Variable gain amplifier
First Claim
1. A gain-controlled amplifier stage comprising:
- first and second transistors having respective emitter electrodes, respective base electrodes, and respective collector electrodes;
means for connecting said first and second transistors in emitter-coupled differential amplifier configuration, which means includesmeans for applying a direct base bias voltage to the base electrode of said first transistor,means for applying said direct base bias voltage to the base electrode of said second transistor,means for applying an input signal voltage between the base electrodes of said first and second transistors,means for coupling the emitter electrodes of said first and second transistors together, andmeans for causing similar direct emitter current flows through said first and second transistors;
a first resistance, having a first end connected to conduct the entirety of a direct current flowing through the collector electrode of said first transistor responsive to its said direct emitter current flow, and having a second end;
a second resistance, having a first end connected to conduct the entirety of a direct current flowing through the collector electrode of said second transistor responsive its said direct emitter current flow, and having a second end;
means for receiving a direct operating voltage for application to the second ends of said first and said second resistances;
means for taking an output signal voltage from at least one of the first ends of said first and said second resistances; and
means for providing a controllable conductance between the first ends of said first and said second resistances, which said means for providing a controllable conductance includes;
first and second diodes of unilaterally conductive type, having respective first electrodes respectively connecting to the first end of said first resistance and to the first end of said second resistance, and having respective second electrodes connecting together at a control node; and
means for supplying a direct control current to said control node for controlling the unilateral conduction of said first and second diodes which direct control current has a value regulated responsive to an electric control signal, said electric control signal being applied to said means for supplying a direct control current through connections other than at the second ends of said first and said second resistances.
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Accused Products
Abstract
Variable-gain amplifier stages, such as may be used in a television receiver intermediate-frequency (IF) amplifier, each comprise a pair of transistors connected as an emitter-coupled differential amplifier with resistive collector loads. An electrically controlled conductance is connected between the collector electrodes of the transistors, to shunt the resistive collector loads in controllable amount to set the voltage gain of the stage. The electrically controlled conductance in each variable-gain amplifier stage is constructed so as not to change the DC operating conditions of the emitter-coupled differential amplifier and its resistive collector loads with variation in the conductance of the electrically controlled conductance. Front end portions of television receivers or video tape recorders are described each of which uses separate intermediate-frequency (IF) amplifiers for the FM sound carrier and vestigial-AM picture carrier. In each front end the two IF amplifiers comprise matched cascade connections of the variable-gain amplifiers with tracking automatic gain control (AGC). The AGC signals are generated by an AGC detector supplied composite video signal from a video detector, which video detector responds to amplified IF signal supplied by the IF amplifier for the vestigial-AM picture carrier.
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Citations
27 Claims
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1. A gain-controlled amplifier stage comprising:
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first and second transistors having respective emitter electrodes, respective base electrodes, and respective collector electrodes; means for connecting said first and second transistors in emitter-coupled differential amplifier configuration, which means includes means for applying a direct base bias voltage to the base electrode of said first transistor, means for applying said direct base bias voltage to the base electrode of said second transistor, means for applying an input signal voltage between the base electrodes of said first and second transistors, means for coupling the emitter electrodes of said first and second transistors together, and means for causing similar direct emitter current flows through said first and second transistors; a first resistance, having a first end connected to conduct the entirety of a direct current flowing through the collector electrode of said first transistor responsive to its said direct emitter current flow, and having a second end; a second resistance, having a first end connected to conduct the entirety of a direct current flowing through the collector electrode of said second transistor responsive its said direct emitter current flow, and having a second end; means for receiving a direct operating voltage for application to the second ends of said first and said second resistances; means for taking an output signal voltage from at least one of the first ends of said first and said second resistances; and means for providing a controllable conductance between the first ends of said first and said second resistances, which said means for providing a controllable conductance includes; first and second diodes of unilaterally conductive type, having respective first electrodes respectively connecting to the first end of said first resistance and to the first end of said second resistance, and having respective second electrodes connecting together at a control node; and means for supplying a direct control current to said control node for controlling the unilateral conduction of said first and second diodes which direct control current has a value regulated responsive to an electric control signal, said electric control signal being applied to said means for supplying a direct control current through connections other than at the second ends of said first and said second resistances. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A gain-controlled amplifier stage comprising:
