Input system for variable gain amplifier having transconductance stages with feedforward paths diverted to AC ground

A method of operating an input stage for a variable gain amplifier, the input stage comprising:

• an attenuator having an input port for receiving an input signal and a plurality of tap ports for generating a plurality of attenuated signals responsive to the input signal;
• and a plurality of gm stages, each gm stage coupled to one of the tap ports to receive one of the attenuated signals;
• wherein each of the gm stages includes a transistor cell for generating two output currents responsive to the attenuated signal, and a node for receiving one of a plurality of interpolator signals for controlling the gain of the transistor cell;
• the method comprising:
• diverting a first one of the output currents from each gm stage to an AC ground.

An input system for a variable gain amplifier comprising:

• means for generating a plurality of attenuated signals responsive to an input signal;
• and
• a plurality of means for generating two output currents responsive to one of the attenuated signals and one of a plurality of interpolator signals;
• wherein each of the means for generating two output currents is arranged to divert one of the output currents to an AC ground.

An input system for a variable gain amplifier comprising:

• an attenuator having an input port for receiving an input signal and a plurality of tap ports for generating a plurality of attenuated signals responsive to the input signal;
• and
• a plurality of gm stages, each gm stage coupled to one of the tap ports to receive one of the attenuated signals;
• wherein each of the gm stages includes a transistor cell for generating two output currents responsive to the attenuated signal, and a node for receiving one of a plurality of interpolator signals for controlling the gain of the transistor cell;
• and
• wherein each of the gm stages further includes a filter coupled to the node.

An input system for a variable gain amplifier comprising:

• an attenuator having an input port for receiving an input signal and a plurality of tap ports for generating a plurality of attenuated signals responsive to the input signal;
• and
• a plurality of gm stages, each gm stage coupled to one of the tap ports to receive one of the attenuated signals;
• wherein each of the gm stages includes a transistor cell for generating two output currents responsive to the attenuated signal, and a node for receiving one of a plurality of interpolator signals for controlling the gain of the transistor cell;
• and
• wherein each of the gm stages further includes means for attenuating a feedforward signal through the transistor cell.

An input system for a variable gain amplifier comprising:

• an attenuator having an input port for receiving an input signal and a plurality of tap ports for generating a plurality of attenuated signals responsive to the input signal;
• and
• a plurality of gm stages, each gm stage coupled to one of the tap ports to receive one of the attenuated signals;
• wherein each of the gm stages includes a transistor cell for generating two output currents responsive to the attenuated signal, and a node for receiving one of a plurality of interpolator signals for controlling the gain of the transistor cell;
• and
• wherein each of the gm stages further includes a compensation transistor coupled to a corresponding one of the tap ports and arranged to generate a third current responsive to the common mode voltage of the tap port.

An input system for a variable gain amplifier comprising:

• an attenuator having an input port for receiving an input signal and a plurality of tap ports for generating a plurality of attenuated signals responsive to the input signal;
• a plurality of gm stages, each gm stage coupled to one of the tap ports to receive one of the attenuated signals, wherein the gm stages are arranged to generate a first main output signal responsive to the attenuated signals and a plurality of interpolator signals;
• and
• a main amplifier having a first input coupled to receive the first main output signal and a second input coupled to receive a second main output signal;
• wherein each of the gm stages further includes means for providing a feedforward component to the second main output signal which is equal to a feedforward component of the first main output signal.