Chopper Amplifier Research Articles

An Ultra-Low Drift Amplifier Using a New Type of Series-Shunt MOSFET Chopper

A chopper amplifier of a new type is proposed for the amplification of nanovolt-order dc voltage. The chopper is built by connecting a shunt switch, which is driven at twice the chopper frequency, to the output terminals of a conventional and balanced-type series-shunt MOSFET chopper. The present chopper is free from offset voltage arising from spike voltages and has an input voltage offset temperature coefficient of less than 0.1 nV/°C for a signal source of less than 1 k?, and a long-term drift of 2 nV/18 h for signal source resistance of 6.1 ?.

Chopper stabilization of MOS operational amplifiers using feed-forward techniques

A monolithic chopper amplifier system has been developed that reduces the effective offset voltage of an NMOS operational amplifier to a few microvolts without compromising bandwidth. Internally, two amplifiers are used, connected in a switched feed-forward configuration. The system is realized in a standard silicon gate enhancement/depletion process.

A gain-stabilised superconducting chopper amplifier

Describes how the gain of a superconducting chopper amplifier can be stabilised by the application of negative feedback. The circuit has the additional advantages of high input impedance and excellent linearity.

Sensitivity and noise in superconducting chopper amplifier systems

The response of a superconducting chopper amplifier system has been calculated with a view towards optimum sensitivity. A chopper operable between 2 and 4K and with sample resistance up to 0.5 m Omega has been constructed. The best noise level (5 pV peak-to-peak for a 1 s integration time) could only be obtained with a bath of superfluid helium. Noise is discussed with reference to a particular circuit.

Improved sensitivity for the superconducting ’’chopper’’ amplifier

A heterodyning modulation technique is described which results in an improved sensitivity for the superconducting chopper amplifier. Dc sensitivities of 3×10−12 V were obtained in a 1 Hz noise bandwidth. An experimental comparison of various modulation schemes is presented.

Analysis of sinusoidal‐wave driven FET chopper amplifiers

Electrical Engineering in JapanVolume 96, Issue 5 p. 106-113 Article Analysis of sinusoidal-wave driven FET chopper amplifiers Haruo Kasai, Haruo Kasai Faculty of Engineering, Chiba UniversitySearch for more papers by this author Haruo Kasai, Haruo Kasai Faculty of Engineering, Chiba UniversitySearch for more papers by this author First published: 1976 https://doi.org/10.1002/eej.4390960514AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Volume96, Issue51976Pages 106-113 RelatedInformation

On the analysis of chopper drives with pulse width modulators

Chopper amplifiers, converters and other similar devices may be modelled as pulse width modulators with natural sampling. Feedback control systems which use natural sampling modulators as power amplifiers are generally muchmore difficult to treat mathematically than uniform sampling ones. In order to overcome these difficulties some equivalent models are set forth in the form of nonlinear uniformly sampled data systems. Lead and lag type pulse width modulators are extensively investigated. As far as critical gains are concerned, the proposed models are evaluated by determining the stability boundaries. The procedure is exemplified by taking into account a critical second order controlled plant. Die Zerhackungsverstaerker, Umsetzer und andere mehrere aehnliche Geraete koennen als Pulsbreitenmodulatoren mit Eigenabtastung gestaltet werden. Die Regelsysteme, die solche Modulatoren benutzen, sind im allgemeinen viel schwieriger, mathematisch zu behandeln, als diejenigen mit gleichmaessiger Abtastung. Um diese Schwierigkeiten zu ueberwinden werden hier einige gleichwertige Muster entwickelt in Form von nichtlinearen Abtastsystemen mit gleichmaess iger Abtastung. Ea werden in Einzelheiten Pulsbreitenmodulatoren vorgedrehten und verzoegerten Type beruecksichtigt. Die Gueltigkeit der vorgeschlagenen Modelle hinaichtlich der kritischen Verstaerkungsfaktoren wird nach Feststellung der Stabilitaetsgrenzen ueberprueft. Eine Anlage des zweiten Ranges mit dem Pol 1m Ursprung wird ale Beispiel des vorgeschlagenen Verfahrens geprueft.

A simple superconducting chopper amplifier for use in magnetic fields

A superconducting chopper amplifier which is simple to build and which can be used adjacent to a 100 kG solenoid is described. At low fields, the sensitivity of the amplifier is 10-11V, decreasing to 10-9V at 100 kG.

The contingent negative variation: some methodological problems in the recording of shifts in steady potentials.

