temperature de-rating of this device."
Min/Max ratings are based on product characterization and simulation. Individual parameters are tested as noted.
(2) Limits are 100% production tested at 25°C. Limits over the operating temperature range are ensured through correlation using Statistical
Quality Control (SQC) methods.
(3) Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary
over time and will also depend on the application and configuration. The typical values are not tested and are not ensured on shipped
production material.
(4) For test schematic, refer to Figure 35.
(5) IBI is referred to a differential output offset voltage by the following relationship: VOD(OFFSET) = IBI*2RF.
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+5V Electrical Characteristics (1) (continued)
Unless otherwise specified, all limits are ensured for TA = +25°C, AV = +2, V+ = +2.5V, V− = −2.5V, RL = 200Ω, VCM = (V++V-
)/2, RF = 200Ω, for single-ended in, differential out. Boldface Limits apply at the temperature extremes.
(2)
(3)
(2)
Symbol
RIN
Parameter
Conditions
Min
Typ
19
Max
Units
Ω
Differential Input Resistance
Differential Input Capacitance
Differential
Differential
CIN
1
pF
V
CMVR
Input Common Mode Voltage Range CMRR > 32 dB
±1.25
±1.3
Output Performance
(3)
Output Voltage Swing
Single-Ended Output
±1.35
±120
±1.42
±150
V
(3)
IOUT
ISC
Output Current
VOUT = 0V
mA
One Output Shorted to Ground
VIN = 2V Single-Ended
Short Circuit Current
Output Balance Error
150
mA
dB
(6)
ΔVOUT Common Mode /ΔVOUT
Differential, ΔVOD = 1V, f < 1 Mhz
−64
Output Common Mode Control Circuit
Common Mode Small Signal
Bandwidth
+
−
VIN = VIN = 0V
500
MHz
+
−
Slew Rate
VIN = VIN = 0V
200
−6.5
6
V/μs
mV
μA
V
VOSCM
IOSCM
Input Offset Voltage
Input Offset Current
Voltage Range
CMRR
Common Mode, VID = 0, VCM = 0V
(7)
−16
4
18
±1.18
±1.25
82
Measure VOD, VID = 0V
dB
Input Resistance
Gain
180
0.995
kΩ
V/V
ΔVOCM/ΔVCM
0.99
1.0
Miscellaneous Performance
ZT
Open Loop Transimpedance Gain
Differential
DC, ΔV+ = ΔV− = 1V
180
95
kΩ
PSRR
Power Supply Rejection Ratio
74
46
dB
57
60
(8)
IS
Supply Current
RL = ∞
52
mA
(9)
Enable Voltage Threshold
Disable Voltage Threshold
Enable/Disable Time
Single 5V Supply
2.5
2.5
15
V
V
(9)
Single 5V Supply
ns
570
600
ISD
Supply Current, Disabled
Enable=0, Single 5V supply
450
510
μA
(6) Short circuit current should be limited in duration to no more than 10 seconds. See the Power Dissipation section of Application
Information for more details.
(7) Negative input current implies current flowing out of the device.
(8) Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary
over time and will also depend on the application and configuration. The typical values are not tested and are not ensured on shipped
production material.
(9) VEN threshold is typically +/-0.3V centered around (V+ + V-) / 2 relative to ground.
4
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Connection Diagram
-
+
V
3
VCM
2
V
1
14 NC
4
5
+FB
-IN
R
F
13
+OUT
-OUT
NC
R
R
G
G
12
11
6
7
+IN
-FB
R
F
8
9
10
+
-
VEN
V
V
Figure 2. 14 Lead UQFN - Top View
See Package Number NHJ0014A
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Typical Performance Characteristics VS = ±2.5V
(TA = 25°C, RF = 200Ω, RG = 90Ω, RT = 76.8Ω, RL = 200Ω, AV = +2, for single ended in, differential out, unless specified).
Frequency Response
Frequency Response
vs.
RF
vs.
Gain
2
1
2
1
RF = 200W
AV = 1 V/V
0
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
RF = 250W
RF = 300W
AV = 2 V/V
AV = 4 V/V
AV = 8 V/V
VOD = 0.2 VPP
10
VOD = 0.2 VPP
10
1
100
1000
10000
10000
10000
1
1100
1000
10000
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 3.
Figure 4.
