US2486776A - Self-biased electric translating device - Google Patents

Description

Nov. 1, 1949 H. L. BARNEY 2,486,775

SELF-BIASED ELECTRIC TRANSLATING DEVICE Filed April 21, 1948 2 Sheets-Sheet 2 FIG. 5

ATTORNEY Patented Nov, l, 1949 UNITED STATE saLF-Bmsm s PATENT OFFICE- v ELECT RIC TRAN SLATING DEVICE Harold L. Barney, Madison, N. J asslgnor to Bell Telephone Laboratories,

Incorporated, New

, York, N. Y., a corporation of New York Application April 21, 1948, Serial No.22,276

. Thisfinvention relatesto signal translation circuits including semiconductive elements.

'The'genera1 object of the invention is to translate electric signals without the assistance of a source of steadypotential. A particular object of the invention is to modulate carrier energy by signal energy without resort to special power supplies or bias 13 Claims. (Cl. 332-52) ment displays remarkable amplification properties, inthat when a signal to be amplified is applied between the emitter and the control elec- ,.trode,. an amplified replica appears across a load connected in series with the absorber.

In an application of H. L. Barney and R. C.

. Mathes, Serial No. 22,854, filed April 23, 1948, there is described a self-bias circuit arrangement sources for the electrodes of the modulator apparatus. A related object is to furnish operating potentials to a signal amplifier without resort to a special power supply.

Another object is to adapt semiconductor modulators and amplifiers for service at unattended repeater stations. U

A related object is to enable a plurality of translating devices to be coupled in tandem, all supplied with operating potential from'one of them.

Another related object is to enable a. plurality of translating devices, one of which is a semiconductor modulator, to be coupled in tandem,

all supplied with energy from a carrier source only, which carrier source may be located at a remote point.

In an application of John Bardeen and W. H. Brattain, Serial No. 11,165, filed February 26, 1948, now superseded by a continuation-in-part application Serial No. 33,466, filed June 17, 1948, and thereafter allowed to become abandoned,

there is described a, circuit element comprising a small block of a semiconductive material such as germanium of which the body is of one conductivity type, for example, N-type, while one surface has been given a sensitizing treatment which is believed to alter the conductivity of a thin surface layer to P-type, which layeris' be- I lieved to be separated from the body of the block.

by a high resistance barrier. Two electrodes, hereinafter denoted the emitter and theabsorber, make contact with the treated surface. The absorber contact is of the rectifier type, while the emitter contact may be. A third electrode, which may be a plated metal film, makes low resistance contact with the opposite face,

namely, the base of the block.

which comprises a resistor in series with the control electrode, across which a bias voltage is developed by flow of current dueto the collector bias potential source. The resistor may be bypassed for1signa1. frequencies by a condenser. "This-permits the emitter-control electrode bias battery tobe dispensed with. The present in- ;vention' has to do with 1 the elimination of the absorber bias battery...

g 'The circuit arrangement of the Bardeen-Brattain application pr'esentscertain obvious similarities to. a conventional amplifier circuit introl "ofjthe absorber current which, far from be- A small bias battery of one sign is applied from w the control electrode to the emitter, and a larger bias battery of opposite sign is applied to-the absorber. When the body material is of -N-type,

the emitter is biased positively, the absorber negatively. When it is of P-type, the signs are operated in its reverse direction.

It has been discovered that this circuit eleing cut-ofi, flows more strongly than ever, by virtue: oi the fact that theabsorber is now being operated in the x-fOl'WHJd direction. Heretofore this forward-direction current in the absorber circuit has ,been regarded as a disadvantage of the circuit element inv question as compared with a vacuum tube triode, and as imposing limitations on they magnitudeof the absorber voltage swing which canbe tolerated,1since with a .voltage swing whose nominal 'peak value exceeds'the bias battery voltage, .the large, undesired for- I ward-direction current would flow, limiting the U voltage and destroying the amplification.

By the present invention the forward direction currentjis turned to advantage in the following manner. An alternating voltage, for example of carrierirequency, is applied, to the absorbenand a condenser-is included in the ab,-

sorber circuit; 'The forward-direction current reversed. Thus the absorber rectifier contact is.

which flowsat the ,jvoltage peaks-of. one sign charges the condenser, and-the resulting condenser voltage serves, as a bias, for I the absorber on the voltage swings of opposite sign. The circuitelementoperates in alternation as a rectifier, when the condenser'is charged, and as an amplifier, when the charged condenser furnishes the absorber bias. Inasmuch as the amplification of the input signal is dependent in part on the net instantaneous absorber potential, the unit operates both as a signal amplifier, a carrier translator, and a modulator, delivering at its output terminals energy'having components of signal frequency, of carrier frequency, and of their v various modulation products. The desired output components may be selected, and undesired ones may be rejected, by filtering.

