| Table of Contents | ||
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| Technical Publications |
Journal papers Journal Comments Dissertation Conference tutorials Conference papers Magazine articles Books Other publications |
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| Philosophical Publications |
Journal Papers Newsletter Articles |
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| Technical Publications | ||
| Journal Papers |
Why 'Current Mode' Does Not Guarantee Good Performance Hanspeter Schmid, Analog Integrated Circuits and Signal Processing, vol. 35, no. 1, pp. 79–90, April 2003. |
Paper (pdf) Abstract |
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An 8.25-MHz 7th-Order Bessel Filter Built with
Single-Amplifier Biquadratic MOSFET C Filters Hanspeter Schmid, Analog Integrated Circuits and Signal Processing, vol. 30, no. 1, pp. 69–81, January 2002. |
Paper (pdf) Abstract |
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Approximating the Universal Active Element Hanspeter Schmid, IEEE Transactions on Circuits and Systems—II, vol. 47, no. 11, pp. 1160–1169, November 2000. |
Paper (pdf) Abstract |
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Active MOSFET–C single-amplifier biquadratic
filters for video frequencies Hanspeter Schmid and George S. Moschytz, IEE Proceedings on Circuits, Devices, and Systems, (Special issue on High-Frequency Analogue Filters), vol. 147, no. 1, pp. 35–41, February 2000. |
Paper (pdf) Abstract |
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| Journal Comments |
Comments on “A CMOS Fully Balanced Four-Terminal Floating Nullor” Hanspeter Schmid, IEEE Transactions on Circuits and Systems—I, vol. 50, no. 12, p. 1601, December 2003. | Paper (pdf) |
| Dissertation |
Single-Amplifier Biquadratic MOSFET–C
Filters Hanspeter Schmid, Dissertation ETH Zürich, No 13878, Hartung-Gorre, Konstanz, Series in Signal and Information Processing, Vol. 1, ISBN 3-89649-616-6, ISSN 1616-671X, November 2000. |
Contents (pdf) Book (pdf) Abstract |
| Conference Tutorials |
Analog Circuit Design on Digital CMOS: Why it is difficult, and which ideas help. Hanspeter Schmid, ISCAS Tutorial, Taipei, Taiwan, May 2009. Updated version of the 2007 tutorial. |
Slides (pdf) |
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Analog Circuit Design on Digital CMOS: Why it is difficult, and which ideas help. Hanspeter Schmid, ISCAS Tutorial, New Orleans, U.S.A., May 2007. |
Slides (pdf) | |
| Conference Papers |
Efficient simulation of harmonic distortion in discrete-time circuits Hanspeter Schmid, Proceedings of the ISCAS, Taipei, Taiwan, pp. 2757–2760, May 2009. |
Paper (pdf) Abstract Talk (pdf) |
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Why the terms `current mode' and `voltage mode'
neither divide nor qualify circuits Hanspeter Schmid, Proceedings of the ISCAS, Phoenix, Arizona, vol. 2, pp. 29–32, May 2002. |
Paper (pdf) Abstract Talk (html with png images) |
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Circuit transposition using signal-flow graphs Hanspeter Schmid, Proceedings of the ISCAS, Phoenix, Arizona, May 2002, vol. 2, pp. 25–28, May 2002. |
Paper (pdf) Abstract |
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The Current-Feedback OTA Hanspeter Schmid, Proceedings of the ISCAS, Sydney, Australia, May 2001, vol. 1, pp. 655–658, May 2001. |
Paper (pdf) Poster (pdf) Abstract |
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A 8.25 MHz 7th-order Bessel filter built with
MOSFET-C single-amplifier biquads Hanspeter Schmid and George S. Moschytz, Proceedings of the NORCHIP, Turku, Finland, November 6–7 2000, pp. 217–224. |
Paper (pdf) Poster (pdf) Abstract |
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A Charge-Pump-Controlled MOSFET–C
Single-Amplifier Biquad Hanspeter Schmid and George S. Moschytz, Proceedings of the ISCAS, Geneva, Switzerland, May 28–31, vol. 2, pp. 677–680, May 2000. |
Paper (pdf) Poster (pdf) Abstract |
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Minimum-Sensitivity Single-Amplifier Biquadratic Filters Hanspeter Schmid and George S. Moschytz, Proceedings of the ECCTD, Stresa, Italy, August 29–September 2, vol. 2, pp. 1027–1030, 1999. |
Paper (pdf) Talk (pdf) Abstract |
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A Continuously Adjustable Video-Frequency Current Amplifier for Filter Applications Hanspeter Schmid and George S. Moschytz, Proceedings of the ECCTD, Stresa, Italy, August 29–September 2, vol. 1, pp. 305–308, 1999. |
Paper (pdf) Talk (pdf) Abstract |
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A Video-Frequency, Low-Power, Single-Amplifier Biquadratic Filter in CMOS Hanspeter Schmid and George S. Moschytz, Proceedings of the ISCAS, Orlando, Florida, May 30–June 2, vol. 2, pp. 128–131, 1999. |
Paper (pdf) Poster (pdf) Abstract |
