1960 IRE TRANSACTIONS ON MEDICAL ELECTRONICS 29 A Pulse Power Amplifier for Biological Stimulation* HARRY LUDWIGt Summary-A power amplifier designed for use as a biological on-off toggle switch. In the ON position it connects the stimulator is described. It is driven by a dc voltage or a pulse grid of section B to the minus supply, thereby insuring that generator with an amplitude of 50 volts. The output power of up it is cut off even without an input signal. V,B is directly to 250 volts and loo ma is precisely controlled. The rise time is less than 5 I&sec. A dual-channel version whose outputs may be coupled to the grid of V2A through voltage level adjusting independently controlled and mixed is also described. The cir- resistors R12 and R,, and speed up capacitor C4. V2, the cuit for the +400 volts and -300 volts regulated power supplies second 12AT7, is also a regenerative trigger amplifier de- is shown. signed to provide the necessary pulse amplitude at the N biophysical reserchtioftnnccssrproper voltage level to drive the output cathode followers ;[ -N biophysical research it IS often necessary to stimu- V, and V5. Its operation is exactly like V,; when V71B is late a biological preparation in various ways. Some- conducting, the voltage level at the grid of ViA iS IOW times this is done by direct electric shock, usually one enough to hold it off. The voltage at the grid of VZ2B is or a series of pulses of current. It may be done also through therefore sufficiently high to cause this section of the tube various transducers to produce brief or prolonged stimuli to conduct. When VTIB is switched off, then V2A is driven on either optical, tactile, or acoustic. To measure animal re- sponse time it is necessary that the stimuli be accurately timed and synchronized with the sweep of the measuring oscilloscope. To measure animal sensitivity, the stimulus amplitude must be accurately determined. In addition, suffi- cient power is required to drive the transducers. In our laboratories the Tektronix 160 series waveform generators are used to generate the timed pulses of varying duration, amplitude, and repetition rate. This provides a very con- venient, versatile, and accurate system of sequence control and synchronization, but sometimes more power is required f or direct stimulation or maximum drive of the transducers. This paper describes a power amplifier designed to be driven and controlled by a Tektronix pulse generator or equivalent, and capable of providing up to 250 volts and 100 ma to an animal preparation or transducer. Fig. 1 is the single channel version of the pulse power amplifier. A dual channel model has also been constructed and used in neurophysiological research at the University of Wisconsin Medical School for two years. Fig. 2 shows the circuit of one channel. Fig. 3 illustrates the regulated power supplies required for the amplifier. The circuit de- scription follows. The input tube V1 is a 12AT7 connected as a regenera- tive trigger amplifier designed to be triggered by a pulse or a dc voltage connected to the input terminals. Section B of the tube is normally conducting and section A is cut off. This is indicated on the diagram by the shading of the second triode section. The tube remains in this condition until a voltage of sufficient magnitude, about 45 volts, is ap- plied to the input. This causes section A of the tube to con- duct, the output of which is transmitted by coupling capaci- tor C3 and resistor R8 to the grid of section B and therefore cuts off its plate current. When the input voltage is removed the tube reverts to its original state. Switch 1 is a manual * Manuscript received by the PGME, September 25, 1959. t Medical Electronics and Lab. of Neurophysiology, University of Wisconsin, Madison, Wis. Fig. 1.
Transcript
1960 IRE TRANSACTIONS ON MEDICAL ELECTRONICS 29
A Pulse Power Amplifier for Biological Stimulation*HARRY LUDWIGt
Summary-A power amplifier designed for use as a biological on-off toggle switch. In the ON position it connects thestimulator is described. It is driven by a dc voltage or a pulse grid of section B to the minus supply, thereby insuring thatgenerator with an amplitude of 50 volts. The output power of up it is cut off even without an input signal. V,B is directlyto 250 volts and loo ma is precisely controlled. The rise time isless than 5 I&sec. A dual-channel version whose outputs may be coupled to the grid of V2A through voltage level adjustingindependently controlled and mixed is also described. The cir- resistors R12 and R,, and speed up capacitor C4. V2, thecuit for the +400 volts and -300 volts regulated power supplies second 12AT7, is also a regenerative trigger amplifier de-is shown. signed to provide the necessary pulse amplitude at the
N biophysicalreserchtioftnnccssrproper voltage level to drive the output cathode followers;[-N biophysical research it IS often necessary to stimu- V, and V5. Its operation is exactly like V,; when V71B is
late a biological preparation in various ways. Some- conducting, the voltage level at the grid of ViA iS IOWtimes this is done by direct electric shock, usually one enough to hold it off. The voltage at the grid of VZ2B is
or a series of pulses of current. It may be done also through therefore sufficiently high to cause this section of the tubevarious transducers to produce brief or prolonged stimuli to conduct. When VTIB is switched off, then V2A is driven oneither optical, tactile, or acoustic. To measure animal re-sponse time it is necessary that the stimuli be accuratelytimed and synchronized with the sweep of the measuringoscilloscope. To measure animal sensitivity, the stimulusamplitude must be accurately determined. In addition, suffi-cient power is required to drive the transducers. In ourlaboratories the Tektronix 160 series waveform generatorsare used to generate the timed pulses of varying duration,amplitude, and repetition rate. This provides a very con-venient, versatile, and accurate system of sequence controland synchronization, but sometimes more power is requiredfor direct stimulation or maximum drive of the transducers.This paper describes a power amplifier designed to be drivenand controlled by a Tektronix pulse generator or equivalent,and capable of providing up to 250 volts and 100 ma to ananimal preparation or transducer.
