Ahmed Allam

Mutual compensation of mobility and threshold voltage temperature effects with applications in CMOS circuits

Mutual compensation of mobility and threshold voltage temperature variations may result in a zero temperature coefficient bias point of a MOS transistor. The conditions under which this effect occurs, and stability of this bias point are investigated. Possible applications of this effect include voltage reference circuits and temperature sensors with linear dependence of voltage versus temperature. The theory is verified experimentally investigating the temperature behavior of a simple voltage reference circuit realized in 0.35 /spl mu/m CMOS process.

On phase noise in quadrature cross-coupled oscillators

A cross-coupled relaxation oscillator has two outputs of the same frequency, which are in quadrature. In this paper a comparative study of the phase noise in a cross-coupled relaxation oscillator is given. We present a high level (system) study of the oscillator and analyse the oscillator stability. The derivation proves analytically that cross-coupling reduces the influence of a perturbation (noise) on the oscillator output. Both high-level and circuit simulations at 5GHz are presented to confirm the theoretical results. Close to 10dB improvement in phase noise performance due to coupling was found, and the phase noise performance compared with that of a coupled LC oscillator was achieved.

Synchronization of mutually coupled LC-oscillators

It is shown that synchronization is similar to amplitude stabilization: both mechanisms involve creation of harmonics and frequency reduction. Synchronization of LC-oscillators can be achieved using similar synchronizing circuits in each oscillator connected in parallel with the tank. The output of the first synchronization circuit is routed to the second oscillator and vice versa. This scheme provides coupling using first, third and other odd harmonics. In addition, introducing coupling between common mode outputs of the synchronizing circuits provides second and other even harmonic coupling. This type of coupling may be also used between common mode outputs of amplitude stabilization circuits. The benefits of using simultaneous first and second harmonic coupling were verified designing a low-power, low phase noise 5 GHz LC oscillator with quadrature outputs. The oscillator phase noise is lower than -121.2 dBc/Hz at 1-MHz offset over the tuning range with a power consumption of 1.8 mW achieving a FOM lower than -192.2 dBc/Hz

Synchronization of two LC- oscillators using capacitive coupling

This paper considers two oscillators (van der Pol or Robinson type) synchronized using capacitive coupling. Equations are derived for the oscillation frequency and amplitudes. They show that the frequency of synchronous oscillation is different from the frequencies of individual oscillators. The amplitudes of oscillation are also different: one oscillator becomes a master and the second oscillator becomes a slave. A method of quasilinear approximation is used to evaluate the stability of synchronous oscillation. Simulation results for a 5 GHz oscillator confirm the theoretical analysis.

Quadrature Van der Pol oscillators using second harmonic coupling

A new coupling mechanism is used to synchronize two Van der Pol oscillators. This coupling uses the second harmonic appearing in common mode current of each oscillator. The common mode current is measured by a current mirror, and is amplified by a current amplifier. The amplifier introduces negative feedback, so that the current in the current mirror measuring diode of the first oscillator is nearly equal to the common mode current of the second oscillator, hence the coupling is established. It is shown that the system of two oscillators is described by two differential equations where the coefficients in one equation have the perturbations defined by the second oscillator, and vice versa. The coupling amplifier gain is defined. The developed concepts are demonstrated on a 5 GHz CMOS LC oscillator with quadrature outputs. The oscillator phase noise is lower than -116 dBc/Hz at 1-MHz offset

Temperature dependence of output voltage generated by interaction of threshold voltage and mobility of an NMOS transistor

Mutual compensation of mobility andthreshold voltage temperature variations mayresult in a zero temperature coefficient (ZTC)bias point of an NMOS transistor. Theconditions under which this effect occurs,stability of this bias point, and thetemperature dependence of the output voltagefor a diode-connected transistor operating inthe vicinity of ZTC point are investigated inthis paper. Some possible applications of thiseffect include temperature sensors with lineardependence of voltage versus temperature, andvoltage and current reference circuits. Thetheory is verified experimentallyinvestigating the temperature behavior of anNMOS transistor realized in 0.35 μm CMOSprocess. The design and simulation results ofsimple current and voltage reference circuitsfor implementation in 0.18 μm CMOStechnology are given.

0.6-V supply voltage references for CMOS technology based on threshold-voltage-difference architecture

A group of low-voltage power supply voltage references has been developed. The circuits are designed with the assumptions that the difference of threshold voltages is nearly constant in the wide range of temperatures, and that mobilities are tracking each other with temperature. The circuits are obtained by substitution of transistors with different thresholds in the same basic configuration that produces the output voltage proportional to the difference of transistor threshold voltages. The best result achieved in simulations shows that one can obtain the output voltage of 332 mV plusmn 2mV in the range of temperatures 0 to 75 degC and with variation of power supply voltage from 1.8 V down to 0.6 V

Experimental comparison of coupling effects on the performance of quadrature CMOS LC and RC oscillators

RC oscillators are known for their high phase noise compared with LC oscillators. However, by increasing coupling in RC oscillators one can obtain a quadrature oscillator with noise performance and quadrature error comparable with that of LC coupled oscillators. Measurements were performed on 5 GHz LC and RC quadrature oscillators built in 0.18 mum technology.

A new CMOS wideband RF front-end for multistandard low-IF wireless receivers

A wideband radio-frequency (RF) receiver front-end is designed in 0.18 /spl mu/m CMOS technology with a new linearization technique that makes the circuit suitable for operating at low supply voltage. The proposed front-end circuit includes an input low noise wideband amplifying stage (LNA) of new configuration with output linearized transconductance stage, and a switching stage. Dual-loop resistive feedback applied around the LNA allows one to achieve input wideband matching. Linearity is enhanced by attenuating the effective transconductance of the transconductance stage. With an RF input signal of 1.9 GHz, the proposed front-end circuit exhibits 15.5 dB conversion gain, 7.2 dB SSB noise figure, -11.2 dBm 1-dB compression point, and -1.5 dBm third-order input intercept-point (IIP3) in simulations. The input wideband matching to 50 /spl Omega/ is achieved with -3 dB bandwidth of around 3 GHz. The input return loss (S11) varies from -26 dB to -10.5 dB in the frequency range of DC to 3.5 GHz. The proposed front-end consumes 22.3 mA DC current from 1.8 V supply voltage and occupies an area of 0.9/spl times/0.85 mm/sup 2/.

Synchronization of Van der Pol Oscillator By External Voltage of Double Frequency

Synchronization of the van der Pol oscillator is performed by an external sinusoidal voltage source of double frequency connected is series with the power supply and the oscillator. Modifying the oscillator effective supply voltage, this source modifies the coefficients of the van der Pol oscillator differential equation, and synchronizes the oscillator. The conditions and borders of synchronization are considered.