LMH6702MFX - Texas Instruments High-Performance Analog

LMH6702

LMH6702 1.7 GHz, Ultra Low Distortion, Wideband Op Amp

Literature Number: SNOSA03E

LMH6702

1.7 GHz, Ultra Low Distortion, Wideband Op Amp

General Description

The LMH6702 is a very wideband, DC coupled monolithic

operational amplifier designed specifically for wide dynamic

range systems requiring exceptional signal fidelity. Benefit-

ing from National’s current feedback architecture, the

LMH6702 offers unity gain stability at exceptional speed

without need for external compensation.

With its 720MHz bandwidth (A

= 2V/V, V

=2V

), 10-bit

distortion levels through 60MHz (R

= 100Ω), 1.83nV/

input referred noise and 12.5mA supply current, the

LMH6702 is the ideal driver or buffer for high-speed flash

A/D and D/A converters.

Wide dynamic range systems such as radar and communi-

cation receivers, requiring a wideband amplifier offering ex-

ceptional signal purity, will find the LMH6702’s low input

referred noise and low harmonic and intermodulation distor-

tion make it an attractive high speed solution.

The LMH6702 is constructed using National’s VIP10™com-

plimentary bipolar process and National’s proven current

feedback architecture. The LMH6702 is available in SOIC

and SOT23-5 packages.

Features

=±5V, T

= 25˚C, A

= +2V/V, R

= 100Ω,V

OUT

=2V

Typical unless Noted:

Harmonics (5MHz, SOT23-5) −100/−96dBc

n−3dB Bandwidth (V

OUT

= 0.5 V

) 1.7 GHz

nLow noise 1.83nV/

nFast settling to 0.1% 13.4ns

nFast slew rate 3100V/µs

nSupply current 12.5mA

nOutput current 80mA

nLow Intermodulation Distortion (75MHz) −67dBc

nImproved Replacement for CLC409 and CLC449

Applications

nFlash A/D driver

nD/A transimpedance buffer

nWide dynamic range IF amp

nRadar/communication receivers

nLine driver

nHigh resolution video

Inverting Frequency Response Harmonic Distortion vs. Load and Frequency

20039002 20039007

May 2005

1.7 GHz, LMH6702 Ultra Low Distortion, Wideband 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.

±6.75V

OUT

(Note 3)

Common Mode Input Voltage V

−

to V

Maximum Junction Temperature +150˚C

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

Soldering Information

Infrared or Convection (20 sec.) 235˚C

Wave Soldering (10 sec.) 260˚C

ESD Tolerance (Note 4)

Human Body Model 2000V

Machine Model 200V

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

Operating Ratings (Note 1)

Thermal Resistance

Package (θ

)(θ

)

8-Pin SOIC 75˚C/W 160˚C/W

5-Pin SOT23 120˚C/W 187˚C/W

Operating Temperature −40˚C to +85˚C

Nominal Supply Voltage ±5V to ±6V

Electrical Characteristics (Note 2)

= +2, V

=±5V, R

= 100Ω,R

= 237Ω; unless specified

Symbol Parameter Conditions Min

(Note 6)

Typ

(Note 6)

Max

(Note 6)

Units

Frequency Domain Performance

SSBW

-3dB Bandwidth V

OUT

= 0.5V

1700

MHz

SSBW

OUT

=2V

720

LSBW

OUT

=4V

480

SSBW

OUT

=2V

= +10 140

0.1dB

0.1dB Gain Flatness V

OUT

=2V

120 MHz

LPD Linear Phase Deviation DC to 100MHz 0.09 deg

DG Differential Gain R

=150Ω, 3.58MHz/4.43MHz 0.024/0.021 %

DP Differential Phase R

= 150Ω, 3.58MHz/4.43MHz 0.004/0.007 deg

Time Domain Response

TRS/TRL Rise and Fall Time 2V Step 0.87/0.77 ns

6V Step 1.70/1.70 ns

OS Overshoot 2V Step 0 %

SR Slew Rate 6V

, 40% to 60% (Note 5) 3100 V/µs

Settling Time to 0.1% 2V Step 13.4 ns

Distortion And Noise Response

HD2L 2

Harmonic Distortion 2V

, 5MHz (Note 9)

(SOT23-5/SOIC)

−100/ −87 dBc

HD2 2V

, 20MHz (Note 9)

(SOT23-5/SOIC)

−79/ −72 dBc

HD2H 2V

, 60MHz (Note 9)

(SOT23-5/SOIC)

−63/ −64 dBc

HD3L 3

Harmonic Distortion 2V

, 5MHz (Note 9)

