Patent Grant
10200079
The present invention generally relates to a transceiver. The present invention also relates to a communication device capable of frequency division duplex communication comprising such a transceiver.
Transceivers comprise both a transmitter and a receiver, and are commonly used in a variety of communication apparatuses. Transceivers can be arranged to be operated in semi-duplex, i.e. the receiver and transmitter operate separated in time to prevent the transmitter signal from concealing the received signal. This approach is therefore commonly referred to as time division duplex (TDD). Transceivers can also be operated in full duplex, i.e. the receiver and transmitter operate simultaneously wherein some special arrangements are provided to prevent the transmitter from concealing the received signal. One approach to achieve this is to assign different frequencies for transmission and reception. This approach is therefore commonly referred to as frequency division duplex (FDD).
Often the receiver and the transmitter use the same antenna, or antenna system which may comprise several antennas, which implies that some kind of circuitry may be desired to enable proper interaction with the antenna. This circuitry should be made with certain care when operating the transceiver in full duplex since the transmitter signal, although using FDD, may interfere with the received signal, i.e. internal interference within the transceiver.
Typically the performance of cheap duplexers, commonly used for handsets, is not enough for base stations, not even small base stations, e.g. micro- and pico-base stations, etc. Therefore, traditionally larger and more costly filter technologies have to be used in such applications. It has therefore been a problem for such small base stations that in order to get the desired performance, bulky and costly filter technologies have been used.
An object of embodiments of the invention is to at least alleviate the above stated problem. The inventors have found that contribution by the transmitter signal at the receiver input via one branch can be counteracted by the contribution by the transmitter signal at the receiver input via another branch including a cross connection, wherein the aggregate contribution by the transmitter signal at the receiver input is ideally zero. By a filtering structure, less transmitter energy is lost in the dummy load. In a similar way, less received signal is lost in the dummy load.
According to a first aspect, there is provided a transceiver arrangement comprising a receiver arranged for frequency-division duplex communication; a transmitter arranged for frequency-division duplex communication; an transmission port for connecting to an antenna; a balancing impedance circuit arranged to provide an impedance arranged to mimic the impedance at the transmission port; and a filtering arrangement, which comprises filters of a first type and filters of a second type, connecting the receiver, transmitter, transmission port and balancing impedance circuit.
The filters of the first type may be arranged to pass signals at transmitter frequency and attenuate signals at receiver frequency and are connected between the transmitter and the transmission port and between the receiver and the balancing impedance circuit. The filters of the second type may be arranged to attenuate signals at transmitter frequency and pass signals at receiver frequency and may be connected between the transmitter and the balancing impedance circuit and between the receiver and the transmission port.
The transceiver arrangement may further comprise a connection network which includes a differential cross-connection and the filtering arrangement differentially connecting the receiver, transmitter, transmission port and balancing impedance circuit.
The transceiver arrangement may further comprise a connection network which includes the filtering arrangement connecting the receiver, transmitter, transmission port and balancing impedance circuit by a first transformer arrangement having a primary winding connected to the transmitter, and a secondary winding connected via one of the filters of the first type to a terminal of the transmission port and via one of the filters of the second type to a terminal of the balancing impedance circuit. A second transformer arrangement of the connection network has a primary winding connected to another one of the filters of the second type, which filter is connected to the terminal of the transmission port, and to another one of the filters of the first type, which filter is connected to the terminal of the balancing impedance circuit, and a secondary winding connected to the receiver. The primary winding of the first transformer arrangement may be connected between a single-ended output of the transmitter and a first reference voltage point, and the secondary winding may comprise a first partial winding connected between the filter of the first type and a second reference voltage point, and a second partial winding connected between the filter of the second type and the second reference voltage point. The secondary winding of the second transformer arrangement may be connected between a single-ended input of the receiver and a third reference voltage point, and the primary winding of the second transformer arrangement may comprise a first partial winding connected between the filter of the first type and a fourth reference voltage point, and a second partial winding connected between the filter of the second type and the fourth reference voltage point. The first and second partial windings of one of the first and second transformer arrangements may be wound to give mutually aggregate magnetic field and the first and second partial windings of the other one of the first and second transformer arrangements may be wound to give mutually opposite magnetic field.
