acquisitionZONE Products for the week of November 3, 2003
National Semiconductor Corporation released a family of high-speed operational amplifiers for the military and aerospace market. Originally designed for commercial and industrial applications, these products will replace many of the functions of the company's popular Comlinear line of operational amplifiers. Each of the products is produced on National's unique patented VIP10 manufacturing process, which enables space-level radiation tolerance to 300K rads/si total dose.
The parts are the LMH6715, a high-speed dual wideband current feedback video amplifier, the LMH6628 a dual low noise operational amplifier, and the LMH6624 a single very low noise voltage feedback operational amplifier.
"National is a leader in high-performance operational amplifiers, said Erroll Dietz, director of National's amplifiers product line. "Our new radiation-tolerant products represent major enhancements that extend the usability of our op amps into the most demanding space applications."
LMH6715 Dual Wideband Video Op Amp
The LMH6715 is a current feedback, unity gain stable, high-speed dual video
amplifier. It is designed for used in dual 5V supply systems. It uses a
current feedback architecture to maintain high-bandwidths for large signals.
It excels on the key video specifications of differential phase and differential
gain (Dp/Dg) of only 0.02°/0.02%. The LMH6715 is designed to meet the
market needs of the CLC412. The LMH6715 far exceeds the performance of the
CLC412 with only a marginal increase of supply current. A key specification
of high-speed amplifiers is their large signal bandwidth (LSWB). At 175MHz,
the LMH6715 exceeds the LSBW of the CLC412 by over 60%. LSBW is a key customer
spec for driving video signals and is a less subjective parameter then the
more commonly mentioned slew rate. The LMH6715 exceeds both the 3dB and
0.1dB flatness of the CLC412. A 3dB small signal bandwidth of 400MHz @ AV=+2
and 0.1dB gain flatness to 100MHz make it ideal for wideband systems. Customers
that could not use the CLC412 because of its lower frequency response now
have a part available with almost double the usable bandwidth. The LMH6715
is available in 10-pin SOIC and 8-pin ceramic DIP. The improved AC parameters
and better output drive makes the LMH6715 the ideal amplifier for many video
applications.
LMH6628 Dual Wideband, Low-Noise, Voltage Feedback Op Amp
The LMH6628 is the lowest noise 300MHz Bandwidth, 500V/usec slew rate dual
amplifier on the market. It features unity gain stability and an easy to
use voltage feedback topology and is well suited for single or dual 5V supply
applications that require high output current and wide bandwidth. The bandwidth
of 300MHz at a gain of AV=+1 and fast slew rate of 500V/usec make it ideal
for a wide range of communication applications. The fast settling time of
12ns and low THD make it a great choice for 12bit data acquisition systems.
The ability to drive heavy capacitive loads also makes it suitable for directly
driving analog to digital converters (ADCs) in data acquisition systems.
This allows the elimination of a multi chip front end in many receiver applications.
The combination of very low noise and high output drive ability makes the
LMH6628 the ideal amplifier for many receiver/driver applications. The LMH6628
is available in 10-pin SOIC and 8-pin ceramic DIP package types.
LMH6624 Ultra Low Noise Voltage Feedback Op Amp
National's LMH6624 is an ultra-low-noise operational amplifier designed
to provide outstanding dynamic range in systems. The low offset of 100uV
and low drift of 2uV/C provide the high DC accuracy that is needed for precise,
high-resolution applications. This allows system designers to reduce the
amount of error correction circuitry required, which reduces costs. The
large Gain Bandwidth Product of 1.9 GHz allows low distortion, high frequency
operation. The LMH6624 is stable for gains greater than ten and is available
in 10-pin SOIC and 8-pin ceramic DIP package types.
analogZONE Says . . .
The star part in this release, to my way of thinking, is the LMH6715. With other vendors releasing "video" op amps this year, the position of the relatively old Comlinear CLC412 has been very threatened, and while it represented a huge jump in performance at the time of its design -- in an atmosphere where the people involved really understood video, which is increasingly rare -- but its days had to be numbered, even if it was just because of basic bandwidth issues.
The differential phase and gain numbers from the LMH6715 at 0.02° and 0.02% typical are not the best to be seen this year but this part is not going to be specified for volume NTSC/PAL designs anyway so it is mostly immaterial. What is material and is not specified in any way is how linearity vs. level vary at frequencies up to about 30MHz and that is a consistent problem across the industry. What is extremely annoying about the data sheet, however, is that a part which has "video" in its title is characterized (except for diff phase/gain) with 100 Ohm loads. Why? There may well be applications where the part can be very successfully used in low RF circuits but National does not claim that in the part's title.
The small-signal 3-dB bandwidth (which is likely to be a bit higher with a 150 Ohm load) is a typical 400 MHz (300 Ohm feedback, gain 2 V/V, <0.5 V output) while the large signal bandwidth is a typical 170 MHz. The small-signal 0.1-dB gain flatness is a typical 100 MHz (both peaking and roll-off) which is surprisingly high as a normal rule-of-thumb is 10% of the 3 dB bandwidth, which would be 40 MHz, but National has a graph in the data sheet to support the claim with a 140 MHz example. The linear phase in that graph also shows a total swing of a little over 0.25°. Slew rate with a 2-V step is a typical 1300 V/µs.
Second harmonic distortion at 20 MHz with 2 Vpp output is -60 dBc typical which worsens by about 10 dB at 50 MHz and improves by about the same amount at 10 MHz. Likewise 3rd harmonic distortion is a typical -75 dBc at 20 MHz but worsens by about 20 dB at 50 MHz and improves only about 5 dB at 10 MHz. Crosstalk between channels is a typical -70 dB at 10 MHz, which drops to -50 dB at 100 MHz.
Typical PSRR at dc is 60 dB, while CMRR is 56 dB; the latter falls to about 10 dB at 100 MHz and is around 20 dB for some video frequencies of interest at about 30 MHz.
The performance of the amplifier is significant considering that the amount of power being pushed at the solution is only 5.8 mA, typical, per amplifier from split rail ±5 V supplies -- preferred by video designers for true dc performance, and when using color-difference signals does not require a different design. The channels can drive up to 70 mA into the loads. Channel matching is not spelled out in the characteristics but from a graph the differences appear negligible.
The LMH6715 will find sockets in professional video applications, some lower frequency I/Q channels, wide-bandwidth transimpedance amplifiers, current-feedback integrators, active filters, and various cable drivers -- beyond video. Typically, National is not really demanding a price premium for performance.
The LMH6715 is available in SOIC-8 (not the SOIC-10 in the press release) and a ceramic DIP-8. The commercial SOIC-8 is priced at $1.69 in 1000-piece lots while the ceramic versions are priced from $28.80 to $33.30 in 250+ piece lots.