LMH6628
LMH6628 Dual Wideband, Low Noise, Voltage Feedback Op Amp
Literature Number: SNOSA02C
LMH6628
Dual Wideband, Low Noise, Voltage Feedback Op Amp
General Description
The National LMH6628 is a high speed dual op amp that
offers a traditional voltage feedback topology featuring unity
gain stability and slew enhanced circuitry. The LMH6628’s
low noise and very low harmonic distortion combine to form
a wide dynamic range op amp that operates from a single
(5V to 12V) or dual (±5V) power supply.
Each of the LMH6628’s closely matched channels provides
a 300MHz unity gain bandwidth and low input voltage noise
density (2nV/ ). Low 2nd/3rd harmonic distortion (−65/
−74dBc at 10MHz) make the LMH6628 a perfect wide dy-
namic range amplifier for matched I/Q channels.
With its fast and accurate settling (12ns to 0.1%), the
LMH6628 is also an excellent choice for wide dynamic
range, anti-aliasing filters to buffer the inputs of hi resolution
analog-to-digital converters. Combining the LMH6628’s two
tightly matched amplifiers in a single 8-pin SOIC package
reduces cost and board space for many composite amplifier
applications such as active filters, differential line drivers/
receivers, fast peak detectors and instrumentation amplifi-
ers.
The LMH6628 is fabricated using National’s VIP10™com-
plimentary bipolar process.
To reduce design times and assist in board layout, the
LMH6628 is supported by an evaluation board
(CLC730036).
Features
nWide unity gain bandwidth: 300MHz
nLow noise: 2nV/
nLow Distortion: −65/−74dBc (10MHz)
nSettling time: 12ns to 0.1%
nWide supply voltage range: ±2.5V to ±6V
nHigh output current: ±85mA
nImproved replacement for CLC428
Applications
nHigh speed dual op amp
nLow noise integrators
nLow noise active filters
nDriver/receiver for transmission systems
nHigh speed detectors
nI/Q channel amplifiers
Connection Diagram
8-Pin SOIC
20038535
Top View
Inverting Frequency Response
20038515
May 2005
LMH6628 Dual Wideband, Low Noise, Voltage Feedback Op Amp
© 2005 National Semiconductor Corporation DS200385 www.national.com
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
ESD Tolerance (Note 4)
Human Body Model 2kV
Machine Model 200V
Supply Voltage 13.5
Short Circuit Current (Note 3)
Common-Mode Input Voltage V
+
-V
−
Differential Input Voltage V
+
-V
−
Maximum Junction Temperature +150˚C
Storage Temperature Range −65˚C to +150˚C
Lead Temperature (soldering 10 sec) +300˚C
Operating Ratings (Note 1)
Thermal Resistance (Note 5)
Package (θ
JC
)(θ
JA
)
SOIC 65˚C/W 145˚C/W
Temperature Range −40˚C to +85˚C
Nominal Supply Voltage ±2.5V to ±6V
Electrical Characteristics (Note 2)
V
CC
=±5V, A
V
= +2V/V, R
F
= 100Ω,R
G
= 100Ω,R
L
= 100Ω; unless otherwise specified. Boldface limits apply at the
temperature extremes.
