Reducing intermodulation distortion in a radio frequency circuit
Embodiments of the disclosure relate to reducing intermodulation distortion (IMD) in a radio frequency (RF) circuit. In examples discussed herein, the RF circuit operates in an uplink carrier aggregation (ULCA) mode to transmit an RF uplink signal simultaneously in a first uplink band and a second transmit band. However, nonlinear components in the RF circuit can create an IMD product(s) that can fall into a downlink band of an RF downlink signal, thus impairing a receive filter's ability to receive the RF downlink signal in the downlink band. The receive filter can be opportunistically reconfigured to form an IMD shunt path to attenuate the IMD product. By reconfiguring the receiver filter to form the IMD shunt path, it is possible to suppress the IMD product in the RF uplink signal, thus leading to an improved desense performance in the ULCA mode without incurring additional cost and/or battery life penalty.
1. A radio frequency (RF) circuit comprising:
a common node coupled to an antenna;
multiplexer circuitry coupled to the common node and comprising a first transmit filter, a second transmit filter, and a first receive filter, wherein:
the first transmit filter is configured to provide an RF uplink signal in a first uplink band to the common node in an uplink carrier aggregation (ULCA) mode;
the second transmit filter is configured to provide the RF uplink signal in a second uplink band to the common node in the ULCA mode;
the first receive filter is configured to receive an RF downlink signal in a first downlink band from the common node; and
at the common node, the RF uplink signal comprises an intermodulation distortion (IMD) product that falls within the first downlink band;
tunable reflection circuitry coupled to a ground;
a shunt path switch disposed between the first receive filter and the tunable reflection circuitry; and
control circuitry configured to control the shunt path switch to couple the first receive filter to the tunable reflection circuitry to form an IMD shunt path from the common node to the ground to attenuate the IMD product to the ground in the RF uplink signal in the ULCA mode.
2. The RF circuit of claim 1 wherein in the ULCA mode the control circuitry is further configured to reconfigure the first receive filter to be an IMD bandstop filter to attenuate the IMD product from the RF uplink signal.
3. The RF circuit of claim 1 wherein in the ULCA mode:
the RF uplink signal comprises a third-order IMD (IMD3) product that falls within the first downlink band; and
the control circuitry is further configured to control the tunable reflection circuitry to form the IMD shunt path to attenuate the IMD3 product in the RF uplink signal in the ULCA mode.
4. The RF circuit of claim 1 wherein:
the first uplink band is long-term evolution (LTE) uplink band one;
the second uplink band is LTE uplink band three; and
the first downlink band comprises LTE downlink band one.
5. The RF circuit of claim 1 wherein:
the first uplink band is long-term evolution (LTE) uplink band sixty-six;
the second uplink band is LTE uplink band twenty-five; and
the first downlink band is LTE downlink band sixty-six.
6. The RF circuit of claim 1 wherein the IMD shunt path comprises impedance of approximately 1 ohm.
7. The RF circuit of claim 1 wherein the control circuitry is further configured to adjust the first receive filter and the tunable reflection circuitry to provide one or more notches for attenuating the IMD product.
8. The RF circuit of claim 1 wherein in the ULCA mode the control circuitry is further configured to couple the tunable reflection circuitry to an end node of the first receive filter.
9. The RF circuit of claim 1 wherein in the ULCA mode the control circuitry is further configured to couple the tunable reflection circuitry to an intermediate node of the first receive filter.
10. The RF circuit of claim 1 wherein in a non-ULCA mode the control circuitry is further configured to control the shunt path switch to decouple the tunable reflection circuitry from the first receive filter.
11. The RF circuit of claim 1 wherein the multiplexer circuitry further comprises a second receive filter configured to receive the RF downlink signal in a second downlink band.
12. The RF circuit of claim 11 further comprising:
a second common node coupled to a second antenna; and
second multiplexer circuitry coupled to the second common node and comprising a first diversity receive filter configured to receive the RF downlink signal in the first downlink band in a multiple-input multiple-output (MIMO) mode.
13. The RF circuit of claim 12 wherein in the ULCA mode the control circuitry is further configured to reconfigure the first diversity receive filter to receive the RF downlink signal in the first downlink band.
14. The RF circuit of claim 13 wherein the second multiplexer circuitry further comprises a second diversity receive filter configured to receive the RF downlink signal in the second downlink band in the MIMO mode.
15. The RF circuit of claim 14 wherein the control circuitry is further configured to configure the second diversity receive filter to receive the RF downlink signal in the second downlink band in the ULCA mode.
16. The RF circuit of claim 12 wherein the second antenna is disposed in close proximity to the antenna.
17. The RF circuit of claim 1 further comprising switching circuitry provided between the common node and the antenna.
18. The RF circuit of claim 1 further comprising switching circuitry provided between the multiplexer circuitry and the common node, wherein in the ULCA mode:
the first transmit filter and the second transmit filter are coupled to the common node via the switching circuitry; and
the first receive filter is coupled to the common node independent from the switching circuitry.