Photodetector Capacitance Research Articles

A novel 2.5 Gbps pre-transimpedance amplifier with the gain adaptively adjusted

A 2.5 Gbps transimpedance amplifier (TIA) with the feedback resistance self-adaptively adjusted is designed for the application of optical receivers in passive optical network and implemented in Global Foundries (GF) 0.18 [Formula: see text]m CMOS standard process. The main structure of the circuit consists of an improved three-stage current multiplexing push-pull inverter. With the diode-connected-transistor placed at each end of the inverter, the extra pole will be pulled away in order to increase the stability of the loop system. The feedback resistance of TIA is connected in parallel with the NMOS transistor, and the gate voltage of the tube is adjusted automatically to control the resistance value of this parallel structure in order to overcome the defect of the inverter which will work in the linear region on the condition of excessive optical power. A low-dropout linear regulator (LDO) is adopted from the power supply to the TIA to isolate power supply noise. The measured results demonstrate that the fabricated TIA with a photodetector capacitance of 3.2 pF has a transimpedance gain of 41.64 dB[Formula: see text] with a current signal frequency of 2.5 Gbit/s, and a −3 dB bandwidth of 2.35 GHz. The average input-referred noise current spectral density within the bandwidth is185 pA/Hz[Formula: see text], signal rise time is 195 ps, fall time is 227 ps, eye diagram height is 28 mV, optical sensitivity is −30.6 dBm, and power consumption is only 52 mW at 3.3 V power supply voltage, the chip area is [Formula: see text] mm2.

A low noise transimpedance amplifier for optical receiver.

In this paper, a regulated cascode (RGC) structure and a shunt-feedback transimpedance amplifier are cascaded. By analyzing the average input-referred noise current, this paper used the method of adjusting the metal-oxide-semiconductor size and increasing the transimpedance gain to optimize the circuit noise characteristics without introducing redundant structures and noise sources. The measured results demonstrated that when the photodetector capacitance is 300 pF and the supply voltage is 1.8V, the fabricated transimpedance amplifier has a transimpedance gain of 59.5 dBΩ and a -3 dB bandwidth of 4GHz. Simultaneously, the average input-referred noise current spectral density is less than 7 pA/√Hz, and the data rate is as high as 5 Gb/s. The circuit takes advantage of the traditional shunt-feedback transimpedance amplifier and introduces a RGC structure between it and the input terminal as a current buffer structure. A π-type matching network was formed by adding an inductor between the shunt-feedback amplifier and the introduced RGC. All these structures can effectively improve the gain-bandwidth product of the designed amplifier.

A 42-dB$\Omega~25$ -Gb/s CMOS Transimpedance Amplifier With Multiple-Peaking Scheme for Optical Communications

This brief presents a low-power, broadband, inverter-based transimpedance amplifier (TIA) design employing the input series peaking and shunt–shunt inductive feedback in a 65-nm CMOS process. The design optimization of the TIA core amplifier is described in detail. The proposed multiple-peaking scheme incorporates an input bond-wire and two on-chip inductors to mitigate the photodetector capacitive loading, achieving an overall bandwidth enhancement ratio of 2.8. A transimpedance gain of 42 dB $\Omega $ is measured up to 24 GHz without the off-chip photodetector capacitance. A low-dropout regulator (LDO) with full-spectrum power supply rejection is integrated to suppress supply noise and parasitic effect due to the power supply bond-wires. Optical measurements at 25 Gb/s show that the data eye RMS and peak-to-peak jitters are improved by 15% and 24%, respectively, when the LDO is enabled. The measured TIA sensitivity is −7.3 dBm at 25 Gb/s with a BER $ for a $2^{{15}}{-}1$ PRBS optical input. The 1-V TIA with on-chip LDO consumes 3 mW from a 1.2-V external power supply.