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first and second transistors having respective emitter electrodes, respective base electrodes, and respective collector electrodes; means for connecting said first and second transistors in emitter-coupled differential amplifier configuration, which means includes means for applying a direct base bias voltage to the base electrode of said first transistor, means for applying said direct base bias voltage to the base electrode of said second transistor, means for applying an input signal voltage between the base electrodes of said first and second transistors, means for coupling the emitter electrodes of said first and second transistors together, and means for causing similar direct emitter current flow as though said first and second transistors; a first resistance, having a first end connected to conduct the entirely of a direct current flowing through the collector electrode of said first transistor responsive to its said direct emitter current flow, and having a second end; a second resistance, having a first end connected to conduct the entirely of a direct current flowing through the collector electrode of said second transistor responsive its said direct emitter current flow and having a second end; a source of first control current, said source of first control current exhibiting a source impedance of said first and second resistances; and means for providing a controllable conductance between the first ends of said first and said second resistances, which said controllable conductance is arranged to be controlled responsive to said control current and comprises first and second variable conductance means having respective first ends connected to said respective first ends of said first and second resistances and having respective second ends connected together to receive said first control current from said source thereof. - View Dependent Claims (17, 18)
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15. A gain-controlled amplifier stage comprising:
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first and second transistors having respective emitter electrodes, respective base electrodes, means for connecting said first and second transistors in an emitter-coupled differential amplifier configuration, which means includes means for applying a direct base bias voltage to the base electrode of said first transistor, means for applying said direct base bias voltage to the base electrode of said second transistor, means for applying an input signal voltage between the base electrodes of said first and second transistors, means for coupling the emitter electrodes of said first and second transistors together, and means for causing similar direct emitter current flows through said first and second transistors; first and second resistances having respective first ends coupled to the respective collector electrodes of said first and second transistors and respective second ends connected to a terminal for receiving a direct operating voltage; a source of first control current said source of first control current exhibiting a source impedance value within a range extending upward from a value comparable with the impedance of said first and second resistances; means for providing a controllable conductance between the first ends of said first and said second resistances, which said controllable conductance is arranged to be controlled responsive to said control current and comprises first and second variable conductance means having respective first ends connected to said respective first ends of said first and second resistances and having respective second ends connected together to receive said first control current from said source thereof; a source of second control current having the same magnitude as said control current, but being of the opposite polarity, said source of second control current exhibiting a source impedance value within a range extending from a first value comparable with the impedance of said first and second resistance to a second value high in comparison therewith; and third and fourth variable conductance means having respective first ends connected to said respective first ends of said first and second resistances and having respective second ends together to receive said second control current from said source thereof, for providing a further controllable conductance responsive to said control current. - View Dependent Claims (16)
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19. A gain-controlled amplifier stage comprising:
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first and second transistors having respective emitter electrodes, respective base electrodes, and respective collector electrodes; means for connecting said first and second transistors in emitter-colored differential amplifier configuration, which means includes means for applying a direct base, bias voltage to the base electrode of said first transistor, means for applying a direct base bias voltage to the base electrode of said second transistor, means for applying an input signal voltage between the base electrodes of said first and second transistors, means for coupling the emitter electrodes of said first and second transistors together, and means for causing similar direct emitter current flows through said first and second transistors; first and second resistances having respective first ends coupled to the respective collector electrodes of said first and second transistors and respective second ends connected to a terminal for receiving a direct operating voltage; a source of first control current, said source of first control current exhibiting a source impedance value within a range extending upward from a value comparable with the impedance of said first and second resistances; means for providing a controllable conductance between the first ends of said first and said second resistances, which said controllable conductance is arranged to be controlled responsive to said control current and comprises first and second variable conductance means having respective first ends connected to said respective first ends of said first and second resistances and having