The filters of the first and second types of the filtering arrangement may be any one of Surface Acoustic Wave, Bulk Acoustic Wave, and Film Bulk Acoustic Resonator filters.
The transceiver arrangement may comprise four duplexer arrangements, wherein each duplexer arrangement functionally comprises a filter of the first type and a filter of the second type of the filters of the filtering arrangement.
The transceiver arrangement may comprise two differential duplexer arrangements, wherein each differential duplexer arrangement functionally comprises two filters of the first type and two filters of the second type of the filters of the filtering arrangement.
According to a second aspect, there is provided a communication device, capable of frequency division duplex communication via a communication network, comprising a transceiver arrangement according to the first aspect. Other objectives, features and advantages of the present invention will appear from the following detailed disclosure, from the attached dependent claims as well as from the drawings. Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the [element, device, component, means, step, etc]” are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.
The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings.
The transceiver arrangement 300 works differentially and has a symmetry between the antenna port 306 and the balancing impedance circuit 308, wherein a portion of the circuitry connected to the balancing impedance circuit 308 to the receiver 302 is cross-connected with respect to the portion of the circuitry connected to the antenna port 306. This provides for cancelling of transmitter signal contribution at receiver input when balancing impedance circuit 308 is perfectly mimicking the impedance at the antenna port 306. Considering that an absolutely perfect mimic of impedance may not be present at all times, the transmitter signal contribution at receiver input is further reduced. This is accomplished by filters 310, 311, 312, 313, 314, 315, 316, 317 that are symmetrically arranged and symmetrically valued with respect to the differential connections. They are however not symmetrical in sense of passing signals from the transmitter towards the antenna port and balancing impedance circuit and passing signals from the antenna port and the balancing impedance circuit towards the receiver, as will be elucidated below.
Filters 310, 312, 315, 317 are of a first type which are arranged to pass signals at transmitting frequency, i.e. the frequency at which the transmitter 304 transmits, and are arranged to attenuate signals at receiving frequency, i.e. the frequency at which the receiver 302 receives desired signals. The transmitting frequency and the receiving frequencies are distinguished since the transceiver 300 is arranged to work with FDD communication.
Filters 311, 313, 314, 316 are of a second type which are arranged to pass signals at the receiving frequency and attenuate signals at the transmitting frequency. Thus, a differential signal at transmitting frequency from the transmitter 304 is passed via filters 310, 317 towards the differential input of the antenna port 306 such that it is enabled to be transmitted efficiently through an antenna connected to the antenna port 306. The transmit signal is attenuated by filters 313, 314 to not cause interference at the input of the receiver 302. The differential transmit signal is attenuated by filters 311, 316 such that only very little transmit energy is wasted in the balancing impedance circuit 308, and also similar transmit energy reaches the receiver 302 via the cross-coupling 326, 327 as through the non cross-coupled path, which reduces interference.
A received signal from an antenna connected to the antenna port 306 reaches the receiver 302 via filters 313, 314 which passes the receiving signal but attenuates the transmit signal which also is present at the antenna port. Input of the receiver 302 is also connected to the balancing impedance circuit 308 via the cross coupling 326, 327 and filters 312, 315, but the filters 312, 315 attenuates the receiving signal wherein very little signal energy of the received signal is wasted in the balancing impedance circuit 308.
Thus, the transceiver 300 provides a structure which efficiently provides signals from the transmitter to the antenna port, efficiently provides signals from the antenna port to the receiver, and at the same time reduces interfering signals from the transmitter to reach the receiver.
Symmetry is desired to keep the aggregate contribution by the transmitter signal at the receiver input close to zero, i.e. cancellation will then occur through the cross coupling 326, 327. This is accomplished by using the same type of filters in the cross-coupled and non cross-coupled paths.
