Browsing by Author "Taghavi, Mohammad Hossein"

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    10-Gb/s 0.13-um CMOS Inductorless Modified-RGC Transimpedance Amplifier
    (IEEE, 2015-07-17) Taghavi, Mohammad Hossein; Belostotski, Leonid; Haslett, James W.; Ahmadi, Peyman
    This paper presents an inductorless 0.13-um CMOS TIA structure that is a modified version of a regulated cascode (RGC) TIA. An immittance converter is incorporated to reduce power consumption while increasing ransimpedance gain. Measured 3-dB bandwidth is 7 GHz, sufficient for 10-Gb/s operation, in the presence of 250 fF capacitance at the TIA input, representative of typical CMOS photodiode capacitance. The transimpedance gain of the single-stage TIA is 50 dB, and the group-delay variation is less than ±19 ps over the 3-dB bandwidth. The circuit occupies an active area of 180um x 90um and consumes 7 mW from a 1.5-V supply. The measured average input-referred current noise of the TIA is 31 pA/sqrt(Hz). Simulations and analysis show that the proposed single-stage TIA architecture is capable of achieving improvement in the transimpedance limit over a single-stage RGC TIA designed for the same data rate and the same input photodiode capacitance. A comparison of measurement results to published TIAs also demonstrates the competitive performance of the proposed TIA in terms of the TIA transimpendance gain, bandwidth, area, and power consumption.
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    A CMOS Optical Receiver for the Square Kilometer Array Radio Telescope
    (2015-06-19) Taghavi, Mohammad Hossein; Belostotski, Leonid
    The Square Kilometer Array (SKA) is an international effort to construct the world 's largest radio telescope with an effective area of one square kilometer. By their nature signals arriving from astronomical sources are very weak. An SKA receiver therefore will require a wideband high-frequency gain in the order of 70 dB to condition the signals for data processing. This large wideband gain makes the conventional data transfer through coaxial cables problematic as any amount of signal leaking back into the receiver front-end can either overpower the desired signals and desensitize the receiver and/or cause stability issues. Therefore, optical data transfer is desirable and is being considered in this thesis. This thesis presents a study of using CMOS technologies, which are attractive due to their lower costs, higher integration densities, and lower power consumption, to implement an optical transfer for an SKA receiver. Four different transimpedance amplifiers (TIAs) were designed and experimentally verified in this work. One of these TIAs that employs an immittance converter, which provides both a negative input resistance to increase the input pole frequency and a negative inductance to improve the circuit stability, was chosen as an optical receiver front end. The proposed TIA achieves a 6 GHz 3-dB bandwidth with a 250 fF photodiode capacitance. The transimpedance gain of a single-stage TIA is 54 dBohm, the group-delay variation and average input-referred noise current are 6 ps and 24 pA/sqrt(Hz), respectively, over its entire bandwidth. A fully integrated CMOS optical receiver front end was proposed and experimentally verified in this work. The receiver achieves a transimpedance gain of 77.7 dBohm with a 12-GHz 3-dB bandwidth. With a photodiode, whose responsivity is 0.8 A/W, the simulated sensitivity of the optical receiver at 15 Gb/s is about -12 dBm for a bit error rate (BER) of less than 10^{-12}. A time-to-digital (TDC) converter that utilizes an optimum detection concept was designed and fabricated in a TSMC 65nm CMOS process as an optical receiver back end.