US2265291A - Broad band amplifier - Google Patents

Description

Dec, 9, 1941. U. KNICK 2,265,291

BROAD BAND AMPLIFIER Filed Aug. 29, 1940 /n ven for:

Patented Dec. 9, 1941 2,265,291 BROAD BAND AMPLIFIER Ulrich Knick, Berlin-Zehlendorf, Germany, assignor to Fernseh G. m. b. H., Berlin-Zehlen- 'dorf, Germany Application August 29, 1940, Serial No. 354,737 In Germany September 7, 1939 3 Claims.

The invention relates to amplifier arrangements particularly for the amplification of broad frequency bands.

It is an object of the invention to provide an amplifier arrangement adapted for the uniform amplification of broad frequency bands for television and similar purposes. It is a further object to provide an amplifier connected with its input circuit to a television pick-up tube or a photo-electric cell, having an output with uniform amplification over the complete range of input signal frequencies.

It is known to use an amplifier in which the output resistor of the television pick-up tube has a larger value than would be required by the width of the frequency band to be amplified. This has the advantage that the input voltage of the amplifier is much larger than in the usual arrangements with the exception of the highest frequencies so that the amplifier is safe against hum and disturbing noise. Arrangements of this kind however hav the drawback that the frequency response is not uniform and that it is necessary to amplify the higher frequencies more than the lower frequencies in order to obtain a uniform amplification over the entire range.

According to the invention a uniform amplification is obtained by means of a very simple arrangement. An element comprising a condenser and a resistor is arranged in the cathode circuit of an amplifier tube to the grid of which is applied the uncorrected input voltage. This element is so dimensioned that the resistor is bypassed by the condenser only for the highest frequencies so that for all medium and low frequencies below a critical value the amplification of this tube is determined by the comparatively larg cathode resistor and is therefore low for these frequencies. The amplification is increased for high frequencies as a consequence of the capacitive by-pass of the cathode resistor. In such an arrangement the increase in amplification with increasing frequency is extremely gradual until the effective impedance of the condenser equals the internal impedance of the amplifier tube. For values of the effective impedance of the condenser smaller than the internal resistance, the amplification then increases rapidly with increasing frequency. In order to emphasize lower frequencies, it would then be necessary to make the condenser larger and thereby its impedance smaller with respect to the internal impedance of the tube, which would tend to decrease the over-all amplification of the tube.

According to the invention the increase of the effective amplification of .an amplifier with single frequency is enhanced by providing means for making the voltage of the by-pass condenser substantially independent of the frequency with-in the limits of the frequency band to be transmitted. In order to produce such a voltage at the by-pass condenser a negative resistance element is placed in series with the condenser having approximately the same value as the internal resistance of the amplifier tube. For this purpose a small resistor is placed into the cathode lead of the subsequent amplifier tube and the bypass condenser is connected to the end of the resistor connected-to the cathode of this following tube. The resistor situated between the cathode of the subsequent tube and ground has the phase of a negative resistance in consequence of the phase reversal of the first tube and is so dimensioned that its voltage is equal to the drop of voltage at the cathode of the first tube. The bypass condenser carries therefore a current increasing with the frequency. The anode current of the amplifier will therefore also increase with higher frequencies.

Other aspects of my invention will be apparent or will be specifically pointed out in the description forming a part of this specification, but I do not limit myself to the embodiment of the invention herein described, as various forms may be adopted within the scope of the claims.

The single figure of the drawing shows a circuit arrangement embodying the invention.

Th figure of the drawing represents a circuit of the last stage and its preceding stage of a picture signal amplifier disposed in the camera of a television pick-up tube. The picture signals amplified in a number of preamplifier stages (not shown) are applied by way of input lead I to the circuit. The input lead contains a condenser 2 of P and a grid resistor 3 connected to the control grid 4 of an amplifier tube 5. The cathode circuit of tube 5 contains a fixed resistor 6 of l kOhm connected in series relation with an adjustable resistor l of l kOhm. The screen grid 8 of tube 5 is connected by way of a lead 9 to the positive terminal of a source of potential indicated by the plus sign and by way of a condenser ID of 16 l to ground. The anode of tube 5 is connected to the anode resistor I l and by way of a condenser I2 of 50 ,u.,u.F to the grid M of tube 15 and to the grid leak resistor 13 of this tube. The output of tube I5 is taken off from line I! connected to the anode resistor l6 of this tube. The cathode of tube 5 is connected to the cathode of tube l5 by means of a by-pass condenser ill of 500 P. A series arrangement consisting of the drop across the resistor l9 and therefore the cathode potential of tube l5 or the potential of the terminal of the condenser I 8 connected thereto is in opposite phase to the voltage developed in p the cathode circuit of tube 5 across resistors 6 and 1.

circuit of tube 5 and as previously mentioned the high frequencies are amplified to a higher degree than low frequencies. The adjustable resistor 1 in the cathode circuit of tube 5 enables an adjustment of the frequency limit above which the amplification is increased.

What I claim is:

l. A signal amplifying arrangementfor uniform amplification of signals having a wide band of frequencies comprising an electron discharge tube having a cathode, a control grid, and an anode, an input circuit connected to said control grid for applying thereto signals to 'be amplified, an output circuit connected to said anode for developing uniformly amplified signals, a circuit connected to said cathode comprising a resist ance element connected in parallel relation to a series combination of a capacitance element and an element capable of exhibiting a negative resistance in the order of the internal resistance of said tube. I 2. A signal amplifying arrangement for uniformamplification of signals having a wide bandv of frequencies comprising an electron discharge tube having a cathode, a control grid and an anode, an input circuit connected to said control grid for applying thereto signals to be amplified, an output circuit connected to said anode for developing uniformly amplified signals, a resistance element connected to said cathode, a capacitance element connected in parallel relation to said resistance element, and means connected in series relation with said capacitance element for maintaining the voltage developed across said capacitance element substantially independent of The resistor [9 therefore has the effect of a negative resistance in relation to thecathode 7 frequency over a predetermined frequency band.

3;:A 'signal amplifying arrangement for uniform amplification of signals having a wide band of frequencies comprising a first electron discharge tube having a cathode, a control grid, and

' an anode, an input circuit connected to said control grid for applying thereto signals to be amplified, an output circuit connected to said anode for developing uniformly amplified signals, a resistance element connected to said cathode, a

second electron discharge tube having a cathode,v

a control grid and an anode, an input circuit connected to said last-named control grid and coupled to said output circuit of said first tube, a resistance element connected to said cathode of said second discharge tube, a capacitance element connecting said cathodes, said last-named resistance element-being s0 proportioned as to exhibit a negative resistance equal in magnitude to the internal resistance of said first discharge tube, and an output circuit connected to said anode of said second discharge tube for developingsubstantially uniformly amplified signals.

ULRICH KNICK.

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