Patent ID: 8217720

Claim:
A cascode amplifier comprising: a gain control circuit for receiving a gain adjusting voltage, thereby generating a resistance adjusting signal and a current steering control signal, wherein when the gain adjusting voltage is in a high gain-adjusting range, the resistance adjusting signal is adjusted but the current steering control signal is kept unchanged, wherein when the gain adjusting voltage is in a low gain-adjusting range, the current steering control signal is adjusted but the resistance adjusting signal is kept unchanged; a load circuit comprising plural variable resistors, wherein the resistances of the variable resistors are adjusted according to the resistance adjusting signal; a current steering circuit connected to the load circuit through plural current paths for adjusting a current ratio between the plural current paths according to the current steering control signal, wherein the current steering circuit has differential signal output terminals; and an input circuit connected to the current steering circuit, wherein the input circuit has differential signal input terminals.