(SOT23-5/SOIC)

−96/ −98 dBc

HD3 2V

, 20MHz (Note 9)

(SOT23-5/SOIC)

−88/ −82 dBc

HD3H 2V

, 60MHz (Note 9)

(SOT23-5/SOIC)

−70/ −65 dBc

OIM3 IMD 75MHz, P

= 10dBm/ tone −67 dBc

Input Referred Voltage Noise >1MHz 1.83 nV/

Input Referred Inverting Noise

Current

>1MHz 18.5 pA/

Input Referred Non-Inverting

Noise Current

>1MHz 3.0 pA/

SNF Total Input Noise Floor >1MHz −158 dBm

1Hz

LMH6702

www.national.com 2

Electrical Characteristics (Note 2) (Continued)

= +2, V

=±5V, R

= 100Ω,R

= 237Ω; unless specified

Symbol Parameter Conditions Min

(Note 6)

Typ

(Note 6)

Max

(Note 6)

Units

INV Total Integrated Input Noise 1MHz to 150MHz 35 µV

Static, DC Performance

Input Offset Voltage ±1.0 ±4.5

±6.0

Input Offset Voltage Average

Drift

(Note 8) −13 µV/˚C

Input Bias Current Non-Inverting (Note 7) −6 ±15

±21

µA

Input Bias Current Average Drift Non-Inverting (Note 8) +40 nA/˚C

Input Bias Current Inverting (Note 7) −8 ±30

±34

µA

Input Bias Current Average Drift Inverting (Note 8) −10 nA/˚C

PSRR Power Supply Rejection Ratio DC 47

52 dB

CMRR Common Mode Rejection Ration DC 45

48 dB

Supply Current R

=∞11.0

10.0

12.5 16.1

17.5

Miscellaneous Performance

Input Resistance Non-Inverting 1.4 MΩ

Input Capacitance Non-Inverting 1.6 pF

OUT

Output Resistance Closed Loop 30 mΩ

Output Voltage Range R

= 100Ω±3.3

±3.2

±3.5 V

CMIR Input Voltage Range Common Mode ±1.9 ±2.2 V

Output Current 50 80 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.

Min/Max ratings are based on production testing unless otherwise specified.

Note 3: The maximum output current (IOUT) is determined by device power dissipation limitations.

Note 4: Human body model: 1.5kΩin series with 100pF. Machine model: 0Ωin series with 200pF.

Note 5: Slew Rate is the average of the rising and falling edges.

Note 6: Typical numbers are the most likely parametric norm. Bold numbers refer to over temperature limits.

Note 7: Negative input current implies current flowing out of the device.

Note 8: Drift determined by dividing the change in parameter at temperature extremes by the total temperature change.

Note 9: Harmonic distortion is strongly influenced by package type (SOT23-5 or SOIC). See Application Note section under "Harmonic Distortion" for more

information.

LMH6702

www.national.com3

Connection Diagrams

8-Pin SOIC 5-Pin SOT23

20039024

Top View 20039025

Top View

Ordering Information

Package Part Number Package Marking Transport Media NSC Drawing

8-pin SOIC LMH6702MA LMH6702MA 95 Units/Rail M08A

LMH6702MAX 2.5k Units Tape and Reel

5-Pin SOT23 LMH6702MF A83A 1k Units Tape and Reel MF05A

LMH6702MFX 3k Units Tape and Reel

LMH6702

www.national.com 4

Typical Performance Characteristics (T

= 25˚C, V

=±5V, R

= 100Ω,R

= 237Ω; Unless Speci-

fied).

Non-Inverting Frequency Response Inverting Frequency Response

20039001 20039002

Small Signal Bandwidth Frequency Response for Various R

’s, A

=+2

20039030 20039018

Frequency Response for Various R

’s, A

= +4 Step Response, 2V

20039017 20039005

LMH6702

www.national.com5

Typical Performance Characteristics (T

= 25˚C, V

=±5V, R

= 100Ω,R

= 237Ω; Unless

Specified). (Continued)

Step Response, 6V

Percent Settling vs. Time

20039006 20039020

Harmonic Distortion vs. Load and Frequency

(SOIC package)

2 Tone 3rd Order Spurious Level

(SOIC package)

20039007 20039021

and Settling Time vs. C

HD2 vs. Output Power (across 100Ω)

(SOIC package)

20039013 20039008

LMH6702

www.national.com 6

Typical Performance Characteristics (T

= 25˚C, V

=±5V, R

= 100Ω,R

= 237Ω; Unless

Specified). (Continued)

