wirelessZONE Products for the week of September 24, 2007

National Semiconductor Says…

LMH6552/6515/6555: High-Speed Amplifier Line Of Energy-Efficient Products
Targeted at Wireless Infrastructure, Test and Measurement, and Defense and Space Applications

National Semiconductor Corporation introduced three new energy-efficient, high-speed differential amplifiers that are well-suited for a wide variety of communications, test, instrumentation, and defense and space applications. These amplifiers are part of National’s PowerWise line of energy-efficient analog integrated circuits (ICs) that deliver outstanding performance-to-power ratios. The creation of the PowerWise line demonstrates National’s heightened focus on products that enable more energy-efficient designs for design engineers.

The LMH6552 is the industry’s highest-bandwidth, current feedback differential amplifier at 1.5 GHz, with the industry’s lowest power consumption at 112 mW. This translates to dissipating 44 percent less power than competitive products. The LMH6515 digital-controlled variable gain amplifier (DVGA) offers an excellent 8 dB noise figure and a 40 dBm output intercept point (OIP3) at 70 MHz for WCDMA, GSM and WiMAX receiver signal paths, at 20 percent lower power than the competition. The LMH6555 enables an 8-bit, 3 Giga-sample data acquisition system with less than half the power consumption of competitive solutions.

National offers these high-speed amplifiers as part of an analog signal-path solution to help system designers jump start development and accelerate their designs. The LMH6552, LMH6515 and LMH6555 are combined with National’s analog-to-digital converters (ADCs), clock conditioners and power management ICs on three reference design boards targeting WiMAX and 2G/3G wireless base stations, test and measurement equipment, and high-speed communications systems used in defense and space applications. Each reference design board is optimized for power and performance to manage high-speed signal conditioning and processing across the entire analog signal path. These boards are supported by National’s WaveVision hardware and software as well as application specifications, schematic diagrams, bills of materials (BOMs) and layout guidelines.

Key Features – LMH6552 1.5 GHz Current Feedback Differential Amplifier
The LMH6552 differential amplifier’s proprietary, patent-pending circuitry delivers high-gain operation without compromising bandwidth, harmonic distortion or output noise performance; This reduces component count and system power by eliminating the need for multiple gain stages. The LMH6552 also provides a wide 1.5 GHz bandwidth along with an industry-leading 0.1 dB gain flatness to 450 MHz. Low total harmonic distortion of -90 dBc at 20 MHz and -74 dBc at 70 MHz and superior noise performance of 1.1 nV/sqrtHz enable the LMH6552 to drive 14-bit ADCs at frequencies up to 70 MHz. The LMH6552 can be configured as either a differential-input-to-differential-output gain block or single-ended-input-to-differential-output gain block. It also can be AC- or DC-coupled at the input, making the amplifier suitable for a wide range of applications including communication systems and high-speed data acquisition front-ends. The LMH6552 is available in an 8-pin SOIC package and a space-saving, thermally enhanced 8-pin LLP package.

EN-Genius Says…

Although National launched the PowerWise branding of products this last week, the name actually dates back to 2003 when National and ARM got together to develop better power solutions for portables using ARM processors; it resulted in adaptive voltage scaling technology.

The PowerWise name is being reborn, rather than being launched for the first time, to bracket National parts that they consider to be performance-to-power ratio higher than most. The name is used by multiple others, including power consortiums in Toronto, Scotland and Australia. It is also the brand name for an ink pump, but in this context it is catchy.

But designers aren't looking for a brand name when they put a circuit together. They are looking for a solution for their particular problem, today. If they have the luxury of finding a better part with lower power use after their problem days are over, great. Most do not have that luxury.

Each of these three products could have stood on their own, with individual press releases. National has, instead, chosen to group them to push the brand -- which is a good approach for investors but not for those are going to be users.

What follows are, necessarily, quick reviews of all three parts. They deserve better coverage but we don't have the luxury of production time to give each a full review.

This is billed as a digitally-controlled variable gain amplifier. It is an attenuator with 31 1-dB steps followed by a SiGe fixed-gain amplifier to give an overall gain range from +24.2 dB to -6.9 dB. The gain control is by way of a parallel 5-bit system. Gain step error is a typical 0.02 dB at dc and 0.07 dB at 150 MHz and the differential input resistance to the part is a fixed 186 Ω. With a single 5-V rail typical total supply current is 107 mA.

