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Focus On: High-Speed Op Amps — Vendors Target GHz Speeds for Video

With an eye on next generation applications, amplifier suppliers are
pushing the performance barriers with their newest round of high-speed
operational amplifiers. These new devices offer system designers such features
as 1-GHz speed, three amps in a package and pin-outs optimized for
high-performance systems.

Vendors such as Intersil Corp., Analog Devices Inc., National Semiconductor
Corp., Linear Technology Corp., Maxim Integrated Products Inc., Texas Instruments Inc., and
STMicroelectronics NV, among others have been expanding their lines with new
offerings in recent months.

Intersil Corp. (Milpitas, Calif.), for example, claims its new EL5367 is
the world's fastest triple amplifier — breaking the 1-GHz barrier. Providing an
optimal slew rate, the high-speed op amp utilizes a proprietary, patent pending
custom architecture to isolate its triple amp. With a total supply current of
just 25 mA and the ability to run from a single supply voltage of 5 V to 12 V,
the EL5367 offers very high performance for extremely little power
consumption, according to Intersil. The new EL5367 drives resolutions greater
than QXGA (2048 pixel x 1536 pixel video graphics standard) at gain of 2 for
very high-speed video and monitor applications.

Now, the race is on between Analog Devices (Norwood, Mass.) and National
Semiconductor (Santa Clara, Calif.) to see who will produce the next
triple amp at the GHz speed. ADI's latest high-speed op amps called the AD8045
were introduced in August. These devices combine an easy-to-use
voltage-feedback architecture, unity-gain stability, and pin-outs optimized for
high-performance systems. This unique set of features, combined with 1-GHz
speed, low noise, and low distortion, simplifies design and makes the AD8045
practical for many high-speed applications including medical instrumentation,
automatic test equipment (ATE), and data-acquisition systems.

The AD8045 is a unity-gain stable, 1-GHz voltage-feedback amplifier that
can slew at 1350 V/μs and settles to 0.1% in 7.5 ns. With
spurious-free dynamic range of 101 dBc at 5 MHz and noise figure of 3 nV per
square root of hertz (rtHz), the amplifier is suited for systems that demand high
resolution at high speeds. In addition to these ac specifications, the AD8045
is said to have superior dc characteristics with a voltage offset of 200 μV
and input bias current of 2 μA. The amplifier can operate on supply voltages
between 3.3 V and 12 V.

The AD8045 features an advanced pin-out to enhance performance and stability
over traditional amplifier pin-outs. The AD8045 uses this new standard pin-out
to reduce the mutual inductance, and resulting distortion caused by the
coupling between positive input and negative supply. Additionally, the amplifier
provides two output pins to reduce feedback parasitics. This simplifies board
layout and increases the stability of the amplifier. The AD8045 is now
available in full production quantities. The part is specified over the extended
industrial temperature range and is available in a tiny 3mm x 3mm LFCSP and an
8-lead SOIC. Both packages feature an exposed paddle that provides better
thermal characteristics. In either packaging option, the device is priced at
$1.39 per unit in 1,000-piece quantities.


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Intersil's EL5367

Intersil's EL5367 is a current-feedback operational amplifier that offers a
wide -3 dB bandwidth of 1 GHz and a low supply current of 8.5 mA per amplifier.
The device works with supply voltages ranging from a single 5 V to 12 V and it
is also capable of swinging to within 1 V of either supply on the output.
Because of their current-feedback topology, the EL5367 does not have the normal
gain-bandwidth product associated with voltage-feedback operational amplifiers.
This device is meant for driving high-resolution video. With a gain of 2, and
bandwidth of 800 MHz on all three channels this device will drive a double
terminated 75-Ω cable easily. The EL5367 is now available in 16-lead QSOP
packaging for a price of $2.99 in 1,000-unit quantities.

National Semiconductor and Analog Devices are independently developing triple amps in the
GHz range. ADI said it would be begin sampling a 1.5-GHz triple amplifier early
next year.