Frequency Response
Frequency Response
vs.
Output Voltage (VOD
vs.
RL
)
6
4
2
1
VOD = 0.2 VPP
RL = 1kW
0
RL = 500W
2
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
VOD = 1.6 VPP
0
-2
-4
-6
-8
-10
VOD = 2 VPP
RL = 200W
VOD = 0.2 VPP
10
1
100
1000
1
10
100
1000
10000
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 5.
Figure 6.
Frequency Response
vs.
Capacitive Load
Suggested ROUT
vs.
Capacitive Load
3
2
70
60
50
40
30
20
10
0
LOAD = 1kW || CAP LOAD
CL=2.2 pF, RO=38W
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
CL=6.8 pF, RO=22W
CL=18 pF, RO=14W
CL=68 pF, RO=5W
VOD = 200 mVPP
1
10
100
1000
5
10
15
20
25
30
35
40
FREQUENCY (MHz)
CAPACITIVE LOAD (pF)
Figure 7.
Figure 8.
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Typical Performance Characteristics VS = ±2.5V (continued)
(TA = 25°C, RF = 200Ω, RG = 90Ω, RT = 76.8Ω, RL = 200Ω, AV = +2, for single ended in, differential out, unless specified).
0.5 VPP Pulse Response Single Ended Input
0.3
2 VPP Pulse Response Single Ended Input
1.5
0.2
0.1
0
1.0
0.5
0
-0.1
-0.2
-0.3
-0.5
-1.0
-1.5
0
1
2
3
4
5
6
7
8
9
10
0
1
2
3
4
5
6
7
8
9
10
TIME (ns)
TIME (ns)
Figure 9.
Figure 10.
Distortion
vs.
Frequency Single Ended Input
4 VPP Pulse Response Single Ended Input
2.5
-60
RL = 200W
VOD = 2 VPP
VOCM = 0V
2.0
1.5
1.0
0.5
0
-65
-70
-75
-80
-85
-0.5
-1.0
-1.5
-2.0
-2.5
-90
HD3
125
-95
-100
-105
-110
0
1
2
3
4
5
6
7
8
9
10
25
75
175
225
275 300
TIME (ns)
FREQUENCY (MHz)
Figure 11.
Figure 12.
Distortion
vs.
Output Common Mode Voltage
Distortion
vs.
Output Common Mode Voltage
-50
-40
-50
RL = 200W
VOD = 2 VPP
fc = 25 MHz
RL = 200W
VOD = 2 VPP
fc = 75 MHz
-60
-70
-60
HD3
-80
-70
HD3
-90
-80
-100
-110
-90
-100
-1.0
-1.0
-0.5
0
0.5
1.0
-0.5
0
0.5
1.0
VOCM (V)
VOCM (V)
Figure 13.
Figure 14.
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Typical Performance Characteristics VS = ±2.5V (continued)
(TA = 25°C, RF = 200Ω, RG = 90Ω, RT = 76.8Ω, RL = 200Ω, AV = +2, for single ended in, differential out, unless specified).
Distortion
3rd Order Intermodulation Products
vs.
vs
Output Common Mode Voltage
VOUT
-20
-30
-40
-50
-60
-70
-80
-90
-100
-80
-85
RL = 200W
VOD = 2 VPP
fc = 150 MHz
150 MHz
-90
HD3
-95
75 MHz
-100
-105
-1.0
-0.5
0
0.5
1.0
0.8
1.0
1.2
1.4
1.6
1.8
2
DIFFERENTIAL V
(V
)
OUT PP_EACH_TONE
VOCM (V)
Figure 15.
Figure 16.
OIP3
vs
OIP3
vs
Center Frequency
Output Power POUT
55
50
45
40
35
30
25
20
55
50
45
40
35
30
25
20
15
10
150 MHz
250 MHz
450 MHz
-4
-3
-2
-1
0
1
2
3
4
50 100 150 200 250 300 350 400 450 500
DIFFERENTIAL OUTPUT POWER P
(dBm/tone)
CENTER FREQUENCY (MHz)
OD
Figure 17.
Figure 18.
Noise Figure
vs
Frequency
Maximum VOUT
vs.
