FI110968B - RF filtering resolution for a radio transmitter - Google Patents

Description

RF filtering solution for radio transmitter / receiver - RF-filtereringsupplösning för en radiosändtagare 110968 1 '! The invention relates generally to the architecture of radio transmitters / receivers, and in particular to the application of filter technology to increase the degree of integration of the radio transceiver / receiver and to reduce the physical size.

Prior art radio equipment employing bidirectional frequency division multiple duplex (TDD) (Frequency Division Duplex) (TDD) includes a plurality of RF and intermediate frequency filters on both the transmitter and receiver sides. Figure 1 illustrates a prior art TDD radio 10 including a duplex filter 33 coupled to an antenna 21 for separating transmission and reception signals. The output port of the duplex filter is coupled to a Low Noise Amplifier (LNA) 17 via an impedance matching network 12. The LNA amplifies the received radio signal. This is followed by a second bandpass filter 18, which further filters the received signal. There is also an impedance matching circuit 16 between the LNA and the bandpass filter 18. All of the image impedance matching circuits are illustrated by certain combinations of inductive and capacitive components, but it will be apparent to one skilled in the art that other types of impedance matching networks are possible. The output port of the filter 18 is coupled to a mixer 11, where the received signal is mixed with the first injection signal from the synthesizer 22. The intermediate frequency (IF) signal resulting from the mixing is applied to the receiver's RF circuit for demodulation and other processing.

The transmitter portion of the radio 10 includes a second local oscillator signal (LO) 26, which is produced at the transmitter preamble (not shown) and mixed in the mixer 30 with the first injection signal. The output of the mixer 30 is applied to a bandpass filter-30 timer 13, usually located before the transmitter power amplifier 14. The output of the power amplifier 14 is coupled to the input of the duplex filter 33 via an impedance matching circuit 19. Further, a similar impedance matching network 20 is located between the power amplifier 14 and the bandpass filter 13. There is often a directional switch (not shown) between the power amplifier 14 and the duplex filter 33 for measuring the power level of the signal going to the antenna 35. The antenna port of the duplex filter 33 is coupled to the transmitter / receiver antenna via an impedance matching circuit 23.

110968 2

Integration of two successive radio frequency signal processing blocks, i.e. the RF block (e.g., LNA 17 and mixer 11), and the "off-chip" filter 18 between them is generally difficult. The filter may be, for example, a helix filter, a dielectric filter, or the like, and its use is necessary for operation 5 of the radio structure 10 shown. The difficulty is mainly due to the fact that if the "off-chip" filter and the RF blocks are integrated on the same substrate, the large size of the filter requires, by extension, IC interconnection strips, which are caused by electrical spreading and inductive coupling to degrade the filter. . The use of an "off-chip" filter between the RF blocks makes the complete integration of the 10 structures practically unprofitable. Thus, prior art portable radio devices, such as mobile phones, consist of a plurality of RF blocks implemented with centralized or discrete components, between which filters are coupled.

15 At the interfaces between the discrete components and the filters, the standard impedance is 50Ω. Filter and semiconductor manufacturers adjust the input and output impedances of their products to a standard value to facilitate modular design. The input and output impedances of the RF circuits would often be preferably lower or higher, for example, the input impedance of the LNA 17 may itself be about 100 to 20 Ω. Adaptation to the standard value must be made by an adapter circuit constructed from non-discrete components or integrated by the semiconductor manufacturer into an RF circuit. The adaptive couplings required by the Standar-di interface impedance take up space, increase interference and attenuation and increase manufacturing costs. In order to substantially reduce the manufacturing cost of the radio equipment assembler, a transmitter / receiver filtering solution must be developed that allows easier integration of said blocks.

The impedance adaptations can also be considered in terms of the antenna and the antenna filtering solution to be connected to it. Digital communication networks generally employ 30 Time Division Multiple Access (TDMA) transmissions, which are received in different time slots. If the transmit and receive frequencies are the same, the cellular telephone uses an antenna switch, which alternately connects the antenna to the transmitter and receiver branches of the device. If the transmission and reception are in different frequency bands, a filter similar to the duplex filter used in analogue helices 35 may be used as the separating unit. The latter option also applies to systems employing Frequency Division Multiple Access (FDMA).

110968 I

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FDD (Frequency Division Duplex) cellular phones require filters in addition to the RF switch above, because, the receiver must have selectivity and be protected by a low-noise preamplifier. The transmitter output must attenuate the output frequency harmonics, 5 multiples, and other biases such as mirror frequencies. In addition, the filters eliminate the noise generated by the transmitter chain on the receiver band. The frequencies below the transmit band must also be attenuated as a separate filter. In a system using time-duplex, such as DECT (Digital European Cordless Telephone), various arrangements must be made to ensure that the transmissions generated by the receiver towards the antenna are sufficiently attenuated during signal transmission.

Regardless of whether the radio device uses an antenna switch or frequency-selective filtering alone to separate the transmit and receive signals, the impedance of the antenna must be matched to the associated switch or filter block. The standard 50Ω: η interface impedance again requires at least one impedance matching circuit, denoted by reference numeral 23 in FIG. 1. This circuit is subject to the same loss interference and cost considerations as outlined above for circuits 12, 16, 19 and 20.