The 3 dB bandwidth of the LMH6515 is a typical 600 MHz. Third-order IMP ranges from -76 dBc at 75 MHz to -58 dBc at 450 MHz. Similarly, OIP3 ranges from about 40 dBm at 75 MHz to 34 dBm at 250 MHz Both with a 200 Ω load), while P1dB is 16.7 dBm at 75 MHz and 14.7 dBm at 250 MHz (both also with a 200 Ω load). The noise figure is 8.3 dB at maximum gain, while input noise voltage is 1.8 nV/rtHz at 40 MHz and the output noise voltage is 18 nV/rtHz at the same frequency.

The LMH6515 looks ideal to set the range on the input of an ADC -- up to 14 bits, maybe -- with a great power number for the performance. It will find sockets in higher IF sampling receivers of various kinds and in basestations.

The LMH6515 is in production in LLP-16 and is priced at $5.25 in 1000-piece lots. A free reference design is available and a fully-loaded board can be purchased for $800.

Data Sheet LMH6515

The LMH6555 is a SiGe differential driver with a 1.2 GHz 3-dB bandwidth (and a 180 MHz 0.1 dB gain flatness). It can also, and most likely nearly always will be, driven single-ended with a differential output. Slew rate is 1300 V/µs. The input can be dc coupled. The common-mode voltage can be set from the output of a following ADC. From a single 3.3-V rail the typical total current is 120 mA.

Group delay is a typical 0.75 ns at each output and the fixed gain of the part is 13.7 dB. P1dB is 1 V at 1 GHz. 2nd harmonic distortion is -53 dBc at 750 MHz and 3rd is -54 dBc. OIP3 is 27.5 dBm at 1 GHz while 3rd-order IMD is -67 dBc, also at 1 GHz. Noise figure is 15 dB. Common-mode PSRR is -39 dB. It has a 100 Ω differential load capability.

This is a specialized part and is clearly intended to provide a low distortion differential solution for potential users of the GHz 8-bit family of ADCs, now hitting 3 GHz with the ADC083000. The analog bandwidth there is 748 MHz which is why we see the specifications for the driver at 750 MHz. If you can afford the GHz ADCs in your design you can certainly afford the driver, which is priced at a premium. This will be a relatively low volume part for the next couple of years but the applications are opening up quite fast.

The LMH6555 is in production in LLP-16 and is priced at $5.95 in 100-piece lots. A free reference design is available and a full-loaded board, including an ADC083000, is available for $4,900.

Data Sheet LMH6555

The LMH6552 is another high-frequency part, although non-SiGe, with differential input and output, although the input can be driven single-ended. It requires split rails and can be operated at ±5 V down to ±2.5 V. At both, quiescent is about 20 mA.

With the higher rail the small-signal bandwidth is 1.5 GHz (falls to 1.1 GHz with the lower rail) while the 0.1 dB flatness bandwidth (with the higher rails) is 450 MHz. Slew rate is a high 3800 V/µs.

At 70 MHz (the most likely frequency of operation for most of the applications of the part) 2nd harmonic distortion is -74 dBc while 3rd is -84 dBc. Two-tone intermod is -87 dBc. At frequencies higher than 1 MHz input voltage noise is 1.1 nV/rtHz while input noise current is 19.5 pA/rtHz.

This is an adjustable gain part, set as usually, with an external feedback resistor. At a gain of 9, in a 50 Ω system, at 10 MHz the noise figure is 10.3 dB. With the split 5-V rails the input range is  ±3.8 V. CMRR is a typical 80 dB, as is PSRR.

The LMH6552 is billed as a 1.5 GHz fully-differential amplifier, which it is, but I see it more as an adjustable-gain, lower power, lower priced version of the LMH6555. It could be used just like that part with slightly lower frequency performance but most of the applications will be in low-frequency IF paths driving ADCs up to 14 bits (because of the noise numbers). The reference design that National offers is for just such an application. This is going to be a high volume part and will find numerous applications -- from SAW filter buffering to video, signaling, etc.

The LMH6552 is in production in SOIC-8 and LLP-8 priced at $3.95 in 1000-piece lots. A free reference design is available with a fully-loaded board priced at $800.

Data Sheet LMH6552