IOUT
1.6
8.0
7.8
7.6
7.4
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
A = 7.3 V/V
v
7.2
7.0
R = 50ꢀ
s
Single Ended Input
V
= 1.7V SINGLE-ENDED INPUT
IN
0
-20
-40
-60
-80
-100
0
100
200
300
400
500
FREQUENCY (MHz)
OUTPUT CURRENT (mA)
Figure 19.
Figure 20.
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Typical Performance Characteristics VS = ±2.5V (continued)
(TA = 25°C, RF = 200Ω, RG = 90Ω, RT = 76.8Ω, RL = 200Ω, AV = +2, for single ended in, differential out, unless specified).
Minimum VOUT
vs.
IOUT
Overdrive Recovery
1.2
0.8
0.4
0
0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-1.6
3
2
V
= 1.7V SINGLE-ENDED INPUT
IN
1
0
-0.4
-0.8
-1.2
-1
-2
-3
0
20
40
60
80
100
1000
1000
0
200
400
600
800
1000
OUTPUT CURRENT (mA)
TIME (ns)
Figure 21.
Figure 22.
PSRR
CMRR
90
85
80
75
70
65
60
55
50
45
40
90
85
80
75
70
65
60
55
50
45
40
-PSRR
VIN = 0V
VOD = 1VPP
VIN = 0V
1
10
100
1
10
100
1000
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 23.
Figure 24.
Balance Error
Open Loop Transimpedance
-30
-35
-40
-45
-50
-55
-60
-65
120
100
80
60
40
20
0
0
A
= 1 V/V
V
-30
-60
-90
-120
-150
-180
Gain
Phase
1
10
100
100k 1M
10M 100M 1G
10G
FREQUECNY (Hz)
FREQUENCY (MHz)
Figure 25.
Figure 26.
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Typical Performance Characteristics VS = ±2.5V (continued)
(TA = 25°C, RF = 200Ω, RG = 90Ω, RT = 76.8Ω, RL = 200Ω, AV = +2, for single ended in, differential out, unless specified).
Differential S-Parameter Magnitude
vs.
Frequency
Closed Loop Output Impedance
10
0
1k
100
10
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
S22
S21
S11
(SINGLE-ENDED INPUT)
1
AV = 1 V/V
100m
3000
1000
1
10
100
1
10
100
1k
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 27.
Figure 28.
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APPLICATION INFORMATION
The LMH6554 is a fully differential, current feedback amplifier with integrated output common mode control,
designed to provide low distortion amplification to wide bandwidth differential signals. The common mode
feedback circuit sets the output common mode voltage independent of the input common mode, as well as
forcing the V+ and V− outputs to be equal in magnitude and opposite in phase, even when only one of the inputs
is driven as in single to differential conversion.
The proprietary current feedback architecture of the LMH6554 offers gain and bandwidth independence with
exceptional gain flatness and noise performance, even at high values of gain, simply with the appropriate choice
of RF1 and RF2. Generally RF1 is set equal to RF2, and RG1 equal to RG2, so that the gain is set by the ratio RF/RG.
Matching of these resistors greatly affects CMRR, DC offset error, and output balance. A maximum of 0.1%
tolerance resistors are recommended for optimal performance, and the amplifier is internally compensated to
operate with optimum gain flatness with RF value of 200Ω depending on PCB layout, and load resistance.
The output common mode voltage is set by the VCM pin with a fixed gain of 1 V/V. This pin should be driven by a
low impedance reference and should be bypassed to ground with a 0.1 µF ceramic capacitor. Any unwanted
signal coupling into the VCM pin will be passed along to the outputs, reducing the performance of the amplifier.
The LMH6554 can be configured to operate on a single 5V supply connected to V+ with V- grounded or
configured for a split supply operation with V+ = +2.5V and V− = −2.5V. Operation on a single 5V supply,
depending on gain, is limited by the input common mode range; therefore, AC coupling may be required. Split
supplies will allow much less restricted AC and DC coupled operation with optimum distortion performance.
Enable / Disable Operation
The LMH6554 is equipped with an enable pin (VEN) to reduce power consumption when not in use. The VEN pin,
when not driven, floats high (on). When the VEN pin is pulled low, the amplifier is disabled and the amplifier
output stage goes into a high impedance state so the feedback and gain set resistors determine the output
impedance of the circuit. For this reason input to output isolation will be poor in the disabled state and the part is
not recommended in multiplexed applications where outputs are all tied together.
