Transmitter receiver leakage reduction in a full duplex system without the use of a duplexer

1. A transmitter leakage reduction circuit for a transceiver having a transmitter and a receiver, the transceiver capable of operating in a frequency division duplex (FDD) communications system having transmit and receive frequency bands, the transmitter leakage reduction circuit comprising:

an auxiliary power amplifier configured to provide an auxiliary power amplifier output signal that represents an output signal of a power amplifier of the transmitter with a controllable phase shift or gain output;

a first filter coupled between the power amplifier and a radio frequency (RF) connecting point that is capable of being coupled to an antenna, the first filter configured to attenuate any signals in the receive frequency band of the power amplifier output signal;

a second filter coupled to the auxiliary power amplifier and configured to attenuate any signals in the receive frequency band of the auxiliary power amplifier output signal; and

a signal transmission arrangement coupled between the first and second filters and between the RF connecting point and the receiver, the signal transmission arrangement configured to suppress a contribution of the power amplifier output signal from a signal received from the RF connecting point using the auxiliary power amplifier output signal to obtain a received signal that is input to the receiver.

2. The transmitter leakage reduction circuit of claim 1 , wherein the signal transmission arrangement includes:

a first impedance element coupled between the auxiliary power amplifier and the receiver;

a second impedance element coupled between the power amplifier and the receiver and between the RF connecting point and the receiver; and

wherein the first and second impedance elements have a certain relationship between their impedances.

3. The transmitter leakage reduction circuit of claim 2 , wherein the first or second impedance element has a controllable impedance.

4. The transmitter leakage reduction circuit of claim 1 , wherein the auxiliary power amplifier output signal is controllable to have a certain relationship in phase or gain to the power amplifier output signal.

5. The transmitter leakage reduction circuit of claim 1 , wherein:

the auxiliary power amplifier output signal is controllable to have opposite phase and an equivalent amplitude to the power amplifier output signal; and

the first and second impedance elements have equivalent impedances.

6. The transmitter leakage reduction circuit of claim 2 , wherein:

the second impedance element comprises a first and a second impedance connected in series; and

the phase shift or gain output is controlled based on a measurement of a signal at a point between the first and second impedances.

7. The transmitter leakage reduction circuit of claim 2 , further comprising:

a parallel resonance tank circuit and a third impedance element connected between the first and second filters; and

wherein the parallel resonance tank circuit is tuned to a frequency of the received signal.

8. The transmitter leakage reduction circuit of claim 2 , further comprising:

a receiver impedance element coupled between the signal transmission arrangement and the receiver, the receiver impedance element having a controllable impedance so that the second impedance element and the receiver impedance element together have a resonance frequency equivalent to a frequency of the received signal.

9. The transmitter leakage reduction circuit of claim 1 , wherein:

the receive frequency band is lower in frequency than the transmit frequency band;

the first filter is a high-pass filter or a band-pass filter; and

the second filter is a high-pass filter or a band-pass filter.

10. The transmitter leakage reduction circuit of claim 9 , wherein the band-pass filters of the first and second filters each includes a capacitance and a first inductance coupled in parallel, the parallel coupling being coupled in series with a second inductance.

11. The transmitter leakage reduction circuit of claim 10 , wherein at least one of the capacitance and the first and second inductances of each of the first and second filters are controllable.

12. The transmitter leakage reduction circuit of claim 1 , wherein:

the receive frequency band is lower in frequency than the transmit frequency band;

the first filter is a low-pass filter or a band-pass filter; and

the second filter is a low-pass filter or a band-pass filter.

13. The transmitter leakage reduction circuit of claim 12 , wherein the band-pass filters of the first and second filters each includes a first capacitance and an inductance coupled in parallel, where the parallel coupling is coupled in series with a second capacitance.

14. The transmitter leakage reduction circuit of claim 13 , wherein at least one of the inductance and the first and second capacitances of each of the first and second filters are controllable.

15. The transmitter leakage reduction circuit of claim 1 , wherein the signal transmission arrangement includes:

a connection coupling the first filter to the RF connecting point; and

a transformer having interacting primary and secondary windings, the primary winding being coupled between the RF connecting point and the receiver, the secondary winding being coupled to the second filter so as to provision the auxiliary power amplifier output signal, the transformer being configured to couple the received signal to the receiver.

