Manfred Berroth

Broad-band determination of the FET small-signal equivalent circuit

A method to determine the broadband small-signal equivalent circuit of field-effect transistors (FETs) is proposed. This method is based on an analytic solution of the equations for the Y parameters of the intrinsic device and allows direct determination of the circuit elements at any specific frequency or averaged over a frequency range. The validity of the equivalent circuit can be verified by showing the frequency independence of each element. The method can be used for the whole range of measurement frequencies and can be applied to devices exhibiting severe low-frequency effects. >

A dual-frequency wilkinson power divider

In this paper, a Wilkinson power divider operating at two arbitrary different frequencies is presented. The structure of this power divider and the formulas used to determine the design parameters have been given. Experimental results show that all the features of a conventional Wilkinson power divider, such as an equal power split, impedance matching at all ports, and a good isolation between the two output ports can be fulfilled at two arbitrary given frequencies simultaneously

Ge-on-Si vertical incidence photodiodes with 39-GHz bandwidth

Vertical-incidence Germanium photodiodes grown on thin strain-relaxed buffers on Silicon substrates are reported. For a mesa-type detector with a diameter of 10 /spl mu/m, a resistance-capacitance-limited 3-dB bandwidth of 25.1 GHz at an incident wavelength of 1552 nm and zero external bias has been measured. At a reverse bias of 2 V, the bandwidth is 38.9 GHz. The detector comprises a 300-nm-thick intrinsic region, and thus, has the potential for easy integration with Si circuitry and exhibits zero bias external quantum efficiencies of 23%, 16%, and 2.8% at 850, 1298, and 1552 nm, respectively.

High-frequency equivalent circuit of GaAs FETs for large-signal applications

The application of GaAs field effect transistors in digital circuits requires a valid description by an equivalent circuit at all possible gate and drain bias voltages for all frequencies from DC up to the gigahertz range. An equivalent circuit is presented which takes into account the gate current of positively biased transistors as well as the symmetrical nature of the devices at low drain voltages. A fast method of determining the elements of the equivalent circuit at all bias points without frequency limitations is presented. Direct computation from analytical expressions, without iteration, allows this parameter extraction procedure to be used for real-time on-wafer parameter extraction. Large-signal calculations are possible by inserting the voltage dependences evaluation for the elements into suitable simulation programs, such as SPICE. >

Bridging the gap between optical fibers and silicon photonic integrated circuits

We present a rigorous approach for designing a highly efficient coupling between single mode optical fibers and silicon nanophotonic waveguides based on diffractive gratings. The structures are fabricated on standard SOI wafers in a cost-effective CMOS process flow. The measured coupling efficiency reaches -1.08 dB and a record value of -0.62 dB in the 1550 nm telecommunication window using a uniform and a nonuniform grating, respectively, with a 1 dB-bandwidth larger than 40 nm.

High bandwidth Ge p-i-n photodetector integrated on Si

The authors present a germanium on silicon p-i-n photodiode for vertical light incidence. For a Ge p-i-n photodetector with a radius of 5μm a 3dB bandwidth of 25GHz is measured at an incident wavelength of 1.55μm and zero external bias. For a modest reverse bias of 2V, the 3dB bandwidth increases to 39GHz. The monolithically integrated devices are grown on Si with solid source molecular beam epitaxy. The complete detector structure consisting of a highly p-doped Ge buried layer, an intrinsic absorption region, and a highly n-doped top contact layer of Ge∕Si is grown in one continuous epitaxial run. A low growth temperature sequence was needed to obtain abrupt doping transitions between the highly doped regions surrounding the intrinsic layer. A theoretical consideration of the 3dB bandwidth of the Ge detector was used to optimize the layer structure. For a photodiode with 5μm mesa radius the maximum theoretical 3dB frequency is 62GHz with an intrinsic region thickness of 307nm.

CMOS ring oscillator with quadrature outputs and 100 MHz to 3.5 GHz tuning range

A 100 MHz to 3.5 GHz four-stage CMOS ring oscillator with quadrature outputs and oscillator core current consumption roughly proportional to operating frequency is presented. A novel oscillator topology consisting of a chain of four static single-ended CMOS inverters, four additional feedforward inverters and frequency control by steering the total oscillator core current is proposed. The circuit is implemented in a 0.18/spl mu/ standard CMOS technology. Oscillator core current consumption is 90/spl mu/A at 100 MHz and 9mA at 3.5 GHz with a 1.8V supply. Measured phase noise at 4 MHz offset is -114dBc/Hz at 100MHz and -106dBc/Hz at 3.5GHz oscillation frequency. Quadrature error is better than 3.5/spl deg/ over the 100 MHz to 3GHz frequency range.

Small-signal and temperature noise model for MOSFETs

The present CMOS technology provides n-channel MOSFETs with a transit frequency beyond 30 GHz, which are attractive for RF integrated circuits, e.g., low-noise amplifiers. This paper presents an improved deembedding procedure for extraction of parasitic elements of MOSFETs. The extraction determines the intrinsic elements of the small-signal equivalent circuit. As a result, a new method to determine the gate capacitance is presented. This deembedding procedure is based on an analytical solution of the equations and facilitates the determination of the elements at any specific frequency. Moreover, a temperature noise model is presented, which is based on the small-signal equivalent circuit with an analytical description of the channel noise. This enables a complete noise modeling of all four noise parameters and the determination of the dominant noise sources. Finally, the noise-figure measurements are compared with the simulation results.

The design of 5 GHz voltage controlled ring oscillator using source capacitively coupled current amplifier

A 5 GHz voltage controlled ring-oscillator (VCO) has been designed using 0.18 /spl mu/m CMOS technology. Source Capacitively Coupled Current Amplifier (SC3A) is adopted to realize this VCO. Because of the band-pass characteristic of the SC3A, this VCO exhibits the low noise performance with a large tuning range. It can operate from 4.3 GHz up to 6.1 GHz with a phase noise of about -85 dBc/Hz at 1 MHz frequency offset. For the 2 V supply voltage, the power consumption is about 80 mW.A 5 GHz voltage controlled ring-oscillator (VCO) has been designed using 0.18 /spl mu/m CMOS technology. Source Capacitively Coupled Current Amplifier (SC3A) is adopted to realize this VCO. Because of the band-pass characteristic of the SC3A, this VCO exhibits the low noise performance with a large tuning range. It can operate from 4.3 GHz up to 6.1 GHz with a phase noise of about -85 dBc/Hz at 1 MHz frequency offset. For the 2 V supply voltage, the power consumption is about 80 mW.

Determination of small-signal parameters of GaN-based HEMTs

The small-signal equivalent circuit of AlGaN/GaN HEMT is discussed It is shown that an extremely high gate voltage has to be applied to correctly determine series resistances. Effects appearing at high forward gate voltages are discussed. Good agreement between measured and simulated data has been achieved.