It is an object of the present invention to provide a radio transmitter / receiver filtering solution that increases the degree of device integration by eliminating and / or reducing the above-mentioned disadvantages of the prior art. It is also an object of the invention to provide a compact and reasonably priced manufacturing device architecture that is readily applicable to systems with different operating frequencies and other specifications.

The objects of the invention are achieved by combining radio frequency filters of transmitter and receiver chains into a single structure having ports for connecting other components. The gate impedances are selected by dimensioning the parts of the filter unit so that other components can be connected to them without separate matching networks.

. The filtering solution according to the invention is characterized in that it comprises in a coherent filtering unit - to filter the signal of the first filter before passing it outside the filtering unit to a particular first active radio frequency component and 4 110968 - to filter the signal of the second filter through said first active radio frequency.

The invention also relates to a radio apparatus employing a filtering solution as described above. The radio device according to the invention is characterized in that it comprises a unitary filtering unit and means for transferring the filtered signal from said filtering unit to a certain first active radio frequency component and means for returning the signal from said first active radio frequency component to said uniform filtering unit.

The invention is based on taking the capabilities of filter technology as the starting point for radio architecture design. The state-of-the-art RF filter consists of transmission line resonators, possible discrete components, transmission lines connecting these and a frame structure, which is usually a low loss substrate plate, a dielectric (usually ceramic) frame block or a combination thereof. The filter assembly is surrounded by an electrically conductive housing. According to the invention, the filters of the transmitter and receiver branches are integrated into a single filtering unit, in which all the parts are assembled on the same low-loss substrate and are located inside a common interference shield. This assembly forms a single component on the circuit board of a mobile phone or other radio device.

The active components can be implemented as discrete components, as a single GaAs circuit or as a multichip module, which is known per se and belongs to the prior art. In the present invention, the integrated filter unit comprises the necessary ports for connecting the active components and the antenna. The transmission lines and other circuit elements contained in the filter unit are dimensioned such that the impedance of each port corresponds to the impedance level inherent in the component to be connected to it. This eliminates the need for any adapter connections that match individual component interfaces to a standard value of 50Ω: η 30. Individual filtration modules are eliminated and the reliability of the entire structure increases, total weight decreases and physical size decreases. In addition, cost savings in manufacturing are achieved. Significant for electrical operation is the elimination of parasitic Ste elements, which results in faster electrical operation of the circuits and a reduction in overall power consumption.

The invention will now be described in more detail with reference to an exemplary preferred embodiment and the accompanying drawings, in which Fig. 1 illustrates a prior art radio apparatus, Fig. 2 illustrates a radio apparatus according to the invention, and Fig. 3 schematically illustrates an embodiment of an integrated filter unit.

In the foregoing description of the prior art reference is made to Figure 1, so that in the following description of the invention and its preferred embodiments reference will be made mainly to Figure 10. In the drawings, like reference numerals are used for like parts.

Figure 2 is a block diagram of a radio device in which a filtering solution follows a preferred embodiment of the invention. A central part of the transmitting and receiving circuits of the radio device is an integrated filtering unit 25 comprising a duplex filter consisting of two filter branches 15a and 25b and two band pass filters 25c and 25d. The duplex filter receiving branch 25b and the first band-pass filter 25c have ports for switching the low-noise amplifier 17 so that its input is coupled to the duplex filter and the output to the band-pass filter. Similarly, the second bandpass filter 25d and the duplex filter transmitter-branch branch 25a have ports for switching the power amplifier 14 so that its input is coupled to the bandpass filter and the output to the duplex filter. Further, the first bandpass filter 25c has a port for signal transmission to mixer 11 and the second bandpass filter 25d has a port for signal transfer from mixer 30. The duplex filter has a port for connection to antenna 21.

25

The aforementioned gates of the filter unit 25 each have a certain impedance level. The impedance level of the ports associated with the low noise amplifier 17 is shown in Figure 2 as Zrx: M and the impedance level of the ports associated with the power amplifier 14 is designated as Zxx. The impedance level of the input and output ports of a particular amplifier may not necessarily be the same, so that the levels in the filtering unit also need to be adjusted differently, but for clarity only one notation is used for each amplifier. The impedance level of the ports connected to the probes 11 and 30 is denoted by Z2 and the impedance level of the port connected to the antenna 21 is denoted by Z2.

f 35 Combining filters 25a-25d into one integrated filter unit means that in practice all parts associated with these filters are implemented with the same frame design and conductive protective housing. For example, suppose that filters based on dielectric resonators are selected as filters. In this case, one possible structure is shown in Figure 3. The frame structure consists of an interconnected low-loss substrate plate 40 and a ceramic body block 41, the latter of which, in a manner known per se, is formed with resonator holes 42. The surface of the ceramic body block facing the substrate plate 40 Transmission lines 43 and switch pads 44 are formed on the surface of the substrate plate, the former of which mediate the internal connections of the structure and the latter of which components to be attached affect the electrical properties of the structure. The ports through which the integrated filtration unit 25 is connected to the antenna, amplifiers 10 and mixers are conductive strips 45 extending to the edge of the substrate plate. The structure includes a protective cover 46 made of a thin sheet of metal or other electrically conductive material.

