Manuel M. Silva

Analysis and Design of Quadrature Oscillators

The following are some features of Analysis and Design of Quadrature Oscillators make it different from the existing literature on electronic oscillators: (1) focus on quadrature oscillators with accurate quadrature and low phase-noise, required by modern communication systems; (2) a detailed comparative study of quadrature LC and RC oscillators, including cross-coupled LC quasi-sinusoidal oscillators, cross-coupled RC relaxation oscillators, a quadrature RC oscillator-mixer, and two-integrator oscillators; (3) a thorough investigation of the effect of mismatches on the phase-error and the phase-noise; (4) the conclusion that quadrature RC oscillators can be a practical alternative to LC oscillators when area and cost should be minimized (in cross-coupled RC oscillators both the quadrature-error and phase-noise are reduced, whereas in LC oscillators the coupling increases the phase-noise.

Noise Performance of a Regulated Cascode Transimpedance Amplifier for Radiation Detectors

A low noise transimpedance amplifier (TIA) is used in radiation detectors to transform the current pulse produced by a photo-sensitive device into an output voltage pulse with a specified amplitude and shape. We consider here the specifications of a PET (positron emission tomography) system. We review the traditional approach, feedback TIA, using an operational amplifier with feedback, and we investigate two alternative circuits: the common-gate TIA, and the regulated cascode TIA. We derive the transimpedance function (the poles of which determine the pulse shaping); we identify the transistor in each circuit that has the dominant noise source, and we obtain closed-form equations for the rms output noise voltage. We find that the common-gate TIA has high noise, but the regulated cascode TIA has the same dominant noise contribution as the feedback TIA, if the same maximum transconductance value is considered. A circuit prototype of a regulated cascode TIA is designed in a 0.35 μm CMOS technology, to validate the theoretical results by simulation and by measurement.

A Pulse Generator for UWB-IR Based on a Relaxation Oscillator

We propose the adaptation of a well-known relaxation oscillator to produce a modulated Gaussian pulse suitable for ultra-wide-band (UWB) impulse radio (IR). The proposed circuit has low area and low power consumption, can easily be modulated by a digital signal, and requires no special technology options; these features make it suitable for UWB-IR low-cost applications. The circuit behavior is confirmed by simulation and by experimental results on a prototype designed in austriamicrosystems 0.35-mum SiGe-BiCMOS technology.

Techniques for Dual-Band LNA Design using Cascode Switching and Inductor Magnetic Coupling

In the last years we have assisted to a great development of wireless receivers working in narrow frequency bands. Nowadays, this development goes towards more flexible wireless receivers which accommodate different wireless applications - wide-band and multi-band receivers. In this paper we study techniques suitable for the design of dual-band CMOS low noise amplifiers (LNA), based on cascode switching and inductor magnetic coupling. Two LNA topologies were evaluated and implemented in a 0.35mum CMOS process. A proof of concept, a prototype of a proposed dual-band CMOS LNA was designed to work simultaneously at 0.9 GHz and 1.8 GHz. It uses a voltage supply of 2.4 V consuming 4.8 mA

Regulated Common-Gate Transimpedance Amplifier Designed to Operate With a Silicon Photo-Multiplier at the Input

A transimpedance amplifier (TIA) in the front-end of a radiation detector is required to convert the current pulse produced by a light-detector to a voltage pulse with amplitude and shape suitable for the subsequent processing. We consider in this paper the specifications of a positron emission tomography (PET) scanner for medical imaging. The conventional approach is to use an avalanche photo-diode (APD) as the light-detector and a feedback TIA. We point out here that, when the APD is replaced by the more recent silicon photomultiplier (SiPM), a feedback TIA is not suitable, and we propose the use of a regulated common-gate (RC-G) TIA. We derive the transimpedance function of the RC-G TIA considering the parasitic capacitances that have a dominant effect on the pulse shaping. We use the result obtained to establish TIA design guidelines, and we show that these should be different with an APD and with a SiPM at the input. We identify the dominant noise source in the RC-G TIA, and we derive a closed form equation for the output noise rms voltage. A prototype TIA was designed for UMC 130 nm CMOS technology. We present simulation and experimental results that confirm that the RC-G circuit is suitable for implementation of the TIAs in the front-end of a PET scanner using SiPMs at the input.

Balun LNA with continuously controllable gain and with noise and distortion cancellation

In this paper we present a balun LNA with gain adjustable continuously by a voltage. The LNA is based on the combination of a common-gate and a common-source stage to cancel the noise and distortion of the common-gate stage. To obtain higher gain with the same DC voltage drop we replace resistors by PMOS transistors. This also allows continuous gain control and we show that by proper design, the effect on IIP3 and IIP2 can be neglected. With this approach, we avoid the use of switches, and the input impedance and the noise figure are not affected. Simulation results with a 130 nm CMOS technology show that the balun LNA has gain continuously tunable between 12 and 20 dB. The NF is below than 3.2 dB and the best IIP3 is higher than 0 dBm and the maximum IIP2 is 14 dBm. The total power dissipation is only 4.8 mW for a bandwidth of 5 GHz.

Switched-Capacitor Multiply-By-Two Amplifier Insensitive to Component Mismatches

This brief describes a new mismatch-insensitive amplifier with an accurate gain of two and with the parasitic effects compensated. It is based on associating four sets of two capacitors in series during the amplification phase. The amplifier operates within a single clock cycle and uses only one amplifier. A detailed study of the different nonideal effects is presented. Simulated results demonstrate that a gain accuracy enhancement of the order of 4-5 bits can be achieved with respect to conventional realizations

Multi-band combined LNA and mixer

In this paper we investigate the performance of the multi-band low noise amplifier (LNA) based on the concept of using multiple cascode transistors for band selection; thus, avoiding switches in the signal path. We also show that this circuit can perform mixing of two signal bands with two different local oscillator frequencies, which provides great flexibility in the design of dual-band RF front-ends. The operation of both as LNA and as combined LNA/mixer is demonstrated by simulation.

An inductorless CMOS quadrature oscillator continuously tuneable from 3.1 to 10.6 GHz

Modern RF front-ends require wide tuning-range oscillators with quadrature outputs. In this paper we present a two-integrator quadrature oscillator, which covers the whole bandwidth of UWB applications. A circuit prototype in a 130 nm CMOS technology is continuously tuneable from 3.1 to 10.6 GHz. The circuit die area is less than 0.013mm2, leading to a figure-of-merit FOMA of −176.7dBc/Hz at the upper frequency. The supply voltage is 1.2 V, and the power consumption is 7 mW at the lower frequency and 13 mW at the upper frequency. Copyright

A comparison by simulation and by measurement of the substrate noise generated by CMOS, CSL, and CBL digital circuits

Current-steering logic (CSL) and current-balanced logic (CBL) are logic families that have been proposed with the objective of reducing the substrate noise in mixed-signal integrated circuits. These two families are compared here with conventional CMOS by simulation, using a substrate model extracted from the layouts, and also by measurements on a test chip. With small, low-power cells, noise reduction of CSL and CBL with respect to CMOS is only marginal; the same result is obtained with large, high-power (buffer) cells, if the supply wire inductance is very low. For large cells with typical wire bonding supply inductance (of the order of 10 nH), CBL cells provide significant noise reduction and are more effective than CSL cells; these become even noisier than CMOS cells for large inductance values. The results here, considering the real substrate noise, are more reliable than previous evaluations considering only the amplitude of the supply current spikes.