Publications

An overview of my publications. Abstract, publication details and, where applicable, bonus material such as Gerber files are given.

Low-Distortion, Low-Noise Composite Operational Amplifier

In state-of-the-art implementations of instrument devices, a single amplifier stage may be required to provide a THD figure of better than −140 dB for a 5V RMS, 20 kHz signal in order to support a total instrument dynamic range of 120 dB in an 80 kHz measurement bandwidth. Currently it is not possible to achieve this performance level using available commercial monolithic operational amplifiers in a standard configuration. A proposed design approach achieves this goal. A unity gain stable composite operational amplifier is presented that consists of a cascade of two operational amplifiers, an intermediate compensation network and a frequency-selective feedback network for the second amplifier. This configuration achieves very high open-loop gain (100 dB at 100 kHz) and thus shows exceptionally good distortion characteristics. Furthermore, the noise characteristics of the first operational amplifier are preserved. The open-loop response is designed for conditional stability, such that a very-large-gain-bandwidth product at signal frequencies can be achieved. A numerical optimization procedure is then introduced to derive the frequency compensation, based on specific stability criteria. Measurement results confirm the predicted high-gain-bandwidth product (10 GHz at 100 kHz) and excellent distortion performance (−180 dB). Applications for the new composite operational amplifier include audio frequency distortion measurement equipment.

Journal of the Audio Engineering Society, Volume 65, Issue 5, May 2017

This article is co-authored by Martin Polak.

Reed Relay Distortion

In this brief we discuss nonlinear distortion in reed relays. We present measurement data and a simple model to estimate the 3^rd harmonic distortion contribution in a circuit. We have tested several types and found no substantial difference regarding their distortion behavior.

Linear Audio, Volume 13, April 2017

This article is co-authored by Bruno Putzeys.

Quadrature Bridge Measures Harmonic Distortion in Capacitors

This article considers the measurement of harmonic distortion in capacitors using a bridge circuit. Each arm of the bridge consist of one resistor and one capacitor. The bridge is driven in quadrature, such that both the differential and common-mode output voltage are nominally zero. The article introduces a procedure to construct a capacitor with very low distortion contribution, which is used in the reference arm of the bridge. The resolution of the bridge is estimated to exceed −150 dB. Measurement results for various capacitor types are presented. These show that parts with ceramic C0G dielectric have more consistent, and generally speaking also lower, distortion than Polyester, Polypropylene or Polystyrene film capacitors.

Linear Audio, Volume 12, September 2016

This article is co-authored by Scott Wurcer.

Reducing Transformerless Microphone Preamplifier Noise at Low Gain Settings

Contemporary high-quality condenser microphones offer noise performance close to the theoretical limit. Because large-diaphragm capsules and transformerless electronics have a high sensitivity, only modest gain from the preamplifier is required. Yet, designers of microphone preamplifiers have traditionally focused on the noise performance at highest gain, where the equivalent input noise (EIN) is at a minimum. At lower gain settings this figure worsens by an amount that depends on the detailed implementation, and may dominate the noise of the microphone. The EIN at highest gain is an insufficient and possibly even misleading criterion. The author presents a detailed noise analysis of the classic current-feedback instrumentation amplifier topology. The collector load resistors and the voltage noise of the operational amplifiers were identified as significant noise sources at low-gain settings. Connecting the collector load resistors to a higher supply rail is an effective technique for reducing the magnitude of the noise sources. Practical verification was found to be in excellent agreement with the predicted performance.

Journal of the Audio Engineering Society, Volume 63, Issue 3, March 2015

A Low Noise Laboratory-Grade Measurement Preamplifier

This article presents the design of a low noise laboratory preamplifier, which is particularly aimed at noise measurement tasks. Its design features a single-ended JFET input stage, an active drain load for good power supply rejection and a novel input AC coupling network which attains, together with a DC servo, a second-order response. The achieved performance includes an equivalent input voltage noise density of 390 pV/rtHz (1 kHz) and 500 pV/rtHz (10 Hz), a frequency response of ±0.1 dB (10 Hz–100 kHz), a power supply rejection of at least 95 dB (10 Hz–100 kHz) and a quiescent current of just 17 mA. Detailed theoretical background on low noise design along with concise construction and application notes are included.

Linear Audio, Volume 3, April 2012

Bonus material: a_low_noise_laboratory-grade_measurement_preamplifer.zip

A New Amplifier Topology With Push-Pull Transimpedance Stage

In this article I introduce an amplifier topology which uses a novel push-pull transimpedance stage. Compared to known standard amplifier configurations, the new circuit offers a substantial improvement in power supply rejection. Furthermore secondary slew rate limits are addressed, and sensitivity to loading from the output buffer is reduced. This makes this amplifier architecture particularly suitable for high quality audio power amplifier designs. Experimental results using model amplifiers are presented.

Linear Audio, Volume 2, August 2011

This article is also available online in the AudioDesign Line magazine of EETimes.