In one variation of the structure shown in Figure 3, not all resonators are included in the same ceramic body block, but the filter includes a plurality of separate blocks. Because of the separate blocks, the resonators can easily be of different lengths, which would require a stepwise shape at the other end surface of the dielectric block in a single block filter. In addition, the resonator groups, which must not be electromagnetically coupled, are easily isolated from one another by providing a metallized interface between two blocks. On the other hand, as the number of blocks increases, the number of steps involved in fabricating the filter increases.

The invention does not limit the internal structure of the integrated filtration unit. In addition to dielectric resonators, for example, helix, strip-wire or coaxial resonators can be used as resonators. In a structure based on helix resonators, the frame structure most preferably functions as a circuit board having finger-like projections on one side to which the cylindrical coil conductors of the helix resonators are attached. The same circuit board also serves as a base for transmission lines and discrete components. The electrically conductive protective housing is divided into helix resonators into a housing housing, where the reso-30s are separated by partitions which may have connection openings. The basic structure of a filter based on helix resonators is well known in the art per se.

In some cases, modular design may require that one of the filters included in the integrated filtering unit 25 in Figure 2, such as, for example, the bandpass filter 25d, 35. It is possible to apply the idea of the invention so that only some of the filters belong to the same integrated structure. However, in this case, some of the advantages of the invention are lost, since the same disadvantages of the prior art discussed above in the description of the prior art apply to the separate filter.

Mobile phones are currently the most important application of portable radio technology.

Since there are many different mobile phone systems in the world, it is expected that so-called dual-mode phones, i.e. mobile phones operating in different systems, will become more common. Alternative systems can use very different frequencies. For example, a dual-mode telephone in GSM and DECT systems must have radio frequency bands of both 900 MHz and 1900 MHz. In the dual-mode embodiment of the present invention, all or at least a significant portion of the transmission and reception frequency passive filter sections of the various systems are combined to form an integrated filter unit, thereby avoiding up to ten separate impedance matching networks and several separate filter components. The radio frequency active components of the various rigid systems can be further implemented as a single GaAs circuit or multichip module connected to the integrated filtering unit via impedance-compatible signal ports, thereby making the structure extremely compact and compact in nature.

Claims (12)

110968 A filter structure (25) for filtering radio frequency signals in a radio transmitter / receiver device comprising a first active radio frequency component (17), characterized in that the filter structure comprises a unitary filter unit - a first filter (25b) for filtering the transmitting or receiving signal. before passing it outside the filtering unit to said first active radio frequency component, and - a second filter (25c) for filtering a parallel signal after passing through said en-10 first active radio frequency component. The filter structure of claim 1, further comprising impedance matching means in said unitary filter unit for adjusting the impedances of the ports of the filter unit associated with said first active radio frequency component to match the impedance of corresponding ports of said first active radio frequency component. A filter structure according to claim 1, characterized in that said unitary filtering unit further comprises 20. a third filter (25d) for filtering a signal before passing it outside the data unit to a specific second active RF component and a fourth filter (25a) to filter the signal through said second active RF component. after leadership. The filter structure of claim 3, further comprising impedance matching means in said unitary filtering unit for adjusting the impedances of the ports of the filtering unit associated with said second active radio frequency component to match the impedance of the respective ports of said second active radio frequency component. 30 A filter structure according to claim 3, characterized in that said first (25b) and fourth (25a) filters together form a duplex filter and said filter structure comprises an antenna port for transmitting signals between said duplex filter and an antenna (21) 35 to be connected to said antenna port. . 110968 The filter structure of claim 1, further comprising impedance matching means in said unitary filter unit for adjusting the impedance of said antenna port to match the impedance of the antenna to be connected thereto. 5 Filter structure according to claim 1, characterized in that it comprises a low-loss substrate plate (40) for making connections (43, 44, 45), forming a dielectric body block (41) associated with said substrate plate, and electrically conductive protective cover (46). 10 for covering the substrate plate and the body block. A radio transmitter / receiver device comprising a first active radio frequency component (17), characterized in that it comprises a unitary filtering unit (25) and means for transmitting a filtered transmit or receive direction signal from said filtering unit to said first active radio frequency component. conducting a parallel signal from said first active radio frequency component back to said uniform filtering unit for further filtering. A radio transmitter / receiver device according to claim 8, characterized in that said first active radio frequency component (17) is a low noise preamp of the receiving chain. The radio transmitter / receiver device according to claim 8, characterized in that it further comprises a second active radio frequency component (14) and means for transmitting the filtered signal from said filtering unit to said second active radio frequency component and means for transmitting the signal from said second active radio frequency component to said further filtering unit. 30 The radio transmitter / receiver device of claim 10, characterized in that said second active radio frequency component (14) is a transmission chain power amplifier. i A radio transmitter / receiver device according to claim 8, characterized in that it comprises an antenna (21) communicating with said unitary filtering unit, said unitary filtering unit comprising means (21a, 21b) for separating transmission and reception signals. 10 110968