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Fundamental Frequency Limitations in Current-Mode Sallen-Key Filters Hanspeter Schmid and George S. Moschytz, Proceedings of the ISCAS, Monterey, California, May 31–June 3, vol. 1, pp. 57–60, 1998. |
Paper (pdf) Poster (pdf) Abstract |
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Tunable CCII-MOSFET-C Filter Biquads for Video Frequencies Hanspeter Schmid and George S. Moschytz, Proceedings of the ECCTD, Budapest, Hungary, August 30–September 3, vol. 1, pp. 82–87, 1997. |
Paper (pdf) Talk (pdf) Abstract |
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| Magazine articles | Aaargh! I Just Loooove Flicker Noise Hanspeter Schmid, IEEE Circuits and Systems Magazine, First Quarter 2007, pp. 32-35. |
Article (pdf) |
| Books and book chapters |
Circuits at the Nanoscale: Communications, Imaging, and Sensing edited by Kris Iniewski, Chapter 7 on Flicker Noise by Hanspeter Schmid. CRC Press LLC, 2008, ISBN 978-1-4200-7062-0. The preliminary version of the chapter's full text is provided here because the annotated literature list unfortunately was omitted in the published book. |
Chapter 7, preliminary version (pdf) |
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Analoge Schaltungstechnik für integrierte Schaltungen (zweite überarbeitete Auflage) Hanspeter Schmid, Alex Huber, IME Windisch 2008, ISBN 3-9523090-1-X, German only. |
Book excerpt (pdf) |
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Analoge Schaltungstechnik für integrierte Schaltungen Hanspeter Schmid, Alex Huber, Guido Keel, IME Windisch 2006, ISBN 3-9523090-1-X, German only. |
Book excerpt (pdf) | |
| Other publications | IME Report 01/2009: How to use the FFT for signal and noise simulations and measurements Current version: May 11, 2009. |
Paper (pdf) Abstract |
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Two-Port Tables Hanspeter Schmid. This short text is nothing more than a helpful collection of tables for two-port matrices. Current version: May 25, 2000. |
Paper (pdf) | |
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Technical Reports by
Hanspeter Schmid. The two internal reports «The ideal amplifier myth, and a complete amplifier classification» and «Understanding integrated amplifiers» that appeared as Tech. Reports 9801 and 9802 (Swiss Federal Institute of Technology, Signal and Information Processing Laboratory, Zürich, Switzerland, January/March 1998) are just preliminary stages of the paper Approximating the Universal Active Element. It does not seem to make sense to still distribute them. |
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| Philosophical Publications | ||
| Journal Papers |
Theory and Practice - Thinking Styles in Engineering and Science Hanspeter Schmid, Australian Journal on Information Systems, special issue on knowledge management, pp. 106–115, December 2001. I was invited to submit this paper after I gave a Talk at Monash University, Melbourne, May 14 2001 (html/jpg, 741kB). |
Paper (html) Abstract |
| Other publications |
Black Tools Hanspeter Schmid. Appeared in seven parts, «The Art of Misinterpretation,» «Salami Tactics,» «To Mock a Mockingbird,» «Making Conclusions,» «Common Nonsense,» «This May Work in Theory,» «End of the Debate,» in the Newsletter of the IEEE Professional Communication Society, 1999–2000. |
Black Tools Web Site |
| IME Report 01/2009: How to use the FFT for signal and noise simulations and measurements: Paper (pdf) |
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| This short text describes how information on signal an noise levels can be extracted from an FFT when windowing is used. The target group of readers are engineers who want to simulate (or measure) signal-to-noise ratios using FFTs in Matlab or on a captured signal, e.g., a sigma-delta bitstream. |
| Why 'Current Mode' Does Not Guarantee Good Performance: Paper (pdf) |
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It is often said that there is a fundamental difference
between current-mode and voltage-mode circuits. This conjecture is
discussed in technical and philosophical terms, and it is shown that
there is no such performance difference to be found, and that it is
not possible to make a clear divide between voltage mode and current
mode. And yet performance differences appear in the literature. It is shown that they come from the different design practices of the current-mode and the voltage-mode research groups. The conclusion of this paper is that the practical knowledge of the current-mode research groups should be re-integrated into main-stream IC design, and that all propaganda of the type current-mode is better than voltage-mode should be stopped immediately. |
| An 8.25-MHz 7th-Order Bessel Filter Built with Single-Amplifier Biquadratic MOSFET C Filters: Paper (pdf) |