With a 5V difference between V+ and V-, the VEN threshold is ½ way between the supplies (e.g. 2.5V with 5V
single supply) as shown in Figure 29. R2 ensures active (enable) mode with VEN floating, and R1 provides input
current limiting. VEN also has ESD diodes to either supply.
V+
R2
LMH6554
Bias
Circuitry
R
R
20k
Supply
Mid-Point
R1
10k
Q1
VEN
Q2
I Tail
V-
Figure 29. Enable Block Diagram
Fully Differential Operation
The LMH6554 will perform best in a fully differential configuration. The circuit shown in Figure 30 is a typical fully
differential application circuit as might be used to drive an analog to digital converter (ADC). In this circuit the
closed loop gain is AV= VOUT / VIN = RF / RG, where the feedback is symmetric. The series output resistors, RO,
are optional and help keep the amplifier stable when presented with a capacitive load. Refer to the Driving
Capacitive Loads section for details.
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Here is the expression for the input impedance, RIN, as defined in Figure 30:
RIN = 2RG
When driven from a differential source, the LMH6554 provides low distortion, excellent balance, and common
mode rejection. This is true provided the resistors RF, RG and RO are well matched and strict symmetry is
observed in board layout. With an intrinsic device CMRR of greater than 70 dB, using 0.1% resistors will give a
worst case CMRR of around 50 dB for most circuits.
The circuit configuration shown in Figure 30 was used to measure differential S-parameters in a 100Ω
environment at a gain of 1 V/V. Refer to Figure 28 in Typical Performance Characteristics VS = ±2.5V for
measurement results.
200W
RF
50W
R
50W
S
67W
67W
200W
+
V
RG
S
-
VOUT
+
+
VIN
-
V
CM
R =100W
L
LMH6554
RIN
~
RG
-
R
50W
200W
S
V
EN
50W
RF
200W
Figure 30. Differential S-Parameter Test Circuit
Single Ended Input To Differential Output Operation
In many applications, it is required to drive a differential input ADC from a single ended source. Traditionally,
transformers have been used to provide single to differential conversion, but these are inherently bandpass by
nature and cannot be used for DC coupled applications. The LMH6554 provides excellent performance as a
single-ended input to differential output converter down to DC. Figure 31 shows a typical application circuit where
an LMH6554 is used to produce a balanced differential output signal from a single ended source.
R
F
A , R
V
IN
+
V
R
R
R
G
S
O
G
+
IN-
-
V
+
V
S
V
CM
R
ADC
IN+
O
R
LMH6554
T
~
-
O
R
-
R
M
V
+
-
R
F
«
«
∆
∆
≈
∆
∆
≈
≈
∆
∆
«
2(1 - b1)
+ b
R
≈
∆
∆
«
G
A
V
=
b =
1
b
R
+ R
1
2
G
F
=
=
R
R
R
|| R
IN
«
∆
∆
≈
«
∆
∆
≈
S
T
≈
R
+ R
M
≈
∆
«
2R + R (1-b )
G
G
M
2
∆
∆
«
=
b =
2
R
IN
R
|| R
S
M
∆
T
RG + R + R
1 + b
F
M
2
Figure 31. Single Ended Input with Differential Output
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When using the LMH6554 in single-to-differential mode, the complimentary output is forced to a phase inverted
replica of the driven output by the common mode feedback circuit as opposed to being driven by its own
complimentary input. Consequently, as the driven input changes, the common mode feedback action results in a
varying common mode voltage at the amplifier's inputs, proportional to the driving signal. Due to the non-ideal
common mode rejection of the amplifier's input stage, a small common mode signal appears at the outputs which
is superimposed on the differential output signal. The ratio of the change in output common mode voltage to
output differential voltage is commonly referred to as output balance error. The output balance error response of
the LMH6554 over frequency is shown in the Typical Performance Characteristics VS = ±2.5V.
To match the input impedance of the circuit in Figure 31 to a specified source resistance, RS, requries that RT ||
RIN = RS. The equations governing RIN and AV for single-to-differential operation are also provide in Figure 31.
These equations, along with the source matching condition, must be solved iteratively to achieve the desired gain
with the proper input termination. Component values for several common gain configuration in a 50Ω
environment are given in Table 1.
