DESCRIPTION

The OPA651 is a low power, wideband voltage feed-
back operational amplifier. It features a bandwidth at
G = +2 of 470MHz as well as a 12-bit settling time of
only 16ns. The wide bandwidth and true differential
input stage make it suitable for use in a variety of
applications. Its low distortion gives exceptional per-
formance for telecommunications, medical imaging
and video applications.

The OPA651 is compensated for stability in gains of
two or more, differentiating it from the unity gain
stable OPA650. Its unusual combination of speed,
accuracy and low power make it an outstanding choice
for many portable, multi-channel and other high speed
applications, where power is at a premium.

Wideband, Low Power Voltage Feedback

OPERATIONAL AMPLIFIER

PDS-1265E

Printed in U.S.A. March, 1998

OPA651

FEATURES

STABLE IN GAINS:

2V/V

LOW POWER: 50mW

BANDWIDTH: 470MHz at G = 2

FAST SETTLING TIME: 16ns to 0.01%

LOW HARMONICS: 78dB at 5MHz

LOW INPUT BIAS CURRENT: 4

DIFFERENTIAL GAIN/PHASE ERROR:
0.01%/0.025

LOW VOLTAGE NOISE: 4.6nV/

APPLICATIONS

HIGH RESOLUTION VIDEO

MONITOR PREAMPLIFIER

CCD IMAGING AMPLIFIER

ULTRASOUND SIGNAL PROCESSING

ADC/DAC GAIN AMPLIFIER

BASEBAND SIGNAL PROCESSING

Current

Mirror

Output

Stage

Inverting

Input

Non-Inverting

Input

Output

1.5pF

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OPA651

OPA651

SPECIFICATIONS

At T

= +25

C, V

5V, R

= 100

, R

= 402

G = +2

unless otherwise noted.

OPA651U, N

OPA651UB, NB

PARAMETER

CONDITIONS

MIN

TYP

MAX

MIN

TYP

MAX

UNITS

FREQUENCY RESPONSE
Closed-Loop Bandwidth

(2)

G = +2

470

(1)

MHz

G = +5

MHz

G = +10

MHz

Gain Bandwidth Product

340

MHz

Slew Rate

G = +2, V

= 2V step

300

Over Specified Temperature

275

Rise Time

0.2V Step

0.8

Fall Time

0.2V Step

0.8

Settling Time

0.01%

G = +2, V

= 2V step

16.2

0.1%

G = +2, V

= 2V step

11.5

G = +2, V

= 2V step

7.2

Spurious Free Dynamic Range

G = +2, f = 5.0 MHz, V

= 2Vp-p,

= 100

dBc

= 400

dBc

Differential Gain

G = +2, NTSC, V

= 1.4Vp, R

= 150

0.01

Differential Phase

G = +2, NTSC, V

= 1.4Vp, R

= 150

0.025

Degrees

Bandwidth For 0.1dB Flatness

G = +2

MHz

INPUT OFFSET VOLTAGE
Input Offset Voltage

5.0

2.0

Average Drift

Power Supply Rejection (+V

)

4.5V to

5.5V

)

INPUT BIAS CURRENT
Input Bias Current

= 0V

Over Temperature

Input Offset Current

= 0V

0.4

1.5

Over Temperature

0.9

3.0

INPUT NOISE
Input Voltage Noise

Noise Density, f = 100Hz

nV/

f = 10kHz

4.6

nV/

f = 1MHz

4.6

nV/

Voltage Noise, BW = 10Hz to 100MHz

Vrms

Input Bias Current Noise

Current Noise Density, f = 0.1Hz to 20kHz

1.1

pA/

Noise Figure (NF)

= 10k

3.2

= 50

INPUT VOLTAGE RANGE
Common-Mode Input Range

3.5

Over Specified Temperature

3.0

Common-Mode Rejection

0.5V

INPUT IMPEDANCE
Differential

60 || 1

|| pF

Common-Mode

2.6 || 1

|| pF

OPEN-LOOP GAIN
Open-Loop Voltage Gain

2V, R

= 100

Over Specified Temperature

2V, R

= 100

OUTPUT
Voltage Output

Over Specified Temperature

No Load

2.2

3.0

2.4

= 250

2.2

2.5

2.4

= 100

2.0

2.3

2.1

Current Output, Sourcing

110

Over Specified Temperature

Current Output, Sinking

Over Specified Temperature

Short Circuit Current

150

Output Resistance

0.1MHz, G = +2

0.05

POWER SUPPLY
Specified Operating Voltage

Operating Voltage Range

4.5

5.5

Quiescent Current

5.1

7.75

6.5

Over Specified Temperature

8.75

7.5

TEMPERATURE RANGE
Specification: U, N, UB, NB

+85

Thermal Resistance,

SO-8

125

C/W

SOT23-5

150

C/W

NOTES: (1) An asterisk (*) specifies the same value as the grade to the left. (2) Frequency response can be strongly influenced by PC board parasitics. The OPA651
is nominally compensated assuming 2pF parasitic load. The demonstration boards show low parasitic layouts for the different package styles.