Because the forward-direction current is much larger, for a given potential, than the reverse current, it need flow only for a small fraction of the carrier frequency-period and can still charge the condenser to a substantial voltage. Amplifier operation takes place throughout thegreater fraction of the carrier period, so that the duty cycle is favorable.

The invention will be fully apprehended from the following detailed description of certain preferred embodiments thereof taken in connection with the appended drawings in which:

Fig. 1 is a schematic circuit diagram of a signal translator embodying the invention;

Figsyz and 3 are wave form diagrams illustrating certain principles of the invention;'

Fig. 4 is a schematic diagram of an alternative to Fig. 1; V

Fig. 5 is a schematic diagram illustrating the extension of Fig. 1 to a system including an emplifier and a modulator which may be located remotely from a power source; and

Fig. 6 is a schematic diagram illustrating the extension of Fig. l to a system including a signal amplifier, a modulator, and a sideband amplifier.

Referring now to the figures, Fig. 1 is a schematic diagram showing a circuit for translating the voltage of a voice signal of frequency q. The translation may be both amplification of this voice signal and modulation of it onto a carrier signal of frequency 1). The heart of the circuit is a. three electrode semiconductor unit which may be of the type which forms the subject-matter of the aforesaid Bardeen-Brattain application. As a preferred example it may be a small block I of germanium prepared in accordance with the teachings of an application of J. H. Scan? and H. C. Theuerer, SerialNo. 638,351, filed December 29, 1945, and to one surface 2 of which a sensitizing treatment has been applied, for example, an anodic oxidation process as described and claimed in an application of R. B. Gibney,

Serial No. 11,167, filed February 26, 1948. TWO

. the emitter 4 which may be at ground potential,

and the control electrode 6. The output circuits of the device include the primary windings of two transformers II, it by which output voltages are delivered to outgoing lines l3, l4. These primary windings are connected in the circuit oi the absorber 5 and the emitter 4. Filters l8, it may be included in the outgoing lines l3, M, to pass desired components of the output of the device and reject unwanted ones.

In accordance with the invention, the voltage of an alternating source, here symbolically represented by an oscillator I! is applied by way of a transformer l8 in series with a condenser l3 between the absorber 5 and the emitter 4. The

source ll may, for example, be a source of carrier frequency which is high compared with the frequency of the signal to be translated.

The device as described in the aforementioned Bardeen-Brattain application does not include this carrier source I! or the condenser l8. Rather, it includes a battery in the circuit of the absorber electrode, by way of which an operating bias of approximately 40 to 100 volts is applied to the absorber. According to current theory as to the operation of the device as an emplifier, the surface treatment to which the semiconductor block has been subjected results in the formation on the surface 2 of a thin layer of P-type-material, perhaps 10- centimeters in thickness, separated from the body of the block by a high resistance barrier 3. With the emitter 4 biased positively with respect to the body of the block I by a, volt or so, as by a battery 9, and the absorber 5 negatively by 40 to 100 volts, the emitter 4 operates in the forward direction and the absorber 5 in the reverse direction. These terms are familiar in the point contact rectifier art. As a consequence, mobile positive charges flow from the emitter 4'to the block I, but because of the transverse resistance of the barrier 3 which is considerably higher than the lateral resistance of the surface layer 2, these mobile positive charges travel laterally in the surface layer away from the emitter rather than immediately crossing the barrier. In the course of this lateral spread of current it comes within the influence of a strong electric field which exists in the neighborhood of the absorber 5, i. e., between it and fixed charges in the body of the material. The mobile charges are here collected and fiow out of the layer by way of the absorber electrode. A signal applied between the emitter 4 and the body of the block produces an electric field whose strength is greatest across the barrier 3. This field modifies the current of mobile charges flowing from the emitter to the surface layer and so the current in the external absorber circuit and the voltage across a. suitable load. Thus amplification is obtained.

In the Bardeen-Brattain application, the control of the emitter current by a signal applied between the emitter and the body of the block is exerted only when there is applied to the absorber '5 a bias of substantial magnitude and of a sign such as to cause the absorber to operate in its reverse direction; that is to say with a negative bias on the absorber in the case of a block of. N-type material and a positive bias in the case of a-block of P-type material. When the bias is applied with the wrong sign, the absorber operates in its forward direction, a large current flows and control of the absorber current by a voltage applied to the control electrode is lost.