Table 1. Gain Component Values for 50Ω System
Gain
0dB
RF
RG
RT
RM
200Ω
200Ω
200Ω
191Ω
91Ω
62Ω
27.7Ω
30.3Ω
37.3Ω
6dB
76.8Ω
147Ω
12dB
35.7Ω
Single Supply Operation
Single 5V supply operation is possible: however, as discussed earlier, AC input coupling is recommended due to
input common mode limitations. An example of an AC coupled, single supply, single-to-differential circuit is
shown in Figure 32. Note that when AC coupling, both inputs need to be AC coupled irrespective of single-to-
differential or differential-differential configuration. For higher supply voltages DC coupling of the inputs may be
possible provided that the output common mode DC level is set high enough so that the amplifier's inputs and
outputs are within their specified operation ranges.
R
F
R
O
R
G
R
0.1 mF
S
+
V
S
C
L
R
L
V
O
V
CM
LMH6554
R
T
~
-
R
G
R
M
0.1 mF
R
O
R
F
V
EN
Figure 32. AC Coupled for Single Supply Operation
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Split Supply Operation
For optimum performance, split supply operation is recommended using +2.5V and −2.5V supplies; however,
operation is possible on split supplies as low as +2.35V and −2.35V and as high as +2.65V and −2.65V.
Provided the total supply voltage does not exceed the 4.7V to 5.3V operating specification, non-symmetric supply
operation is also possible and in some cases advantageous. For example, if a 5V DC coupled operation is
required for low power dissipation but the amplifier input common mode range prevents this operation, it is still
possible with split supplies of (V+) and (V-). Where (V+)-(V-) = 5V and V+ and V- are selected to center the
amplifier input common mode range to suit the application.
Driving Analog To Digital Converters
Analog-to-digital converters present challenging load conditions. They typically have high impedance inputs with
large and often variable capacitive components. Figure 34 shows the LMH6554 driving an ultra-high-speed
Gigasample ADC the ADC10D1500. The LMH6554 common mode voltage is set by the ADC10D1500. The
circuit in Figure 34 has a 2nd order bandpass LC filter across the differential inputs of the ADC10D1500. The
ADC10D1500 is a dual channel 10–bit ADC with maximum sampling rate of 3 GSPS when operating in a single
channel mode and 1.5 GSPS in dual channel mode.
Figure 33 shows the SFDR and SNR performance vs. frequency for the LMH6554 and ADC10D1500
combination circuit with the ADC input signal level at −1dBFS. In order to properly match the input impedance
seen at the LMH6554 amplifier inputs, RM is chosen to match ZS || RT for proper input balance. The amplifier is
configured to provide a gain of 2 V/V in single to differential mode. An external bandpass filter is inserted in
series between the input signal source and the amplifier to reduce harmonics and noise from the signal
generator.
90
85
80
75
SFDR (dBm)
70
65
60
55
50
45
40
0
100 200 300 400 500 600 700 750
INPUT FREQUENCY (MHz)
Figure 33. LMH6554 / ADC10D1500 SFDR and SNR Performance vs. Frequency
The amplifier and ADC should be located as close together as possible. Both devices require that the filter
components be in close proximity to them. The amplifier needs to have minimal parasitic loading on it's outputs
and the ADC is sensitive to high frequency noise that may couple in on its inputs. Some high performance ADCs
have an input stage that has a bandwidth of several times its sample rate. The sampling process results in all
input signals presented to the input stage mixing down into the first Nyquist zone (DC to Fs/2).
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200W
91W
R
= 50W
S
V
S
+
C
V
~
76.8W
0.1 mF
50W
50W
AC-Coupled
Source
ADC
+
-
V
CM
Up To 16-Bit
Data Converter
LMH6554
+
-
91W
0.1 mF
-
30W
0.1 mF
V
V
CMO
V
EN
200W
Figure 34. Driving a 10-bit Gigasample ADC
Output Noise Performance and Measurement
Unlike differential amplifiers based on voltage feedback architectures, noise sources internal to the LMH6554
refer to the inputs largely as current sources, hence the low input referred voltage noise and relatively higher
input referred current noise. The output noise is therefore more strongly coupled to the value of the feedback
resistor and not to the closed loop gain, as would be the case with a voltage feedback differential amplifier. This
allows operation of the LMH6554 at much higher gain without incurring a substantial noise performance penalty,
simply by choosing a suitable feedback resistor.