HD3 vs. Output Power (across 100Ω)

(SOIC package) Input Offset for 3 Representative Units

20039009 20039014

Inverting Input Bias for 3 Representative Units Non-Inverting Input Bias for 3 Representative Units

20039015 20039016

Noise CMRR, PSRR, R

OUT

20039012 20039019

LMH6702

www.national.com7

Typical Performance Characteristics (T

= 25˚C, V

=±5V, R

= 100Ω,R

= 237Ω; Unless

Specified). (Continued)

Transimpedance DG/DP (NTSC)

20039011 20039004

DG/DP (PAL)

20039003

LMH6702

www.national.com 8

Application Section

FEEDBACK RESISTOR

The LMH6702 achieves its excellent pulse and distortion

performance by using the current feedback topology. The

loop gain for a current feedback op amp, and hence the

frequency response, is predominantly set by the feedback

resistor value. The LMH6702 is optimized for use with a

237Ωfeedback resistor. Using lower values can lead to

excessive ringing in the pulse response while a higher value

will limit the bandwidth. Application Note OA-13 discusses

this in detail along with the occasions where a different R

might be advantageous.

HARMONIC DISTORTION

The LMH6702 has been optimized for exceptionally low

harmonic distortion while driving very demanding resistive or

capacitive loads. Generally, when used as the input amplifier

to very high speed flash ADCs, the distortions introduced by

the converter will dominate over the low LMH6702 distor-

tions shown in the Typical Performance Characteristics sec-

tion. The capacitor C

, shown across the supplies in Figure

1and Figure 2, is critical to achieving the lowest 2

har-

monic distortion. For absolute minimum distortion levels, it is

also advisable to keep the supply decoupling currents

(ground connections to C

POS

, and C

NEG

in Figure 1 and

Figure 2) separate from the ground connections to sensitive

input circuitry (such as R

, and R

ground connections).

Splitting the ground plane in this fashion and separately

routing the high frequency current spikes on the decoupling

caps back to the power supply (similar to "Star Connection"

layout technique) ensures minimum coupling back to the

input circuitry and results in best harmonic distortion re-

sponse (especially 2

order distortion).

If this lay out technique has not been observed on a particu-

lar application board, designer may actually find that supply

decoupling caps could adversely affect HD2 performance by

increasing the coupling phenomenon already mentioned.

Figure 3 below shows actual HD2 data on a board where the

ground plane is "shared" between the supply decoupling

capacitors and the rest of the circuit. Once these capacitors

are removed, the HD2 distortion levels reduce significantly,

especially between 10MHz-20MHz, as shown in Figure 3

below:

At these extremely low distortion levels, the high frequency

behavior of decoupling capacitors themselves could be sig-

nificant. In general, lower value decoupling caps tend to

have higher resonance frequencies making them more ef-

fective for higher frequency regions. A particular application

board which has been laid out correctly with ground returns

"split" to minimize coupling, would benefit the most by having

low value and higher value capacitors paralleled to take

advantage of the effective bandwidth of each and extend low

distortion frequency range.

Another important variable in getting the highest fidelity sig-

nal from the LMH6702 is the package itself. As already

noted, coupling between high frequency current transients

on supply lines and the device input can lead to excess

harmonic distortion. An important source of this coupling is in

fact through the device bonding wires. A smaller package, in

general, will have shorter bonding wires and therefore lower

coupling. This is true in the case of the SOT23-5 compared

to the SOIC package where a marked improvement in HD

can be measured in the SOT23-5 package. Figure 4 below

shows the HD comparing SOT23-5 to SOIC package:

20039028

FIGURE 1. Recommended Non-Inverting Gain Circuit

20039027

FIGURE 2. Recommended Inverting Gain Circuit

20039022

FIGURE 3. Decoupling Current Adverse Effect on a

Board with Shared Ground Plane

LMH6702

www.national.com9

Application Section (Continued)

The LMH6702 data sheet shows both SOT23 and SOIC data

in the Electrical Characteristic section to aid in selecting the

right package. The Typical Performance Characteristics sec-

tion shows SOIC package plots only.

2-TONE 3

ORDER INTERMODULATION

The 2-tone, 3rd order spurious plot shows a relatively con-

stant difference between the test power level and the spuri-

ous level with the difference depending on frequency. The

LMH6702 does not show an intercept type performance,

(where the relative spurious levels change at a 2X rate vs.

the test tone powers), due to an internal full power bandwidth

enhancement circuit that boosts the performance as the

output swing increases while dissipating negligible quiescent

power under low output power conditions. This feature en-

hances the distortion performance and full power bandwidth

to match that of much higher quiescent supply current parts.