16. The transmitter leakage reduction circuit of claim 1 , wherein the signal transmission arrangement includes:

a transformer having interacting primary and secondary windings, the primary winding being coupled between the RF connecting point and a third filter, the third filter also being coupled to a reference voltage so that a current swing at a frequency of the received signal is enabled in the primary winding, the primary winding also being coupled to the second filter so as to provision the power amplifier output signal, the secondary winding being coupled to the receiver, the transformer being configured to couple the received signal to the receiver.

17. The transmitter leakage reduction circuit of claim 1 , wherein the signal transmission arrangement includes:

a first transformer having first interacting primary and secondary windings;

a second transformer having second interacting primary and secondary windings; and

wherein the first secondary winding is coupled between the RF connecting point and the receiver, the first primary winding is coupled between the RF connecting point and the second primary winding, the second primary winding also being operationally coupled to a reference voltage so that current swing at a frequency of the received signal is enabled in the first primary winding, the second primary winding being coupled to the second filter so as to provision the auxiliary power amplifier output signal.

18. The transmitter leakage reduction circuit of claim 1 , wherein the signal transmission arrangement includes:

a first transformer having first and second primary windings that each interact with a secondary winding; and

wherein the secondary winding is coupled between the RF connecting point and the receiver, the first primary winding being coupled between the RF connecting point and a third filter, the third filter also being operationally coupled to a reference voltage so that current swing at a frequency of the received signal is enabled in the first primary winding, the second primary windings being coupled to the second filter so as to provision the auxiliary power amplifier output signal.

19. The transmitter leakage reduction circuit of claim 1 , wherein the signal transmission arrangement includes:

a connection coupling the first filter to the RF connecting point;

a third filter coupling a signal from the RF connecting point to the receiver; and

wherein the output of the second filter is directly connected to the input of the receiver.

20. A transceiver capable of operating in a frequency division duplex (FDD) communications system having transmit and receive frequency bands, the transceiver comprising:

a radio frequency (RF) connecting point that is capable of being coupled to an antenna;

a receiver;

a transmitter having a power amplifier that is coupled to the RF connecting point; and

a transmitter leakage reduction circuit comprising:

an auxiliary power amplifier configured to provide an auxiliary power amplifier output signal that represents an output signal of the power amplifier with a controllable phase shift or gain output;

a first filter coupled between the power amplifier and the RF connecting point, the first filter configured to attenuate any signals in the receive frequency band of the power amplifier output signal;

a second filter coupled to the auxiliary power amplifier and configured to attenuate any signals in the receive frequency band of the auxiliary power amplifier output signal; and

a signal transmission arrangement coupled between the first and second filters and between the RF connecting point and the receiver, the signal transmission arrangement configured to suppress a contribution of the power amplifier output signal from a signal received from the RF connecting point using the auxiliary power amplifier output signal to obtain a received signal that is input to the receiver.

21. A communication device capable of operating in a frequency division duplex (FDD) communications system having transmit and receive frequency bands, the communication device comprising:

a transceiver, comprising:

a radio frequency (RF) connecting point that is capable of being coupled to an antenna;

a receiver;

a transmitter having a power amplifier that is coupled to the RF connecting point; and

a transmitter leakage reduction circuit comprising:

an auxiliary power amplifier configured to provide an auxiliary power amplifier output signal that represents an output signal of the power amplifier with a controllable phase shift or gain output;

a first filter coupled between the power amplifier and the RF connecting point, the first filter configured to attenuate any signals in the receive frequency band of the power amplifier output signal;

a second filter coupled to the auxiliary power amplifier and configured to attenuate any signals in the receive frequency band of the auxiliary power amplifier output signal; and

a signal transmission arrangement coupled between the first and second filters and between the RF connecting point and the receiver, the signal transmission arrangement configured to suppress a contribution of the power amplifier output signal from a signal received from the RF connecting point using the auxiliary power amplifier output signal to obtain a received signal that is input to the receiver.