US2212204A

US2212204A - Amplifier

Info

Publication number: US2212204A
Application number: US249221A
Authority: US
Inventors: Hepp Gerard
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1938-01-04
Filing date: 1939-01-04
Publication date: 1940-08-20
Anticipated expiration: 1957-08-20
Also published as: GB510503A; BE431973A; FR848402A; NL58853C; DE1080610B

Description

Aug. 20, 1940. EPP' 2,212,204

AMPLIFIER Filed Jan. 4, 1939 2 Sheets-Sheet l INVENTOR GERA RDv H PP Wf/L/ ATTORNEY Aug. 20, 1940. HEPP 2,212,204

AMPLIFIER Filed Jan. 4, 1939 2 Sheets-Sheet 2 INVENTOR GERARD HEPP BY j-kgg ATTORNEY Patented Aug.. 20, 1940 UNITED STATES PATENT AMPLIFIER Delaware Application January 4, 1939, Serial No. 249,221 In Germany January 4, 1938 5 Claims.

. This invention relates to amplifying arrangements particularly adapted for uniform amplification of broad frequency bands including Very low frequencies.

Wide band amplifiers having uniform amplification or frequency-independent characteristics are of considerable importance in electrical arts, and especially in television. Hitherto, the construction of such amplifiers have been exceedingly dimcult and costly and, in many cases, could only provide uniform amplification at the cost of non-uniform time delay of signals of different frequency known as non-linear phase response characteristic. This invention provides a relatively simple and cheap means of obtaining uniform amplification through a wide band of frequencies and at the same time preserving uniform phase response.

Accordingly, it is an object of this invention to provide an improved wide band amplifier.

Another object of the invention is to provide a simple wide band amplifier having uniform amplification and time delay.

Other objects of my invention Will become apparent upon reading the detailed description, together with the drawings.

In the drawings,

Fig. 1 schematically shows a single stage amplifier having embodied therein impedances chosen in accordance with my invention,

Figs. 2, 3, 5 and 6 show modifications of the embodiment in Fig. 1 in more detail and structural elements shown in Fig. 1; while Fig. 4 shows a circuit arrangement for reducing the efiect of the stray capacity of a large condenser. I

As is well known, the frequency dependency of an amplifier is first of all determined by the frequency dependency of the coupling means provided between the individual amplifying stages, such as the impedance Z8. in the anode circuit of an amplifying tube, the impedance Z2 in the grid circuit of the succeeding tube and the coupling impedance Z1 between the anode circuit and the grid circuit. Furthermore, the frequency-dependency of an amplifier, more particularly at low frequencies, is materially afiected by the impedance Zk which is inserted in the cathode lead for obtaininga suitable grid bias and which usually comprises a resistance and a condenser connected. in parallel therewith. When using tubes having a plurality of grids, the screengrid lead may further include an impedance ZS which serves for smoothing the screen-grid voltage and the common lead of anode and screen grid may comprise an impedance Z (such as the internal impedance of the source of anode voltage). These impedances, also, affect the frequency-dependency of the amplifier.

Considering all of the above mentioned impedances, we obtain the diagram of connections of an amplifying stage represented in Fig. 1.

The present invention allows by means of such a circuit arrangement, which includes one or more frequency-dependent impedances, to obtain a frequency-independent amplification i. e. a frequency-independent ratio between the voltage 62 set up between the' output terminals A1A2 and the voltage 61 set up between the input terminals E1, E2.

The amplifier may comprise a plurality of am- I plifying stages of the type illustrated in Fig. 1,

in which case the invention allows not only of rendering each individual stage frequency-independent, but also to compensate in one stage the frequency-dependency of another stage.

According to the present invention the impedance Za in the anode-circuit and the impedance Z2 between the output terminals of the amplifying stage consist for this purpose of a resistance in series with impedances which are proportional respectively to the impedance Zk in the cathode lead, to the impedance 25 in the screen-grid lead, to the impedance Zc in the common anodeand screen-grid lead, which impedances form part of the said amplifying stage and/or of another amplifying stage, whereas the impedance Z... furthermore comprises impedances proportional to the coupling impedance Z1 in the said amplifying stage and/or in another amplifying stage.

The arrangement of an amplifying stage according to the invention is represented in Fig. 2. As appears therefrom, the anode impedance Za consists of a resistance Ra in series with impedances ZS, flZc, 'yZk and 5Z1 which are proportional to the impedances ZS, Zc, Zr and Z1 respectively, whereas the impedance Z2 between the output terminals A1 and A2 consists of a resistance in series with impedances The proportionality factors a, c, 'y and 8 must be chosen so as to fulfill the following conditions.

cc Raqss fi =(1+q) (RaSs-1) y =Ra(SI-Ss) (1+q) 6 =any positive Value EE=Ra( +q) Ss wherein: 1

q is the ratio between the screen grid, alternating current s and the anode alternating current ia, which ratio may be considered to be constant,

SS is the mutual conductance of the characteristic curve of the anode current/screen-grid voltage, and

S is the mutual conductance of the characteristic curve of the anode current/control-grid voltage.

