Analog Devices Inc. calls any amp above 50 MHz a high-speed amplifier, while everything between 25 MHz and 50 MHz is defined more by the parameters and design optimization. The new AD8099, at 500 MHz, is certainly a high-speed op amp. It addresses such issues as package size and speed/power trade-offs as well as noise performance. Indeed, the part's noise performance, distortion and slew rate make it exceptional.
The company is most proud of the AD8099's noise performance because it is difficult to achieve low noise (0.95 nanovolts/the square root of Hz) while also getting -100-dBc distortion levels at frequency. Doubtless, there are parts on the market that have lower noise than the ADI device and others that have lower distortion, or even a better slew rate, but only the ADI part combines them all.
The AD8099 has a 1,400-microvolts slew rate at a gain of 10 and holds a 400-microvolts slew rate typical at a gain of 2. There are some competitive parts that operate at a gain of 2, but not at that slew rate. And you can get relatively good noise performance from most amplifiers, but you don't get the very low distortion or the slew rate associated with it.
ADI controlled the noise, distortion and slew rate at such exceptional levels by developing a “common-mode linear rise” architecture. In essence, ADI changed the way the front-end and gain stage are structured.
The design change in the package pinout impressed me. The AD8099 provides good performance in the SO-8 packaging, but in the smaller, lead frame chip-scale package (LFCSP) it exhibits better thermal performance and even better parasitics.
The company further discovered that it could improve the performance of the part by varying the pinout. In the old pinout, the input (pin 3) is next to the supply (pin 4). That creates coupling because of the significant current flowing through the supply pin, especially in high-speed amplifiers. ADI took the supplies and rotated them to the other side of the chip. Ordinarily the inductance between the pins is very small and adversely affects the performance of the part. By rotating the pinout, you locate the higher-voltage-output side on pin 7 next to the supply pins, where the coupling is less critical.
The part is also externally compensated with a capacitor. By varying the capacitor, you can get 500 MHz at different gains. That gives customers the opportunity to trim and control the part as they see fit. A typical amplifier is internally compensated, and you get 500 MHz at low gain but not at higher gains. But the AD8099 can still achieve 500 MHz at gains between 2 and 10.
The device's feedback line is a new design idea. If you ran a feedback capacitor from the output to the inputs on a classic amplifier, it would include a resistor and a trace that would have to go either under or around the part. That could make for an unwanted antenna. So ADI put an internal resistor between pins 2 and 3. That eliminates excess capacitance in the trace and thus improves stability.
Milpitas, Calif. – Xicor Inc.'s X98000 line of five high-speed analog front ends is said to provide the performance needed for high-resolution flat-panel monitors, LCD projectors and high-definition televisions. The fastest product, the high-end X98027, operates at up to 275 Msamples/second. The other four devices in the new family operate at 240, 210, 170 and 140 Msamples/s.
Each analog front end in the family has three independent 8-bit channels to capture the red, green and blue or YPbPr component-video signals sent from personal computers, workstations, DVD players or video set-top boxes. The devices combine high performance and low-noise signal processing with a low-jitter digital phase-locked loop of 250 picoseconds peak to peak (at 275 Msamples/s) to produce ultrasharp high-resolution images, according to Xicor.
The three analog-front-end channels have high linearity and matching for superior gray-scale performance, the company said. A very high-input bandwidth yields ultrasharp images even at QXGA pixel rates, according to Xicor.
Additional peaking control can restore image sharpness when long cable lengths are used. An automatic black-level compensation circuit eliminates offset errors due to mismatch and drift.
The internal digital PLL has 64 phase steps with high linearity, in comparison to a maximum of 32 phase steps in competitive products, the company said. The X98000 family is said to be easy to program and has low sensitivity to pc-board noise.
The X98027 is Xicor's flagship product, targeted at high-resolution QXGA (2,048 x 1,536-pixel) displays, said Fred Hamilton, director of technical marketing for Xicor's display products.
Other key specs for the unit are its 64 interpixel sampling positions, programmable analog input bandwidth from 100 MHz to 780 MHz, automatic black-level compensation for continuous offset calibration and 1.4-volt peak-to-peak analog input range. It has a two-channel input multiplexer. The X98027 also supports QXGA resolution up to a refresh rate of 60 Hz.
The X98024 supports WUXGA resolution (1,920 x 1200), the X98021 supports UXGA (1,600 x 1,200), the X98017 supports WSXGA (1,536 x 1,024) and the X98014 supports SXGA (1,280 x 1,024) and all lower resolutions.
Samples are available now, with production scheduled for the fourth quarter. Pricing for the X98014 analog front end starts at $9 in lots of 1,000.
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