US2280532A - Wide band amplifier - Google Patents

Description

April 2l, 1942. D. E. NQRGAARD WIDE BANP AMPLIFIER Fiied May 1, 1941 gaard, M4

Patented Apr. 21, 1942- WIDEBANDAMPLTFIER. W Donald E. Norgaard, Schenectady, N. Y., assigner to General Electric Company, a corporation of New York Application May 1, 1941, Serial No. 391,318 12 Claims. (Ci. 179-171) My invention relates to wide band amplifiers such as those employed for the amplification of vrvideo frequency currents used intelevision.

It has for one of its objects to provide a method and means for producing, uniform amplification at all frequencies of such currents from a level only slightly in excess of the undesired disturbing, or noise, currents to substantially higher level notwithstanding 'the attenuating'eiects of such shunt capacitiesas are usually present,

In television transmitters, camera tubes are employed which are exposed to the scene to be televised and which produce currents representing such scene. This discharge device has very high impedance such that the currents owing therefrom are not materially affected by the load impedance into which the tube operates. These currents may have frequencies extending over the range from zero to about ve megacycles. An object of my invention is toprovide improvedmeans method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description for producing uniform amplication for these currents throughout this frequency range.

It so happens, in the use of the camera tube, that the currents produced thereby most faithfully represent the televised scene if adjustedto be as small as possible; i. e., the smaller the currents the better they represent the televised picture. Accordingly, one normally adjusts the electron beam of the camera tube to as low intensity as possible and still produce ampliilable output currents. Of course, the undesired disturbing, or,

so called, noise, currents produced in the amplifier chain define the lower limit, it being necessary that the camera tube output currents be of intensity such that when amplified in the amplifier chain they have an intensity level sufciently above the undesired noise level. These undesired currents extend throughout the frequency band to be transmitted lbut the most objectionable of them are in the frequency range below two thousand cycles, or substantially below the line repetition rate employed in the scanning process.

Difllcultyis amplification over the band of frequencies to be amplified because of the low level of the desired signal with respect to the noise level and because of the attenuating effects of shunt capacity in.- herently present throughout the amplifier.

An object of my invention is to overcome this difficulty and secure uniform amplication throughout the band while minimizing the effects of disturbing currents introduced by the amplit fier.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and encountered in effecting uniform i taken in connection with the accompanying drawing, in which Fig. 1`rep'resents yan embodiment of my invention, and Fig; f2a, Fig. 2b, Fig. 2c and Fig. 2d represent-.certain characteristics pertaining to its operation.

Referring to Fig. 1 of the drawing,` I have shown therein an amplification channel extending from terminals I, 2 to terminals 3,. I. The terminals i, 2 may, of course, be connected tothe output terminals of a. cathoderay. or camera, tube used in picking up the scene to beA televised and these terminals are connected to the input electrodes of an amplifier represented by the rectangle AB. l.

Fig. 1 includes three rectangles E, 8 and 1, each of which may be` taken to represent either a single stage electron discharge amplier or almultistage amplier but in the usual case these rectangles represent a multi-stage ampliiier. Preferably the last stage in each of these amplifiers is of the pentode type, such high internal output impedance and produces output current which is independent of the magnitude of the load impedance.

The terminal l may be considered to be connected to the input grid that it has extremely of such an amplifier and means as may be employed. Operating potential for the anodes of the discharge devices represented by the rectangles 5, 6, and `'I may be supplied through conductors 8, 9, and l0 respectively to the respective anodes -of the different discharge devices.

The network Ii between rectangles 5 and is the interstage coupling network connected between the anode and the cathode of the last discharge device represented by rectangle 5 and the grid and cathode of the first discharge device represented by rectangle 6.A Similarly, the network i2 between rectangles 6 `and i represents the coupling network connected between the anode and cathode of the last discharge device represented by rectangle 6 and the grid' and cathode of the iir'st discharge device represented by rectangle The output network i3 may be connected from the anode and cathode of the lastv discharge device represented by the rectangle 1 to the input of any additional stages of amplification that may be required. v As previously stated, the camera tube is one having extremely high impedance and thus the current produced thereby is ,not materially affected by the load impedance into which the tube operates. This current, we may consider to be represented by the dotted line A of Fig. 2a and it is desired that this current be amplified with uniform amplification over the frequency band to produce a voltage at the output terminals 3 and 4, which voltage may likewise be represented by a straight line, as indicated by the curve A' of Fig, 2d. l

'Ihis current fiows through the impedance between terminals I and 2. This impedance is made up of the input capacitance of the first discharge device represented by rectangle which capacitance is indicated by dotted lines at I4, in shunt with such impedances as are present across the circuit, including, for example, resistance such as that indicated at I6 and I1 through whichbias voltage may be supplied to the grid of the first stage of the amplifier 5. Such resistance is necessary to produce a limiting finite impedance at low frequencies across the input to the first discharge device of amplifier 5. The voltage across these terminals produced by the camera tube may, by reason of these impedances, vary with frequency as indicated, for example, by the curve B of Fig. 2a.

