Ivars G. Finvers

2 GHz

A tunable Q-enhanced filter with low passband distortion is presented. The Q of the on-chip spiral inductors that form the filter resonators is enhanced by using a cross-coupled differential pair which is degenerated by a second LC tank. This technique allows for frequency dependent compensation of inductor losses and ensures that the Q-enhanced LC resonators have a frequency behaviour close to the ideal in the passband of the filter. The circuit allows DC voltage control of Q-enhancement. The filter centered at 2.0 GHz with a 130 MHz bandwidth is tunable in frequency by 3%, exhibits a -6.6 dBm 1-dB compression point and a 15 dB noise figure while consuming 17 mW of DC power. The circuit was fabricated in 0.18-mum CMOS and the performance was verified experimentally

rm Q

A precision operational amplifier has been developed for instrumentation applications in which the circuitry must operate in ambient temperatures as high as 200/spl deg/C. At 200/spl deg/C the amplifier maintains an input offset voltage and current of less than 200 /spl mu/V and 1 nA respectively, a gain bandwidth product of 2.2 MHz, and a slew rate of 5.4 V//spl mu/S. The amplifier is fabricated in a standard CMOS process and consumes 5.5 mW of power at a supply voltage of 5 V. A continuous time auto-zeroed amplifier topology is used to achieve the low offset voltage levels. At high temperatures the leakage currents of the sample and hold switches used to achieve auto-zeroing, degrading the offset correction voltages stored on the hold capacitors. This degradation is reduced by using large external hold capacitors and by minimizing the diffusion area of the switches through the use of a doughnut shaped layout. The effect of the voltage degradation is reduced by sensing the offset correction voltage with a low sensitivity differential auxiliary input stage. A new input switch topology is used to reduce the amplifiers input offset current at high temperatures. >

-Enhanced Active Filter With Low Passband Distortion and High Dynamic Range

Stochastic data traffic models for medical wireless sensor networks (WSNs) are presented that represent the traffic generated by a single WSN node monitoring body temperature and electrocardiogram (ECG) data. The models are based on empirical data from public domain medical signal databases. In the interest of conserving energy, it is likely that some medical WSN nodes will employ source coding to reduce the amount of data that must be transmitted. As a result, traffic models are presented for nodes that use compression and nodes that do not.

A high temperature precision amplifier

Two variants of a new current feedback amplifier (CFA) are presented in this paper. These CFAs are realized in CMOS technology and both are capable of working at low voltages. It is shown that one circuit performs better than the other by virtue of an increased impedance at its Z terminal achieved through the use of additional transistors. Analysis of both variants of the current conveyor and buffer that form the current feedback amplifier gives an insight into the location of primary poles and zeros of the CFAs. Simulation results indicate an overall gain bandwidth product in excess of 59 MHz and 102 MHz for each circuit at a gain of −10 and with a 3.3 V supply. Experimental results from a chip fabricated in a 0.35 μm CMOS technology agree closely with the simulation results.

Traffic models for medical wireless sensor networks

A new CMOS realization of an operational transconductance amplifier is presented. It is based on the cross-coupled configuration and is biased by the common-mode voltage. The circuit has only two transistors between the supply line and ground which makes it suitable for low-voltage applications. Simulation results show that the circuit is highly linear and tunable over a wide range bias voltage. The circuit is used to realize 2/sup nd/ generation current conveyor (CCII) and differential current conveyor (DCC) that have excellent performance.

Alternative Realizations of CMOS Current Feedback Amplifiers for Low Voltage Applications

A bandage based thermometer placed on the temple region of the forehead provides an non-invasive means of measuring a patientpsilas core body temperature. An array of temperature sensors spaced along the length of the bandage is used to determine the skin temperature over the temporal artery. Temperature sensors buried within the bandage allow the direct measurement of the heat flow leaving the skin over the temporal artery. By using the method of heat balance in conjunction with the skin temperature and heat flux measurements, the temperature of the blood within the temporal artery, which is at the core body temperature, can be estimated. Compared to the traditional hand-held Temporal Artery Thermometer, this approach decreases the sensitivity of the core temperature estimation to errors arising from air flow across the forehead, perspiration, and the local environment. A wireless link transmits the data to a remote monitoring station, allowing long term monitoring of patient temperature.

A novel low-voltage operational transconductance amplifier and its applications

A novel variation of the cross-coupled operational transconductance cell is presented in this paper. The conventional cross-coupled cell has a differential input linearity range that is dependent on the control voltage. The proposed design removes that restriction while allowing the same tunability using the control voltage. Its input may also be single or fully differential unlike the conventional cross-coupled cell, which requires a fully differential input. Results were confirmed using HSPICE simulations.

Wireless temporal artery bandage thermometer

The special LNA topologies resulting from loading a simple LNA with a set of Q-enhanced inductors are analyzed and compared. The Q of the on-chip spiral inductors that form the LNA load is enhanced by using a negative resistance realized with a cross-coupled differential pair degenerated and biased in various ways. The performance of the LNA is presented for the following types of Q-enhancement circuit: ideal negative resistor (ideal cell), tail-biased non-degenerated cross-coupled differential pair (classic cell), tail-biased resistively degenerated cross-coupled differential pair (resistive cell), tail-biased LC degenerated cross-coupled differential pair (B-cell), self-biased LC degenerated cross-coupled differential pair (BB-cell). The analysis focuses on the benefits of each cell related to s-parameter response, noise and linearity and the interdependency of Q vs. center frequency during tuning. Low voltage design challenges are addressed by presenting the advantages of the novel self-biased LC degenerated cross-coupled differential pair (BB-cell).

Cross coupled transconductance cell with improved linearity range

The effect of auto-zeroing on the internal noise of a continuous-time auto-zeroed amplifier is analyzed and a set of empirical expressions are developed which predict the important aspects of its noise shaping behavior. The dependence of the output noise power spectral density on the auxiliary signal path gain, nulling amplifier bandwidth, and auto-zeroing clock frequency are all demonstrated. The results are confirmed experimentally.

Comparative Analysis of Tunable Q-Enhancement Filter Cell Topologies in a 2.4 GHz LNA

A simple CMOS second generation negative current conveyor (CCII-) is presented which is suitable for low supply voltage operation. By restricting the CCII- to applications where the Y input is effectively referenced to signal ground, a greatly simplified circuit topology is realized. With only two devices stacked between the supply rails, low voltage operation is achieved. Internal negative feedback is used to reduce the input resistance of the X input. Simulation results demonstrate the use of the CCII- in lowpass and bandpass filter applications.