Integrated transversal equalizers in high-speed fiber-optic systems

Abstract

Abstract-Intersymbol interference (ISI) caused by intermodal dispersion in multimode fibers is the major limiting factor in the achievable data rate or transmission distance in high-speed multimode fiber-optic links for local area networks applications. Compared with optical-domain and other electrical-domain dispersion compensation methods, equalization with transversal filters based on distributed circuit techniques presents a cost-effective and lowpower solution. The design of integrated distributed transversal equalizers is described in detail with focus on delay lines and gain stages. This seven-tap distributed transversal equalizer prototype has been implemented in a commercial 0.18-m SiGe BiCMOS process for 10-Gb/s multimode fiber-optic links. A seven-tap distributed transversal equalizer reduces the ISI of a 10-Gb/s signal after 800 m of 50-m multimode fiber from 5 to 1.38 dB, and improves the bit-error rate from about 10 5 to less than 10 12 .

Carrierless amplitude and phase modulation in wireless visible light communication systems

“…Digital circuits such as feedforward equalizers (FFEs) and decision feedback equalizers (DFEs) can provide similar bandwidth enhancement and additionally allow easy real-time adaptation of their response, which is particularly useful in the case of time-varying channel responses, such as in indoor VLC systems due to user mobility. The most common linear equalizer is the FIR filter which consists of delay lines and taps with variable tap coefficients [69][70][71][72]. The optimum values of the equalizer tap coefficients depend on the channel response and therefore need to be optimized through a training process using appropriate algorithms such as the least mean squares (LMS) and recursive least squares (RLS) algorithms [73].…”

Extending Distributed-Based Transversal Filter Method to Spectral Amplitude Encoded CDMA

“…The filter structures are not reconfigurable in terms of variable delay adjustment and thus code dictates their specific design. It is worth mentioning that DTF structures with the capacity to adjust tap gain weights and switch the sign of taps have been reported in the literature (for example in [9] and [10]), where distributed active stages are implemented as Gilbert cells providing balanced characteristics and broadband matching. However, the complexity at transistor-level design will be a key point to be taken into consideration in the selection of the filter topology.…”

“…Several experiments have been reported in the literature from early developments based on Charge Transfer Devices (CTDs) working at moderate speeds (2 Gchip/s and 62.5 Mbit/s) [7] to prototyping transversal equalizers operated as data encoders and correlators at rate of 18 Gchip/s and 1.25 Gbit/s [8]. The fractionally-spaced equalizer, which is typically used to effect dispersion compensation in high speed fiber optic links [9], [10], were employed to encode data and despread Direct Sequence (DS) code-modulated pulses and transversal filter structures were used for group velocity dispersion compensation in [11].…”

Multilevel pre-equalization using an analog FIR filter with multiple binary delay lines for 20-Gb/s 4-PAM multimode fiber transmission

“…For example, electrical-domain compensation using multipurpose digital-signal processors (DSPs) has been reported; in this approach digital filters, such as finite impulse response (FIR) filters, are calculated by the DSPs [2,3]. On the other hand, analog FIR filters based on analog electronic circuit technology are also attractive for achieving cost-effectiveness and low power consumption [4,5,6,7,8]. We have investigated analog FIR filters using binary delay-line components based on complementary metal-oxide-semiconductor (CMOS) inverters which can realize smaller integrated-circuit (IC) chip size [9].…”