Datasheet LMH6628 Datasheet (National Semiconductor)

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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 (

Each of the LMH6628’s closely matched channels provides
a 300MHz unity gain bandwidth and low input voltage noise
density (2nV/

−74dBc at 10MHz) make the LMH6628 a perfect wide dy­namic 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 amplifi­ers.

The LMH6628 is fabricated using National’s VIP10
plimentary bipolar process.

±

5V) power supply.

). Low 2nd/3rd harmonic distortion (−65/

™

com-

To reduce design times and assist in board layout, the
LMH6628 is supported by an evaluation board
(CLC730036).

Features

n Wide unity gain bandwidth: 300MHz
n Low noise: 2nV/
n Low Distortion: −65/−74dBc (10MHz)
n Settling time: 12ns to 0.1%

±

85mA

±

2.5V to±6V

n Wide supply voltage range:
n High output current:
n Improved replacement for CLC428

Applications

n High speed dual op amp
n Low noise integrators
n Low noise active filters
n Driver/receiver for transmission systems
n High speed detectors
n I/Q channel amplifiers

LMH6628 Dual Wideband, Low Noise, Voltage Feedback Op Amp

January 2003

Connection Diagram

8-Pin SOIC

Top View

Inverting Frequency Response

20038535

20038515

© 2003 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/

LMH6628

Distributors for availability and specifications.

ESD Tolerance (Note 4)

Maximum Junction Temperature +150˚C

Storage Temperature Range −65˚C to +150˚C

Lead Temperature (soldering 10 sec) +300˚C

Operating Ratings (Note 1)

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

−

Thermal Resistance (Note 5)

Package (θ

)(θJA)

JC

SOIC 65˚C/W 145˚C/W

Temperature Range −40˚C to +85˚C

Nominal Supply Voltage

±

Electrical Characteristics (Note 2)

VCC=±5V, AV= +2V/V, RF= 100Ω,RG= 100Ω,RL= 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

SSBW -3dB Bandwidth, A

SSBW -3dB Bandwidth, A

=+1 V

V

=+2 V

V

GFL Gain Flatness V

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

HD3 3rd Harmonic Distortion 1V

Equivalent Input Noise

V

N

I

N

Voltage 1MHz to 100MHz 2 nV/

Current 1MHz to 100MHz 2 pA/

XTLKA Crosstalk Input Referred, 10MHz −62 dB

Static, DC Performance

G

V

DV

I

BN

DI

I

OS

I

OSD

OL

IO

IO

BN

Open-Loop Gain 56

Input Offset Voltage

Average Drift 5 µV/˚C

Input Bias Current

Average Drift 150 nA/˚C

Input Offset Current 0.3

Average Drift 5 nA/˚C

PSRR Power Supply Rejection Ratio 60

CMRR Common-Mode Rejection Ratio 57

I

CC

Supply Current Per Channel, RL=

<

0.5V

O

O

O

O

PP

<

0.5V

PP

<

0.5V

PP

<

0.5V

PP

, 10MHz −65 dBc

PP

, 10MHz −74 dBc

PP

180 300 MHz

200 MHz

100 MHz

63 dB

53

±

.5

±

.7

±

2

±

2.6

±

20

±

30

±

6µA

70 dB

46

62 dB

54

∞

7.5

7.0

912

12.5

2.5V to±6V

mV

µA

mA

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Electrical Characteristics (Note 2) (Continued)

VCC=±5V, AV= +2V/V, RF= 100Ω,RG= 100Ω,RL= 100Ω; unless otherwise specified. Boldface limits apply at the
temperature extremes.

Symbol Parameter Conditions Min Typ Max Units

Miscellaneous Performance

R

IN

C

IN

R

OUT

V

O

V

OL

CMIR Input Voltage Range Common- Mode

I

O

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 T
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, 1.5kΩ in series with 100pF. Machine model, 0Ω In series with 200pF.

Note 5: The maximum power dissipation is a function of T

P

=(T

D

Input Resistance Common-Mode 500 kΩ

Differential-Mode 200 kΩ

Input Capacitance Common-Mode 1.5 pF

Differential-Mode 1.5 pF

Output Resistance Closed-Loop .1 Ω

Output Voltage Range RL=

RL= 100Ω

Output Current

. No guarantee of parametric performance is indicated in the electrical tables under conditions of internal self heating where T

J=TA

, θJAand TA. The maximum allowable power dissipation at any ambient temperature is

)/ θJA. All numbers apply for packages soldered directly onto a PC board.

J(MAX)-TA

J(MAX)

∞

±

3.2

±

3.1

±

50

±

3.8 V

±

3.5 V

±

3.7 V

±

85 mA

J

LMH6628

>

TA.