When an alternating voltage derived, for example, from the carrier source I! is applied by way of the transformer I8 to the absorber electrode 5, it is of the right polarity to work the absorber in its reverse direction and produce amplification during one half of each cycle, while during the other half of the cycle it is of the opposite polarity trode bias battery is a compromise between the correct bias values for the various absorber volt- .ages occurring in the absorber cycle. These defects may be overcome by the use of a square wave the present invention, a condenser I9 is included in the circuit, the forward direction cur-rent flows only during the short time necessary to charge the condenser. Because of the low forward'resistance of the barrier 3 of the semiconductor block, the condenser i8 is charged toa substantial fraction of the peak voltage of the carrier. On the ensuing half cycle, its voltage is added to the applied carrier voltage. Thus the. condenser,

charged in the fashion described, serves as a bias source for the absorber 5.

The condenser charge once applied leaks of! only slowly by way of the high reverse resistance of the absorber contact. Therefore, on later positive half cycles of the carrier voltage, still less current is required to charge the condenser. Indeed, only that small current flows which is required to replace the small fraction of the condenser charge which may have leaked off during the prior cycle.

Fig. 2 is a voltage-time diagram illustrating the foregoing in the steady state after the initial 1 transient conditions which arise when the syscarrier as indicated in Fig. 3, which comprises swings of one polarity and of short durations t2, alternating with swings of the opposite polarity and of longer durations ti. As before, the polarities are so chosen that the longer times are in reverse direction with respect to the absorber rectifler contact. As before, the condenser is charged by the forward direction currentwhich flows during the fraction is of each cycle, and the resulting charged condenser voltage is added to that .of the carrier during the longer fraction t1 of each cycle.

' Now, however, the absorber voltage is substantem is first turned on have died away. Thecurve Va represents the wave form of a sinusoidal carrier voltage of frequency 10 derived from the carrier source l1 and applied from the emitter 4 to the absorber 5. Were it not for the addition of the condenser l9 in the absorber circuit, the voltage would be symmetrically located about the zero voltage axis. Due, however, to the charging of the condenser i9 in the manner described above, the carrier voltage wave form is displaced in a negative direction so that it lies symmetrically about'a negative voltage. In the illustration shown which is based on experimental resuits, the negative condenser voltage Vc about which the carrier wave form is symmetrically distributed is -32 volts, so that the carrier voltage, whose peak to peak magnitude is 110 volts, swings from +23 volts to 87 volts. It has positive values greater'than zero only for a fraction is, approximately one-flfth, of each period. Therefore, the system operates as an amplifier throughout the fraction t1, while the smaller fraction tz is utilized for maintaining the condenser charge. During the working fraction t1, the absorber voltage is being changed from 0 to a negative voltage of 87 volts and back to zero in approximately sinusoidal fashion. Therefore, the amplification of the unit is correspondingly varied. As a result, the output of the system which appears on the output transformers l I, l2 and is delivered to the outgoing lines l3, contains, in addition to the signal frequency q, components of the carrier frequency p and of the modulation products between them, for example, upper and lower side frequencies p+q and p-q. Any desired frequency band,

or several together, may be supplied to a load clrcuit. Thus a low pass filter l5 blocks all components of frequencies higher than the'voice frequencies, passing these to'an outgoing line 2|, while a band pass filter l6 passes the carrier and the two sidebands to another outgoing line 22, and blocks all other frequencies.

With a sinusoidal carrier,the signal frequency output is low. Furthermore, any control electially constant throughout the fraction if, so that the control electrode bias may be selected at the A best value for this particular absorber voltage, without compromise.

A further advantage of the square wave carrier is that the signal frequency output of the device is increased as compared with the carrier and side frequency output. Therefore the square wave is to be preferred for an amplifier while, unless the control. electrode bias compromise is too great, the sine wave is generally to be preferred for a modulator.

Instead of a control electrode bias battery, the control electrode bias may be supplied from the carrier source l'l, whether the wave form of the latter be sinusoidal or square. Fig. 4 shows such a system wherein the carrier source I! is applied by way of one winding 26 of a transformer 25 to the absorber 5 and by way of another winding 21 of the transformer 25 to the control electrode 6. The windings 26, 21 are so poled that the absorber 5 and the control electrode 6 are simultaneously positive and simultaneously negative with respect to the emitter 4, and the transformer 25 is wound to apply one or two volts through winding 21 to the control electrode 6 and 50 to volts through winding 26 to the absorber 5. During the working fractions iii of the cycle, the magnitude and polartiy of the control electrode bias are then correct while during the fractions t2 of the cycle, it is incorrect, but at these times the condenser I9 is being charged by the carrier source H, the unit is not translating the signal, and the sign of the control electrode bias is of no importance.

