US Patent 7345545 Enhancement mode transceiver and switched gain amplifier integrated circuit

Methods and apparatus are provided for RF switches (504, 612) integrated in a monolithic RF transceiver IC (500) and switched gain amplifier (600). Multi-gate n-channel enhancement mode FETs (50, 112, 114, Q1-3, Q4-6) are used with single gate FETs (150), resistors (Rb, Rg, Re, R1-R17) and capacitors (C1-C3) formed by the same manufacturing process. The multiple gates (68) of the FETs (50, 112, 114, Q1-3, Q4-6) are parallel coupled, spaced-apart and serially arranged between source (72) and drain (76). When used in pairs (112, 114) to form a switch (504) for a transceiver (500) each FET has its source (74) coupled to an antenna RF I/O port (116, 501) and drains coupled respectively to second and third RF I/O ports (118, 120; 507, 521) leading to the receiver side (530) or transmitter side (532) of the transceiver (500). The gates (136, 138) are coupled to control ports (122, 124; 503, 505; 606, 608). When used in pairs (Q1-3, Q4-6) to form a variable switched attenuator, the first FET (Q1-3) is a pass device and the second FET (Q4-6) is a shunt device that respectively bridge two series resistors (R1, R2) and block a shunt resistor (R3) of a T-type attenuator.