Gain boosting RF gain stage with cross-coupled capacitors

A radio frequency (RF) amplifier comprising:

• a plurality of transistors arranged as a differential amplifier stage in which differential input signals are to be received on corresponding first and second input nodes, the differential amplifier stage having the first input node and a first output node associated with a first amplification branch, in which a first input transistor and a first cascode transistor are coupled in series between the first output node and a common leg of the differential amplifier stage, and the second input node and a second output node associated with a second amplification branch, in which a second input transistor and a second cascode transistor are coupled in series between the second output node and the common leg of the differential amplifier stage;
• a pair of inductors coupled between the corresponding first and second output nodes and a supply node to operate as inductive loads for the transistors;
• and
• a cross-coupled pair of capacitors in which a first capacitor is coupled between a gate of the first input transistor at the first input node and a drain of the second cascode transistor at the second output node of the differential amplifier stage and a second capacitor is coupled between a gate of the second input transistor at the second input node and a drain of the first cascode transistor at the first output node of the differential amplifier stage, the cross-coupled pair of capacitors to provide feedback to boost gain of the differential amplifier stage to compensate for resistance of the inductors, but without putting the differential amplifier stage into oscillation.

A method comprising:

• inputting differential input signals to a differentially arranged radio frequency (RF) amplifier stage having an inductive load and cross-coupled capacitors, wherein the differentially arranged RF amplifier has a first input node and a first output node associated with a first amplification branch of the differentially arranged RF amplifier stage, in which a first input transistor and a first cascode transistor are coupled in series between the first output node and a common leg of the RF amplifier stage, and a second input node and a second output node associated with a second amplification branch of the differentially arranged RF amplifier stage, in which a second input transistor and a second cascode transistor are coupled in series between the second output node and the common leg of the RF amplifier stage, and wherein the cross-coupled capacitors include a first capacitor coupled between a gate of the first input transistor at the first input node and a drain of the second cascode transistor at the second output node and a second capacitor coupled between a gate of the second input transistor at the second input node and a drain of the first cascode transistor at the first output node;
• using the cross-coupled capacitors to provide feedback to boost gain of the differentially arranged RF amplifier stage to compensate for resistance of the inductive load, but without putting the differentially arranged amplifier stage into oscillation;
• and
• outputting differential output signals from the differentially arranged RF amplifier stage.