National Semiconductor Corporation introduced three new LMH amplifier products for the high-speed analog market that are based on National's industry-leading VIP10ý manufacturing process. These new products offer low noise, low power, and high bandwidth for communications and other high-speed applications such as xDSL modems, cable and set-top boxes, contact image scanners and DVD players.

"National is committed to the high-speed analog market," said Jeff Hooker, marketing manager for National's amplifier product group. "As a leader in operational amplifier innovation, we continue to drive the market by developing products with the best output power and bandwidth and better AC specifications at lower supply current than our competitors. We can do this cost-effectively by implementing our VIP10 process technology. The VIP10 process allows National to design the most power-efficient, performance-oriented, high-speed amplifiers on the market today."

LMH6622

National's LMH6622 is a very low-noise, high-speed dual amplifier. Its low input voltage noise of 1.6nV per root hertz and low input current noise of 1.5pA per root hertz improve front-end and receiver dynamic range. This makes it ideal for receiving small signals over long twisted pair telephone lines such as those used in ADSL applications. The LMH6622 exceeds the bandwidth and slew rate requirements for all forms of ADSL and ADSL Lite, as well as many other xDSL applications such as HDSL and SDSL.

The LMH6622 features an easy-to-use voltage feedback topology and is well-suited for single 5V or dual 6V supply applications. A bandwidth of 160MHz at a gain of Av >=+2 makes the LMH6622 an effective solution for a wide range of communications applications.

LMH6639

The LMH6639 is a single supply, rail-to-rail output amplifier with micro-power shutdown. It offers 190MHz on a supply current of only 3.6mA, and operates from single 3V to 10V supplies. In shutdown, the supply current drops to 400 microA, making the LMH6639 ideal for battery-powered applications. The input voltage range includes ground, and there is no phase reversal if common mode input range is exceeded. The LMH6639 is designed for low-power portable applications such as cellular phones, PDAs and portable modems.

LMH6644

National's LMH6644 is a single supply, rail-to-rail quad amplifier. Like the LMH6639, it has an input range that includes ground, and has no phase reversal. The input common mode voltage and rail-to-rail output make it ideal for single 3V to 10V applications. The LMH6644 has an improved output stage that allows it to sink or source 75mA, using only 2.7mA per amplifier. An Av=+1 bandwidth of 130MHz, and a full power bandwidth of 46 MHz allow the LMH6644 to be used in very demanding signal conditions.

Applications for the LMH6644 include cable and digital set-top boxes, contact image scanners, PHS basestations, DVD-RAM and DVD players, as well as many other general-purpose high-speed applications such as PC projectors, active filters, ADC buffers, portable video, current sense buffers and professional-quality video systems.

VIP10 Manufacturing Process

Developed in National's wafer fabrication site in Arlington, Texas, 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. Trench technology with bonded wafers helps minimize parasitic capacitance for optimal power-to-bandwidth performance, lower distortion and decreased die size. The VIP10 process allows National to design the most power-efficient, performance-oriented, high-speed amplifiers on the market.

National Semicondcutor, Design Support Group, Tel: 800-272-9959; Web site: www.national.com

National decided that they wanted to compete in the high-speed op amp arena but realized they needed to improve their process to offer something more than the competition. They developed their VIP10 process specifically for high-speed amplifiers. This complementary bipolar process aided development of some significant features of their LMH product line. National thinks that this process will enable many of the high-speed amplifiers, that have been very expensive in the past, to become a much lower cost item. In April 2001, National Semiconductor released the first members of the LMH 66xx family. The 6642 and 43 were the first members, offering single and dual amps respectively. The latest introductions include the 6622, 6639 and 6644, which have features enabling them to compete in the market and meet the needs of xDSL products. The 6622 is for a vertical market for the ADSL. The 6639 and 66444 are more general purpose products for low-cost consumer applications.

It is very typical for high-speed amplifiers to drive heavy loads like cables, xDSL, twisted pair and even ADCs that have high capacitance. Typically, you need a little more current to drive the heavier loads of video products. The LMH is made to drive video type loads of 50, 75, 100 ohm loads. To do that they need quite a few milliamps and the 66xx has about 75 milliamps.

The LMH series also prevents phase reversal in the amplifier, which means if the common mode range of the amplifier is exceeded something strange happens to the output - it produces a phase reversal of 180 degrees - and that's not good for the application. The LMH series has circuitry built into it to prevent phase reversal, something the competition doesn't have.

The key with many applications for high-speed amplifiers, especially those with voltage feedback, has to do with gain and voltage feedback. If you provide any gain to the amplifiers and they have voltage feedback, the bandwidth decreases significantly. This means you need to have large bandwidth margins. When you push the bandwidth you get distortion, peaking and drooping of the bandwidth. The general rule of thumb is that the bandwidth needs to be 10X the application, so if you run the application at 1 or 2 MHz the amplifier should have a bandwidth of about 20 MHz. The 6622 has 160 MHz bandwidth, so it has plenty of margin for typical 1-2 MHz applications. However, in many applications you don't need to look at the 3 dB bandwidth, you need to observe the 0.1 dB bandwidth. For the 6622 the 0.1 dB bandwidth is 30 MHz, still a comfortable margin.

One of the most important features of the 6622 is the low noise. It offers possibly the lowest noise on the market at 6nV/root Hertz. National says you really need a complementary bipolar process to accomplish this kind of noise spec.

Another important spec for op amps is the slew rate. If you look closely at the data sheet you will see that the slew rate is only 80 V/microsecond. That's about half of what some other products offer. National says the slower slew rate easily covers the target market, ADSL applications. They decided to scale down the output stage to get a slower slew rate and make the product less expensive.

The 6639 part is a product that is helping fill a void in the market created when one of National's competitors couldn't meet demand. The 6639 is a single supply version with a significant improvement in shutdown power. National reduced the power by approximately one half, while still achieving the same performance, for portable applications that allows you to sustain longer battery life. The shut-down is less than 1/2 the competition's shut-down power. The 6644 is quad amp version of the 6639.

The LMH6622 is available now in 8-pin SOIC and MSOP packaging and is priced at $1.85. The LMH6639 is available in 8-pin SOIC and 6-pin SOT23 packaging and is priced at $1.09. The LMH6644 is available in TSSOP-14 and SOIC-14 packaging and is priced at $1.48. All three product prices are for 1000-unit quantities.

Data sheets and more information on these products is available at:
LMH6622,
LMH6639 and
LMH6644

For more information on National's amplifier products, visit http://www.national.com/appinfo/amps/.