This voltage isas minute as it is practicable to make it and still be amplifable in the presenceof the noise level of the amplifier, the most objectionable of the noise currents introduced by the amplifier being at low frequency, below the line repetition rate, or below two thousand cycles.

Of course, one way to correct for the attenuation at high frequency, represented by the curve B is to connect across the circuit, a series combination of inductance and resistance proportioned with respect to capacity I4 to produce uniform impedance at all frequencies to be arnplied. This, however, is not feasible because such inductance and resistance would have such low values that they would so reduce the input voltage available for amplification at all freout of the question. my invention, no attempt of the circuit, to effect the Instead, a condenser I5 is employed connected between the terminal 2 and a point between the two resistors I5 and I1, this condenser being so proportioned relative to resistances I 6 and I1 as to produce substanthe reactance tial reduction in impedance at the intermediate l frequencies without materially affecting the impedance at either the low frequencies orl the high frequencies. Thus, the .voltage across capacitance I4 may now, by reason of the presence of condenser I5, be represented by the curve C of Fig. 2a. 'Ihe attenuation, equal to the difference between curves B and C,.may be effected while still maintaining the signal intensity above the noise level at all frequencies.

It will be seen that curve C of Fig-2a lies below curve B to a substantial extent only in' the intermediate part of the range. At the extreme right end of the curve, corresponding to frequencies between about one megacycle and iive megacycles, where condenser I5 has substantially zero reactance, the two curves substantially coincide.

In-this range of frequencies the shape of both curves is determined primarily by the capacitance I4, the reactance of which at these frequencies is low relative to the resistance of resistor I6. In this range of frequencies current flowing between terminals I and 2 flows largely through capacitance I4.

At frequencies below one megacycle the reactance of condensers I4 and I5 bothincrease but since the reactance of capacitance I4 is much greater than that of condenser I5 it becomes very high relative to resistance I6 while of condenser I5 remains negligible with respect to resistance I 6. This is true at about one hundred and fifty thousand cycles. Since the reactance of condenser I4, at the frequency corresponding to the point Y of curve C, is already large relative to resistance I6, it, at this and lower frequencies, has little-or no effect upon the shape of the curve C. Similarly, since the reactance of condenser I5 is negligible at the frequency corresponding to the point Y; it has little effect upon the shape of the curvey C at that point Y. The shape of the curve at'this point Y is determined by the resistance I6 and, therefore, 'curve C in the region of point Y is substantially a straight line nearly parallel to the horizontal, or frequency, axis of the graph.

At frequencies below the point Y, the reactance of condenser I5 increases and first becomes high relative to resistance I6 and finally becomes'high as compared with resistance II, which is about ten times greater than resistance I6. Thus, the voltage between terminals I and 2 rises with reduced frequency until the point X is reached where the reactance of condenser I5 is that it no longer is effective in determining the shape of the curve. Below this pointX,curves B and C coincide.

While the use of condenser I5 results in a loss of signal input over a region of intermediate frequencies, it does not reduce the signal input at low frequencies where the noise level is highest. It produces the important advantage of dividing the signal frequency band in two distinct portions each having distinctly different signal levels and which may be treated separately. ,Both portions may now be amplified until the lower frequency portion, which is of higher intensity, becomes of such amplitude that further amplification with a given tube complement results in distortion due to overloading. The lower frequency band may then be attenuated to produce uniform amplification over the entire lower frequency portion of the band without loss in amplincation in the higher frequency portion of the band, without changing the characteristic relation between voltage and frequency in the high frequency portion of the band, and without reducing the signal level to a point objectionably close to the noise level at low frequencies.

Now the entire band may be amplified to such a level that circuits may be employed to increase the intensities of currents of the highest frequencies in the band to a level of the low frequency currents. Such circuits are of such character, as will presently be explained, that they produce a loss at all frequencies and especially the low frequencies. However, by reason of my invention, such circuits may be employed after sufiicient amplification has been had that this loss may be tolerated without reducing the signal to a level too close to the noise level of the amplifier.

