DE1063656B - Bridge circuit for decoupling the oscillator interference voltage in grid base precursors, in which the anode-side resonant circuit is formed as a pot circle from the series connection of the grid-anode capacitance, a tuning inductance and a tuning capacitance - Google Patents

Description

GERMAN

In the case of receiver input stages, it is known that the oscillator interference voltage occurring at the antenna input must be kept as small as possible. The oscillator voltage on the mixer tube is indeed through the selective HF circuit or the HF band filter between the pre- and mixer stage attenuated at the anode The rest of the oscillator interference voltage remaining in the pre-tube is transferred to the antenna terminals. according to the amount of back attenuation of the pre-tube.

In the case of cathode base precursors, the back attenuation is increased in a known manner by neutralizing the reaction capacitance C _ga between the grid and the anode of the tube. This achieves a high degree of decoupling between the input and output circuit of the preamp.

Furthermore, it is already known in the case of cathode base stages, the internal resistance of the tube by a corresponding To neutralize resistance.

The grid base circuit is used in pre-amps, especially at high frequencies. The retroactive effect is then determined by the retroactive conductance between the cathode and anode. In the simplest case (assuming sufficiently short transit times and grid inductance), this is composed of the parallel connection of the retroactive conductance Gi = SD (S tube steepness, D penetration) and the retroactive susceptibility j · ω ■ C _ak , where j is the imaginary unit , ω is the angular frequency and C _{ak is} the capacitance between the anode and cathode of the tube.

The reactive component can be neutralized in a known manner. You reach for the exit a partial voltage, turns it 180 ° in phase and feeds it back to the input.

The invention shows a possibility of the oscillator interference voltage still present at the anode of the pre-tube, which is coupled to the antenna input via the ohmic internal resistance of the pipes, to compensate in an extremely simple way.

■ Based on a bridge circuit for decoupling the oscillator interference voltage in the grid-base pre-stages, in which the anode-side resonant circuit as a pot circle from the series connection of the grid-anode capacitance, a tuning inductance and a tuning capacitance is formed according to the invention suggested that the internal resistance, the grid-anode capacitance of the tube and the tuning capacitance resulting in a bridge circuit in which the tuning inductance is in the bridge zero branch, are added that between the cathode of the tube and the connection point of the tuning capacitance with the Tuning inductance a resistor is connected, which according to the adjustment condition

Bridge circuit for decoupling

the oscillator noise voltage

for grid-based pre-stages,

in which the anode-side resonant circuit as a pot circle from the series connection.

the grid-anode capacitance,

a tuning inductance.

and a tuning capacitance is formed

Applicant:

Telefunken G.m.b.H., Berlin NW 87, Sickingenstr. 71

Robert Maurer, Ulm / Danube, has been named as the inventor

is sized.

In the exemplary embodiment in FIG. 1, a grid base preliminary stage is shown. The grid G is here at ground potential. K is the cathode and A is the anode. The internal tube capacitances between the grid anode C _ga and the grid cathode C _k g are shown in the tube. The is at the cathode input of the grid base stage

Antenna input circuit E.

Ri = - ^ r is

the return

effective resistance of the tube. In the exemplary embodiment, the anode circle is a 2/2 cup circle. The inductance L _{1 of} this circle, which is connected to the tuning capacitance C _A at point Z, has been drawn in as a concentrated element for the sake of simplicity, although the inductance is actually distributed over the length of the inner conductor of the cup circle. The capacitor Ca at the base of the 2/2-pot circle is used for coordination. The mixer is coupled to the λ / 2 cup circle in the usual way. In order to prevent the interference voltage Ustar from acting on the antenna circuit E via the reaction resistance R _{t of} the tube, a bridge circuit is implemented according to the invention. At the hot end of the base capacitor C _{A of} the Λ / 2-pot circle becomes

,, ..,. 909 608/293

a counter voltage is tapped, which is fed back to the cathode of the tube via the (ohmic) resistor R _2. This voltage is equal to that at the cathode via the feedback effective resistance; The interference voltage generated by the tube is practically in phase opposition, since it is tapped approximately at the end of the A / 2 cup circle facing away from the anode A and the switching capacitances caused by the wiring cause a corresponding phase shift. The amplitude of the resistor R% is dimensioned accordingly so that the undesired interference voltage is compensated for at the cathode K. The antenna input is thus decoupled from the anode circuit of the grid base stage and thus also from the downstream oscillator.

In FIG. 2, the equivalent image of the circuit shown in FIG. 1 is drawn. As can be seen from this, the arrangement represents a bridge circuit. The zero branch is formed by the inductance L _{1 of} the A / 2 cup circle at the anode. The other two bridge branches are formed by the ohmic resistors R ₁ and Rz as well as by the two capacitances C _ea and C _A. The designation of the individual elements and the bridge points is the same as in Fig. 1. The bridge condition for this arrangement is:

τ? ■ ff ° ρ

For C _A = constant, the arrangement is frequency-independent.

Claims (1)

Claim: Bridge circuit for decoupling the oscillator interference voltage in grid base precursors, in which the anode-side resonant circuit is formed as a pot circle from the series connection of the grid-anode capacitance, a tuning inductance and a tuning capacitance, characterized in that the internal resistance (Ri), the grid-anode Capacitance (C _ea ) of the tube and the tuning _{capacitance (C A} ) thereby to form a bridge circuit in which the tuning inductance (L ₁ ) is in the bridge zero branch, that between the cathode (K) of the tube and the connection point (Z) of the Tuning capacitance with tuning inductance a resistor (R ₂ )
is switched according to the calibration condition C ₁ , is sized. Considered publications: German Patent No. 593 050;
U.S. Patent Pencil No. 2,426,185;
W. Taeger, "Transistor Pocket Book", Berlin, 1957, p. 129. 1 sheet of drawings