5962-0254501VZA - National Semiconductor

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

January 2003

LMH6628 Dual Wideband, Low Noise, Voltage Feedback Op Amp

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

)(θ

)

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)

=±5V, A

= +2V/V, R

= 100Ω,R

= 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

<0.5V

200 MHz

SSBW -3dB Bandwidth, A

=+1 V

<0.5V

180 300 MHz

SSBW -3dB Bandwidth, A

=+2 V

<0.5V

100 MHz

GFL Gain Flatness V

<0.5V

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

, 10MHz −65 dBc

HD3 3rd Harmonic Distortion 1V

, 10MHz −74 dBc

Equivalent Input Noise

Voltage 1MHz to 100MHz 2 nV/

Current 1MHz to 100MHz 2 pA/

XTLKA Crosstalk Input Referred, 10MHz −62 dB

Static, DC Performance

Open-Loop Gain 56

63 dB

Input Offset Voltage ±.5 ±2

±2.6

Average Drift 5 µV/˚C

Input Bias Current ±.7 ±20

±30

µA

Average Drift 150 nA/˚C

Input Offset Current 0.3 ±6µA

OSD

Average Drift 5 nA/˚C

PSRR Power Supply Rejection Ratio 60

70 dB

CMRR Common-Mode Rejection Ratio 57

62 dB

Supply Current Per Channel, R

=∞7.5

7.0

912

12.5

LMH6628

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Electrical Characteristics (Note 2) (Continued)

=±5V, A

= +2V/V, R

= 100Ω,R

= 100Ω; unless otherwise specified. Boldface limits apply at the

temperature extremes.

Symbol Parameter Conditions Min Typ Max Units

Miscellaneous Performance

Input Resistance Common-Mode 500 kΩ

Differential-Mode 200 kΩ

Input Capacitance Common-Mode 1.5 pF

Differential-Mode 1.5 pF

OUT

Output Resistance Closed-Loop .1 Ω

Output Voltage Range R

=∞±3.8 V

= 100Ω±3.2

±3.1

±3.5 V

CMIR Input Voltage Range Common- Mode ±3.7 V

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

= +25˚, A

= +2, V

=±5V, R

=100Ω,R

= 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

= +25˚, A

= +2, V

=±5V, R

=100Ω,R

= 100Ω,

unless specified) (Continued)

Channel Matching Channel to Channel Crosstalk

20038514 20038509

Pulse Response (V

= 2V) Pulse Response (V

= 100mV)

20038511 20038512

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

20038507 20038508

LMH6628

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Typical Performance Characteristics (T

= +25˚, A

= +2, V

=±5V, R

=100Ω,R

= 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

= +25˚, A

= +2, V

=±5V, R

=100Ω,R

= 100Ω,

unless specified) (Continued)

Open Loop Gain & Phase (±5V) Recommended R

vs. C

20038520

20038526

DC Errors vs. Temperature Maximum V

vs. R

20038546 20038545

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

20038544 20038547

LMH6628

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Typical Performance Characteristics (T

= +25˚, A

= +2, V

=±5V, R

=100Ω,R

= 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

and

, 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

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

) multiplied by the

desired gain (A

). 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

vs. C

" 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

and R

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)

d=1

360

φ;

(2)

where T

is the delay of the op amp at A

= +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

) is connected across R and forms

differential amplifier for the signals transmitted by driver A

). If R

equals R

, receiver A

) will then reject the

signals from driver A

) and pass the signals from driver

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

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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

is less than

. 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

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

frequency circuits - R

between 10Ωand 5kΩ, C between

10pF and 2000pF. Use Eq. 7 to determine the parallel com-

bination of R

and R

. Select R

and R

by either the 10Ωto

5kΩcriteria or by other requirements based on the imped-

ance V

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

is 2.3MHz. The component values are as

follows: R

=2.1kΩ,R

= 68.5Ω,R

= 4.22kΩ,R=500Ω,KR

=50Ω, C = 120pF.

20038537

FIGURE 6.

20038506

FIGURE 7.

20038543

FIGURE 8.

LMH6628

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Physical Dimensions inches (millimeters)

unless otherwise noted

8-Pin SOIC

NS Package Number M08A

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COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

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systems which, (a) are intended for surgical implant

into the body, or (b) support or sustain life, and

whose failure to perform when properly used in

accordance with instructions for use provided in the

labeling, can be reasonably expected to result in a

significant injury to the user.

2. A critical component is any component of a life

support device or system whose failure to perform

can be reasonably expected to cause the failure of

the life support device or system, or to affect its

safety or effectiveness.

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LMH6628 Dual Wideband, Low Noise, Voltage Feedback Op Amp

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.