Symbol Parameter Conditions Min Typ Max Units
Frequency Domain Response
GB Gain Bandwidth Product V
O
<0.5V
PP
200 MHz
SSBW -3dB Bandwidth, A
V
=+1 V
O
<0.5V
PP
180 300 MHz
SSBW -3dB Bandwidth, A
V
=+2 V
O
<0.5V
PP
100 MHz
GFL Gain Flatness V
O
<0.5V
PP
GFP Peaking DC to 200MHz 0.0 dB
GFR Rolloff DC to 20MHz .1 dB
LPD Linear Phase Deviation DC to 20MHz .1 deg
Time Domain Response
TR Rise and Fall Time 1V Step 4 ns
TS Settling Time 2V Step to 0.1% 12 ns
OS Overshoot 1V Step 1 %
SR Slew Rate 4V Step 300 550 V/µs
Distortion And Noise Response
HD2 2nd Harmonic Distortion 1V
PP
, 10MHz −65 dBc
HD3 3rd Harmonic Distortion 1V
PP
, 10MHz −74 dBc
Equivalent Input Noise
V
N
Voltage 1MHz to 100MHz 2 nV/
I
N
Current 1MHz to 100MHz 2 pA/
XTLKA Crosstalk Input Referred, 10MHz −62 dB
Static, DC Performance
G
OL
Open-Loop Gain 56
53
63 dB
V
IO
Input Offset Voltage ±.5 ±2
±2.6
mV
DV
IO
Average Drift 5 µV/˚C
I
BN
Input Bias Current ±.7 ±20
±30
µA
DI
BN
Average Drift 150 nA/˚C
I
OS
Input Offset Current 0.3 ±6µA
I
OSD
Average Drift 5 nA/˚C
PSRR Power Supply Rejection Ratio 60
46
70 dB
CMRR Common-Mode Rejection Ratio 57
54
62 dB
I
CC
Supply Current Per Channel, R
L
=∞7.5
7.0
912
12.5
mA
LMH6628
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Electrical Characteristics (Note 2) (Continued)
V
CC
=±5V, A
V
= +2V/V, R
F
= 100Ω,R
G
= 100Ω,R
L
= 100Ω; unless otherwise specified. Boldface limits apply at the
temperature extremes.
Symbol Parameter Conditions Min Typ Max Units
Miscellaneous Performance
R
IN
Input Resistance Common-Mode 500 kΩ
Differential-Mode 200 kΩ
C
IN
Input Capacitance Common-Mode 1.5 pF
Differential-Mode 1.5 pF
R
OUT
Output Resistance Closed-Loop .1 Ω
V
O
Output Voltage Range R
L
=∞±3.8 V
V
OL
R
L
= 100Ω±3.2
±3.1
±3.5 V
CMIR Input Voltage Range Common- Mode ±3.7 V
I
O
Output Current ±50 ±85 mA
Note 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 guaranteed. For guaranteed specifications, see the Electrical Characteristics tables.
Note 2: 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=T
A. No guarantee of parametric performance is indicated in the electrical tables under conditions of internal self heating where TJ>TA.
See Note 6 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.
Note 3: Output is short circuit protected to ground, however maximum reliability is obtained if output current does not exceed 160mA.
Note 4: Human body model, 1.5kΩin series with 100pF. Machine model, 0ΩIn series with 200pF.
Note 5: The maximum power dissipation is a function of TJ(MAX),θJA and TA. The maximum allowable power dissipation at any ambient temperature is
PD=(T
J(MAX)-TA)/ θJA. All numbers apply for packages soldered directly onto a PC board.