The I–V zero-drift mechanism of quantum effect photodetector

The zero-drift phenomenon of the I–V (current–voltage characteristics) of the quantum effect photodetector and the variation of zero-drift voltage are researched in the paper. The photovoltaic quantum dots infrared photodetector (QDIP) has the photocurrent zero-drift and the dark current oscillation. It has proved by simulated that related to the InAs QDs layer number. The photoconductive QDIP has a zero-drift that related to sweep voltage with time delay. With the time delay decreasing, the zero-drift voltage increases. When time delay is fixed, zero-drift voltage decreases at the illumination. In addition, the photodetector capacitance may be calculated by zero-drift voltage formula.

A Low-Power 26-GHz Transformer-Based Regulated Cascode SiGe BiCMOS Transimpedance Amplifier

Low-power high-speed optical receivers are required to meet the explosive growth in data communication systems. This paper presents a 26 GHz transimpedance amplifier (TIA) that employs a transformer-based regulated cascode (RGC) input stage which provides passive negative-feedback gain that enhances the effective transconductance of the TIA's input common-base transistor; reducing the input resistance and isolating the parasitic photodiode capacitance. This allows for considerable bandwidth extension without significant noise degradation or power consumption. Further bandwidth extension is achieved through series inductive peaking to isolate the photodetector capacitance from the TIA input. The optimum choice of series inductive peaking value and key transformer parameters for bandwidth extension and jitter minimization is analyzed. Fabricated in a 0.25-µm SiGe BiCMOS technology and tested with an on-chip 150 fF capacitor to emulate a photodiode, the TIA achieves a 53 dBΩ single-ended transimpedance gain with a 26 GHz bandwidth and 21.3 pA/ <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sqrt{\rm Hz}$</tex></formula> average input-referred noise current spectral density. Total chip power including output buffering is 28.2 mW from a 2.5 V supply, with the core TIA consuming 8.2 mW, and the chip area including pads is 960 µm x 780 µm.

An 850-nm Normal-Incidence Germanium Metal–Semiconductor–Metal Photodetector With 13-GHz Bandwidth and 8-$\mu$A Dark Current

This letter presents a new germanium metal-semiconductor-metal photodetector (PD), in which an amorphous silicon (a-Si) layer is added on top of the undoped germanium substrate. The a-Si under the Ti-Au contacts serves as a barrier enhancement layer and mitigates Schottky barrier height lowering due to fermi-level pinning, hence reducing dark current. In the active region, the a-Si layer passivates surface states, thus preventing low-frequency gain due to charge accumulation and image force lowering, and improving the device bandwidth. A prototype PD with an area of 47 × 47 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with 2-μm contact spacing and 1.25-μm contact width achieved a small-signal 3-dB bandwidth over 10 GHz. In an ultrafast electrooptic sampling measurement, its impulse response exhibited 15-ps pulsewidth and 30-ps rise time, which corresponds to 13-GHz bandwidth. The measured PD capacitance was 40 fF. The responsivity and dark current were 0.23 A/W and 8 μA, respectively, at 850-nm wavelength and 7-V bias.

Device Requirements for Optical Interconnects to Silicon Chips

We examine the current performance and future demands of interconnects to and on silicon chips. We compare electrical and optical interconnects and project the requirements for optoelectronic and optical devices if optics is to solve the major problems of interconnects for future high-performance silicon chips. Optics has potential benefits in interconnect density, energy, and timing. The necessity of low interconnect energy imposes low limits especially on the energy of the optical output devices, with a ~ 10 fJ/bit device energy target emerging. Some optical modulators and radical laser approaches may meet this requirement. Low (e.g., a few femtofarads or less) photodetector capacitance is important. Very compact wavelength splitters are essential for connecting the information to fibers. Dense waveguides are necessary on-chip or on boards for guided wave optical approaches, especially if very high clock rates or dense wavelength-division multiplexing (WDM) is to be avoided. Free-space optics potentially can handle the necessary bandwidths even without fast clocks or WDM. With such technology, however, optics may enable the continued scaling of interconnect capacity required by future chips.

