Despite the continued and anticipated advance of modern digital communications, instrumentation, electronics warfare, and radar systems that require high-speed digital and mixed-signal integrated circuits (ICs) operating at frequencies from DC to 100 GHz, solutions designed to meet these needs have been slow in coming.

Broadband requirements have placed severe constraints on available semiconductor technologies and design expertise resulting in commercial off-the-shelf digital and mixed-signal ICs based on silicon germanium (SiGe) or gallium arsenide (GaAs), technologies typically available only at speeds reaching to 13 GHz. For higher speeds, custom solutions have been the only viable option and involve significant development time and cost.

High-speed digital and mixed-signal ICs based on advanced InP heterojunction bipolar transistor (InP HBT) technology may pave the way for the development of future 100 GHz digital and mixed-signal ICs.

InP HBT has long been recognized as the high-speed leader among modern semiconductor technologies^1,2,3. The following attributes make InP HBT technology ideally suited for high-speed digital and mixed-signal ICs with low to medium levels of integration:

• Highest speed

  InP HBT exhibits the highest cutoff frequency (fT) of all commercially available semiconductor technologies, and is significantly faster than competing technologies at similar or smaller critical dimensions.

• High reproducibility

  Tremendous progress has been made in the high-volume production of GaAs and InGaP HBT circuits in the past decade. For example, the reproducibility of InP HBT turn-on voltage is typically a few millivolts versus hundreds of millivolts achieved with GaAs PHEMT.

Figure 1 compares the cutoff frequency of InP HBT with that of competing technologies. Today, InP HBT technology is commercially available in 1.0-µm emitter size, which exhibits a cutoff frequency as high as 150 GHz and represents a 25 percent improvement over competing technologies.

New products based on 1.0-µm InP HBT technology, 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 — open a new range of performance for an expanded base of applications.

High-speed D flip-flops are often the fastest digital circuit, and, thus, the most demanding component, in high-speed data transmission or test equipment. These ICs are used extensively in optical transmission systems, satellite communications ground terminals, 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. Figure 2 demonstrates the use of a 50 GHz D flip-flop to make correct “1” and “0” decisions on a noisy 50 Gbps 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 data is recovered at the receiver by performing a similar XOR operation between the received signal and the same PN code. Figure 3 shows how such a code 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 approximately 14 GHz.

To provide phase locking, DRO and YIG, manufacturers typically rely on traditional analog components, such as step recovery diodes and/or subharmonic mixers, which are noisy and expensive.

For high-performance applications, high-speed prescalers are preferable to analog components because a divide-by-n prescalers reduce the phase noise of the RF input signals by 20log(n). 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.

The time has come for commercial digital and mixed-signal ICs to achieve frequencies as high as 50 GHz. High-speed InP HBT ICs 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.

Engineers should expect these products to facilitate the development of advanced digital communications, instrumentation, electronics warfare, and radar systems at microwave and millimeter wave frequencies.

• Y.-K. Chen, R. N. Nottenburg, M. B. Panish, R. A. Hamm, and D. A. Humphrey, “Subpicosecond InP/InGaAs Heterostructure Bipolar Transistors,” IEEE Electron Device Letters, vol. 10, pp. 267-269, June 1989.

• G. Raghavan, M. Sokolich, and W. E. Stanchina, “Indium Phosphide ICs Unleash the High-Frequency Spectrum, IEEE Spectrum, vol. 37, pp. 47-52, October 2000.

• M. Ida, K. Kurishima, and N. Watanabe, “Over 300 GHz fT and fmax InP/InGaAs Double Heterojunction Bipolar Transistors With a Thin Pseudomorphic Base,” IEEE Electron Device Letters, vol. 23, pp. 694-696, December 2002.

Dr. Loi Nguyen is the founder and vice president of technology for Inphi Corp. (www.inphi-corp.com). He holds seven U.S. patents and is widely recognized for his development of devices and ICs using advanced GaAs and InP technologies.

His thesis, which focused on the development of GaAs devices, stimulated the commercialization of GaAs for direct broadcast satellite, millimeter wave radios, automotive radars, and defense applications.

Dr. Nguyen set a world-record cutoff frequency for GaAs transistors in 1988 and established a world-record cutoff frequency for high-speed transistors in 1992. This earned him the IEEE Paul Rappaport Award. He holds a B.S. and Ph.D. in electrical engineering from Cornell University and an M.B.A. from the Anderson School at UCLA. Dr. Nguyen can be reached via email at lnguyen@inphi-corp.com.