Ordering Information
Package Part Number Package Marking Transport Media NSC Drawing
8-pin SOIC LMH6628MA LMH6628MA Rails M08A
LMH6628MAX 2.5k Units Tape and Reel
LMH6628
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Typical Performance Characteristics (T
A
= +25˚, A
V
= +2, V
CC
=±5V, R
f
=100Ω,R
L
= 100Ω, un-
less specified)
Non-Inverting Frequency Response Inverting Frequency Response
20038513 20038515
Frequency Response vs. Load Resistance Frequency Response vs. Output Amplitude
20038525 20038510
Frequency Response vs. Capacitive Load Gain Flatness & Linear Phase
20038516
20038524
LMH6628
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Typical Performance Characteristics (T
A
= +25˚, A
V
= +2, V
CC
=±5V, R
f
=100Ω,R
L
= 100Ω, unless
specified) (Continued)
Channel Matching Channel to Channel Crosstalk
20038514 20038509
Pulse Response (V
O
= 2V) Pulse Response (V
O
= 100mV)
20038511 20038512
2nd Harmonic Distortion vs. Output Voltage 3rd Harmonic Distortion vs. Output Voltage
20038507 20038508
LMH6628
www.national.com5
Typical Performance Characteristics (T
A
= +25˚, A
V
= +2, V
CC
=±5V, R
f
=100Ω,R
L
= 100Ω, unless
specified) (Continued)
2nd & 3rd Harmonic Distortion vs. Frequency PSRR and CMRR (±5V)
20038517 20038522
PSRR and CMRR (±2.5V) Closed Loop Output Resistance (±2.5V)
20038523 20038518
Closed Loop Output Resistance (±5V) Open Loop Gain & Phase (±2.5V)
20038519 20038521
LMH6628
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Typical Performance Characteristics (T
A
= +25˚, A
V
= +2, V
CC
=±5V, R
f
=100Ω,R
L
= 100Ω, unless
specified) (Continued)
Open Loop Gain & Phase (±5V) Recommended R
S
vs. C
L
20038520
20038526
DC Errors vs. Temperature Maximum V
O
vs. R
L
20038546 20038545
2-Tone, 3rd Order Intermodulation Intercept Voltage & Current Noise vs. Frequency
20038544 20038547
LMH6628
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Typical Performance Characteristics (T
A
= +25˚, A
V
= +2, V
CC
=±5V, R
f
=100Ω,R
L
= 100Ω, unless
specified) (Continued)
Settling Time vs. Accuracy
20038548
Application Section
LOW NOISE DESIGN
Ultimate low noise performance from circuit designs using
the LMH6628 requires the proper selection of external resis-
tors. By selecting appropriate low valued resistors for R
F
and
R
G
, amplifier circuits using the LMH6628 can achieve output
noise that is approximately the equivalent voltage input
noise of 2nV/ multiplied by the desired gain (A
V
).
DC BIAS CURRENTS AND OFFSET VOLTAGES
Cancellation of the output offset voltage due to input bias
currents is possible with the LMH6628. This is done by
making the resistance seen from the inverting and non-
inverting inputs equal. Once done, the residual output offset
voltage will be the input offset voltage (V
OS
) multiplied by the
desired gain (A
V
). National Application Note OA-7 offers
several solutions to further reduce the output offset.
OUTPUT AND SUPPLY CONSIDERATIONS
With ±5V supplies, the LMH6628 is capable of a typical
output swing of ±3.8V under a no-load condition. Additional
output swing is possible with slightly higher supply voltages.
For loads of less than 50Ω, the output swing will be limited by
the LMH6628’s output current capability, typically 85mA.
Output settling time when driving capacitive loads can be
improved by the use of a series output resistor. See the plot
labeled "R
S
vs. C
L
" in the Typical Performance section.
LAYOUT
Proper power supply bypassing is critical to insure good high
frequency performance and low noise. De-coupling capaci-
tors of 0.1µF should be placed as close as possible to the
power supply pins. The use of surface mounted capacitors is
recommended due to their low series inductance.
A good high frequency layout will keep power supply and
ground traces away from the inverting input and output pins.
Parasitic capacitance from these nodes to ground causes
frequency response peaking and possible circuit oscillation.
See OA-15 for more information. National suggests the
730036 (SOIC) dual op amp evaluation board as a guide for
high frequency layout and as an aid in device evaluation.
ANALOG DELAY CIRCUIT (ALL-PASS NETWORK)
The circuit in Figure 1 implements an all-pass network using
the LMH6628. A wide bandwidth buffer (LM7121) drives the
circuit and provides a high input impedance for the source.
As shown in Figure 2, the circuit provides a 13.1ns delay
(with R = 40.2Ω, C = 47pF). R
F
and R
G
should be of equal
and low value for parasitic insensitive operation.
20038501
FIGURE 1.
