US2202361A - Amplifier circuit - Google Patents

Description

May 28, 1940.

H. P. J. VERBEEK ET AL AMPLIFIER CIRCUIT Fil ed Oct. 28, 1936 INVENTORS HENRI PETRUS JOHAN venom m nikmwsnommcusuusimms BY LlEGEN A'ITORN EY Patented May t 'umrrosmrrs f mm AMPLIFIER CIRCUIT Henri Petrus .Johan Verbeek, Voorbnrg, and Bernardus "Dominicus' Hubertns Tellegen, Eindhoven, Netherlanda assignors, by mesne 'as-. signments, to Radio Corporation of America; 1 New York, N. Y., a corporation of Delaware i Application October 28, 1936, Serial'No. 107,020"

In Germany. November '11, 1935- I 2 Claims. (Cl. 179-171) I t t t I arrangement is consequently/S25. For the circuit arrangement of F'ig.'1, the amplification for oscil- This invention has reference to a circuit arrangement for amplifying electric oscillations which transmits a particularly large range of frequencies, for example, from to 2 l0 cycles. Such amplifier arrangements are used inter alia for television purposes.

It'is well-known that in the usual aperiodic amplifiers (r esistance amplifiers) amplification decreases inthe case of comparatively high fre- .quencies; due to the unavoidable parasitical capacity between the anodeand the cathode of the amplifier. valves and between the conductors connected to said electrodes. In order to increase amplification for comparatively high frequencies,

Q acteristicis obtained. I According to the inventioma further improve-' it has .been proposedbefore that the anode circuit of the amplifier valves should include inv series an-inductance and a resistance. Thus, as amat .ter. of fact, a flatter curve .of the frequency charment is ensured in anamplifier circuit arrangement in which the anode circuit of one or more amplifier valves includes an impedance formed by the series combination ofan-inductance and a resistance by connecting in; parallel with part of this impedancea capacity or the. series combination ofan inductance and a capacity.

In order that the invention may be clearly understood and readily carried into effect, it will now be described more fullyhereinafter with.

reference to the accompanying drawing, in which: Figs. 1 and 2 show familiar amplifier circuits;

' Figs. 3, 4 and 5 show three examples of circuitv arrangements embodying the invention.

Fig. 1 showsa customary resistance amplifier. The oscillations to be amplified are supplied to the terminals a and 12, whereas theoscillations amplified are obtained from/the terminals 0 and d which are connected to the control grid and the cathode of a second amplifier valve (not shown). In the case of particularly low 'frequencies of the oscillations to be, amplified a decrease in amplification occursas aresult of the influence of the coupling condenser'C and ofthe leak R This influence is, however, negligible in the case of comparatively high frequencies.

If the reaction of the anode is but small, an 'a1-.

ternating current 'SV occurs in the anode cir-.

cuit by reason of the voltage Vg supplied between the control grid and the cathode, S desighating, the mutual conductance of the amplifier valve. For comparatively high frequencies, the voltage between the terminals 0 and. dis consequently: SV Za, Za being the impedance 'ofthe anode circuit. The amplification of the circuit ations having .an angularfrequencyg is:

in which Ca is theparasitical capacity between [the anode. and cathode of the amplifier valxjzeand between the conductors fconnected to the elec trodes. Forlower frequencies, the' amplification is, approximately Ve SR. COnse uentIy For ensuring a frequency characteristic thecurve of which is as'fiatj'as possible, the factor 'a should be a minimum, that is to say R should be amini mum. The fiatterthe curve of the frequencycharacteristic; the'fsmall eriis consequently the amplification. t f f Thus, when*considering the familiar circuit arrangement of Fig. 2 in which the anode circuit includes" in -series an inductance L and a resistance R, the following equation maybe set up for this circuit arrangement.

I sible. It is found that in the case of equal amplification a flatter curve of the frequency characteristic is obtained than in the circuit arrangement shown in,Fig.;1.

According to the invention, the circuit 'arrangements shown in Figs. 3 and 4 have a ca pacity C connected in parallel with part of the impedance of the anode circuit, which is constituted by the series combination of an inductance L and a resistance R, the capacity C being connected in the circuit arrangement shown in Fig. 3 in parallel with the resistance R, and in the circuit'arrangement shown in Fig. 4 in parallel with the inductance L. As an alternative.

the capacity C may be connected in parallel with part of theresistance- R and/or with part of'the inductance L. f f

In the circuit arrangements shown in Figs. 3

and 4, calculation discloses for Vw/Vn a form of the shape:

The curve of the frequency characteristic is rendered as flat as possible by making a1=a2, b1=bz and 01:02 and by reducing (is as far as possible.

When in the circuit arrangements shown in Figs. 3, 4 and 5, the said conditions (001::22, and

so forth) are dropped, the frequency characteris tie is possessed of a few maximum or minimum values. These maximum and minimum values may be used in certain cases for the purpose either of increasing the range of frequencies transmitted or of obtaining higher amplification.

When an amplifier circuit arrangement according totheinvention is used for television purposes it is not only desirable that the frequency characteristic curve should beflat, but also that .the phase .displacement (p brought about by the amplifier should be proportional to the frequency of the oscillations to be amplified since otherwise distortion ofthe picture occurs. Thus, in the amplifier circuit arrangement the condition should be observed that the ratio /w should be constant throughout the range of frequencies. It is possible also to satisfy this requirement for a large range of frequencies by means of the circuit arrangements according to the invention.

What is claimed is:

l. A circuit arrangement for amplifying electric oscillations comprising a plurality of vacuum tubes, at least one of said tubes having an anode circuit including an inductance and an ohmic resistance connected in series, and a second inductance and a condenser connected in series across said ohmic resistance, the circuit elements in said anode circuit being so chosen that in the equation representing the ratio of the amplification at an arbitrary frequency V01 to the amplification at a second and lower frequency V0 V l.+c w +b ti tc w -td a wherein the cocmcients cm, In, 11 are functions of said circuit elements at the frequency Vw and the coefficients (12, b2, 02, d2 are functions of the said circuit elements at the frequency V0, the coefficients of the terms of equal order in the numerator and denominator being substantially equal to each'ether andthe coefficient 112 being as small as possible whereby the response of said circuit is substantially flat over the band between said two frequencies.

2. A circuit arrangement for amplifying electrical oscillations having input and output terminals and comprising a vacuum tube having at least an anode a cathode and a control grid, said control grid and cathode being connected to said input terminals, 2. series connection of an inductance and an ohmic resistance connected between said anode and a source of anode potential, said inductance being adjacent said anode. a second series connection of an inductance and a condenser connected in parallel with-said ohmic resistance,a second. condenser connected between said anode and one of said output terminals, and

the other of said output terminals being connected to said cathode, the elements in said anode circuit being so dimensioned that the response of said amplifier is substantially uniform over a Wide band of frequencies.

HENRI PETRUS J OHAN VERBEEK. BERNARDUS DOMINICUS HUBERTUS TELLEGEN.

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