Feedback-type variable gain amplifier and method of controlling the same

A feedback-type variable gain amplifier, comprising;

• a first field effect transistor configured to receive an input voltage signal through an input node, to amplify the input voltage signal, and to output the amplified input voltage signal through an output node;
• a feedback circuit coupled between the input node and the output node, and configured to generate a feedback impedance that is changed in response to a control signal fed thereto;
• and
• a load circuit coupled between the output node and a voltage source, and configured to generate a load impedance that is changed in response to the control signal to cancel a change of an input impedance of the variable gain amplifier due to a change of the feedback impedance,
• wherein the load impedance and the feedback impedance are changed simultaneously in response to the control signal, and
• wherein the feedback circuit includes:
• a first circuit of a first capacitor, a first resistor, and a first inductor that are coupled in series between the input node and the output node;
• and
• a second circuit of a second capacitor, a second resistor, a second field effect transistor, a third resistor, and a third capacitor that are coupled in series between the input node and the output node.

A feedback-type variable gain amplifier, comprising:

• a first field effect transistor configured to receive a first input voltage signal through a first input node, to amplify the first input voltage signal, and to output the amplified first input voltage signal through a first output node;
• a first feedback circuit coupled between the first input node and the first output node, and configured to generate a first feedback impedance that is changed in response to a first control signal fed thereto;
• a first load circuit coupled between the first output node and a voltage source, and configured to generate a first load impedance that is changed in response to the first control signal to cancel a change of an input impedance of the variable gain amplifier due to a change of the first feedback impedance;
• a second field effect transistor configured to receive a second input voltage signal that is a differential pair with the first input voltage signal through a second input node, configured to amplify the second input voltage signal, and configured to output the amplified second input voltage signal through a second output node;
• a second feedback circuit coupled between the second input node and the second output node, and configured to generate a second feedback impedance that is changed in response to the second control signal fed thereto;
• and
• a second load circuit coupled between the second output node and the voltage source, and configured to generate a second load impedance that is changed in response to the second control signal to cancel a change of the input impedance of the variable gain amplifier due to a change of the second feedback impedance,
• wherein the first and second toad impedances and the first and second feedback impedances are changed in response to the first and second control signals, respectively.

A feedback-type variable gain amplifier, comprising:

• a first field effect transistor configured to receive an input voltage signal through an input node, and configured to amplify the input voltage signal;
• a second field effect transistor coupled between a first output terminal of the first field effect transistor and an output node, and configured to have a control terminal for receiving a bias voltage;
• a feedback circuit coupled between the input node and the output node, and configured to generate a feedback impedance that is changed in response to a control signal;
• and
• a load circuit coupled between the output node and a voltage source, and configured to generate a load impedance that is changed in response to the control signal to cancel a change of an input impedance of the variable gain amplifier due to a change of the feedback impedance,
• wherein the load impedance and the feedback impedance are changed simultaneously in response to the control signal.

A feedback-type variable gain amplifier, comprising:

• a first field effect transistor configured to receive a first input voltage signal through a first input node, and to amplify the first input voltage signal;
• a second field effect transistor coupled between a first output terminal of the first field effect transistor and a first output node, and configured to have a control terminal for receiving a first bias voltage;
• a first feedback circuit coupled between the first input node and the first output node, and configured to generate a first feedback impedance that is changed in response to a first control signal fed thereto;
• a first load circuit coupled between the first output node and a voltage source, and configured to generate a first load impedance that is changed in response to the first control signal to cancel a change of an input impedance of the variable gain amplifier due to a change of the first feedback impedance;
• a third field effect transistor configured to receive a second input voltage signal that is a differential pair with the first input voltage signal through a second input node, and to amplify the second input voltage;
• a fourth field effect transistor coupled between a first output terminal of the third field effect transistor and a second output node, and configured to have a control terminal for receiving a second bias voltage;
• a second feedback circuit coupled between the second input node and the second output node, and configured to generate a second feedback impedance that is changed in response to the second control signal fed thereto;
• and
• a second load circuit coupled between the second output node and the voltage source, and configured to generate a second load impedance that is changed in response to the second control signal to cancel a change of the input impedance of the variable gain amplifier due to a change of the second feedback impedance,
• wherein the first and second load impedances and the first and second feedback impedances are changed in response to the first and second control signals, respectively.