The voltage represented by the curve C is amplified by the amplifier 5 and produces a. current represented by the curve. I1 of Fig. 2b at the output of the amplifier 5. This curve I1 has the sameshapeasthecurvecofllig.2asincethe amplifier 6 has uniform amplication at all frequencies involved vand its last stage has high internal impedance to currents in its output circuit as previously mention This current is supplied by amplifier to the network II coupling that amplier to the amplifier 6. A portion of this .current flows through resistance I3 and by-pass condenser I3. The voltage on the resistance I6I is supplied through coupling condenser 20 to the grid of the first discharge device of the amplifier 6. Between the grid and cathode of this discharge device is connected the series combination of inductance 2l and resistance 22,- which are proportioned relative to the shunt capacitance 23, effective across the input of the amplier 6 to have uniform impedance throughout the band to electromotive force existing across the combination 2l, 22, and

Connected across 'condenser 2li is a path comprising resistance 24, condenser 25, and resistance 26, the elements I3, 20, 24, 25, 26, 2| and 22 being proportioned relative to resistances I6 and I1 and capacitance I5 4to attenuate the low frequency currents in the band, thereby to produce voltage across capacitance 23, which voltage may be represented by the curve Ec of Fig. .2b.

This is effected by so proportioning the ele-- ments that the sum of resistances I6 and 22 bears the same ratio to resistance I6 that the sum of resistances 24 and 26 bears to resistance I1, and that the capacitance of condenser I5 bears to the capacitance of condenser 20. l,

In the path 24, 25, and 26, the resistances 24 and 26 are of equal value and the condenser 25 is of negligible reactance as compared with the sum of resistances 24 and 26 at thelowest frequency to be amplified; for example, ten cycles per second. In other words, the path 24, 25, 26 is essentially purely resistive throughout the band. Resistances 24 and 25 are so large that capacity betweencondenser 25 and ground does not materially affect the transmission characteristics of the channel.

Such proportioning of the elements not only produces uniform amplification over the lband including frequencies up to 150,000 cycles, but it also renders the system as will later be shown, independent of frequency so that no undesired phase shifts at the different frequencies are produced.

This network produces attenuation at the lower frequencies amplification desired. `This attenuation occurs. however, after the amplification of amplifier 5 has'been had so that the voltage Es is still above the noise level of amplier 6`even at low frequencies where the disturbing currents are the most intense.

Having produced uniform amplification over the low frequency portion of the band: i. e., up to 150,000 cycles, it now remains to accentuate the high frequencies sumciently to produce uniform amplication over the entire` band. The band over which accentuation is to be effected and the magnitude of accentuation required is now much less than would be the case if all of the compensation were to be effected in a single stage of the amplifier.

The voltage represented by the curve En is amplified by amplifier 6 in the presence, of course, of such noise currents as are produced by amplifier 6. 'I'his amplifier supplies to the network l2 an output current which is represented by the curve In of Fig. 2c. The signal voltage on resistance 21 is supplied through coupling condenser 30 to the input of the iirst discharge device of amplifier 1 between the grid and cathode of which is connected a network comprising an inductance 3l, resistance 32, resistance 33 and bias battery 34, a condenser 35 being connected between ground and a point between resistances -rightgr end offthe curves C,

-`by the condenser to bring about the uniform necessary that inductance 32 and 33. The resistance 33 may be variable, if desired, to correct for changing internal resistance in the source 34 which may be a battery.

Resistor 21, which comprises a portion of the network I2 is connected in the path -through which unidirectional anode current tothe last stage of amplifier 6 is supplied, and has, therefore, a high resistance. 0nly a small fraction of the signal currentoutput of the amplifier 6 flows through this resistor, the remainder of the output current flowing through condenser 30 and the series parallel combination represented by elements, 32, 33,-34, 35 and 36. That is, the impedance looking to the right of the juncture of resistance 21 and condenser 30 is considerably lower than the resistance 21 over the entire range of frequencies involved. Condenser 30 serves as a blocking condenser to prevent application of unidirectional anode voltage to the grid of the first stage of amplifier 1. This condenser must have a reactance substantially lower than the resistance 21 at the lowest frequency considered, i. e., ten cycles per second, so that the impedance into which amplier 6 works is determined principally by elements 30, 3l, 32, 33, 34, 35-and 36 ofithe network I2.