OPA651

Input

Output

+Input

Output

Input

+Input

PIN CONFIGURATION

Top View

SO-8

Supply ...............................................................................................

5.5V

Internal Power Dissipation

(1)

: .............................. See Thermal Conditions

Differential Input Voltage ..................................................................

1.2V

Input Voltage Range ............................................................................

Storage Temperature Range: U, UB, N, NB ................ 40

C to +125

Lead Temperature (soldering, 10s) .............................................. +300

(soldering, SO-8 3s) ...................................................................... +260

Junction Temperature (T

) ............................................................ +175

ABSOLUTE MAXIMUM RATINGS

SOT23-5

ELECTROSTATIC
DISCHARGE SENSITIVITY

Electrostatic discharge can cause damage ranging from per-
formance degradation to complete device failure. Burr-Brown
Corporation recommends that all integrated circuits be handled
and stored using appropriate ESD protection methods.

ESD damage can range from subtle performance degradation
to complete device failure. Precision integrated circuits may
be more susceptible to damage because very small parametric
changes could cause the device not to meet published speci-
fications.

PACKAGE
DRAWING

TEMPERATURE

PACKAGE

ORDERING

PRODUCT

PACKAGE

NUMBER

(1)

RANGE

MARKING

(2)

NUMBER

(3)

OPA651U

SO-8 Surface Mount

182

C to +85

OPA651U

OPA651UB

SO-8 Surface Mount

182

C to +85

OPA651UB

OPA651N

5-pin SOT23-5

331

C to +85

A51

OPA651N-250

OPA651N-3k

OPA651NB

5-pin SOT23-5

331

C to +85

A51B

OPA651NB-250

OPA651NB-3k

NOTE: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. (2) The "B" grade of the SO-8 package
will be marked with a "B" by pin 8. The "B" grade of the SOT23-5 will be marked with a "B" near pins 3 and 4. (3) The SOT23-5 is only available on a 7" tape and reel
(e.g. ordering 250 pieces of "OPA651N-250" will get a single 250 piece tape and reel. Ordering 3000 pieces of "OPA651N-3k" will get a single 3000 piece tape and reel).
Please refer to Appendix B of Burr-Brown IC Data Book for detailed Tape and Reel Mechanical information.

PACKAGE/ORDERING INFORMATION

The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user's own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.

OPA651

DISCUSSION OF
PERFORMANCE

The OPA651 is a low power, wideband voltage feedback
operational amplifier, internally compensated to provide gain
of +2 stability. The OPA651's voltage feedback architecture
features true differential and fully symmetrical inputs. This
minimizes offset errors, making the OPA651 well suited for
implementing filter and instrumentation designs. The
OPA651's AC performance is optimized to provide a gain
bandwidth product of 340MHz and a fast 0.1% settling time
of 11.5ns, which is an important consideration in high speed
data conversion applications. Along with its excellent settling
characteristics, the low DC input offset of

1mV and drift of

C support high accuracy requirements. In applica-

tions requiring a higher slew rate and wider bandwidth, such
as video and high bit rate digital communications, consider
the current feedback OPA658.

CIRCUIT LAYOUT AND BASIC OPERATION

Achieving optimum performance with a high frequency am-
plifier like the OPA651 requires careful attention to layout
parasitics and selection of external components. Recommen-
dations for PC board layout and component selection include:

a) Minimize parasitic capacitance to any ac ground for all
of the signal I/O pins. Parasitic capacitance on the output
and inverting input pins can cause instability; on the non-
inverting input it can react with the source impedance to
cause unintentional bandlimiting. To reduce unwanted ca-
pacitance, a window around the signal I/O pins should be
opened in all of the ground and power planes. Otherwise,
ground and power planes should be unbroken elsewhere on
the board.