Figure 35 shows a circuit configuration used to measure noise figure for the LMH6554 in a 50Ω system. A
feedback resistor value of 200Ω is chosen for the UQFN package to minimize output noise while simultaneously
allowing both high gain (7 V/V) and proper 50Ω input termination. Refer to Single Ended Input To Differential
Output Operation for the calculation of resistor and gain values.
200W
+
V
1 mF
2:1 (TURNS)
R
= 50W
50W
S
8W
8W
+
-
V
CM
50W
V
O
LMH6554
V
S
~
+
-
1 mF
-
V
200W
= 7 V/V
A
V
Figure 35. Noise Figure Circuit Configuration
Driving Capacitive Loads
As noted previously, capacitive loads should be isolated from the amplifier output with small valued resistors.
This is particularly the case when the load has a resistive component that is 500Ω or higher. A typical ADC has
capacitive components of around 10 pF and the resistive component could be 1000Ω or higher. If driving a
transmission line, such as 50Ω coaxial or 100Ω twisted pair, using matching resistors will be sufficient to isolate
any subsequent capacitance. For other applications see Figure 8 in Typical Performance Characteristics VS =
±2.5V.
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Balanced Cable Driver
With up to 5.68 VPP differential output voltage swing the LMH6554 can be configured as a cable driver. The
LMH6554 is also suitable for driving differential cables from a single ended source as shown in Figure 36.
200W
50W
91W
R
S
= 50W
V
2 V
+
S
PP
V
LMH6554
CM
~
76.8W
Input
Source
-
91W
V
EN
50W
30.3W
100W
TWISTED PAIR
200W
Figure 36. Fully Differential Cable Driver
Power Supply Bypassing
The LMH6554 requires supply bypassing capacitors as shown in Figure 37 and Figure 38. The 0.01 μF and 0.1
μF capacitors should be leadless SMT ceramic capacitors and should be no more than 3 mm from the supply
pins. These capacitors should be star routed with a dedicated ground return plane or trace for best harmonic
distortion performance. Thin traces or small vias will reduce the effectiveness of bypass capacitors. Also shown
in both figures is a capacitor from the VCM and VEN pins to ground. These inputs are high impedance and can
provide a coupling path into the amplifier for external noise sources, possibly resulting in loss of dynamic range,
degraded CMRR, degraded balance and higher distortion.
+
V
10 mF
0.1 mF
0.01 mF
-OUT
+IN
-IN
+
V
CM
LMH6554
+OUT
-
VEN
0.1 mF
0.1 mF
-
V
10 mF
0.1 mF
0.01 mF
Figure 37. Split Supply Bypassing Capacitors
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+
V
0.01 mF
0.1 mF
10 mF
+IN
-IN
+
-OUT
V
CM
LMH6554
+OUT
-
VEN
0.1 mF
0.01 mF
Figure 38. Single Supply Bypassing Capacitors
Power Dissipation
The LMH6554 is optimized for maximum speed and performance in a small form factor 14 lead UQFN package.
To ensure maximum output drive and highest performance, thermal shutdown is not provided. Therefore, it is of
utmost importance to make sure that the TJMAX is never exceeded due to the overall power dissipation.
Follow these steps to determine the maximum power dissipation for the LMH6554:
1. Calculate the quiescent (no-load) power:
PAMP = ICC * (VS)
where
•
VS = V+ − V-. (Be sure to include any current through the feedback network if VCM is not mid-rail)
(1)
2. Calculate the RMS power dissipated in each of the output stages:
PD (rms) = rms ((VS − V+OUT) * I+OUT) + rms ((VS − V-OUT) * I-OUT
)
where
•
•
•
VOUT and IOUT are the voltage
the current measured at the output pins of the differential amplifier as if they were single ended amplifiers
VS is the total supply voltage
(2)
(3)
3. Calculate the total RMS power:
PT = PAMP + PD
The maximum power that the LMH6554 package can dissipate at a given temperature can be derived with the
following equation:
PMAX = (150° − TAMB)/ θJA
where
•
•
•
TAMB = Ambient temperature (°C)
θJA = Thermal resistance, from junction to ambient, for a given package (°C/W)
For the 14 lead UQFN package, θJA is 60°C/W
(4)
NOTE
If VCM is not 0V then there will be quiescent current flowing in the feedback network. This
current should be included in the thermal calculations and added into the quiescent power
dissipation of the amplifier.
