Broadband circuit with rapidly variable resistor
AssigneeRobert Bosch GmbH
InventorKlaus Lehmann
Life of this patent
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Abstract
To provide for essentially inertia-free amplitude adjustment of video signals, an electrical circuit is provided with a field effect transistor having variable source-drain resistance. The circuit includes two junction transistors which are connected to the gate electrode of the field effect transistor and either to the source electrode or the drain electrode. One such transistor is connected as an impedance converter, and the other in grounded base configuration. By means of a variable voltage applied to a resistor is connected to the gate electrode of the field effect transistor, source-drain resistance of the field effect transistor can be varied essentially linearly.
Claims8
Variable resistance electrical circuit comprising:
- a first field effect transistor (20;
- 30;
- 40) having a source electrode, a drain electrode, and a single gate electrode;
- a first resistor (27;
- 34;
- 50) which is connected to said gate electrode;
- first transistor (25;
- 33;
- 44) connected to said gate electrode;
- a second transistor (21, 22;
- 31;
- 43, 44) in a first emitter follower circuit having its input connected to a first electrode, which is either said source electrode or said drain electrode, and furnishing an output to said gate electrode by way of a connection through an electrode of said first transistor other than the electrode thereof most directly connected to said gate electrode,
- said first transistor (25;
- 33;
- 44) being connected for common-base mode of operation between said connection through which said second transistor acts and said gate electrode,
- whereby, by means of a variable voltage applied to said resistor (27;
- 34;
- 50), the resistance of the source-drain path of said first field effect transistor (20;
- 30;
- 40) is variable.
Dependencies are inferred from the claim text.