Fine trimming of a radio frequency gain by modulating the periphery of a radio frequency switch
A switched attenuator comprising a radio frequency input, a radio frequency output and an attenuation cell connected between the RF input and the RF output. The attenuation cell includes a variable switch with a variable on-resistance (R on ).
1 . A switched attenuator comprising:
a radio frequency (RF) input;
an RF output; and
an attenuation cell connected between the RF input and the RF output and including a variable switch with a variable on-resistance, the variable switch including a first field-effect transistor (FET) having a first independently trimmed periphery and a second FET having a second independently trimmed periphery different than the first independently trimmed periphery, each of the first and second FETs being a single FET, the variable switch being configured to enable the first FET and disable the second FET in a first mode of operation and enable the second FET and disable the first FET in a second mode of operation to fine-tune the variable on-resistance of the variable switch.
2 . The switched attenuator of claim 1 wherein the variable switch is configured for fine trimming an insertion loss of the variable switch.
3 . The switched attenuator of claim 1 wherein the attenuation cell comprises an attenuation network, the attenuation network optionally comprising at least one of a PI-network, a T-network, and a bridged T-network.
4 . The switched attenuator of claim 3 wherein the attenuation network comprises two impedances connected in series between input and output terminals of the attenuation network.
5 . The switched attenuator of claim 4 wherein the attenuation network further comprises a bridge impedance connected between the input and the output terminals of the attenuation network.
6 . The switched attenuator of claim 5 wherein the two series connected impedances and the bridge impedance are connected in parallel between the input and the output terminals of the attenuation network.
7 . The switched attenuator of claim 3 wherein the variable switch is connected between input and output terminals of the attenuation network.
8 . The switched attenuator of claim 4 wherein the attenuation network comprises a shunt impedance coupled between the two series connected impedances.
9 . The switched attenuator of claim 1 wherein the variable switch comprises a stack of a plurality of FETs, the plurality of FETs including at least one of the first FET and the second FET.
10 . The switched attenuator of claim 9 wherein the at least one of the first FET and the second FET comprises a trimmed on-resistance forming, at least in part, the variable on-resistance of the variable switch.
11 . The switched attenuator of claim 10 wherein one of the plurality of FETs has a fixed on-resistance forming, at least in part, the variable on-resistance of the variable switch.
12 . The switched attenuator of claim 9 wherein the variable on-resistance of the variable switch is equal to a sum of a respective on-resistance of each of the plurality of FETs of the stack.
13 . A method of controlling a switched attenuator comprising a radio frequency (RF) input, an RF output, and an attenuation cell connected between the RF input and the RF output and including a variable switch with a variable on-resistance, the method comprising fine-tuning the variable on-resistance of the variable switch, the fine-tuning including
enabling a first FET of the variable switch having a first independently trimmed periphery and disabling a second FET of the variable switch having a second independently trimmed periphery different than the first independently trimmed periphery in a first mode of operation, and
disabling the first FET and enabling the second FET in a second mode of operation, each of the first and second FETs being a single FET.
14 . The method of claim 13 wherein the variable switch comprises a stack of a plurality of FETs, the plurality of FETs including at least one of the first FET and the second FET.
15 . The method of claim 14 wherein the at least one of the first FET and the second FET comprises a trimmed on-resistance forming, at least in part, the variable on-resistance of the variable switch.
16 . The method of claim 15 wherein one of the plurality of FETs has a fixed on-resistance forming, at least in part, the variable on-resistance of the variable switch.
17 . The method of claim 14 wherein the variable on-resistance of the variable switch is equal to a sum of a respective on-resistance of each of the plurality of FETs of the stack.
18 . A mobile device including a switched attenuator comprising:
a radio frequency (RF) input;
an RF output; and
an attenuation cell connected between the RF input and the RF output and including a variable switch with a variable on-resistance, the variable switch including a first field-effect transistor (FET) having a first independently trimmed periphery and a second FET having a second independently trimmed periphery different than the first independently trimmed periphery, each of the first and second FETs being a single FET, the variable switch being configured to fine-tune the variable on-resistance of the variable switch, the fine-tuning including
enabling the first FET and disabling the second FET in a first mode of operation, and
disabling the first FET and enabling the second FET in a second mode of operation.
19 . The mobile device of claim 18 wherein the variable switch comprises a stack of a plurality of FETs, the plurality of FETs including at least one of the first FET and the second FET.
20 . The mobile device of claim 19 wherein the variable on-resistance of the variable switch is equal to a sum of a respective on-resistance of each of the plurality of FETs of the stack.