Derek F. Bowers

Mixed-mode simulation of a continuous-time Sigma Delta ADC

The use of the C programming language and a commercially available analog and digital (mixed-mode) circuit simulator in the design of a continuous-time multibit sigma-delta ( Sigma Delta ) analog-to-digital converter (ADC) for integration is detailed. The use of the bilinear transformation to generate a discrete-time model of the ADC is shown with an implementation in C. The circuit simulator is introduced and its mixed-mode capabilities are discussed with another implementation of the Sigma Delta ADC. Simulation data is analyzed with the fast Fourier transform (FFT) and compared with actual prototype data. Results indicate a good correlation between simulator and prototype performance.<<ETX>>

The so-called current-feedback operational amplifier-technological breakthrough or engineering curiosity?

Some of the advantages and disadvantages of the current-feedback approach to operational amplifier design are presented. Specific topics addressed include fundamental bandwidth, limitations, practical bandwidth limitations, slew-rate effects, inverting vs. non-inverting operation, noise and input overdrive.<<ETX>>

The operational conveyor amplifier-a new circuit design block

A circuit design block is proposed which vastly simplifies analog circuit design in addition to performing all functions of an operational amplifier. A third input is added to the op-amp, which follows the potential on the noninverting input and effectively accepts a current input. This current is subsequently inverted in polarity and added to the inverting input. Several applications are described, including noninverting integrators and differentiators and a differential summing amplifier. While implementation of this function is possible in many ways, a simple technique using a modified op-amp technology is described. Extension to class AB operation is also discussed.<<ETX>>

Thin film high dielectric constant metal oxides prepared by reactive sputtering

High dielectric constant, low loss dielectric thin film materials produced by reactive RF sputtering have been investigated for use as capacitor dielectrics in integrated circuits, using oxides of niobium, tantalum, titanium, hafnium, and zirconium and mixtures of these with aluminum oxide. High breakdown fields and low leakage currents are found for the best materials and a reduction in capacitor area of a factor of >3 compared with Si3N4 capacitors of the same value, using a simple production process compatible with semiconductor device manufacturing.

High sheet resistance, low temperature coefficient of resistance resistor films for integrated circuits

High resistance, low temperature coefficient of resistance (TCR) thin-film resistors have been produced by rf sputtering from compound targets using the Cr–Si–B–SiO2/Al2O3 material system. After postdeposition annealing at 450–550 °C sheet resistances of 20 kΩ/sq and TCR<200 ppm/°C were obtained for films of 40 nm thickness. The effect of changes to the proportions of each component in the mixture was investigated and it was found possible to control resistance and TCR. X-ray photoelectron spectroscopic analysis showed a good correlation between the target and film compositions. X-ray diffraction investigation did not show any crystalline structure in the film either before or after thermal treatment.

101 ways to make a circuit fail

A circuit design, whether on first silicon, breadboarded or PCBs will quite often fail to work first time and getting it to work is costly time-consuming, irritating and sometimes very frustrating. If the failure is inevitable, then why are more precautions not taken at the earlier stages of design? What are these mystical failure mechanisms? Human errors, simulation errors, testing errors? etc. The authors attempt to answer some of these questions.<<ETX>>

A fast precision operational amplifier featuring two separate control loops

An operational amplifier is described which uses separate loops to control the output voltage and the error voltage between its inputs. To a large extent this architecture combines the high-speed characteristics of “current feedback” amplifiers with the low input referred errors of precision architectures. The technique has been applied to produce an amplifier with precision characteristics comparable to OP-07 type amplifiers but with over 100 times the bandwidth and slew-rate. Additionally, the power consumption has been reduced by a factor of three.

A precision monolithic waveform generator with 2,000,000:1 exponential sweep range

A 36V, precision monolithic waveform generator with symmetric triangle, square, and sine wave outputs is described. Peak-to-peak values of the triangle and sine waves are equal to 2/3∗Vsy, while the square wave output is referenced from an adjustable digital ground pin. The nominal frequency of all waveforms is set using one external capacitor and resistor. The architecture provides for both linear and exponential frequency control, with temperature drift trimmed to be less than 100ppm/°C. The exponential input is fully differential, and gives a frequency sweep range of 2,000,000:1. Even and odd harmonic distortion are trimmed so that the sine wave distortion measures less than 1% up to 200kHz. Asserting a TTL compatible strobe pin simultaneously disables all outputs.

A 37nV/√Hz 2.5V reference based on dual-threshold JFET technology

A very low-noise voltage reference is described built on a complementary bipolar process with the addition of dual-threshold P-channel JFETs. The difference between the two JFET thresholds exhibits stability and noise suitable for use as the basis of the reference. Additional circuitry amplifies and adjusts the tolerance and temperature coefficient of the threshold difference to create a 2.5 V temperature independent reference voltage capable of operating with supply voltages down to 2.7 volts.

A precision one-volt shunt reference

The shunt reference has for the most part been used where cost is the major concern in the choice of reference. As a result, the most prevalent shunt references have a voltage set to around the bandgap voltage of silicon ( /spl cong/ 1.2-1.25V) and poor precision in terms of slope impedance, initial tolerance and temperature coefficient. This paper describes a shunt reference with a nominal one volt output (a much more convenient value) coupled with greatly improved precision characteristics.