The translator of Fig. l'which, as above explained, draws all its required operating power from the carrier source I1, is adapted to be located at an unattended repeater station, drawing carrier power from a remotely located point. Furthermore, inasmuch as the condenser IQ of Fig. 1 serves as a bias potential source, the potential of this condenser may be applied to provide the bias potential for other units, for example amplifiers. Fig. 5 shows a system in which both of these features are included. A translator unit 35 which may be identical with that of Fig. 1 and which may serve, for example, to modulate a carrier p by a signal q, is supplied with carrier power derived from a remotely located oscillator 30 by way of a hybrid coil 3| and a transmission line 32 which is terminated at the modulator in the winding of a transformer 33. Modulated output likewise passes over the transmission line 22 and is fed to an output circuit by way of a second hybrid coil 34. A terminal impedance Z isincluded in the circuit in well-known fashion.

The input to the modulator 35 is derived from an amplifier 38 such, for example, as the, semiconductor amplifier which forms. the subject-matter of the aforementioned Bardee'n-Brattain application. Its electrodes are designated by the same reference numerals as are used in Fig. 1, distinguished by primes- Control electrode bias may be provided by inclusion of a self-bias resistor 31 in the control electrode-emitter circuit, by-passed by a condenser 38, in the manner described in the aforementioned application of H. L. Barney and R. C. Mathes, Serial No. 22,854, filed April 23, 1948.

The input signal to this amplifier may be derived from any desired source, for example, a telephone transmitter 'l which delivers a voltage of frequency q to the primary winding of a. transformer 8 whose secondary winding is connected in the control-emitter circuit. The amplifier of the aforementioned Barney- Mathes application includes a battery as a bias source in the absorber circuit. In accordance with the present invention, however, a suitable negative voltage is applied to the absorber electrode of the amplifier 36 by way of a choke coil 39 or other decoupling impedance which permits the application of steady voltages but prevents the fiow of signal energy. A signal frequency by-pass condenser 40 may be included in the circuit.

Any number of amplifier stages may be connected ahead of the modulator 35, the limit being determined only by the amount of forward current which can safely be drawn through the absorber contact of the modulator. On the other hand the translator unit may, if preferred, .serve principally as an amplifier. In the general case the output contains all of the components indicated on the figure.

. This aspect of the invention is equally applicable to a sideband amplifier. Fig. 6 shows a signal amplifier 36 and a modulator 35 similar to those of Fig. 5 and similarly coupled, with the amplifier 36 drawing its absorber bias voltage from the charged condenser I3 of the modulator 35. The modulator output instead of being transmitted directly over an outgoing line is first amplified by a sideband amplifier I which may be identical in construction with the signal amplifier and receives carrier and sideband energy from the modulator by way of the interstage I '36 its control electrode may be negatively biased by a self-bias resistor 43 and the latter may be shunted by a condenser 44 as a sideband frequency by-pass. v

The necessary operating bias potential for the absorbers of all stages may be derived from the charged condenser l9 and applied to the absorbers by way of choke coils 39, 33' or other decoupling impedance elements. By-pass condensers 40, 40' may be included in the circuit in each case. The invention has been shown, described and explained in" connection with a semiconductor amplifier unit, connected in the fashion of a conventional triode; that is to say, with the emitter electrode grounded. It is equally applicable to other triode circuits such as the grounded grid circuit and the grounded anode or cathode follower circuit. Furthermore, it is not restricted to use in connection with the semiconductor amplifier specifically shown in the aforementioned Bardeen-Brattain application, but is equally applicable to similar units whose operation is based 'on the same principle.

Still other modifications within the spirit of the invention will be apparent to those skilled in the art.

What is claimed is:

1. In combination with signal translation apparatus comprising a block of semiconductor material, an emitter electrode and a control electrode in contact with said block and an 'absorber electrode making rectifier contact with said block, said apparatus being characterized by reverse direction absorber current which is variable under control of a signal applied to the control electrode and a larger forward direction absorber current which is not so controllable, means for impressing forward and reverse direction potentials in alternation on said absorber, and means for deriving a reverse direction bias for said absorber from forward direction absorber currents which now in response to said forward direction potentials.

2. In combination with signal translation apparatus comprising a block of semiconductor material, an emitter electrode and a control electrode in contact with said block and an absorber electrode making rectifier contact with said block, said apparatus being characterized by reverse direction absorber current which is variable under control of a signal applied to the control electrode and a larger forward direction absorber current which is not so controllable,

an alternating current source, means for causing absorber currents to flow through said rectifier contact in alternately opposite directions, means for utilizing the current now in one of said directions to provide a bias voltage, and means for applying said bias voltage to said absorber in a sense to promote said reverse direction current flow.