National Semiconductor Corp. in July, unveiled its fastest LMH amplifiers
for professional and wideband video applications. The high-speed LMH6738 and
LMH6739, both created using National's proprietary VIP10 process technology, are
designed for applications requiring high bandwidth and low distortion. VIP10 is
a high-speed, dielectrically isolated, complementary bipolar IC process that
utilizes deep trench technology on a bonded wafer for complete dielectric
isolation and optimal high-speed amplifier performance. Operating at 750 MHz
small signal bandwidth, these high-performance devices drive today's
highest-resolution video signals in LCD projectors, multi-media, video switching
and routing, conference room and HDTV systems.

National's LMH6738 is a wideband, triple, current feedback (CFB) operational
amplifier, and the LMH6739 is a wideband, triple, programmable gain buffer
(PGB), both operating at 750-MHz small signal bandwidth. Both devices have
independent disable pins for each amplifier, feature 7.3-ns enable times, and
have low crosstalk, allowing them to be used in multiplexing and
demultiplexing applications. With 400 MHz large signal bandwidth (LSBW), 3300
V/μs slew rate, and a 0.1 dB gain flatness of 200 MHz, the LMH6738/39
outperform the competition in driving high-resolution RGB video signals.
Additionally, the high output current of 90 mA drives low impedance, high
capacitive loads in single-ended cable line driving applications. National's
LMH6738 is available now in SSOP-16 packaging and is priced at $2.95. The
LMH6739 is available now in SSOP-16 packaging and is priced at $3.15. All prices
are for 1,000-unit quantities.

STMicroelectronics, (Geneva, Switzerland), offers a low-cost family of
wide-band, negative input rail and output rail-to-rail operational amplifiers
in tiny packages. The TSH8x meets the requirements of high-volume video
applications, such as RGB signal driving and switching, which need
high-performance signal amplification and signal conditioning at competitive
prices.

The TSH80, TSH81 and TSH82 are single, single with stand-by and
dual-voltage feedback operational amplifiers, respectively. Each device
features a gain/bandwidth product of 100 MHz and a slew rate of 100 V/μs.
These features combine to deliver a total harmonic distortion figure of -61 dB
at 4 MHz for output amplitude of 1 Vp-p into a 150-Ω load, with a 5-V supply.
The TSH81 also features a stand-by function, with a maximum power consumption of
55 μA and high output impedance, useful for switching operations.
The product family has a differential gain of 0.5% and a differential phase of
0.5° at 4.5 MHz. Gain flatness is 0.2 dB at 6 MHz for a gain of 2. The parts
also offer a negative input rail combined with a rail-to-rail output stage (48
mV from rail), which matches the needs of RGB video signal amplification with no
coupling capacitor while keeping a single 5-V power supply.
The amplifiers have a quiescent current of 8 mA and an equivalent input voltage
noise of 11 nV/MHz. They operate from 4.5 V to 12 V dual- or single-supply
voltages and they are tested in full production at 2.5 V and 5 V.

The TSH80 comes in a SOT23-5L plastic package, and is also available in an SO-8 plastic
package. The TSH81 and TSH82 come in TSSOP8 and SO-8 plastic packages. Pricing
in 5.000-piece quantities is 35 cents for the TSH80, 35 cents for the TSH81, and
40 cents for the TSH82.

Some high-speed operational amplifier trends include the migration toward lower supply voltages and smaller packaging. One problem with reducing supply voltages is that it reduces the input and output voltage swing on the amplifier, said Paolo Battezzato, product marketing
manager for STMicro's analog and logic standard ICs. To overcome this problem,
Battezzato suggests using input and output rail-to-rail amplifiers more often.
The rail-to-rail feature requires using more basic components in the
architecture of the amplifiers and often adding another stage to the output
circuitry. The additional stage adds another pole in the frequency response,
which decreases the amplifier's bandwidth, he said.

Packages are getting smaller for two main reasons — to improve dynamic
performance by reducing the length of wire bonding between the die and external
pins, and the length of board layout (especially the length of feedback loops of
amplifiers, which is a critical point for a proper stability), and to allow
customers to reduce the size of their systems when the integration of the
amplifier is not possible.

Packages that fit the bill for the above reasons include quad flat no-load
(QFN), dual flat no lead (DFN) and thin quad flat pack (TQFP). These packages
maintain good thermal performance with an option of an exposed-pad to transfer
heat from the die to the board, Battezzato said. Flip-chip packaging, which
targets portable equipment, is also becoming popular, he said.