Since, as has been shown earlier, the 'extreme Ee, and Ie is affected I4, acting together with resistor I6, the impedance elements 3| and 32 are proportioned in such va manner that the time `4constant of the series combination of elements 3| and 32 is the same 4as the time constant of the parallel combination of elements I4 and I6 in order to eilect compensation for the phaseV and amplitude of the currents and voltages in the upper range of frequencies.

It is important ,that the frequency at which the network I2 resonates be not lower than'2 to 3 times the upper limit of the amplifier system; i. e., from l0 lto l5 megacycles in the embodiment shown, in eilect shall not affect transmission in the band. This resonance is produced primarily by inductance 3l and capacitance 36. Since stray capacity 36 cannot be reduced appreciably, it is 3l be chosen to resonate with the capacity 36 at a .frequency Well outside of the pass-band of the amplifier. Thus, the resistance 32 and the inductance 3|, in general, have exceptionally low values when the circuit is adjusted to give nearly exact compensation. For example, the resistance 32 may be ten ohms and the inductance 3I three microhenries.

By so proportioning these elements, uniform amplification over the entire band up to the input of amplifierA 1 may be had. Itso happens, however, that since the value of resistance 32 and inductance 3l required to produce such uniare very small, they reduce form ampliilcation signal over the entire band.

the intensity of the However, at this point of the circuit, the previous order that the resonance reduced to a pointzinsuiiiciently above the noise level of ampliner I then resistance 33 and condenser 35 may be included in the circuit and proportioned relative to resistance 32 in the same way that resistance I 'I and condenser I5 are proportioned relative to resistance i6 thereby to increase the impedance at low frequencies to produce a voltage across capacitance 36 varying with frequency in the manner illustrated by curve E7 of Fig. 2c. Condenser 35 is a substantial short circuit to resistance 33 at the high frequencies to be accentuated but is of suiciently high reactance at the low frequencies where noise currents are most objectionable to render resistance 33 effective in series with resistance 32 to increase the impedance across the channel and bring about the increased low frequency amplification evidenced by the left end of curve E1.

This voltage Ev is amplified by amplifier 'I. which produces a current in its output which may be represented by the curve I7 ofFig. 2d. This current is supplied to the network I3 which is identical in its action to network II. That is, it reduces the low frequency voltage supplied to the terminals 3 and 4 relative to the high frequency voltagel thereby producing transformation between current at the terminals I and 2 and voltage at the terminals 3 and 4 which is uniform at al1 frequencies in the band of frequencies to be transmitted. This voltage at terminals 3 and 4 is represented by the curve A of Fig. 2d and may be of an intensity of the order of half a volt, well above noise level at all frequencies, and such that it may be readily ampliled to any desired intensity required for the transmission of the picture represented thereby` by modulation be transmitted by radio.

It will thus be seen that an important feature of my invention resides in the use of the network I5, I6, I'I at the input to amplifier 5. 'I'his network, in effect, divides the frequency band into two portions, the low frequency portion below the frequency represented by point Y of Fig. 2a and the high frequency portion above the frequency represented by this point Y. This permits these two portions to be treated separately in the respective networks II and I2, the

network IIl producing uniform amplincation over the low frequency portion of the band with an output intensity above the noise level of amplifier 6 and the network I2 accentuating voltages in the high frequency portion of the band. Since, however, the elements required to accentuate the high frequency currents may reduce the intensity of the low frequency currents to intensities unsatisfactorily small, the elements 35 and 33 may be included to maintain the lows suiiiciently above the noise level of amplifier 1. Network I3 then brings about the uniform amplication over lthe band.

I have now generally set forth the character of my invention. For a more detailed consideration let us first consider the amplifier 5 and the networks between which it operates, and the portion of the band of frequencies below the point Y of Fig. 2a. This point is at a frequency below the frequencies `the transmission of which is affected by capacitance Il and above the-frequencies the transmission of which is aii'ected by condenser I5.

Jn E=1 12m-LJ. R11-T where I represents the current supplied to the input through terminals I and 2; E represents the voltage between terminals I and 2; R and C repupon a carrier wave to p Since the network II compensates for the variation in transmission with frequency caused by elements I5, I 3, II, it, of course, is designed relative to that network.

resent, respectively, the resistance and capacity of the elements of Fig. 1 designated by the reference numeral written as a subscript after the respective character; w represents frequency multiplied by the constant 21|- where'1r=3.1416; and 7 represents the imaginary quantity, V11. f

This nomenclature will be employed throughout the following.

