NRZ-to-NRZM code converter based on gallium-arsenide heterojunction bipolar transistors
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CROELECTRONIC DEVICES AND SYSTEMS
NRZ-to-NRZM Code Converter Based on Gallium-Arsenide Heterojunction Bipolar Transistors V. P. Timoshenkov and V. A. Bratov Moscow Institute of Electronic Technology, proezd 4806, building 5, Zelenograd, Moscow oblast, 103498 Russia e-mail: [email protected] Submitted April 16, 2007
Abstract—Aspects of designing the integrated circuit of the NRZ-to-NRZM code converter based on heterojunction gallium-arsenide transistors are considered. A feature if the circuit is its use of the inductive correction, which makes it possible to broaden the converter passband. A device for a transmission rate of 12.5 Gbit/s was numerically simulated and experimentally studied. The experimental results are in good agreement with the simulation results. PACS numbers: 84.40.Lg, 85.40._e DOI: 10.1134/S1063782608130204
1. INTRODUCTION Code converters are key units of systems of microwave transmission of digital information. At data transmission rates of 10 Gbit/s and higher, specialized technologies for fabricating integrated transistors with a high upper cutoff frequency become in demand. Among such technologies is the fabrication of heterojunction bipolar transistors (HJBTs) based on gallium arsenide, the application of which allows one to design and fabricate integrated circuits (ICs) that provide data transmission rates that significantly exceed 10 Gbit/s. The originality and novelty of the presented study is the development of special circuitry for amplification stages fabricated using this technology and providing a low jitter and a low overshoot in the transient response. To extend the device functionality, integrated delay lines are used in the circuit. 2. DIGITAL DATA CODING Digital data transmission in the form of electrical signals is performed using codes on which the following demands are made: (i) minimum frequency band of the digital signal, which makes it possible to increase the transmission data set through an available physical channel; (ii) insignificant dc voltage level in the transmission line; (iii) sufficient voltage pulse amplitude providing a required signal-to-noise ratio; and (iv) regular (with a set frequency) appearance of certain voltage transitions (low-to-high level and vice versa) required to synchronize receiver and transmitter. The simplest coding algorithm is denoted as NRZ (Non Return to Zero) and is a basis for constructing
more advanced algorithms [1]. Attempts at overcoming the problems associated with transmission of long sequences of “units” without increasing the requirements for the communication channel passband led to the development of the code denoted as NRZI (NRZ-Inverted) or NRZM (NRZ-Mark). This coding method uses the NRZ code as the initial information and performs bit-by-bit data conversion according to the following algorithm [1]: (I) The logical “zero” at the input causes the repetition of the preceding output voltage, i.e., it is coded by the absence of transition at the bit start. (II) The logical “unit” at the input causes a change in the outpu
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