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

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Typical Performance Characteristics (T

less specified)

LMH6628

Non-Inverting Frequency Response Inverting Frequency Response

= +25˚, AV= +2, VCC=±5V, Rf=100Ω,RL= 100Ω, un-

A

20038513

20038515

Frequency Response vs. Load Resistance Frequency Response vs. Output Amplitude

20038525

20038510

Frequency Response vs. Capacitive Load Gain Flatness & Linear Phase

20038516

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20038524

LMH6628

Typical Performance Characteristics (T

unless specified) (Continued)

Channel Matching Channel to Channel Crosstalk

20038514

Pulse Response (VO= 2V) Pulse Response (VO= 100mV)

= +25˚, AV= +2, VCC=±5V, Rf=100Ω,RL= 100Ω,

A

20038509

20038511 20038512

2nd Harmonic Distortion vs. Output Voltage 3rd Harmonic Distortion vs. Output Voltage

20038507 20038508

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Typical Performance Characteristics (T

unless specified) (Continued)

LMH6628

2nd & 3rd Harmonic Distortion vs. Frequency PSRR and CMRR (

= +25˚, AV= +2, VCC=±5V, Rf=100Ω,RL= 100Ω,

A

±

5V)

20038517

PSRR and CMRR (±2.5V) Closed Loop Output Resistance (±2.5V)

20038523 20038518

Closed Loop Output Resistance (±5V) Open Loop Gain & Phase (±2.5V)

20038522

20038519 20038521

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LMH6628

Typical Performance Characteristics (T

unless specified) (Continued)

Open Loop Gain & Phase (

DC Errors vs. Temperature Maximum VOvs. R

±

5V) Recommended RSvs. C

20038520

= +25˚, AV= +2, VCC=±5V, Rf=100Ω,RL= 100Ω,

A

L

L

20038526

20038546

20038545

2-Tone, 3rd Order Intermodulation Intercept Voltage & Current Noise vs. Frequency

20038544

20038547

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Typical Performance Characteristics (T

unless specified) (Continued)

LMH6628

Settling Time vs. Accuracy

= +25˚, AV= +2, VCC=±5V, Rf=100Ω,RL= 100Ω,

A

20038548

Application Section

LOW NOISE DESIGN

Ultimate low noise performance from circuit designs using
the LMH6628 requires the proper selection of external resis­tors. By selecting appropriate low valued resistors for R

, amplifier circuits using the LMH6628 can achieve output

R

G

noise that is approximately the equivalent voltage input
noise of 2nV/

multiplied by the desired gain (AV).

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 non­inverting inputs equal. Once done, the residual output offset
voltage will be the input offset voltage (V
desired gain (A

). National Application Note OA-7 offers

V

) multiplied by the

OS

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

vs. CL" in the Typical Performance section.

S

and

F

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

and RGshould be of equal

F

and low value for parasitic insensitive operation.

20038501

FIGURE 1.

LAYOUT

Proper power supply bypassing is critical to insure good high
frequency performance and low noise. De-coupling capaci­tors 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.

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20038502

FIGURE 2. Delay Circuit Response to 0.5V Pulse

Application Section (Continued)

The circuit gain is +1 and the delay is determined by the
following equations.

(1)

φ

d

1

=

T

d

360

where T

is the delay of the op amp at AV= +1.

d

The LMH6628 provides a typical delay of 2.8ns at its −3dB
point.

;

df

(2)

LMH6628

20038531

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 band­width and high common-mode rejection in a differential am­plifier 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

) is connected across R and forms

2(B2

differential amplifier for the signals transmitted by driver A
(B2). If RFequals RG, receiver A2(B1) will then reject the
signals from driver A

).

B

1(A1

) and pass the signals from driver

1(B1

FIGURE 4.

POSITIVE PEAK DETECTOR

The LMH6628’s dual amplifiers can be used to implement a
unity-gain peak detector circuit as shown in Figure 5.

2

20038505

FIGURE 5.

20038503

FIGURE 3.

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.

The acquisition speed of this circuit is limited by the dynamic
resistance of the diode when charging C

. A plot of the

hold

circuit’s performance is shown in Figure 6 with a 1MHz
sinusoidal input.

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Application Section (Continued)

LMH6628

20038537

FIGURE 6.

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

. A MOS-type switch (not shown) can be used to reset the

V

C

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.

is less than

IN

(4)

To build a boost circuit, use the design equations Eq. 6 and
Eq. 7.

(5)

(6)

Select R
frequency circuits - R

and C using Eq. 6. Use reasonable values for high

2

between 10Ω and 5kΩ, C between

2

10pF and 2000pF. Use Eq. 7 to determine the parallel com­bination of R

and Rb. Select Raand Rbby either the 10Ω to

a

5kΩ criteria or by other requirements based on the imped­ance V

is capable of driving. Finish the design by determin-

in

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
follows: R

a

is 2.3MHz. The component values are as

o

=2.1kΩ,Rb= 68.5Ω,R2= 4.22kΩ,R=500Ω,KR

=50Ω, C = 120pF.

20038506

FIGURE 7.

The overall transfer function is shown in Eq. 5.

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20038543

FIGURE 8.

Physical Dimensions inches (millimeters)

unless otherwise noted

NS Package Number M08A

LMH6628 Dual Wideband, Low Noise, Voltage Feedback Op Amp

8-Pin SOIC

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can be reasonably expected to cause the failure of
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significant injury to the user.

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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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