News Article

InP HBT Technology Enables Digital And Mixed-signal ICs At DC To 100 GHz Frequencies

The advantages offered by InP HBT technology have opened up a range of new applications for high-speed mixed-signal and digital ICs, according to Loi Nguyen of Inphi Corporation.
Modern digital communications, instrumentation, electronics warfare and radar systems require high-speed digital and mixed-signal ICs operating at frequencies from DC to 100 GHz. Broadband requirements place severe constraints on available semiconductor technologies and design expertise. Indeed, commercial off-the-shelf digital and mixed-signal ICs based on SiGe or GaAs technologies are generally available only at speeds up to 13 GHz. For speeds over 13 GHz, custom solutions are the only viable option and involve significant development time and cost.Inphi recently introduced more than 60 high-speed digital and mixed-signal ICs based on 1.0 µm InP HBT technology. The company has also demonstrated a divide-by-2 prescaler operating at a frequency as high as 92 GHz (Srivastava et al. 2002), which will pave the way for the development of future 100 GHz digital and mixed-signal ICs. This article describes how the advantages of InP HBT technology can benefit high-speed ICs such as D flip-flops, prescalers and XOR gates.Inphi is a fabless IC design house that supplies high-speed digital and mixed-signal ICs based on advanced InP HBT technology. InP HBTs have long been recognized as the high-speed leaders among modern semiconductor technologies (Chen et al. 1989; Ida et al. 2002; Raghavan et al. 2000). The following attributes make InP HBT technology ideal for high-speed digital and mixed-signal ICs with low to medium levels of integration:
High speed InP HBTs exhibit the highest cut-off frequency (ft) of all commercial semiconductor technologies. Indeed, they are significantly faster than competing technologies at similar or smaller critical dimensions.
High reproducibility Great progress has been made in the high-volume production of GaAs-based HBT circuits in the past decade, and this expertise can be translated to InP HBT technology. For example, the reproducibility of InP HBT turn-on voltage is typically a few millivolts, compared with hundreds of millivolts achieved with GaAs PHEMT.Figure 1 compares the ft of InP HBT with that of competing technologies. Today, InP HBT technology is commercially available in 1.0 µm emitter size, which exhibits an ft as high as 150 GHz and represents a 25% improvement over competing technologies.Inphi recently introduced more than 60 commercial ICs, including low- to medium-scale integration circuits such as D flip-flops, OR and XOR logic gates, 1:2 clock fanouts, 4:1 multiplexers, 1:4 demultiplexers, and divide-by-2 and divide-by-4 prescalers. The performance and system applications of some of these products are described below.High-speed D flip-flops are often the fastest digital circuits, and thus the most demanding components, in high-speed data transmission or test equipment. These ICs are used extensively in optical transmission systems, ground terminals for satellite communications, and high-speed test and measurement equipment. A high-speed D flip-flop retimes the data and cleans up distortions prior to transmission or makes "1" or "0" decisions on noisy received signals before further processing.InP HBT technology is ideally suited for the realization of high-speed, low- and medium-scale integration circuits such as D flip-flops. Inphi recently introduced a family of D flip-flops operating at frequencies from DC to 50 GHz. These are available at three different speeds: DC to 13 GHz, DC to 25 GHz and DC to 50 GHz. The lower-speed circuits (13 and 25 GHz) are available in die form or in a surface-mount ceramic package. The packaged parts are also available on an evaluation board. The 50 GHz devices are available in die form or in a metal package with V connectors. Figure 2 shows the use of Inphi s 50 GHz D flip-flop to make correct "1" and "0" decisions on a noisy 50 Gbit/s input data signal.High-speed exclusive OR (XOR) gates are versatile building blocks for a wide range of applications that require the direct processing of high-speed data at microwave and millimeter wave frequencies. Examples include various types of encoding schemes such as direct-sequence spread spectrum (DSSS), in which an XOR operation is performed between the transmitted data and a pseudo number (PN) sequence prior to transmission. The PN sequence modulates the carrier signal, producing a stream of encoded data. The data is recovered at the receiver by performing a similar XOR operation between the received signal and the same PN code. Figure 3 shows schematically how the encoded data stream can be generated at microwave frequencies up to 50 GHz.High-frequency prescalers are critical components in phase-locked loop applications, in which the phase of an oscillator is locked to a low-frequency reference source. High-frequency sources such as dielectric resonator oscillators (DROs) or yttrium iron garnet oscillators (YIGs) currently operate above 20 GHz, but until now prescalers have only been available at frequencies up to about 14 GHz. To provide phase locking, DRO and YIG manufacturers typically rely on analog components such as step recovery diodes and/or subharmonic mixers, which are expensive and hard to manufacture in volume.For high-performance applications, high-speed prescalers are preferable to analog components because a divide-by-n prescaler reduces the phase noise of the RF input signal by 20log(n). Inphi s new DC to 25 GHz and DC to 50 GHz prescalers enable the use of a well known digital technique to phase-lock a high-frequency oscillator above 14 GHz. Because of their very low phase noise (see figure 4), these high-frequency prescalers are ideally suited for use with high-performance DRO and YIG oscillators.Technological advances have made it possible for commercial digital and mixed-signal ICs to achieve frequencies as high as 50 GHz. Inphi s high-speed InP HBT ICs are the first commercial products to enable the use of well known digital techniques for the generation, transmission, detection and processing of RF signals at frequencies as high as 50 GHz. We expect these products to facilitate the development of advanced digital communications, instrumentation, electronics warfare and radar systems at microwave and millimeter wave frequencies.Chen et al. 1989 IEEE Electron Device Lett. 10(6) 267.
Ida et al. 2002 IEEE Electron Device Lett. 23(12) 694.
Raghavan et al. October 2000 IEEE Spectrum.
Srivastava et al. 2002 IEEE GaAs IC Symposium, Late News Papers.
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