b) Minimize the distance (< 0.25") from the two power pins
to high frequency 0.1

F decoupling capacitors. At the pins,

the ground and power plane layout should not be in close
proximity to the signal I/O pins. Avoid narrow power and
ground traces to minimize inductance between the pins and
the decoupling capacitors. Larger (2.2

F to 6.8

F) decoupling

capacitors, effective at lower frequencies, should also be
used. These may be placed somewhat farther from the
device and may be shared among several devices in the same
area of the PC board.

c) Careful selection and placement of external compo-
nents will preserve the high frequency performance of the
OPA651. Resistors should be a very low reactance type.
Surface mount resistors work best and allow a tighter overall
layout. Metal film or carbon composition axially-leaded
resistors can also provide good high frequency performance.
Again, keep their leads as short as possible. Never use
wirewound type resistors in a high frequency application.

Since the output pin and the inverting input pin are most
sensitive to parasitic capacitance, always position the feed-
back and series output resistor, if any, as close as possible to
the package pins. Other network components, such as non-
inverting input termination resistors, should also be placed
close to the package.

Even with a low parasitic capacitance shunting external
resistors, excessively high resistor values can create signifi-
cant time constants and degrade performance. This is par-
ticularly true for the OPA651 with its internal 1.5pF feed-
back capacitance. Good metal film or surface mount resis-
tors have approximately 0.2pF in shunt with the resistor. For
resistor values > 1.5k

, this adds a pole and/or zero below

500MHz that can affect circuit operation. Keep resistor
values as low as possible consistent with output loading
considerations. The 402

feedback used for the Typical

Performance Plots is a good starting point for design.

d) Connections to other wideband devices on the board
may be made with short direct traces or through on-board
transmission lines. For short connections, consider the trace
and the input to the next device as a lumped capacitive load.
Relatively wide traces (50 to 100 mils) should be used,
preferably with ground and power planes opened up around
them. Estimate the total capacitive load and set R

ISO

from

the plot of recommended R

ISO

vs capacitive load. Low

parasitic loads may not need an R

ISO

since the OPA651 is

nominally compensated to operate with a 2pF parasitic load.

If a long trace is required and the 6dB signal loss intrinsic to
doubly terminated transmission lines is acceptable, imple-
ment a matched impedance transmission line using microstrip
or stripline techniques (consult an ECL design handbook for
microstrip and stripline layout techniques). A 50

environ-

ment is not necessary on board, and in fact a higher imped-
ance environment will improve distortion as shown in the
distortion vs load plot. With a characteristic impedance
defined based on board material and desired trace dimen-
sions, a matching series resistor into the trace from the
output of the amplifier is used as well as a terminating shunt
resistor at the input of the destination device. Remember
also that the terminating impedance will be the parallel
combination of the shunt resistor and the input impedance of
the destination device; the total effective impedance should
match the trace impedance. Multiple destination devices are
best handled as separate transmission lines, each with their
own series and shunt terminations.

If the 6dB attenuation loss of a doubly terminated line is
unacceptable, a long trace can be series-terminated at the
source end only. This will help isolate the line capacitance
from the op amp output, but will not preserve signal integrity
as well as a doubly terminated line. If the shunt impedance
at the destination end is finite, there will be some signal
attenuation due to the voltage divider formed by the series
and shunt impedances.

The OPA651 is nominally specified for operation using

power supplies. A 10% tolerance on the supplies, or an ECL
5.2V for the negative supply, is within the maximum speci-
fied total supply voltage of 11V. Higher supply voltages can
break down internal junctions possibly leading to catastrophic
failure. Single supply operation is possible as long as com-
mon mode voltage constraints are observed. The common

OPA651

mode input and output voltage specifications can be inter-
preted as a required headroom to the supply voltage. Observ-
ing this input and output headroom requirement will allow
non-standard or single supply operation. Figure 1 shows one
approach to single-supply operation.

ESD PROTECTION

ESD damage has been well recognized for MOSFET de-
vices, but any semiconductor device is vulnerable to this
potentially damaging source. This is particularly true for
very high speed, fine geometry processes.

ESD damage can cause subtle changes in amplifier input
characteristics without necessarily destroying the device. In
precision operational amplifiers, this may cause a noticeable
degradation of offset voltage and drift. Therefore, ESD
handling precautions are strongly recommended when han-
dling the OPA651.

OUTPUT DRIVE CAPABILITY

The OPA651 has been optimized to drive 75

and 100

resistive loads. The device can drive a 2Vp-p into a 75

load.