Equation 1 is true only for frequencies below the point Y of Fig. 2a; i. e., below around 150,000 cycles. I

If G represents the overall mutual conductance of amplifier 5 then the current I1 at the output of amplifier 5 may be expressed by the following equation:

Now, neglecting the capacitance C23 and letting L21; i. e., the reactance of inductance 2|, equal zero, the impedance Zn of network II as reviewed from amplier 5 may be expressed as follows:

[ -R24+R26 ]R Substituting from Equation 2 for I1, and from Equation 3 for Zn;

Simplifying and substituting from Equation 1 for E:

man: s

If Raz-l-R1a=aRis, where ais a .real constant: Rn4+R2e=aRi1 and C1a=aCao, then from Equation 4 the following is obtained: y

the frequency Y if the above proportionalities be made. i Moreover, all of the quantities in Equation 5 are real quantities, which means that there is no phase shift between the current I supplied at terminals I and 2 and the voltage Ea supplied to amplifier 6 over the frequency range below the point Y.

6 and produces current Ie in network l2 where compensation for the effect of capacitance I4 at high frequencies is made.

Now, considering frequencies higher than that corresponding to point Y, it is necessary, as previously stated, that the time constant of the elements 3l and 32 equal that of the elements IB and Il or that %=Rc The series circuitcomprislng inductance 3| and resistance 32. having the same time constant as' the shunt circuit comprising capacitance Il and resistance I6, produces exactly equal and opposite effects upon the transmission through the system, and thus, except for theeffect of elements 35 and 33 at low frequencies, uniform amplincation over the entire band, exists between the terminals I and 2 and the input to amplifier 1.

Elements 35 and 33 may be necessary, however,

in order that the signal voltage be large enough at the low frequencies to override the low frecase after the 'signals have been transmitted through the amplifier`1, the low frequencies may be attenuated sufficiently to match the high frequencies as indicated by curve A' of Fig.` 2d and thus produce uniform ampliiication over the`55 band up tothe output terminals and signal intensity at the output well above the noise level of any subsequent amplifiers. c

While in this specication and claims I have referred to wide band amplifiers and have para0 ticularly mentioned the frequency band extending from ten cycles to four or five megacycles, it will, of course, be understood that my invention is readily applicable to ampliers operating over much narrower bands of frequencies. tion finds utility in any amplifier where the signal level to be amplified and the frequency range over which the amplifier must operate are such that the attenuating effects of shuntcapacitance cannot be compensated in a-single networkl of 'I9 the amplifier without undesirably reducing the.

- signal level.

While 'I have shown a particular embodiment 'of my invention, it will, of course, be understood My inven- 65 1. In an amplifier for producing uniform ratio between input current and output voltage, said amplier having resistance and capacity in shunt with its input to which said current is supplied, said current having frequencies extending over a wide band and having. intensities only slightly above the noise level of 'said amplifier, the method which comprises attenuating currents in the intermediate frequency portion of said band above the frequency of the most intense noise currents of the amplifier without changing the characteristic relation between intensity of voltage on said resistance and capacity-and frequency in the high frequency portion of the band, attenuating in a later stage of the amplifier low frequency currents to produce uniform amplification at all frequencies below said high frequency l 25 portion of the band and thereafter accentuating This voltage Ee is now amplified by amplifier quency accentuation occurs thereby to avoidv overloading said last mentioned stage with currents to be attenuated.

2. In an amplifier for producing 'uniform ratio between input current and output voltage, said amplifier having resistance and capacity in shunt with its input to which said current is supplied.

said current having frequencies extending over a wide band, the method which comprises attenuating currents in the intermediate frequency portion of said band above the frequency of the most intense noise vcurrents of the amplifier without' changing the characteristic relation between intensity of voltage on said resistance and capacity and frequencyin the high frequency portion of vthe band, amplifying the entire band, reducj ing the voltages having frequencies below said quency noise level ofthe amplifier 1. In that high frequency portion of the band to uniform thereafter accentuating the voltages in the high frequency portion of said band sufficiently to overcome the effec-t of said shunt resistance and' gapacityin said high frequency portion of the 3. The combination, in an amplifier for electrol motive forces existing across a capacitance at the input to said amplifier, said electromotive force having frequencies extending over a wide band and having intensity at low frequencies only slightly above the level of undesired low frequency currents, of a resistance across said capacity, a portion of said resistance being shunted by a second capacity, 'said portion and said second capacity being proportioned to reduce voltage across said first capacity above said low frequencies without affecting the characteristic relation between said voltage and frequency at high frequencies, means between stages -of the amplifier to produce uniform amplification at all frequencies below said \high frequencies V while maintaining the voltage above the noise level and means between later stages of said that I do not wish to be limitedthereto sincel amplifier to accentuate the high frequencies :o

produce uniform amplification at said frequencies.