CAPACITIVE LOAD DRIVE

Figure 5 shows a typical application using the LMH6702 to

drive an ADC.

The series resistor, R

, between the amplifier output and the

ADC input is critical to achieving best system performance.

This load capacitance, if applied directly to the output pin,

can quickly lead to unacceptable levels of ringing in the

pulse response. The plot of "R

and Settling Time vs. C

"in

the Typical Performance Characteristics section is an excel-

lent starting point for selecting R

. The value derived in that

plot minimizes the step settling time into a fixed discrete

capacitive load with the output driving a very light resistive

load (1kΩ). Sensitivity to capacitive loading is greatly re-

duced once the output is loaded more heavily. Therefore, for

cases where the output is heavily loaded, R

value may be

reduced. The exact value may best be determined experi-

mentally for these cases.

In applications where the LMH6702 is replacing the CLC409,

care must be taken when the device is lightly loaded and

some capacitance is present at the output. Due to the much

higher frequency response of the LMH6702 compared to the

CLC409, there could be increased susceptibility to low value

output capacitance (parasitic or inherent to the board layout

or otherwise being part of the output load). As already men-

tioned, this susceptibility is most noticeable when the

LMH6702’s resistive load is light. Parasitic capacitance can

be minimized by careful lay out. Addition of an output snub-

ber R-C network will also help by increasing the high fre-

quency resistive loading.

Referring back to Figure 5, it must be noted that several

additional constraints should be considered in driving the

capacitive input of an ADC. There is an option to increase

, band-limiting at the ADC input for either noise or Nyquist

band-limiting purposes. Increasing R

too much, however,

can induce an unacceptably large input glitch due to switch-

ing transients coupling through from the "convert" signal.

Also, C

is oftentimes a voltage dependent capacitance.

This input impedance non-linearity will induce distortion

terms that will increase as R

is increased. Only slight

adjustments up or down from the recommended R

value

should therefore be attempted in optimizing system perfor-

mance.

20039023

FIGURE 4. SOIC and SOT23-5 Packages Distortion

Terms Compared

20039029

FIGURE 5. Input Amplifier to ADC

LMH6702

www.national.com 10

Application Section (Continued)

DC ACCURACY AND NOISE

Example below shows the output offset computation equa-

tion for the non-inverting configuration using the typical bias

current and offset specifications for A

=+2:

Output Offset : V

±I

·R

±V

)(1+R

)±I

·R

Where R

is the equivalent input impedance on the non-

inverting input.

Example computation for A

= +2, R

= 237Ω,R

=25Ω:

±6µA · 25Ω±1mV) (1 + 237/237) ±8µA · 237 =

±4.20mV

A good design, however, should include a worst case calcu-

lation using Min/Max numbers in the data sheet tables, in

order to ensure "worst case" operation.

Further improvement in the output offset voltage and drift is

possible using the composite amplifiers described in Appli-

cation Note OA-7. The two input bias currents are physically

unrelated in both magnitude and polarity for the current

feedback topology. It is not possible, therefore, to cancel

their effects by matching the source impedance for the two

inputs (as is commonly done for matched input bias current

devices).

The total output noise is computed in a similar fashion to the

output offset voltage. Using the input noise voltage and the

two input noise currents, the output noise is developed

through the same gain equations for each term but com-

bined as the square root of the sum of squared contributing

elements. See Application Note OA-12 for a full discussion of

noise calculations for current feedback amplifiers.

PRINTED CIRCUIT LAYOUT

Generally, a good high frequency layout will keep power

supply and ground traces away from the inverting input and

output pins. Parasitic capacitances on these nodes to

ground will cause frequency response peaking and possible

circuit oscillations (see Application Note OA-15 for more

information). National Semiconductor suggests the following

evaluation boards as a guide for high frequency layout and

as an aid in device testing and characterization:

Device Package Evaluation Board

Part Number

LMH6702MF SOT23-5 CLC730216

LMH6702MA SOIC CLC730227

These free evaluation boards are shipped when a device

sample request is placed with National Semiconductor.

LMH6702

www.national.com11

Physical Dimensions inches (millimeters)

unless otherwise noted

8-Pin SOIC

NS Package Number M08A

5-Pin SOT23

NS Package Number MA05A

LMH6702

www.national.com 12

Notes

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.

For the most current product information visit us at www.national.com.

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(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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www.national.com

1.7 GHz, LMH6702 Ultra Low Distortion, Wideband Op Amp

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