Fig. 1 is the single channel version of the pulse poweramplifier. A dual channel model has also been constructedand used in neurophysiological research at the Universityof Wisconsin Medical School for two years. Fig. 2 showsthe circuit of one channel. Fig. 3 illustrates the regulatedpower supplies required for the amplifier. The circuit de-scription follows.The input tube V1 is a 12AT7 connected as a regenera-
tive trigger amplifier designed to be triggered by a pulse ora dc voltage connected to the input terminals. Section Bof the tube is normally conducting and section A is cut off.This is indicated on the diagram by the shading of thesecond triode section. The tube remains in this conditionuntil a voltage of sufficient magnitude, about 45 volts, is ap-plied to the input. This causes section A of the tube to con-duct, the output of which is transmitted by coupling capaci-tor C3 and resistor R8 to the grid of section B and thereforecuts off its plate current. When the input voltage is removedthe tube reverts to its original state. Switch 1 is a manual
* Manuscript received by the PGME, September 25, 1959.t Medical Electronics and Lab. of Neurophysiology, University
of Wisconsin, Madison, Wis. Fig. 1.
30 IRE TRANSACTIONS ON MEDICAL ELECTRONICS January
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1960 Ledley and Lusted: The Use of Electronic Computers in Medical Data Processing 31
and V2B is cut off. The regenerative trigger amplifier was amperes resulting from incomplete cutoff of the 6AQ5's.chosen for the first two stages because the regenerative Fig. 3 shows the conventional regulated supplies designedcathode coupling gives the amplifier an all or none charac- to provide +400 volts and -300 volts. The circuit shownteristic which makes its output relatively independent of is for the single channel amplifier. To provide power forminor variations in tube characteristics and input signal the dual channel amplifier, it is necessary to connect awhile retaining the desirability of direct coupling. shunting resistor, 7.5K at 5 watts, from plate to cathode
V2B is normally conducting and its plate rests at -125 of the 12B4 series regulator in the minus supply.volts. This is directly connected to the paralleled control In the dual channel version two identical channels aregrids of the 6AQ5's and is sufficiently negative to almost built on one chassis. The circuit is the same as given herecompletely cut off their plate currents. In the off state of the except that one of the 6AQ5's is used as a second channelamplifier, the diode clamp V3 does not affect the circuit output tube and one-half of V3 is used as the clamp inoperation because it is reverse biased. When an input pulse the second channel. The dual channel unit can thus supplyof sufficient amplitude to trigger V1 is applied, V2 is also up to 50 ma at 250 volts from each channel. For pulses thatswitched so that V2B is cut off and its plate rises toward do not overlap in time the outputs are readily mixed bythe plate supply voltage. The amount of this rise which simply connecting the 6AQ5 cathodes together so that tworeaches the cathode follower grids is determined by the output pulses with independently variable durations, inter-voltage setting of the amplitude control R23, the action of vals, and amplitudes are obtained.the limiting resistance R21, and the diode clamp. R23 is aten-turn wire wound potentiometer which, in conjunction ACKNOWLEDGMENTwith the output voltmeter, enables precise determination of The author gratefully acknowledges the advice and en-the pulse amplitude. This is done by turning on the am- couragement of Professor J. E. Hind of the Physiologyplifier manually with Switch 1. The zero adjust circuit Department of the University of Wisconsin Medicalconsisting of R28 and R29 is included to compensate for a School. The valuable assistance of E. Pezon in the construc-leakage current in the output of the order of 10 micro- tion of the instrument is also acknowledged.
The Use of Electronic Computers in Medical DataProcessing: Aids in Diagnosis, Current Information
Retrieval, and Medical Record Keeping*R. S. LEDLEYt AND L. B. LUSTED±
Summary-Some of the potential advantages of computer aids INTRODUCTIONto medical data processing are: making available to the physicianquantitative methods in areas relating to data analysis and differ- DECENTLY it has been recognized that electronicential diagnosis; assisting in the evaluation of the best alterna- JjA computers can aid certain aspects of medical diag-tive courses of action during stages of the diagnostic testing proc- nosis. For example, the computer can 1) produce aesses; making easily available to the physician reference to the list of possible diagnoses consistent with medical knowledgemost current information about new preventive measures, and for a given set of symptoms' presented thediagnostic and therapeutic techniques; and periodic recording by p 2)and evaluating of individual physiologic norms for the more sen- indicate further diagnostic tests which best differentiate be-sitive determination of an individual's health trend relative to tween remaining diagnostic possibilities, 3) calculate thedisease prevention. probabilities for the alternate diagnostic possibilities, and
4) enable a more precise statement and analysis of the valuewas presented in part at the Eleventh Annual C'onf.5on Ehliectriocal eiin hc a easoitdwt rTechniques in Biology and Medicine, Minneapolis, Minn., on No- Such computer applications must be based on extensivevemnber 19, 1958. This investigation is supported in part by grant mledical data; hence, a further use of computers is 5) to
t Natl. Acad. of Sciences-Natl. Res. Council, Project on Elec-tronic Computers in Biology and Medicine, and George Washing- 1 For the purposes of this paper, we use the term symptom, orton University School of Engineering, Washington, D.C. test, to include medical history, signs, symptoms, laboratory test4 University of Rochester School of Medicine and Dentistry, results, etc.; that is, these terms include all the information thatRochester, N.Y. can be obtained with respect to the patient's medical state.