3. In combination with signal translation apparatus comprising a block of semi-conductor material, an emitter electrode and a control electrode in contact with said block and an absorber electrode making rectifier contact with said block, said apparatus being characterized by reverse direction absorber current which is variable under control of a signal applied to the control electrode and a larger forward direction absorber current which is not so controllable, and an a'ltemating voltage source and a condenser connected in series with said absorber electrode.

4. Apparatus as defined in the preceding claim, wherein the wave form of the source voltage is rectangular.

5. Apparatus as defined in claim 3 wherein the wave form of the source voltage is rectangular,

r 'having swings of short duration in the condenser-charging polarity and swings of longer duration in the amplifying polarity.

6. In combination with signal translation apparatus comprising a block of semiconductor material, an emitter electrode and a control electrode in contact with said block and an absorber electrode making rectifier contact with said block, said apparatus being characterized by reverse direction absorber current which it variable under control of a signal applied to the control electrode and a larger forward direction absorber current which is not so controllable, an alternating voltage source, a condenser, and a load impedance connected in series with said absorber, and a signal source connected to said control electrode.

, 7. In combination with signal translation apparatus comprising a block of semiconductor material, an emitter electrode and a control electrode in contact with said block and an absorber electrode making rectifier contact with said block, said apparatus being characterized by reverse direction absorber current which is variable under control of a signal applied to the control electrode and a larger forward direction absorber current which is not so controllable, a condenser in series with said absorber, a source of alternating voltage, and means for simultaneously applying the voltage of said source to said absorber and to said control electrode with like polarity.

8. In combination with signal translation apparatus comprising a block of semiconductor material, an emitter electrode and a control electrode in contact with said block and an absorber electrode making rectifier contact with said block, said apparatus being characterized by reverse direction absorber current which is variable under control of a signal applied to the control electrode and a larger forward direction absorber current which is not so controllable, impedance means for deriving a voltage drop from forward direction absorber current flow, and means for applying said voltage drop in a sense to aid said reverse direction absorber current flow.

9. In combination with signal translation apparatus comprising a block of semiconductor material, an emitter electrode and a control electrode in contact with said block and an absorber electrode making rectifier contact with said block, said apparatus being characterized by reverse direction absorber current which is variable under control of a signal applied to the control electrode and a larger forward direction absorber current which is not so controllable, means for applying an alternating voltage to said absorber, means for deriving a steady voltage irom forward direction absorber current flowing under the action of said alternating voltage, and means for applying said-steady voltage in a sense to aid said alternating voltage in producing reverse direction absorber current.

10. In combination with signal translation ap-- ,paratus comprising a block of semiconductor material, an emitter electrode and a control elecinterconnecting said remote point with said impedance element, said line being coupled to said source and to said utilization circuit, and means for preventing substantial amounts of the energy of said source from being directly transmitted to said utilization circuit.

11. The combination which comprises a carrier source, a signal source, a plurality of signal translation stages coupled together, each stage id comprising a block of semiconductor material, an emitter electrode, an absorber electrode, and a control electrode in contact therewith, each oi said stages requiring for proper operation a substantially steady bias potential on the absorber electrode, a carrier source, a signal source, at least one of said stages serving as a modulator of which the absorber electrode makes rectifier contact with the block, said modulator being characterized by a reverse direction absorber current which is variable under control of a signal applied to its control electrode and a larger forward direction absorber current which is not so controllable, connections for applying the voltage of said carrier source to said modulator absorber, means for deriving a steady voltage from forward direction modulator absorber current flowing under the influence of said carrier voltage, and means for applying said steady voltage as a bias potential to the absorber electrode of another stage.

12. In combination with a circuit element comprising a body of semiconductive material, an emitter electrode making contact with said body over an area which is small compared with the dimensions of said body, a control electrode making low resistance contact with said body, and an absorber electrode making rectifier contact with said body, an alternating current source connected to apply a potential to said absorber which is alternately in the forward direction and in the reverse direction with respect to said rectifier contact, a condenser connected in series with said source and said absorber, which condenser becomes charged by current flowing in the forward direction from said source, a signal source connected to said control electrode forinfluencing the magnitude of the reverse current flowing from said source, and an impedance element connected to carry said reverse current, whereby modulation product voltages between the frequencies of said sources are developed across said impedance element.

13. In combination with a circuit element comprising a semiconductive body, an emitter elec- HAROIDL. BARNEY.

REFERENCES CITED The following references are or record in the file of this patent:

Article, Germanium Crystal Diodes, by E. C. Conelius, pages 118-128 of February 1948, issue, Electronics.

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