Patent ID: 7119615

Claim:
An amplifier circuit comprising: input connections; a first and second current branch ( 10 , 11 ), each comprising an input transistor ( 100 , 110 ) and a cascode transistor ( 104 , 114 ), the input connections being coupled to control electrodes of the input transistors ( 100 , 110 ) in respective ones of the current branches ( 10 , 11 ), control electrodes of the cascode transistors ( 104 , 114 ) being coupled to each other; a common current source circuit ( 120 , 122 , 124 ); output connections, each coupled to the common current source circuit ( 120 , 122 , 124 ) via a series connection of the main current channels of the cascode transistor ( 104 , 114 ) and the input transistor successively, of a respective one of the current branches; a high frequency coupling ( 18 ) between the control electrodes of the cascode transistors and a node of the common current source arranged to copy substantially common mode voltage changes of terminals of the main current channels of the input transistors to voltage changes at the control electrodes of the cascode transistors; and a bias circuit coupled to the control electrodes of the cascode transistors for biasing the control electrodes of the cascode transistors, the bias circuit comprising a high frequency current blocking circuit including an inductance for blocking flow of current from the high frequency coupling through the biasing circuit.