ABSTRACTThe various methods that have been used in recording of the Contingent Negative Variation (CNV) were examined with reference to developing selection criteria. Findings revealed that chopper amplifiers with condenser‐coupled input circuits and DC amplifiers with zero‐suppression circuits between stages showed shifts in output level which were the result of changes in resistance of the input circuit. As these artifacts were not negligible with reference to commonly‐reported CNV amplitudes, it was concluded that the two methods should be avoided in recording of low‐level shifts in steady potentials like the CNV.

Analysis of a Chopper Amplifier

Choppers are often required for obtaining low drift performance of low level d.c. amplifiers. The chopper amplifier basically consists of a modulator, an a.c. amplifier, a synchronous demodulator and a low pass filter. The drift-free performance results from the use of the ‘drift-less’ a.c. amplifier for amplification.The a.c. amplifier used may be an untuned amplifier or an amplifier tuned to the chopper frequency. Though the chopper amplifier is discussed well in literature, no information seems to be available regarding the choice of the a.c. amplifier as a tuned or untuned one. In the case of sub-microvolt level d.c. inputs, the noise introduced by the amplifier itself will set a limit to the utility of this arrangement. In such a case, in the first instance, it would appear that the use of an amplifier tuned to the chopper excitation frequency will have advantages, as regards signal to noise ratio, over an untuned amplifier. This aspect has been investigated by a time analysis of modulator and demodu...

Temperature measurement of particulate surfaces

A device has been developed for measuring the surface temperature of particles of 250 μm diameter at temperatures in excess of 300°C. The basic component of the instrument is a liquid-nitrogen cooled indium antimonide cell used in conjunction with a mechanical chopper and signal amplifier. A system of two-colour pyrometry is employed in which two narrow bandpass filters, centred on the 3·1 and 4·5 μm wavelengths are alternately interposed in the beam of radiation from the source at a frequency of 100 Hz. The device has been developed especially for determining the surface temperature of captive fuel particles, but has been used in other applications, notably the temperature measurement of heat exchanger surfaces, where its high sensitivity and non-contact mode of operation have proved particularly advantageous.

Drift reduction in wideband d.c. amplifiers by ‘adding the lacking part’

A method for drift reduction in d.c. amplifiers is described. This reduction is obtained using the principle of ‘adding the lacking part’. The d.c. stabilisation device is a chopper amplifier. The circuit is such that the chopper amplifier does not affect the frequency response of the wideband amplifier.

On the bandwidth of carrier-type dc amplifiers

For a carrier-type amplifier (e.g., a chopper amplifier), it is well known that the low-frequency response may extend to dc. The position regarding the high-frequency response is not as clear, and statements in the literature give various fractions of the fundamental carrier frequency as an upper limit to the input-signal bandwidth that can be recovered from the modulated carrier. It is argued here that there is no simple well-defined theoretical upper limit, and that in practical circuits the fundamental carrier frequency may or may not be one of several factors determining the useful bandwidth. The circuit of a novel wide-band dc amplifier, consisting of two synchronized chopper amplifiers operating in parallel, is described. The frequency response of this amplifier is independent of the chopping rate, and its method of operation may help clarify bandwidth limitations.

Two high power potentiostats for fuel-cell and fused salt electrolysis studies

The application of potentiostatic techniques to large scale laboratory and pilot plant studies in such fields as fuel-cell investigation and metal production by fused salt electrolysis, has led to the development of high power potentiostats, which can supply currents as high as fifty amperes. Two instruments intended for these purposes are described.The first is a carrier-frequency potentiostat, with a twelve-tube (parallel connected) class B output stage, which can supply 10 V, 50 A. Overload protection is secured by a relay circuit.The other instrument illustrates the recent possibilities afforded by the combination of semi-conductors and electron tubes. To have a high input impedance and a low drift, the first stage is fitted with high gain pentodes, in a symmetrical configuration. Dc stability can be further improved by a Goldberg type drift-correcting chopper amplifier (Zerostat), which compares the potential difference between the reference and working electrode with a controlling voltage, and supplies to the main amplifier a corrective signal. The second stage, a cathode follower, drives the transistor output stage. As transistors are easily damaged by overloads, a current-limited dc supply is included. Polarity of output voltage (±20 V) and current (±10 A) can reverse without switching.

