DE1263850B - Electrically adjustable voltage divider with low non-linear distortion - Google Patents

Description

Federal Republic of Germany

JLjLA

german 4μέ1® & patent office

EDITORIAL

Int. Cl .:

H03g

German class: 21 a2- 18/07

Number:
File number:
Registration date:
Display day:

T 29757 VIII a / 21 a2
November 10, 1965
March 21, 1968

The invention relates to an electrically adjustable voltage divider, in particular for level regulators in carrier frequency, directional radio and vocoder devices, in which according to FIG. 1 in a manner known per se (W. Gosling, Circuit Application of Field Effect Transistors - Part 3, Brit. Com. And Electronics, Vol. 11, No. 12 [December 1964], ρ 856 to 858) the input signal alternating voltage U ₀ is applied to the series circuit of a resistor R ₁ and the current path between the source and drain electrode DS of a field effect transistor FET and the output voltage U _{1 is} tapped via this current path. The voltage divider ratio ^ / EZ ₀ can be set in a known manner by the direct voltage U _{r applied to the control electrode G.} A possibly existing substrate connection B of the field effect transistor is in known circuits (DM Griswold, Application Considerations for RCA 3 N 98 and 3 N 99 Silicon MOS Transistors, RCA Application Note AN-201) in the manner shown in dashed lines with the input and output of the Voltage divider common terminal (earth) connected. The term “substrate” here refers to the semiconductor material used as the basis for the field effect transistor, into which the current path is diffused with a doping opposite to that of the substrate.

However, this known arrangement has the major disadvantage that the differential resistance of the current path of the field effect transistor is controlled not only by the voltage between the control and source electrodes, but also by the voltage between the control and drain electrodes. As a result, the size of this differential resistance is also dependent on the instantaneous value of the signal voltage U ₀ applied to the field effect transistor and thus the relationship between the voltage applied to the current path of the field effect transistor and the current flowing through it becomes highly non-linear, which leads to signal distortions leads.

The purpose of the invention is to reduce this non-linear distortion considerably.

For this purpose, according to the invention, a field effect transistor with source, control and drain electrodes is separate led out substrate connection, at least approximately in terms of alternating voltage the same potential is applied as the drain electrode is used.

Due to the physical structure of the field effect transistor, the substrate electrode has an electrically adjustable voltage divider
low non-linear distortion

Applicant:
Telefunken

Patentverwertungsgesellschaft mb H.,
7900 Ulm, Elisabethenstr. 3

Named as inventor:

Dipl.-Ing. Wolfgang Bitzer, 7153 Unterweissach

similar to the control electrode controlling effect. The fact that the substrate electrode is alternating voltage at least approximately the same potential is applied as to the drainage electrode, while the control electrode for the AC voltage signal has the same potential as the Source electrode, it is achieved that the field effect transistor over the barrier layer between the substrate and the source electrode is controlled in exactly the opposite way by the applied alternating voltage signal as for the distance between the control and drainage electrode. These two tax effects cancel each other out largely on each other, and so there is a very good linearization of the differential resistance of the current path between the source and drain electrodes.

All of the above also apply if the source and drain electrodes are interchanged will.

To prevent the between sources and The drainage electrode and the pn junction present on the substrate becomes conductive due to the alternating signal voltage and thereby causes new distortions, it can expediently be biased in the reverse direction by a direct voltage. FIG. 2 shows a highly schematic exemplary embodiment according to the invention, in which the bias of the substrate connection is generated by a direct voltage U.

The F i g. 3 a, 3 b and 3 c show three practical embodiments of the voltage divider according to FIG Invention.

The output voltage U _{1 of} the voltage divider described according to FIG. 2 is fed to an amplifier whose input stage z. B. from a transistor operated in the emitter circuit (Fig. 3a) or from two together to form a Darlington circuit.

809 519/468

volume-filled transistors (FIG. 3 b) or an amplifier stage with a second field effect transistor (FIG. 3c). A resistor R _{2 is} inserted in the emitter lead of this transistor or this Darlington circuit or in the lead to the source electrode of this second field effect transistor FET 2. If this resistor R _{2 is} sufficiently large, practically the same alternating voltage U ₁ occurs at it as that at the output of the voltage divider and, in addition, a direct voltage that is equal to the voltage drop across the emitter junction of the transistor or the sum of the two emitter voltage drops in the Darlington circuit. is the voltage between the source and control electrode of the field effect transistor FET2 . If the substrate connection of the field effect transistor FET is connected to the resistor A ₂ , as shown in FIGS the pn junction between the substrate and the source or drain electrode is biased in the reverse direction with a voltage which is equal to the emitter direct voltage drop or the sum of the emitter direct voltage drop or the source-gate direct voltage.

Instead of the substrate connection of the field effect transistor, a second, in the same sense as the first effective control electrode.

Claims (6)

Patent claims: 1. Electrically adjustable voltage divider, in which the input signal voltage to the series circuit from a resistor and the current path of a field effect transistor, at which between the control electrode and the grounded main electrode not connected to the resistor the DC control voltage is applied to set the voltage divider ratio and the 30th 35 40 output voltage between earth and the connection point between the resistor and the field effect transistor is tapped, characterized in that a field effect transistor (FET) is used with a separately led out substrate connection (B), which in terms of alternating voltage is at least approximately at the same potential as the drain electrode. 2. Adjustable voltage divider according to claim 1, characterized in that the pn junction on the substrate of the field effect transistor (FET) is biased in the reverse direction. 3. Adjustable voltage divider according to claims 1 and 2, characterized in that the bias voltage of the substrate (B) is generated by the voltage drop 'at the emitter-base path of a transistor amplifier stage connected to the output of the voltage divider and operated in emitter circuit by the The substrate connection of the field effect transistor (FET) is connected directly to the emitter connection of this transistor amplifier stage. 4. Adjustable voltage divider according to claim 3, characterized in that the in Emitter circuit operated transistor amplifier stage by two operated in Darlington circuit Transistors is replaced. 5. Adjustable voltage divider according to claim 3, characterized in that instead of the transistor amplifier stage operated in the emitter circuit, a second field effect transistor (FET 2) is used to decrease the output voltage (U ₁ ) of the voltage divider. 6. Adjustable voltage divider according to claims 1 to 5, characterized in that the same occurs in place of the substrate connection (B) of the field effect transistor (FET) a second, in the same sense as the first effective control electrode. 1 sheet of drawings 809 519/468 3 68 © Bundesdruckerei Berlin