US1904524A - Amplifier - Google Patents

Description

April 18, 1933.

K. FOSTHUMUS AMPLIFIER Filed Feb. is, 1951 II a a main INVENTOR KLASS POST HUMUS ATTORN EY Patented Apr. 18, 1933 STATES PATENT OFFICE KLAAS POSTHUMUS, OF EINDHOVEN, NETHERLANDS, ASSIGNOR TO RADIO CORPORA- T1017 OF AMERICA, A CORPORATION OF DELAWARE AMPLIFIER Application filed February 18, 1931, Serial No. 516,573, and. in the Netherlands March 26, 1930.

This invention relates to improvements in amplifiers, and especially to improvements in means for rendering the amplification of an amplifier independent of the frequency of the oscillations impressed upon the amplifier input. It has been shown that the input circuit of an amplifier can be coupled with part of the output impedance in such manner that for all frequencies the alternate potential set up between the terminals of the output impedance is proportional to the voltage amplitudes of the incoming oscillations. In a circuit arrangement of this type the impedance occurring in the external circuit is only considered and not the plate-filament capacity. Especially in the case of higher frequencies, however, this capacity may also have a very annoying effect.

Now the present invention has for its object to provide means for neutralizing the unevenness of the amplification caused by this capacity. It is not possible to directly utilize part of this capacity for back coupling. Therefore a capacity in series with a resistance is inserted in the output circuit in parallel to this internal tube capacity, the input circuit being coupled with part of the first mentioned capacity in combination with the back coupling above referred to.

The currents passing through both capacities have the same phase. When coupling the input circuit with part of the capacity interposed in the output circuit, the same effect may be obtained as if it were directly coupled with the plate filament capacity. Since the total capacity is greater than this inserted capacity, the part of the latter which has to be coupled with the input circuit, will be greater than that of the remaining impedance in the output circuit.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the

invention itself, however, as to both its or- I ganization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically one circuit organization whereby my invention may be carried into efiect.

In the output circuit of the thermionic tube 1 an impedance 2 is inserted, which serves for coupling with the next tube 3, and in series therewith an ohmic resistance R, of which a part R is coupled to the input circuit. A capacity C is connected in parallel to the internal capacity of the tube denoted in dotted lines by C, the capacity also being in series with the ohmic resistances R and R The resistances R and R may be adjustable. Due to the anode currents, voltage variations are set up at these ohmic resistances, said variations being returned in opposite phase to the grid of the tube by a transformer 3 having an amplification factor equal to unity. Instead of this transformer 3, any suitable transmission element may be used; for example, a triode having an amplification factor 1.

One terminal of impedance 2, which is connected to the negative side of the anode potential source E, is connected to the grid of tube 3 through the direct current blocking condenser 3". The cathode of tube 3 is connected to the cathode side of transformer 3, the usual grid bias resistor 4 being connected between the grid and cathode of tube 3.

The following analysis results in the values to be given to R and R in order to obtain a uniform amplification: Letting R denote in this circuit arrangement the internal resistance of the tube; Z the external impedance, the plate filament capacity being included; R, the part of the output impedance serving for coupling with the next tube, R can thus be considered equal to the value Z would have if C=C =O; s the mutual conductance; g the amplification factor; 12,, the anode alternating voltage; z', the anode al-' ternating current; e the grid voltage set up by signals; and 42 the grid voltage set up by back coupling, then:

1 1 i I 12,,( S (1),, 22 (I) Z is constituted by the impedance R which for example, may be inductive, the capacities C and C and the resistances of R and R which may be neglected relatively to the values of R C and C. 1

V is the sum of the tensions set up by R, and C respectively in R and R +R It has been assumed that the resistance of the primary Winding of the 1 to l transformer 3 is so great, that the currents passing therethroughmay be neglected.

Hence the Equation (I) maybe written:

wherein the terms and 8 (e are independent of the frequency, whlle all other terms depend thereon.

Assuming therefore,

was), a

This condition is satisfied if J l S R 01 S n 1, and

Since SR 1,it follows therefrom that A uniform amplification throughout the whole frequency range may consequently be obtained, by giving E and such values that R R like G: O and SR =L Preferably C is given about the same value as C.

While I have indicated and described one arrangement for carrying my invention into effect, it will be apparent to one skilled in theart that my invention is by no me ans limited to the )articular organization shown and described, ut that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

Vhat I claim is 1. In combination, in an amplifier, an electron discharge tube provided with an input and output circuit, a succeeding tube, a coupling path between the output circuit of the first tube and the input circuit of the second tube, said path including an impedance in series with a resistor, a second path in shunt with said impedance and including a condenser in series with a second resistor, and means for transmitting the drop of potential across a predetermined. portion of tial across said second resistor and a presaid first resistor to the input circuit of the first tube.

2. In combination, in an amplifier, an electron discharge tube provided with an input and output circuit, a succeeding tube, a coupling path between the output circuit of the first tube and the input circuit of the second the ratio of the magnitudes of said resistors being equal to the ratio of the magnitudes of the condenser and the cathode to anode capacity of the first tube.

3. In combination, in an amplifier, an electron discharge tube provided with an input and output circuit, a succeeding tube, a couqr pling path between the output circuit of the first tube and the input circuit of the second tube, said path including an impedance in series with a resistor, a second path in shunt with said impedance and including a condenser in series with a second resistor, means I)? for transmitting the drop of potential across a predetermined portion of said first resistor to the input circuit of the first tube, means for adjustably connecting the-condenser to the second resistor, means for adj ustably 0011- All necting the second resistor to the first resistor, and said transmitting means consisting of a l to 1 transformen i I i. In combination, in an amplifier, an elec tron discharge tube provided with an input li and output circuit, a succeeding tube, a coupling path between the output circuit of the first tube and the input circuit of the second tube, said path including an impedance in series with a resistor, a second path inshunt with said impedance and including a condenser in series with a second resistor, and means for transmitting the drop of potendetermined portion of said first resistor to t the input circuit of the first tube. I

KLAAS POSTHUMUS.

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