| This paper is a practical guide to building higher-order filters with single-amplifier biquadratic MOSFET C sections. Theory, design guidelines, and measurement electronics are discussed by example of a 7th-order current-mode filter built to the specifications of a 1×DVD read channel filter. The 7th-order filter was fabricated with the double-poly 0.6-micron CMOS process by AMS. It is continuously tunable from 4.5 MHz up to 10 MHz, covers a chip area of only 0.24 mm^2, and consumes 49 mW from a 3.3-V supply. The SNR at 40 dB of harmonic distortion is between 48 dB and 50 dB over the whole tuning range. The comparatively low power consumption and chip area could be achieved by using single-amplifier biquadratic building blocks implemented as MOSFET-C filters and generating the control voltage of the MOSFET resistors with an on-chip charge pump. The technique is, with a small loss of SNR, also applicable on fabrication processes where only gate-oxide capacitors are available. |
| Efficient simulation of harmonic distortion in discrete-time circuits: Paper (pdf) |
| Espley showed in 1933 how to calculate harmonic distortion (HD) and inter-modulation distortion (IMD) using few equidistant points on the transfer characteristic of a circuit. This method was applied later to derive simplified formulae for HD in continuous-time amplifiers. It is shown in this paper that the main strength of the method lies in HD simulations in discretetime amplifiers and filters. To show this, the theory is presented in a simple way and extended to distortion-induced offset. The precision for different HD levels is discussed for the first time in literature, showing that the method is precise to within 0.1 dB for distortions of -30 dB and below. Application examples are given to show that simulating with this method results in simulation times that are half as long as with the shortest possible (and barely practical) simulations using discrete Fourier transforms. |
| Circuit transposition using signal-flow graphs: Paper (pdf) |
| This paper proves the circuit transposition theorem using signal-flow graphs (SFGs). The proof has two advantages: it is constructive, and it is intuitive for engineers who know SFGs. For these engineers, our technique makes it easy to derive the dual counterpart of any amplifier and enables them to transpose all linear circuits without resorting to the circuit transposition tables that were published in many other papers. Because the main purpose of this paper is to provide a tool for analog circuit analysis and design, the proof is written in tutorial style. |
| Approximating the Universal Active Element: Paper (pdf) |
| The classification of universal amplifiers presented in this paper places all operational amplifiers and current conveyors known from the literature into a common framework, together with abstract concepts such as the universal active element and the nullor. Our approach is new in that we base it on four-terminal theory, which results in a classification that is more extensive but not more complex than classifications derived using two-port theory. It turns out that our classification contains a new type of operational amplifier, which we call current-feedback OTA, and also a new class of voltage-inverting current conveyors. We then demonstrate that our classification is very closely related to integrated-amplifier design by showing how all operational amplifiers and current conveyors can be implemented in CMOS using only a few basic CMOS circuits. Since the basic ideas behind CMOS and bipolar circuits are very similar, this paper can be seen as an attempt to bridge the gap between amplifier theory and amplifier design that has become ever wider in the past few years. |
| Active MOSFET–C single-amplifier biquadratic filters for video frequencies: Paper (pdf) |
| We show in this paper how continuous-time active-RC filters can be implemented in CMOS by replacing all resistors by MOSFETs operating in the linear region. As an example, a 24-MHz active-MOSFET-C single-amplifier biquadratic lowpass filter with a pole-Q of 3 implemented in a 0.6-µm CMOS process is discussed. By comparing measurements of a test chip, simulations, and calculations, we reach the following conclusion: As long as the specifications for frequency, pole-Q, spurious-free dynamic range and supply voltage lie within certain limits, then active-MOSFET-C single-amplifier biquads (MOSFET-C SABs) are preferable, with respect to chip size and power consumption, compared to multi-amplifier biquads, e.g. integrator-connected biquads. Above these limits, the latter must be used. |
| Single-Amplifier Biquadratic MOSFET–C Filters (Dissertation): Contents (pdf); Book (pdf) |
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This dissertation discusses the theory of single-amplifier biquadratic
filters (SABs) and their implementation as CMOS video-frequency
filters. It shows that building filters as cascades of
single-amplifier biquadratic MOSFET–C sections is a viable
alternative to using biquadratic Gm–C filter sections. The advantage
of MOSFET–C SABs is that they typically use less chip area than a
Gm–C filter with equivalent speed, distortion, noise, and power
consumption.