This high-output drive capability makes the OPA651 an ideal
choice for a wide range of RF, IF, and video applications. In
many cases, additional buffer amplifiers are unneeded.

Many demanding high-speed applications such as driving
A/D converters require op amps with low wideband output
impedance. For example, low output impedance is essential
when driving the signal-dependent capacitances at the inputs
of flash A/D converters. As shown in Figure 3, the OPA651
maintains very low-closed loop output impedance over fre-
quency. Closed-loop output impedance increases with fre-
quency since loop gain is decreasing.

402

OPA651

402

OUT

= + 2·V

THERMAL CONSIDERATIONS

The OPA651 will not require heatsinking under most oper-
ating conditions. Maximum desired junction temperature
will limit the maximum allowed internal power dissipation
as described below. In no case should the maximum junction
temperature be allowed to exceed +175

FIGURE 3. Small-Signal Output Impedance vs Frequency.

SMALL-SIGNAL OUTPUT IMPEDANCE

vs FREQUENCY

Frequency (Hz)

100

0.1

0.01

10k

100k

100M

10M

Output Impedance (

)

G = +2

OFFSET VOLTAGE ADJUSTMENT

If additional offset adjustment is needed, the circuit in
Figure 2 can be used without degrading offset drift with
temperature. Avoid external adjustment whenever possible
since extraneous noise, such as power supply noise, can be
inadvertently coupled into the amplifier's inverting input
terminal. Remember that additional offset errors can be
created by the amplifier's input bias currents. Whenever
possible, match the impedance seen by both inputs as is
shown with R

. This will reduce input bias current errors to

the amplifier's offset current.

OPA651

(1)

= R

|| R

Trim

20k

or Ground

Output Trim Range +V

to V

Trim

47k

Trim

0.1µF

NOTE: (1) R

optional and can
be used to cancel
offset errors due
to input bias currents.

FIGURE 2. Offset Voltage Trim.

FIGURE 1. Single Supply Operation.

OPA651

Operating junction temperature (T

) is given by T

. The total internal power dissipation (P

) is a com-

bination of the total quiescent power (P

) and the power

dissipated in of the output stage (P

) to deliver load

power. Quiescent power is simply the specified no-load
supply current times the total supply voltage across the
part. P

will depend on the required output signal and load

but would, for a grounded resistive load, be at a maximum
when the output is a fixed DC voltage equal to 1/2 of either
supply voltage (assuming equal bipolar supplies). Under
this condition, P

= V

/(4·R

) where R

includes feed-

back network loading. Note that it is the power dissipated
in the output stage and not in the load that determines
internal power dissipation. As an example, compute the
maximum T

for an OPA651N at A

= +2, R

= 100

, R

= 402

5V, with the output at |V

/2|, and the

specified maximum T

= +85

C. P

= 10V·8.75mA + (5

(4·(100

||804

)) = 158mW. Maximum T

= +85

C +

0.158W·150

C/W = 109

DRIVING CAPACITIVE LOADS

The OPA651's output stage has been optimized to drive low
resistive loads. Capacitive loads, however, will decrease the
amplifier's phase margin which may cause high frequency
peaking or oscillations. Capacitive loads greater than 10pF
should be isolated by connecting a small resistance, usually
15

to 30

, in series with the output as shown in Figure 4.

This is particularly important when driving high capacitance
loads such as flash A/D converters. Increasing the gain from
+2 will improve the capacitive load drive due to increased
phase margin.

In general, capacitive loads should be minimized for opti-
mum high frequency performance. Coax lines can be driven
if the cable is properly terminated. The capacitance of coax
cable (29pF/foot for RG-58) will not load the amplifier
when the coaxial cable or transmission line is terminated in
its characteristic impedance.

that, from a stability standpoint, an inverting gain of 1V/V
is equivalent to a noise gain of 2.) Frequency response for
other gains are shown in the Typical Performance Curves.

