Derivation of the Equivalent Input Noise of Multiplicative Distributed Amplifiers for Wideband Optical Receiver Applications

In this paper, we derive new models that describe the noise voltage and equivalent input noise current spectral densities for multiplicative distributed amplifiers. Based on the derived models, design optimisation techniques to minimise the noise contribution of transimpedance amplifiers based on the multiplicative DA topologies are proposed

Matrix single stage distributed amplifier design for ultra wideband application

This paper proposes a new amplifier topology, the matrix single stage distributed amplifier (M-SSDA). The amplifier employs only multiplicative gain, hence, potentially offering a higher gain-per-device than both the conventional DA and matrix amplifier. Functionally similar to the cascaded single stage distributed amplifier (C-SSDA), the M-SSDA has advantages in smaller circuit footprint, a potential for lower transmission line losses and better noise performance. A 2-tiered common-emitter (CE) M-SSDA based on a full foundry double heterojunction bipolar transistor (DHBT) model is presented, demonstrating the viability of the proposed design. The S-parameter performance of the proposed circuit is compared with that of a C-SSDA with two gain cells to show the similarity in their gain and bandwidth performance. To further demonstrate the utility of the proposed design concept, a practical 3×1 M-SSDA circuit is presented. In this circuit, improvement in bandwidth performance is achieved by scaling down the inductance on the input and intermediate transmission lines and introducing a high frequency peak on these lines through shunt capacitance. A cascode configuration with negative resistance attenuation compensation is applied in the gain cells to achieve a flat gain profile. Simulations predict a gain of 20dB at 324GHz bandwidth; more than threefold bandwidth improvement compared to the basic CE M-SSDA design

Single-Loop Opto-Electronic Oscillator at 10.4 GHz with a Cascaded Microstrip Bandpass Filter Configuration

The opto-electronic oscillator is a well-known microwave photonic device that produces high-frequency signals in the microwave range. One of the main advantages of the opto-electronic oscillator is that it produces high-frequency signals with low phase noise thanks to the resonator's properties. In most cases the opto-electronic oscillator faces the problem of generating side modes besides the oscillation signal due to non-ideal filtering. In this paper we propose a solution for the additional suppression of these undesired harmonics using a combination of two slightly detuned bandpass microstrip filters. We report an improvement for the side-mode suppression ratio about 8.3 dB with a single-loop 90-m-long opto-electronic oscillator at 10.4 GHz

InP DHBT Single-Stage and Multiplicative Distributed Amplifiers for Ultra-Wideband Amplification

This paper highlights the gain-bandwidth merit of the single stage distributed amplifier (SSDA) and its derivative multiplicative amplifier topologies (i.e. the cascaded SSDA (C-SSDA) and the matrix SSDA (M-SSDA)), for ultra-wideband amplification. Two new monolithic microwave integrated circuit (MMIC) amplifiers are presented: an SSDA MMIC with 7.1dB average gain and 200GHz bandwidth; and the world's first M-SSDA, which has a 12dB average gain and 170GHz bandwidth. Both amplifiers are based on an Indium Phosphide DHBT process with 250nm emitter width. To the authors best knowledge, the SSDA has the widest bandwidth for any single stage amplifier reported to date. Furthermore, the three tier M-SSDA has the highest bandwidth and gain-bandwidth product for any matrix amplifier reported to date

Noise analysis of multiplicative distributed amplifiers

© 2019 IEEE This paper analyses the noise performance of cascaded and matrix single stage distributed amplifiers (C-SSDA and M-SSDA), together termed multiplicative distributed amplifiers. The analytical expressions derived are verified and applied in predicting the noise figure of a two- and three-tiered M-SSDA based on a full foundry model of an TnP double heterojunction bipolar transistor (DHBT). Based on observations from the analytical study, we provide design considerations that optimise noise, gain and bandwidth performance for this class of distributed amplifiers, for improved utility in ultra-wideband applications

Adjustable testing setup for a single-loop optoelectronic oscillator with an electrical bandpass filter

In this paper we present a novel method to measure the free spectral range (FSR) and side-mode suppression ratio (SMSR) of an optoelectronic oscillator (OEO) by adjusting the optical fiber length using an optical path selector and signal source analyzer. We have designed a setup for a single-loop OEO operating around 5 GHz and 10 GHz that features electrical bandpass filters for side-mode suppression. The proposed approach makes it possible to evaluate the FSR and SMSR of OEOs with different optical fiber paths without requiring the changing of fiber spools or optical connectors. This approach could be useful for testbeds that investigate the implementation of an OEO in a 5G radio access network

Transmission Line Synthesis Approach to Extending the Bandwidth of LEDs for Visible Light Communication

This paper proposes, for the first time, a transmission line synthesis approach to extending the bandwidth of light-emitting diodes (LEDs) in the context of high capacity visible light communications links. As opposed to the more traditional pre-distortion, amplitude equalisation or driver circuitry based approaches, the extension in bandwidth is achieved by incorporating the LED diffusion capacitance into a pseudo-artificial transmission line (p-ATL) cell with significantly improved transmission and cut-off properties. With the proposed technique, we show the possibility of achieving close to 400% improvement in bandwidth with studies based on a verified LED equivalent model. It is envisaged that the proposed approach will enable bespoke driver circuits based on the individual characteristics of LEDs, while combination with existing bandwidth extension schemes can lead to further improvement

A Low-Cost Instrument for Estimating the Starch Content of Cassava Roots Based on the Measurement of RF Return Loss

The problem of simply and reliably estimating starch content of cassava roots in the field is addressed by the development of a low cost test instrument that measures return loss at radio frequencies using a coaxial probe. A clear relationship between starch content of cassava roots and the measured return loss of root samples at a specific frequency of 30 MHz is first verified experimentally. A prototype test instrument is then designed with goals of portability, low cost and simplicity of use. The test instrument displays starch content in 5 categories, from “low” to “high” using an array of 5 LEDs. The performance of the test instrument is experimentally verified in the field and a reliable correlation between cassava root starch content and LED indication is demonstrated

Impact of Analog and Digital Pre-emphasis on the Signal-to-Noise Ratio of Bandwidth-limited Optical Transceivers

The ever-growing machine-to-machine traffic in data centers has stimulated the increase of transceiver data rate from 25Gb/s/λ to 100Gb/s/λ and beyond. It is believed that advanced modulation formats and digital-to-analog converters (DACs) will be employed in next generation short-reach transceivers. Digital pre-emphasis techniques are widely employed in DAC-based transceivers to compensate for the high frequency roll-off due to the RF and optoelectronics components in optical transceivers. However, digital pre-emphasis essentially reduces the magnitude of the signal low frequency components for a flat frequency response, which unavoidably increases quantization error, reducing the overall signal-to-noise ratio. This trade-off between SNR and bandwidth conflicts with the high SNR requirement of advanced modulation formats such as the Nyquist-shaped pulse amplitude modulation (PAM). To mitigate the quantization error induced SNR degradation, we show that analog pre-emphasis filters can be used in conjunction with digital pre-emphasis for improved system performance. To understand the impact of the analog pre-emphasis filter on system performance, we analyze the relationship between the flatness of the system frequency response and the SNR degradation due to digital pre-emphasis, and demonstrate 1.1-dB increase of receiver sensitivities, for both 64-Gb/s and 128-Gb/s intensity-modulation direct detection (IM-DD) 20 PAM4 signals, respectively employing a directly modulated laser (DML) and an electroabsorption modulator (EAM)