The first part of this dissertation discusses the theory of integrated amplifiers, provides a new perspective of the current-mode vs. voltage-mode debate, and discusses the theory of SABs and the effects that amplifier non-idealities have on them. The second part discusses second-order MOSFET–C networks and how to design filters with them, presents perfectly symmetrical video-frequency current amplifiers, one with fixed gain and one with variable gain, and contains measurement results of test circuits from two chips. The third part presents a brief comparison of the MOSFET–C SABs presented in this dissertation to other video-frequency filters, and finishes with a discussion of design trade-offs and ideas for future research on the topic. |
| The Current-Feedback OTA: Paper (pdf); Poster (pdf) |
| The current-feedback OTA (CFB OTA) recently appeared in a new classification of operational amplifiers. It is dual to the operational floating amplifier (OFA), so all OFA circuits can readily be transposed into CFB OTA circuits. This paper discusses the theoretical basis of the CFB OTA, shows its relation to the OFA, and compares their performance in a simple V--I converter by showing how both can be built with the same two transistor stages. The advantages and disadvantages of the CFB-OTA implementation are discussed as well, but the main advantage of introducing the CFB OTA is that its introduction is virtually for free: most current opamps from the literature can be converted into CFB OTAs by re-wiring their input stage, without adding or re-sizing a single transistor. |
| A 8.25 MHz 7th-order Bessel filter built with MOSFET-C single-amplifier biquads: Paper (pdf); Poster (pdf) |
| The 7th-order Bessel filter presented in this paper has an edge frequency that is continuously tunable from 4.5 MHz up to 10 MHz. It was fabricated with the 0.6-micron CMOS process by AMS, covers a chip area of 0.24 mm^2, and consumes 49 mW from a 3.3-V supply. The SNR at -40 dB of harmonic distortion is between 48 dB and 50 dB over the whole tuning range. The comparatively low power consumption and chip area could be achieved by using single-amplifier biquadratic building blocks implemented as MOSFET-C filters and generating the control voltage of the MOSFET resistors with an on-chip charge pump. This paper briefly discusses design issues of such filters, sources of harmonic distortion, clock feed-through, and noise. Finally, it is shown that the filter can also be implemented using MOSFET capacitors instead of poly-poly capacitors with only 4 dB loss of SNR. |
| A Charge-Pump-Controlled MOSFET–C Single-Amplifier Biquad: Paper (pdf); Poster (pdf) |
| The spurious-free dynamic range (SFDR) of a MOSFET–C filter can be increased greatly by generating its tuning voltage with a charge pump. In this paper, we apply this technique to build a Sallen-and-Key lowpass filter with a pole frequency of 24 MHz and a pole Q of 3. It has an SFDR better than 50 dB and consumes 16 mW from a 3.3 V supply. Implemented with a double-poly triple-metal 0.6-µm CMOS process, it covers an area of only 0.11 mm^2. In addition to a description of the filter and the charge pump, we also discuss linear and non-linear clock feed-through from the charge pump's own ring oscillator, and derive a formula for the optimum voltage swing at the MOSFET–C network nodes. |
| Minimum-Sensitivity Single-Amplifier Biquadratic Filters: Paper (pdf); Talk (pdf) |
| Evaluating the Schoeffler criterion for Sallen-Key filters leads to expressions having two degrees of freedom and prohibitive complexity. Such expressions are normally solved only after making approximations. We show, using the low-pass filter as an example, how the two degrees of freedom can be separated by a simple non-linear coordinate transform. Exact design equations for the minimum-sensitivity filter result, revealing that this filter has the maximum allowable component spread, that its capacitor spread is larger than the resistor spread, and that the required amplifier gain does not exceed two. We then repeat the analysis for unity-gain filters and show that the minimum-sensitivity filter has minimum component spreads if its pole frequency is below a certain value. |
| A Continuously Adjustable Video-Frequency Current Amplifier for Filter Applications: Paper (pdf); Talk (pdf) |