When these conditions are observed the amplification amounts to 2 e1SRa and this is consequently frequency-independent. The iinpedances Z5, Z and Z1; may, for instance comprise resistances Rs, Re, Rk together with parallel condensers Cs, Cc and Ck as shown in Fig. 3'. The impedances ZS, 5Z0 and "YZk in the anode circuit must then comprise resistances ozRs, [3R0 and 'yRk together with parallel condensers and In the same manner the imp-edances 5 i i 6 7 5 Z and 6 J];

between the output terminals A1 and A2 are constituted by the parallel connections of resistances a c l R 5R and R and condensers 6 6 i C, and (J,, or e y In Fig. 3, the coupling impedance comprises a condenser C1. A condenser proportional thereto must consequently be interposed in the anode circuit. However, this blocks the direct current of the anode and must consequently be bridged by a resistance 631. Since,

on the one hand, this resistance may not be given a high value on account of the excessive voltage drop, which otherwise would be caused by the anode current and may, on the other hand, not be too small, since otherwise amplification of the low frequencies would depend on passes direct current.

the frequency, a resistance R1 is, according to This condenser 0 must have a sufficient capacity so that its impedance may be neglected with respect to the resistance R1 even with the lowest frequencies to be amplified. To avoid that the considerable capacity with respect to earth of such a large condenser may affect the amplification of the high frequencies the resistance R1 is -preferably divided into two'par ts R between which the condenser C is connected as shown in Fig. 4.

The proportionality factor B=(1+q) (Russ-1) may become negative if Ra Ss 1, which would involve a negative impedance ,BZc in the anode circuit, which cannot be realized in most cases.

Then it is advantageous to make use of the circuit arrangements shown in Fig. 5 or 6.

The circuit arrangement shown in Fig. 5 may be deduced in the following manner from the circuit arrangement shown in Fig. 2. When interposing in the latter an impedance in series with Z1 a proportional impedance (l-l-q)Zc must be interposed in the anode circuit. Together with the impedance 52 a positive impedance.

then results.

In Fig. 6, the impedance which is positive for negative 5 is connected in series with Z1; in this case the impedance proportional to Z0 in the anode circuit may be entirely omitted.

It will be appreciated that the invention may also be used in amplifiers in which one or more of the impedances Zk, Z5 and Z0 are equal to zero. Of course, the impedances proportional thereto, which are included in Za and Z2, are then also equal to zero.

Furthermore, it is possible in an amplifying stage to compensate in another amplifying stage the influence of one or more of the impedances Zk, Zs, Z'c and Z1 included in the first-mentioned amplifying stage, by interposing in the impedances Z3. and Z2 of this other stage impedances proportional to Zk, Zs and Zc. In

this case, the proportionality factors a, 5, 'y, 5'

must, of course be chosen in accordance with the particularities of the tubes and circuit arrangements in use.

What is claimed is:

l. A wide band amplifier having uniform amplification comprising an electron discharge tube having a cathode, control electrode, screen grid and anode, a voltage supply source, a common lead, a first impedance connected between said cathode and common lead, a second impedance connected between said screen grid and a third impedance, said third impedance being connected to the common lead through the supply source, a coupling impedance connected between the anode and a first output terminal, a second output terminal connected to the common lead, an anode circuit comprising a first resistor, a fourth impedance proportional to said second impedance, a fifth impedance proportional to said third impedance, a sixth impedance proportional to said first and a seventh impedance proportional to said coupling impedance, said resistor and fourth, fifth, sixth and seventh impedances being serially connected between the anode and said third impedance, and a second resistor connected in series with a plurality of impedances proportional respectively to said first second and third impedances, said second resistor and plurality of impedances being connected across the first and second terminals.

2. An amplifier as claimed in claim 1 and wherein each of the named impedances comprises a parallelly connected resistance and capacity.

3. An amplifier as claimed in claim 1 and wherein the said coupling impedance comprises connected in series in the order named a first resistor element, a first condenser element, and a second resistor element, and a second condenser connected across the serially connected elements.

4. An amplifier as claimed in claim 1 and comprising in addition a further impedance proportional to the third impedance, said further impedance being connected in series with said coupling impedance and to said anode.

5. A wide band amplifier having uniform amplification comprising an electron discharge tube having a cathode, control electrode, screen grid and anode, a voltage supply source, a common lead, a first impedance connected between said cathode and common lead, a second impedance connected between said screen grid and a third impedance, said third impedance being connected to the common lead through the supply source, a coupling impedance connected between the anode and a first output terminal, a second output terminal connected to the common lead, an anode circuit comprising a first resistor, a fourth impedance proportional to said second impedance, a fifth impedance proportional to said third impedance, a sixth impedance proportional to said first and a seventh impedance proportional to said coupling impedance, said resistor and fourth, fifth, sixth and seventh impedances being serially connected between the anode and third impedance, a second resistor connected in series with a plurality of impedances proportional respectively to said first, second and third impedances, said second resistor and plurality of impedances being connected across the first and second terminals, and terminal means to impress control voltage between said control electrode and said common lead.

GERARD HEPP.