4.7The combination, in a multistage amplifier, a circuit at the input to one of the stages of said amplifier having shunt resistance and capacity producing attenuation of high frequency currents in the band to be amplified, a circuit between stages in said amplifier having shunt resistance and capacity, an inductance in series with said last resistance, said inductance and said resistance having a time constant equal to the time constant of said first mentioned shunt resistance and capacity, a shunt` combination of resistance and capacitance in series with said second mentioned shunt resistance proportioned to reduce the attenuation caused by said inductance and the resistance in series with it of low tween stages in said amplifier having shunt rean inductance in series resistance, said inductance and said resistance having a time constant equal to the time constant of said first mentioned shunt resistance and capacity, a shunt combination of mission of high frequency currents.

7. In combination, an amplifier channel having shunt resistance and capacity to which current to be amplified is supplied, said current having such intensities and frequencies extending pling capacity,

form amplification ratio over a band of frequencies intermediate in said first mentioned band, and means, thereafter, to compensate the variation in amplification .of said amplifier with respect to frequency over the portion of said band below said intermediate portion, and a subsequent stage. of said amplifier having means to compensate the variation in amplification over the portion of the band above said intermediate frequency portion, thereby to produce uniform amplification over the entire band.

8. 'Ihe combination, in a wide band amplifier havingv resistance and capacity in shunt with the input thereof and additional capacity shunting a portion of said resistance, and having an interstage network comprising an interstage coupling capacity shunted bya second resistance and having shunt resistance at either side of said coupling capacit said first resistance, said portion and said additional capacity being proportioned to accentuate low frequency current with respect to current of intermediate frequency in the band to be amplified, and said coupling capacity, second resistance and shunt resistances being proportioned relative to said additional capacit said portion and first resistance to attenuate said low frequency currents to produce uniform amplification at alllow frequencies.

9. The combination, having resistance and capacity in shunt with the input thereof, and additionalcapacity shunting a portion of said resistance, and having an interstage network comprising a coupling capacity shunted by a second resistance and having shunt resistance at either side of said coupling capacity, the ratio ofthe sum of said shunt resistances to that part of said first resistance not shunted by said additional capacity being equal to the ratio of said second resistance to said portion of said first resistance, and these ratios both being equal to the ratio of said additional capacity to vsaid series capacity.

10. The combination, in a wide band amplifier having resistance and capacity in shunt with the input thereof, and additional capacity shunting a portion of said resistance, and having an interstage network comprising an interstage coupling capacity shunted by a second resistance and having shunt resistance at either side of said couthe ratio of the sum of said shunt resistances to that part lof said first resistance not shunted by said additional capacity being equal to the ratio of said second resistance to said portion of said first resistance shunted by said additional capacity, and these ratios both being equal to the ratio .of said additional capacity to said coupling capacity, and an amplifier subsequent to said network amplifying the currents of all frequencies in said band, said amplication over the entire band.

Il wlfhe method of amplifying currents having frequencies extending over a wide band in a mulhaving input capacity undeating said low frequency currents,

in a wide band amplifier frequency currents relative to intermediate frequency currents, again amplifying the entire band and then attenuating said low frequency currents to produce uniform amplification at all frequencies in the band.

12. In a multistage amplier for currents having frequencies extending over a wide band and having input capacity undesirably attenuating high frequency currents in said band, means in said input circuit to accentuate low frequency currents in said band to a level well above the low frequency noise level of the first stage of saidV amplifier, means attenuate said low frequency y in said amplifier subsequent to said third stage to currents in a part of said amplifier subsequent to said iirst stage sumciently to permit amplification of the entire band in amplifier without low frequency overloading of said other stage, means between said other stage and a third stage to accentuate both low and high frequency currents in said band relative to currents of intermediate frequency, and means attenuate said low frequency currents to the level of said high frequency currents thereby to produce uniform amplification over said band.

DONALD E. NORGAARD.

another stage of said

Images