Flux distribution in multiaperture ferrite cores

This paper describes a technique of determining the internal flux distribution in a multiaperture core by mapping the fringing magnetic fields in the vicinity of surface discontinuities, which are introduced into the core face by partially slitting the core. The field mapping device employed is a high-resolution Hall probe, used in conjunction with a chopper amplifier and a phase-sensitive detector. By mapping the component of magnetic field normal to the core face in the region of the slot, a characteristic field pattern dependent upon the direction of flux in the core is observed. In regions of reversal of the internal flux, there is a corresponding reversal in the characteristic field pattern. The boundary separating regions of opposite magnetization in a partially switched core has been defined to within 20 microns. Data are presented showing typical fringing field patterns observed for totally switched and partially switched cores.

Silicon planar epitaxial transistors as fast and reliable low-level switches

This paper attempts to accentuate all the salient factors of high-quality switches, such as their static properties, stability under various conditions of high temperature or thermal cycling, and some aspects of their transient response. It is shown that the silicon planar epitaxial transistor possesses the most advantageous combination of properites for general application as a low-level switch, and that simple low-injection level formulas are sufficiently accurate for the calculation of voltage offset and resistance of an "on" switch, as well as the "off" resistance, if extrinsic parameters and current dependence of β <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</inf> and β <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</inf> are taken into account. A simplified procedure is proposed for the selection of temperature-compensated switch pairs. Hysteresis in a single parameter β <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</inf> is shown to be the main cause of instability in voltage offset in germanium alloy-type transistors, an effect which is hardly detectable in silicon planar epitaxial devices. Suitability of the latter for fast operation in chopper amplifiers is discussed, and their capabilities in a rapid-sampling commutator is illustrated.

A general purpose precision magnet supply

Complete details are given of a 1 kw precision magnet current supply. Series transistors are used as the regulating element, controlled by a solid state chopper amplifier. The nature of the feedback system permits use of the supply with magnets of any impedance and with large amplitude (500 v r.m.s. 50 c/s) external magnet modulation. D.C. drift is less than 10 parts per million per hour and noise in the 0.1-1 c/s band less than 1 part per million.

Precision Measurement of Magnetic Flux Changes

Systems which employ two amplifiers—one to amplify, the other to integrate—for precise and/or sensitive determination of magnetic flux changes are described and their operating characteristics reported. One system measures flux changes in time intervals of 10−2 to 10−1 sec using moderately broad band amplifiers and gated circuits. This system discriminates against dc thermals with a gated self-balancing potentiometer, and combines sensitivity and precision with the convenience of rapid readout on a digital voltmeter. The sensitivity of the system is 10−7 V sec, the accuracy better than one part in 104, and combined with pickup coils, permits detection of changes of 10−3 G. This system has been applied to measurements of saturation magnetization, Curie temperature, and susceptibility of iron and its dilute alloys. An alternative system uses a highly stable, dc chopper amplifier in which case the flux changes are produced in seconds and can be followed for minutes. This method has been essential for measurements of the change of magnetization of iron and nickel with pressure where many seconds are necessary to insure isothermal conditions. Sensitivity is the same as above. In another system for the measurement of the temperature dependence of susceptibility, a null coil is wound on the surface of a cylindrical sample which is oscillated near a pair of detector coils at 6 cps. The coil output is amplified, chopped in phase with the signal and integrated. This system has a sensitivity of Δχ = 10−10 and has been used to obtain the temperature dependence of the susceptibility of vanadium.

Chopper Amplifier with Holding Circuit

Chopper Amplifier with Holding Circuit

Small-Field Galvanomagnetic Tensor of Bismuth at 4.2°K

Values of carrier concentrations and mobilities in large monocrystalline samples of bismuth at 4.2\ifmmode^\circ\else\textdegree\fi{}K have been derived from measurements of all the galvanomagnetic tensor components through second order in magnetic field. Fields of the order of one gauss and less are required, and a superconducting chopper amplifier detects the minute voltages involved. The electron concentration is found to be 2.5\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, and the concentration of light holes is very nearly the same. When compared with cyclotron resonance and de Haas-van Alphen experiments, the results are consistent with a three-ellipsoid model for electrons and a single ellipsoid for light holes. There is no indication of the presence of heavy holes in a concentration comparable to the other carriers. Electron and light-hole relaxation times are isotropic to within a factor of 2; for electrons, $\ensuremath{\tau}\ifmmode \dot{e}\else \.{e}\fi{}2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ sec, and for holes, $\ensuremath{\tau}\ifmmode \dot{e}\else \.{e}\fi{}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ sec. Some of the effects of temperature and of larger magnetic fields are discussed.