While the embodiment demonstrated with reference to
The transceiver arrangement 400 has a symmetry between the antenna port 406 and the balancing impedance circuit 408, wherein a portion of the circuitry connecting the balancing impedance circuit 408 to the receiver 402 is cross-connected with respect to the portion of the circuitry connected to the antenna port 406 by arrangement of transformers 418, 426 conveying signals from/to a transmitter 404/receiver 402, respectively. The cross-connection is accomplished by arrangement of windings denoted by the dots at windings 421, 423, 427, 429. This provides for cancelling of transmitter signal contribution at receiver input when balancing impedance circuit 408 is perfectly mimicking the impedance at the antenna port 406. Considering that an absolutely perfect mimic of impedance may not be present at all times, the transmitter signal contribution at receiver input is further reduced. This is accomplished by filters 410, 412, 414, 416 that are symmetrically arranged and symmetrically valued with respect to the differential connections. They are however not symmetrical in sense of passing signals from the transmitter towards the antenna port and balancing impedance circuit and passing signals from the antenna port towards the receiver, as will be elucidated below.
Filters 410, 412 are of a first type which are arranged to pass signal at transmitting frequency, i.e. the frequency at which the transmitter 404 transmits, and are arranged to attenuate signals at receiving frequency, i.e. the frequency at which the receiver 402 receives desired signals. The transmitting frequency and the receiving frequencies are distinguished since the transceiver 400 is arranged to work with FDD communication.
Filters 414, 416 are of a second type which are arranged to pass signals at the receiving frequency and attenuate signals at the transmitting frequency. Thus, a single-ended signal at transmitting frequency from the transmitter 404 is passed via filter 410 towards the single-ended input of the antenna port 406 such that it is enabled to be transmitted efficiently through an antenna connected to the antenna port 406. The transmit signal is attenuated by filter 414 to not cause interference at the input of the receiver 402. The transmit signal is attenuated by filter 416 such that only very little transmit energy is wasted in the balancing impedance circuit 408, and also a similar amount of transmit signal reaches coil 429 as coil 427, which reduces interference to the receiver 402.
A received signal from an antenna connected to the antenna port 406 reaches the receiver 402 via filter 414 which passes the receiving signal but attenuates the transmit signal which also is present at the antenna port 406. Input of the receiver 402 is also connected to the balancing impedance circuit 408 via filters 412, but the filter 412 attenuates the receiving signal wherein very little signal energy of the received signal is wasted in the balancing impedance circuit 408.
Thus, the transceiver 400 provides a structure which efficiently provides signals from the transmitter to the antenna port, efficiently provides signals from the antenna port to the receiver, and at the same time reduces interfering signals from the transmitter to the receiver.
Symmetry is desired to keep the aggregate contribution by the transmitter signal at the receiver input close to zero, i.e. cancellation will then occur through the cross coupling achieved by the arrangement of transformers 418, 426, which will be further elucidated below. This is accomplished by using the same type of filters in the path of the antenna port and the path of the balancing impedance circuit.
The transformer 418 is arranged to convey signals from the transmitter 404 towards the antenna port 406, but also to the rest of the symmetrical circuit as elucidated above. The transformer 418 comprises a primary winding 420 connected between a single-ended output of the transmitter 404 and a reference voltage point 419. In case the transmitter 404 has a differential output, the winding 420 is connected between the differential output terminals of the transmitter 404. The transformer further has a secondary winding 422 connected between the filter 410 and the filter 416. The secondary winding 422 comprises a first partial winding 421 and a second partial winding 423 wherein the first partial winding is connected between the filter 410 and a reference voltage point 425, and the second partial winding is connected between the reference voltage point 425 and the filter 416.
The transformer 426 is arranged to convey signals from the antenna port 406, towards the receiver 402 but also connect the receiver to the rest of the symmetrical circuit as elucidated above. The transformer 426 comprises a primary winding 428 connected between the filter 412 and the filter 414. The primary winding 428 comprises a first partial winding 427 and a second partial winding 429 wherein the first partial winding 427 is connected between the filter 414 and a reference voltage point 432, and the second partial winding 429 is connected between the reference voltage point 432 and the filter 412. The transformer further has a secondary winding 430 connected between a single-ended input of the receiver 402 and a reference voltage point 431. In case the receiver 402 has a differential input, the winding 430 is connected between the differential input terminals of the receiver 402.
