By-pass arrangement of a low noise amplifier
View Patent ↗The invention relates to an arrangement for bypassing a low noise amplifier unit in the front stage of a radio receiver, especially intended for the base stations of mobile communication networks. The front stage includes, in succession, a divider ( 420 ), an amplifier unit ( 430 ) comprising two parallel, low noise amplifier branches, and a first combiner ( 450 ). The by-pass arrangement includes a second combiner ( 443 ), by which the halves (E 11 , E 12 ) of the received signal are combined immediately after the divider before the amplification. A change-over switch (SW) is then used to select either the signal that has propagated through the amplifier unit and then combined (G·E 1 ) or the signal (E 1 ′) that has been directly combined as the output signal of the front stage. Due to the invention, the noise figure of the front stage is improved and the integration of its structure is facilitated.
1. An arrangement for bypassing a low noise amplifier unit in a front stage of a radio receiver, which amplifier unit has two parallel amplifier branches and the front stage comprises, in addition to the amplifier unit, an antenna filter to clean a received input signal, a divider to divide the input signal to said amplifier branches, and a first combiner to combine the output signals of the amplifier branches, the arrangement comprising a by-pass path for the amplifier unit and a change-over switch with a first change terminal, a second change terminal and an output terminal, which first change terminal is connected to the output of the first combiner and the second change terminal is connected to the output of the by-pass path to select a signal received either from the amplifier unit or the by-pass path as an output signal of the whole front stage,
wherein said antenna filter is directly connected to the input of said divider and the outputs of the divider are directly connected to said amplifier branches, and the bypass path comprises a second combiner, a first input of which is connected by a first by-pass line to a first output of said divider and a second input by a second by-pass line to a second output of said divider, and an output of said second combiner is said output of the by-pass path, and
said arrangement further comprises a first closing switch relatively close to a tail end of the first by-pass line, or the end on the side of the second combiner, and a second closing switch relatively close to a tail end of the second by-pass line and the first and the second closing switch and the change-over switch have a shared control such that the closing switches are in a closing state when the first change terminal of the change-over switch is connected to the output terminal of the change-over switch.
2. An arrangement according to claim 1 , said divider being of a type that produces in-phase signals in the first and second output, and the length of said by-pass lines from the head end to the closing switches is a quarter wave length at the operating frequency.
3. An arrangement according to claim 1 , said divider being of a type that produces in-phase signals in the first and second output, and the length of said by-pass lines from the head end to the closing switches is a half-wave length at the operating frequency.
4. An arrangement according to claim 1 , said divider being of a type that produces to the first output a signal, which lags 90 degrees in comparison to the signal of the second output, wherein the second by-pass line comprises at its tail end, or the end on the side of the second combiner, a phase shifter causing a 90-degree phase shift, the length of said by-pass lines from the head end to the closing switches is a quarter wave length at the operating frequency.
5. An arrangement according to claim 1 , the second combiner being of the hybrid type.
6. An arrangement according to claim 1 , the second combiner being of the Wilkinson type.
7. An arrangement according to claim 2 or 3 , the divider being of the Wilkinson type.
8. An arrangement according to claim 4 , the divider being of the hybrid type.
9. An arrangement according to claim 2 , 3 or 4 , said switches having been implemented by pin diodes, MEMS switches or the MMIC technique.