| The adjustable balanced-signal current amplifier presented in this paper amplifies a current by first transforming it into a voltage signal using two poly-silicon resistors and then back into a current signal using a single MOSFET resistor operating in the linear region. We implemented the amplifier in the double-poly 0.6-µm CMOS process by Austria Mikro Systeme International. It consumes 12.4 mW from a 3.3 V supply and covers an area of 0.07 mm^2. Measurements show that it is suitable for building biquadratic filters with a spurious-free dynamic range of more than 45 dB, a pole Q of 3 and a pole frequency of up to 900 kHz. We also show that a modification of the circuit allows building filters with pole frequencies up to 6 MHz. |
| A Video-Frequency, Low-Power, Single-Amplifier Biquadratic Filter in CMOS: Paper (pdf); Poster (pdf) |
| In this paper, a tunable single-amplifier biquadratic lowpass filter is presented. It consists of one balanced low-gain current amplifier and a second-order MOSFET-C feedback network. The filter was integrated in a double-poly 0.6-µm CMOS process and operates from a 3.3 V power supply. The pole frequency is tunable from 15.2 to 17.2 MHz, the pole Q is 3, the spurious free dynamic range is better than 60 dB, and the filter consumes only 2.4 mW per pole. Furthermore, the active area used per pole is only 0.06 mm^2. The filter is well suitable for low-power video-frequency applications, and demonstrates that the MOSFET-C filter technique can be applied successfully to filters other than those based on integrator-connected topologies. |
| Fundamental Frequency Limitations in Current-Mode Sallen-Key Filters: Paper (pdf); Poster (pdf) |
| Single-amplifier filter biquads and especially Sallen-Key filters are widely used to build higher-order filter cascades. This paper investigates high-frequency current amplifier non-idealities and their effects on all-pole Sallen-Key filter biquads. It is shown that a non-ideal current amplifier input causes parasitic zeros in the filter transfer function, and thus imposes fundamental limitations on the realisable pole frequency. Design equations are given, providing compensation for the amplifier's port impedances and its phase lag, by predistortion of the component values. It is also shown how design specifications for a current-amplifier can be derived from the filter specification, minimising the amplifier's power dissipation. Finally, a video-frequency lowpass filter is discussed. |
| Tunable CCII-MOSFET-C Filter Biquads for Video Frequencies: Paper (pdf); Talk (pdf) |
| This paper describes two related topics. First, it is shown how the concept of the MOSFET-C integrator can be extended to single-amplifier filter biquads. Then a new differential-input balanced-output current conveyor (CCII) is presented, which has two essentially symmetrical and balanced signal paths. Using this CCII, a 4th-order lowpass filter cascade suitable for on-chip tuning is presented, whose passband edge frequency is tunable from 2 MHz to 4.5 MHz and whose pole Qs are tunable to within +-5%. Our simulation shows that the filter's total harmonic distortion is below 1% and that the filter dissipates only 2 mW per pole pair at 3 V supply voltage. Finally it is shown how bandpass and highpass filters can be built using the same technique. |
| Theory and Practice - Thinking Styles in Engineering and Science: Paper (html) |
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This paper describes knowledge as an element of thinking styles, which are properties of thinking collectives. According to the theory outlined here, the choice of a thinking style to solve a certain problem is relative, but once the thinking has been chosen, realism prevails. This paper also describes the genesis and development of thinking styles and, with them, of facts. The theoretical concepts are illustrated with two examples of thinking styles: a description of the thinking styles of circuit theorists and circuit designers (theory vs. practice), and a comparison of the thinking styles of two closely related technical societies of the Institute of Electrical and Electronics Engineers (IEEE). Applications of the theory are also presented in this paper; they include information management, documentation tools, and writing styles, and mainly draw from the author's own experience with these topics. |