In August, Texas Instruments (Dallas, Tex.) launched what's claimed to
be the industry's lowest distortion 5-V single-supply operational amplifier
designed for applications requiring high speed, low distortion and low noise.
The THS4304 enables greater resolution and precision in wireless infrastructure,
medical imaging and automatic test equipment, and is intended for high-speed
signal conditioning applications such as driving high-resolution, high-speed
analog-to-digital converters (A/D converters). The THS4304 is the first unity
gain stable op amp released from TI's BiCom-III complementary bipolar silicon
germanium (SiGe) process.

The device offers distortion performance with a 2nd order harmonic distortion of
-85 dBc, a 3rd order harmonic distortion of -100 dBc at 10 MHz, and 2 Vpp-output
into 100-Ω load. The THS4304 provides 3-GHz unity gain bandwidth,
830-V/μs-slew rate and 2.4-nV/rtHz input noise, all while consuming 18 mA
of quiescent current on a 5-V supply. The device is offered in an 8-pin MSOP
package, 8-pin SOIC package and space-saving 5-pin SOT-23 package, with a
suggested resale price of $1.75 each in 1,000-unit quantities.

Among the offerings from Linear Technology (Milpitas, Calif.) are the
LT1991 precision and LT1995 high-speed gain selectable amplifiers. These devices
don't require external components to set the gain because they include precision
resistors on-board. The LT1991 combines a precision micropower operational
amplifier with eight precision resistors to form a single chip solution for
accurately amplifying voltages with better than 0.04% gain accuracy. The
amplifier provides dc characteristics with input offset voltage of less than 50
μV and input offset current of 50 pA. The low offset voltage drift of 1
μV/°C, combined with gain drift below 3 parts per million/°C results in
stable operation over temperature. The LT1991 has a rail-to-rail output and
operates on supplies from 2.7 V to 36 V. It draws less than 110 μA on a
single 5-V supply, making it suitable for low voltage, low power instrumentation
applications.

The LT1995 integrates a high-speed amplifier with eight precision resistors in a
tiny MSOP-10 package. The amplifier features slewing characteristics of 1000
V/μs, and fast settling time, 100 ns to 0.1%. The LT1995 operates on
supply voltages from &plusmn2.5 V to &plusmn15 V. It can be used in data
acquisition cards in industrial and process control, ATE cards, current tester
boards, satellite receiver cards, communications and optical networking
equipment, semiconductor fab equipment and medical imaging systems. Offered in
the 10-lead MSOP package, the LT1991 and LT1995 are specified for operation over
the commercial and industrial temperature ranges. Pricing, in 1,000-piece
quantities, starts at $1.39 each for the LT1991 precision amplifier and $1.89
each for the LT1995 high-speed amplifier.

Maxim Integrated Products Inc.'s (Sunnyvale, Calif.) MAX4027 is a triple,
wideband, 2-channel, noninverting gain-of-two video amplifier with input
multiplexing, capable of driving up to two back-terminated video loads. The
MAX4027 features current-mode feedback amplifiers configured for a gain of two
(+6 dB) with a -3 dB large-signal bandwidth of 200 MHz. The device has low
differential gain and phase errors, and operates from &plusmn5-V supplies.
The MAX4027 is suitable for use in broadcast and graphics video systems because
of the low 2 pF input capacitance, channel-to-channel switching time of only 15
ns, and wide 62 MHz, large-signal 0.1 dB bandwidth. High-impedance output
disabling allows the MAX4027 to be incorporated into large switching arrays with
minimal interaction with the source. Specified over the -40°C to +85°C extended
temperature range, the MAX4027 is available in 14-pin SO and TSSOP packages.
Pricing is $4.20 FOB USA in 1,000-piece quantities.

Company Contacts:

Analog Devices Inc.
www.analogdevices.com
Phone: 1-(800)-Analog-D

Intersil Corp.
www.intersil.com

Phone: 1-(888)-INTERSIL

National Semiconductor Corp.
www.national.com
Phone: 1-(800) 272-9959

Linear Technology Corp.
www.linear.com

Phone: (408) 432-1900

Maxim Integrated Products Inc.
www.maxim-ic.com

Phone: 1-800-998-8800

Texas Instruments, Inc.
www.ti.com

Phone: (972) 644-5580

STMicroelectronics NV
www.st.com
Phone: 1-(781)-861-2650

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