Amplifier circuit having an operation point maintaining input and output voltages constant even if a gain thereof is varied

An amplifier circuit comprising:

• a first conversion circuit including a first active element and for converting an input signal into a first signal current;
• a second conversion circuit including a second active element and for transmitting said first signal current to an output thereof;
• a variable impedance means for converting said first signal current transmitted to said output into a voltage;
• and
• a circuit block including voltage generation means connected in series to said variable impedance means and having a terminal connected to the output of said second conversion circuit.

An amplifier circuit comprising:

• a transistor forming a grounded-base circuit;
• an impedance circuit comprising a series circuit of a resistor and a capacitor;
• and
• voltage generation means having a terminal maintained at a predetermined potential,
• wherein said transistor has a base connected to said terminal of said voltage generation means via said impedance circuit so that said base is grounded for AC signal components,
• wherein an input signal is applied between said base ad an emitter of said transistor via said impedance circuit, and
• wherein an output signal is obtained between said base and a collector of said transistor via said impedance circuit.

An amplifier circuit comprising:

• a first transistor constituting a grounded-base circuit;
• a second transistor having an emitter connected to a base of said first transistor;
• current generation means connected to the emitter of said second transistor;
• and
• means for controlling a current flowing from said current generation means such that a direction of variation of a signal current component included in said current is opposite to a direction of variation of another signal current component which flows into an emitter of said first transistor.

A video signal processing circuit comprising:

• a first conversion circuit including a first active element and for converting an input signal supplied at an input thereof into a first signal current;
• a second conversion circuit including a second active element and for transmitting said first signal current to an output thereof;
• variable impedance means for converting said first signal current transmitted to output side into a voltage;
• and
• an amplifier circuit including a circuit block having voltage generation means connected in series to said variable impedance means and a terminal connected to the output of said second conversion circuit.

An amplifier circuit comprising:

• an output terminal for outputting an output signal voltage;
• a conversion circuit for converting an input signal voltage into a signal current, comprising:
• an input terminal connected to an input signal source,
• a first output terminal connected to said output terminal,
• a second output terminal, and
• an active element having a first terminal connected to said input terminal and a second terminal connected to said second output terminal, wherein a flow direction of variation of a signal current component from said first output terminal is inverse with respect to a flow direction of variation of a signal current component from said second output terminal;
• a variable impedance means for converting said signal current into said output signal voltage, said variable impedance means connected between said first output terminal of said conversion circuit and said second output terminal of said conversion circuit;
• and
• an impedance circuit connected between said second output terminal of said conversion circuit and a reference voltage.