The high frequency response of the OPA651 in a good
layout is very flat with frequency. However, some circuit
configurations such as those where large feedback resis-
tances are used, can produce high-frequency gain peaking.
This peaking can be minimized by connecting a small
capacitor in parallel with the feedback resistor. This capaci-
tor compensates for the closed-loop, high-frequency, trans-
fer function zero that results from the time constant formed
by the input capacitance of the amplifier (typically 2pF after
PC board mounting), and the input and feedback resistors.
The selected compensation capacitor may be a trimmer, a
fixed capacitor, or a planned PC board capacitance. The
capacitance value is strongly dependent on circuit layout and
closed-loop gain. Using small resistor values will preserve
the phase margin and avoid peaking by keeping the break
frequency of this zero sufficiently high. When high closed-
loop gains are required, a three-resistor attenuator (tee-
network) is recommended to avoid using large value resis-
tors with large time constants. The OPA651 includes an
internal 1.5pF feedback capacitor to achieve best gain of +2
flatness (R

= 402

PULSE SETTLING TIME

High speed amplifiers like the OPA651 are capable of
extremely fast settling time with a pulse input. Excellent
frequency response flatness and phase linearity are required
to get the best settling times. As shown in the specifications
table, settling time for a

1V step at a gain of +2 for the

OPA651 is extremely fast. The specification is defined as
the time required, after the input transition, for the output to
settle within a specified error band around its final value. For
a 2V step, 1% settling corresponds to an error band of

20mV, 0.1% to an error band of

2mV, and 0.01% to an

error band of

0.2mV. For the best settling times, particu-

larly into an ADC capacitive load, little or no peaking in the
frequency response can be allowed. Using the recommended
R

ISO

for capacitive loads will limit this peaking and reduce

the settling times. Fast, extremely fine scale settling (0.01%)
requires close attention to ground return currents in the
supply decoupling capacitors. For highest performance, con-
sider the OPA642 which isolates the output stage decoupling
from the rest of the amplifier.

DIFFERENTIAL GAIN AND PHASE

Differential Gain (DG) and Differential Phase (DP) are
among the more important specifications for video applica-
tions. The percentage change in closed-loop gain over a
specified change in output voltage level is defined as DG.
DP is defined as the change in degrees of the closed-loop
phase over the same output voltage change. DG and DP are
both specified at the NTSC sub-carrier frequency of 3.58MHz.
All measurements were performed using an HP 9480.

FIGURE 4. Driving Capacitive Loads.

OPA651

ISO

typically 15

to 30

)

402

FREQUENCY RESPONSE COMPENSATION

The OPA651 is internally compensated and is stable at a
gain of 2 with a phase margin of approximately 60

. (Note

OPA651

DISTORTION

The OPA651's harmonic distortion characteristics into a
100

load are shown versus frequency and power output in

the typical performance curves. Distortion can be signifi-
cantly improved by increasing the load resistance as illus-
trated in Figure 5. Remember to include the contribution of
the feedback network when calculating the effective load
resistance seen by the amplifier.

100

Harmonic Distortion (dBc)

3fo

2fo

G = +2

Load Resistance (

)

FIGURE 5. 5MHz Harmonic Distortion vs Load Resistance.

NOISE FIGURE

The OPA651 voltage noise spectral density is specified in
the Typical Performance Curves. For RF applications, how-
ever, Noise Figure (NF) is often the preferred noise specifi-
cation since it allows system noise performance to be more
easily calculated. The OPA651's Noise Figure vs Source
Resistance is shown in Figure 6.

NOISE FIGURE vs SOURCE RESISTANCE

Source Resistance (

)

100

100k

10k

Noise Figure (dB)

NF = 10 LOG 1 +

+ (I

)

4KTR

FIGURE 6. Noise Figure vs Source Resistance.

SPICE MODELS AND EVALUATION BOARD

Computer simulation of circuit performance using SPICE is
often useful when analyzing the performance of analog
circuits and systems. This is particularly true for Video and
RF amplifier circuits where parasitic capacitance and induc-
tance can have a major effect on circuit performance. SPICE
models are available on a disk from the Burr-Brown Appli-
cations Department.

Demonstration boards are available for each OPA651 pack-
age style. These boards implement a very low parasitic
layout that will produce the excellent frequency and pulse
responses shown in the Typical Performance Curves. For
each package style, the recommended demonstration board
is:

Contact your local Burr-Brown sales office or distributor to
order demonstration boards.

BOARD

LITERATURE

PART

REQUEST

PRODUCT

PACKAGE

NUMBER

OPA651P

8-Pin DIP

DEM-OPA65xP

OPA651U

8-Pin SO-8

DEM-OPA65xU

OPA651N

6-Pin SOT23-6

DEM-OPA6xxN

MKT-348

OPA651

OUT

402

Video

Input

Transmission Line

TYPICAL APPLICATION

FIGURE 7. Low Distortion Video Amplifier.

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