Methods and circuits for detuning a filter and matching network at the output of a power amplifier
In transmitter modules or power amplifier (PA) modules there is at least a possible path for a second and even a third harmonic of a low band to crossover unfiltered into the high band path and reach the antenna and hence cross band isolation is necessary. Forward isolation is necessary in order to limit the input crossing over the PAs into the antenna port. According to the methods and the circuits such cross band isolation and forward isolation is improved by detuning the filter and matching network at the output of the PA. The circuit comprises a trap at the harmonic frequencies of the low band thereby at least reducing the impacts of the cross band and forward isolation.
1. Circuitry comprising:
a first power amplifier (PA) configured to operate in one of an ON state, in which the first PA amplifies one or more signals about a first frequency band, or an OFF state;
a first filter coupled to the first PA and configured to pass signals about the first frequency band between an output of the first PA and a first antenna node;
a second power amplifier (PA) configured to operate in one of an ON state, in which the second PA amplifies one or more signals about a second frequency band that is different from the first frequency band, or an OFF state;
a second filter coupled to the second PA and configured to, in the ON state of the first PA, exhibit a first frequency response in order to attenuate signals about one or more harmonic frequencies of the first frequency band, and in the OFF state of the first PA, exhibit a second frequency response in order to pass signals about the second frequency band between an output of the second PA and a second antenna node.
2. The circuitry of claim 1 , further comprising a signal routing circuit coupled to the first filter and the second filter to route signals from one of the first filter and the second filter to an antenna coupled to the signal routing circuit.
3. The circuitry of claim 1 , wherein the first frequency band and the second frequency band are non-overlapping.
4. The circuitry of claim 1 wherein the first filter comprises:
a first inductor coupled in series between an input node and an intermediary node;
a second inductor coupled in series between the intermediary node and an output node;
a third inductor coupled in series with a first capacitor between the intermediary node and ground;
a fourth inductor coupled in series with a second capacitor between the output node and ground.
5. The circuitry of claim 1 wherein the second filter comprises:
a first inductor coupled in series between an input node and an intermediary node;
a second inductor coupled in series between the intermediary node and an output node;
a third inductor coupled in series with a first capacitor between the intermediary node and ground;
a fourth inductor coupled in series with a second capacitor between the output node and ground; and
a first switchable capacitor coupled in parallel with the first capacitor between the third inductor and ground.
6. The circuitry of claim 5 wherein:
when the first PA is in the ON state, the first switchable capacitor is ON, such that the capacitance of the first switchable capacitor is coupled in parallel with the first capacitor between the third inductor and ground; and
when the first PA is in the OFF state, the first switchable capacitor is OFF, such that the first switchable capacitor forms an open circuit in parallel with the first capacitor between the third inductor and ground.
7. The circuitry of claim 2 , wherein the signal routing circuit is one of: a switch, a diplexer.