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ESD Protection
The LMH6554 is protected against electrostatic discharge (ESD) on all pins. The LMH6554 will survive 2000V
Human Body model and 250V Machine model events. Under normal operation the ESD diodes have no affect on
circuit performance. There are occasions, however, when the ESD diodes will be evident. If the LMH6554 is
driven by a large signal while the device is powered down the ESD diodes will conduct. The current that flows
through the ESD diodes will either exit the chip through the supply pins or will flow through the device, hence it is
possible to power up a chip with a large signal applied to the input pins. Using the shutdown mode is one way to
conserve power and still prevent unexpected operation.
Board Layout
The LMH6554 is a high speed, high performance amplifier. In order to get maximum benefit from the differential
circuit architecture board layout and component selection is very critical. The circuit board should have a low
inductance ground plane and well bypassed broad supply lines. External components should be leadless surface
mount types. The feedback network and output matching resistors should be composed of short traces and
precision resistors (0.1%). The output matching resistors should be placed within 3 or 4 mm of the amplifier as
should the supply bypass capacitors. Refer to Power Supply Bypassing for recommendations on bypass circuit
layout. Evaluation boards are available through the product folder on ti.com.
By design, the LMH6554 is relatively insensitive to parasitic capacitance at its inputs. Nonetheless, ground and
power plane metal should be removed from beneath the amplifier and from beneath RF and RG for best
performance at high frequency.
With any differential signal path, symmetry is very important. Even small amounts of asymmetry can contribute to
distortion and balance errors.
Evaluation Board
See LMH6554 Product Folder for evaluation board availability and ordering information.
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SNOSB30O –OCTOBER 2008–REVISED MARCH 2013
REVISION HISTORY
Changes from Revision N (March 2013) to Revision O
Page
•
Changed layout of National Data Sheet to TI format .......................................................................................................... 18
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PACKAGE OPTION ADDENDUM
www.ti.com
11-Apr-2013
PACKAGING INFORMATION
Orderable Device
LMH6554LE/NOPB
LMH6554LEE/NOPB
LMH6554LEX/NOPB
Status Package Type Package Pins Package
Eco Plan Lead/Ball Finish
MSL Peak Temp
Op Temp (°C)
-40 to 125
Top-Side Markings
Samples
Drawing
Qty
(1)
(2)
(3)
(4)
ACTIVE
UQFN
UQFN
UQFN
NHJ
14
14
14
1000
Green (RoHS
& no Sb/Br)
CU SN
CU SN
CU SN
Level-3-260C-168 HR
Level-3-260C-168 HR
Level-3-260C-168 HR
AJA
AJA
AJA
ACTIVE
ACTIVE
NHJ
NHJ
250
Green (RoHS
& no Sb/Br)
-40 to 125
4500
Green (RoHS
& no Sb/Br)
-40 to 125
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
Multiple Top-Side Markings will be inside parentheses. Only one Top-Side Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a
continuation of the previous line and the two combined represent the entire Top-Side Marking for that device.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
26-Mar-2013
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
B0
K0
P1
W
Pin1
Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant
(mm) W1 (mm)
LMH6554LE/NOPB
LMH6554LEE/NOPB
LMH6554LEX/NOPB
UQFN
UQFN
UQFN
NHJ
NHJ
NHJ
14
14
14
1000
250
178.0
178.0
330.0
12.4
12.4
12.4
2.8
2.8
2.8
2.8
2.8
2.8
1.0
1.0
1.0
8.0
8.0
8.0
12.0
12.0
12.0
Q1
Q1
Q1
4500
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
26-Mar-2013
*All dimensions are nominal
Device
Package Type Package Drawing Pins
SPQ
Length (mm) Width (mm) Height (mm)
LMH6554LE/NOPB
LMH6554LEE/NOPB
LMH6554LEX/NOPB
UQFN
UQFN
UQFN
NHJ
NHJ
NHJ
14
14
14
1000
250
213.0
213.0
367.0
191.0
191.0
367.0
55.0
55.0
35.0
4500
Pack Materials-Page 2
MECHANICAL DATA
NHJ0014A
LEE14A (Rev B)
www.ti.com
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