The mutual relation between the first and second partial windings 421, 423; 427, 429 of the transformers 418, 426 in sense of orientation provides for the cross-connection or cross-coupling to enable zeroing or reducing transmitter contribution at receiver input, as elucidated above. The illustrated orientations in
The filters in the different embodiments demonstrated above can be made more or less complex, and with different constraints on performance. Simple filters comprising single capacitors or inductors may be used, but may not fulfil the demands of constraints set up. High-order filters may on the other hand introduce other problems, and/or cost/space issues.
Depending on whether receiving frequency is higher or lower than the transmitting frequency, an example may be that the filters of the first type can be selected as one of the types illustrated in
The antenna port described above need not necessarily by connected to an antenna, but can equally be connected to a wired line which conveys radio frequency signals. Thus, the communication device 700 described with reference to
The filters used will be discussed below with reference to some examples of transceiver arrangement embodiments. It would be desirable to use cheap filter technology like SAW, BAW, FBAR and other similar technologies instead of the bulky and costly filter technologies have been traditionally used in base stations, but so far the performance requirements are such that this has not been possible. However, it would be a great advantage to be able to use cheap filter technology instead to reduce size and cost of the duplex filters. Some existing solutions use a separate filter in front of the duplexer (cascaded filters) to increase Tx to Rx isolation. This results in worse sensitivity and insertion loss for the Receiver chain and worse insertion loss for the Tx chain of the radio.
Specifically for small cell solutions, dimension, weight and cost restrictions, small filters would be advantageous. Usually the drawback of existing miniature type filters (SAW/BAW/FBAR etc.) is that the Tx to Rx isolation may not be good enough. Other small type filters (small air cavity filters, ceramic waveguide filter, monoblock filter, ceramics filter, etc.) are sometimes preferred due to their ability to handle powers in the magnitude of a few tenths of Watts.
By employing such low cost filters, e.g. based on SAW, BAW or FBAR technology, in a transceiver arrangement as demonstrated above, the above described approach can be used for implementing a duplex filter for such small base stations. The isolation between Tx and Rx is increased by introducing a leakage path that adds cancellation to the inherent isolation achieved by the duplexer, as demonstrated above.
This opens up for the use of small and cheap duplex filter implementations for small base stations instead of larger and more expensive solution used today, for example, air cavity filters. The isolation is increased by introducing the above suggested cancellation.
The insertion-loss of this new duplex configuration will be almost as good as for a normal duplexer while the isolation is much better.
Using the above demonstrated approach, and using SAW/BAW/FBAR or other similar filters implies a small and low cost duplexer, particularly suitable for small base stations, with superior isolation between Tx and Rx.
An advantage of embodiments of this invention is that the insertion loss will be almost as good as for a traditional duplexer, e.g. a stand-alone SAW or BAW duplexer not using the above demonstrated structure, while the isolation performance is much better than the traditional duplexer. The Tx power leaking into the cancellation path should be ˜40 dB lower than what goes into the path to the antenna and vice versa on the Rx side.
Assuming there is 1% matching between the filters/Duplexers used in the
By introducing the leakage path, there may be an improvement of the Tx to Rx isolation performance achieved by a traditional duplexer.
Thus, the embodiments demonstrated with reference to
The filters used in the embodiments demonstrated with reference to
The filters used in the embodiments demonstrated with reference to
Measurements have shown that the filter matching between individual specimens of BAW filters is quite good both for amplitude and phase. If the filters are designed together on the same substrate and in the same package, the matching is expected to be even better.
Better matching of the filters will result in improved isolation due to better cancellation of the leaked signal between the Tx and Rx ports of the duplex arrangement compared to a traditional duplexer.
The termination impedance, i.e. the balancing impedance circuit, should be as close to the antenna impedance as possible. Some tuning of the termination impedance could be useful to match the antenna impedance. As an alternative, the termination impedance could be fixed and an antenna tuner may be used to get the desired antenna impedance. The termination impedance may be set to a value for the antenna in the particular implementation and application.
The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.
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