respective second ends connected together to receive said first control current from said source thereof; and first and second controllable current splitting means each having a respective current input for receiving a respective input current and respective first and second outputs for splitting its said respective input current in a controllable ratio between said its respective first and second outputs, said respective collector electrodes of said first and second transistors being connected to separate ones of the current inputs of said first and second current splitting means, said respective first outputs of said first and second current splitting means being connected respectively to said first ends of said first and second resistances and said respective second outputs of said first and second current splitting means being connected to said second ends of said first and second variable conductance means for providing said first control current. - View Dependent Claims (20)
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21. A gain-controlled amplifier comprising:
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first and second transistors connected as an emitter-coupled differential amplifier for responding to RF signals and having respective collector electrodes for supplying respective collector currents having respective common-mode DC components and having respective differential-mode RF components; bridge diode load means having first, second, third, and fourth nodes, said first and second nodes being balanced with respect to said third and fourth nodes, said first and second nodes being connected to respective ones of said collector electrodes, said diode load means exhibiting between said first and second nodes a controllable impedance having a value controlled by current flow between said third and fourth nodes; and variable control current means comprising a current source output connected to said third node and a current sink output connected to said fourth node, said current source and sink outputs providing equal magnitudes of current. - View Dependent Claims (22)
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23. A gain-controlled amplifier comprising:
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first and second transistors having respective base, emitter and collector electrodes; means for connecting said first transistor and said second transistor in a first emitter-coupled differential amplifier configuration, to cause said first and second transistors to supply from their respective collector electrodes respective collector currents having respective common-mode DC components and having respective differential-mode RF components responsive to RF signals of similar frequency received between their base electrodes; a first controllable current splitter having an input for conducting a direct operating current, having first and second outputs connected for providing first and second fractional parts of aid direct operating current in a ratio determined in accordance with a first control signal, said first fractional part being apportioned to flow as respective direct emitter current flows through said emitter electrodes of said first and second transistors; a first resistance connected between said collector electrode of said first transistor and a point of operating potential, for conducting the entirety of a direct current flowing through the collector electrode of said first transistor responsive to its said direct emitter current flow; a second resistance connected between said collector electrode of said second transistor and said point of operating potential, for conducting the entirety of a direct current flowing through the collector electrode of said second transistor responsive to its said direct emitter current flow; first diode means having a first electrode to which said collector electrode of said first transistor is connected and having a second electrode; second diode means having a first electrode to which said collector electrode of said second transistor is connected and having a second electrode; and an interconnection between said second electrodes of said first and second diode means to which said second output of said first current splitter is connected. - View Dependent Claims (24, 25, 26)
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27. A gain-controlled amplifier comprising:
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first and second transistors having respective base, emitter and collector electrodes; means for connecting the first and second transistors in an emitter-coupled differential amplifier configuration, to cause the first and second transistors to respond to RF signals received between their base electrodes for supplying from their respective collector electrodes respective collector currents having respective common-mode DC components and having respective differential-mode RF components; a first controllable current splitter, having an input for conducting collector current from said first transistor, and having first and second outputs for respectively conducting said first and second fractional parts of said first current in a ratio determined in accordance with a control signal; a second controllable current splitter, having an input for conducting collector current from said second transistor, and having first and second outputs for respectively conducting said first and second fractional parts of said second current in a ratio determined in accordance with said control signal; a first resistance connected between said point of operating potential and a first node, to which said first node the first output of said first current splitter connects; a second resistance connected between said point of operating potential and a second node, to which said second node the first output of said second current splitter connects; first diode means having a first electrode connected to said first node and having a second electrode; second diode means having a first electrode connected to said second node and having a second electrode; and a third node at which said second electrodes of said first and second diode means connect together and to which the second outputs of said first and second current splitters each connect.
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Specification