The Frequency Behavior of the Intermodulation Distortions of Modified Uni-Traveling Carrier Photodiodes Based on Modulated Voltage Measurements

The effect of modulated voltage on the nonlinear response of an InGaAs-InP charge-compensated modified uni-traveling carrier photodiode is characterized using a modulated bias measurement setup. Based on experimental results for the dependence of responsivity and photodetector capacitance on bias voltage, we use a simple equivalent circuit model to explain the frequency characteristics of the intermodulation distortions caused by the modulated bias. Good agreement has been achieved between the simulation and measurement.

A proposed ultra low-noise optical receiver for 1.55 μm applications

A high-sensitivity optical receiver based on InP/InGaAs superlattice avalanche photodiode (SL-APD) followed by an InGaAs MESFET transimpedance pre-amplifier has been proposed for operation in 1.55 μm wavelength region. The proposed optical receiver may be realised in the hybrid integrated circuit form. The low excess-noise factor of the SL-APD significantly reduces the value of minimum detectable optical power and improves the sensitivity of the over all receiver. The proposed receiver has been analysed theoretically. The results of computation show that the device has a high transimpedance gain (∼60 dB-ohm) with a bandwidth of 11 GHz for a photodetector capacitance of 110 fF. The sensitivity of the receiver has been found to be (∼−27.3d Bm) at operating bit rate of 15 Gb/s for a bit-error-rate of 10−9. The performance of the receiver can be optimised in respect of transimpedance gain, bandwidth and sensitivity by following guidelines provided in this paper. The proposed photoreceiver outperforms the existing receivers based on p-i-n/FET or conventional APD/FET photoreceivers.

Analysis of transfer function of metal-semiconductor-metal photodetector equivalent circuit

The response of GaAs metal-semiconductor-metal photodetectors (MSM-PD) is simulated using a phenomenological model of transport equations, which takes into account the electron intervalley transfer. Calculations are performed for intrinsic devices with 1 μm and 0.5 μm interdigital spacing with the corresponding equivalent (parasitic) circuit of the photodetector. It is pointed out that parasitic effects may induce a significant distortion, a delay of intrinsic response, and increase bit error rate. Analysis of the equivalent or parasitic circuit of the MSM-PD transfer function shows that the distortion and delay of the intrinsic signal can be minimized by choosing the optimal photodetector capacitance.

The effects of smear on antiblooming protection and dynamic range of interline CCD image sensors

The effects of a smearing signal on the dynamic range and the amount of antiblooming protection of an interline CCD image sensor are presented. It is shown that there is a tradeoff between these two parameters, and that they are directly related by the amount of smear. These relationships are analyzed for both constant-integration time and constant-irradiance modes of operation. For the constant-irradiance model of operation it is shown that in order to maintain 90% of the maximum dynamic range and an antiblooming protection of 300*, the smear signal must be less than 0.037%. For the constant integration-time mode of operation, it is shown that in order to maintain 75% of a particular device's maximum dynamic range and the same amount of antiblooming protection the smear signal must be less than 0.0074%. It is also found in this mode that this relationship between antiblooming protection and the amount of linear dynamic range is exponential, and dependent on the antiblooming structure's nonideality factor and the individual photodetector's capacitance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optimum design of a 4-Gbit/s GaAs MESFET optical preamplifier

An analysis for determining the optimum MESFET gate width to optimize the sensitivity of a high-speed optical preamplifier is presented. A full MESFET model is employed including correlated gate and drain noise sources. The design of an optimum sensitivity monolithic shunt feedback amplifier, including stability requirements, is investigated. The results show that the optimum gate width for minimizing input equivalent noise is significantly larger than earlier simplfied predictions. A sensitivity improvement of 1.2 dB is demonstrated for a 4-Gbit/s MESFET optical amplifier, and results showing the dependence of optimum FET width on photodetector capacitance are described.