20038502
FIGURE 2. Delay Circuit Response to 0.5V Pulse
LMH6628
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Application Section (Continued)
The circuit gain is +1 and the delay is determined by the
following equations.
(1)
Td
df
d=1
360
φ;
(2)
where T
d
is the delay of the op amp at A
V
= +1.
The LMH6628 provides a typical delay of 2.8ns at its −3dB
point.
FULL DUPLEX DIGITAL OR ANALOG TRANSMISSION
Simultaneous transmission and reception of analog or digital
signals over a single coaxial cable or twisted-pair line can
reduce cabling requirements. The LMH6628’s wide band-
width and high common-mode rejection in a differential am-
plifier configuration allows full duplex transmission of video,
telephone, control and audio signals.
In the circuit shown in Figure 3, one of the LMH6628’s amps
is used as a "driver" and the other as a difference "receiver"
amplifier. The output impedance of the "driver" is essentially
zero. The two R’s are chosen to match the characteristic
impedance of the transmission line. The "driver" op amp gain
can be selected for unity or greater.
Receiver amplifier A
2
(B
2
) is connected across R and forms
differential amplifier for the signals transmitted by driver A
2
(B
2
). If R
F
equals R
G
, receiver A
2
(B
1
) will then reject the
signals from driver A
1
(B
1
) and pass the signals from driver
B
1
(A
1
).
The output of the receiver amplifier will be:
(3)
Care must be given to layout and component placement to
maintain a high frequency common-mode rejection. The plot
of Figure 4 shows the simultaneous reception of signals
transmitted at 1MHz and 10MHz.
POSITIVE PEAK DETECTOR
The LMH6628’s dual amplifiers can be used to implement a
unity-gain peak detector circuit as shown in Figure 5.
The acquisition speed of this circuit is limited by the dynamic
resistance of the diode when charging C
hold
. A plot of the
circuit’s performance is shown in Figure 6 with a 1MHz
sinusoidal input.
20038503
FIGURE 3.
20038531
FIGURE 4.
20038505
FIGURE 5.
LMH6628
www.national.com9
Application Section (Continued)
A current source, built around Q1, provides the necessary
bias current for the second amplifier and prevents saturation
when power is applied. The resistor, R, closes the loop while
diode D2 prevents negative saturation when V
IN
is less than
V
C
. A MOS-type switch (not shown) can be used to reset the
capacitor’s voltage.
The maximum speed of detection is limited by the delay of
the op amps and the diodes. The use of Schottky diodes will
provide faster response.
ADJUSTABLE OR BANDPASS EQUALIZER
A "boost" equalizer can be made with the LMH6628 by
summing a bandpass response with the input signal, as
shown in Figure 7.
The overall transfer function is shown in Eq. 5.
(4)
To build a boost circuit, use the design equations Eq. 6 and
Eq. 7.
(5)
(6)
Select R
2
and C using Eq. 6. Use reasonable values for high
frequency circuits - R
2
between 10Ωand 5kΩ, C between
10pF and 2000pF. Use Eq. 7 to determine the parallel com-
bination of R
a
and R
b
. Select R
a
and R
b
by either the 10Ωto
5kΩcriteria or by other requirements based on the imped-
ance V
in
is capable of driving. Finish the design by determin-
ing the value of K from Eq. 8.
(7)
Figure 8 shows an example of the response of the circuit of
Figure 9, where f
o
is 2.3MHz. The component values are as
follows: R
a
=2.1kΩ,R
b
= 68.5Ω,R
2
= 4.22kΩ,R=500Ω,KR
=50Ω, C = 120pF.
20038537
FIGURE 6.
20038506
FIGURE 7.
20038543
FIGURE 8.
LMH6628
www.national.com 10
Physical Dimensions inches (millimeters)
unless otherwise noted
8-Pin SOIC
NS Package Number M08A
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
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LMH6628 Dual Wideband, Low Noise, Voltage Feedback Op Amp
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