Apparatus in a microwave system

The present invention use the properties of a TDD-transmission on a specific mixer in such a manner that in the transmit mode a first RF signal is amplified in the mixer with an amplification factor greater than, or equal to, or less than one, and in the receive mode the received RF signal is mixed with a second RF signal.

DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 illustrates a part of an exemplary transceiver 100 in a Time Division Duplex (TDD) system. Normally, in such a TDD system the transceiver comprises a complete receiver and transmitter with a switch, controlled by a TDD Control signal S 100 , to change between receive and transmit mode. In the exemplary transceiver 100 in FIG. 1 with a switch 160 in transmit mode, the information carrying baseband signal S 180 with an application specific information bandwidth is modulated by the modulator (MOD) 180 into another signal S 170 with another application specific modulated bandwidth and center frequency f 170 defined by the carrier frequency. The modulated signal S 170 is connected to an amplifier 170 , which amplifies the signal S 140 before it is filtered in the front-end filter 140 . The antenna (ANT) 150 then transmits the modulated and filtered signal S 160 . In the front-end filter 140 , all other components are suppressed as e.g. harmonics, spurious signals and intermodulation products, beside the RF signal S 160 which is to be transmitted by the antenna (ANT) 150 into the air. With the switch 160 in the receive mode, the received RF signal S 150 , from the antenna 150 , is first filtered by the front-end filter 140 resulting in a filtered received RF signal S 130 . Which is then e.g. mixed down in the mixer 130 with a RF signal S 110 produced by a Local Oscillator (LO) 110 . The product from the mixer is the Intermediate Frequency (IF) signal S 120 . The IF signal S 120 is then demodulated by the demodulator (DEM) 120 to extract the baseband signal S 190 . For an ideal transmission system arrangement (i.e. information signal S 180 transmitted from one terminal to a receiving terminal) without distortion the extracted baseband signal S 190 is identical with the information carrying baseband signal S 180 into the modulator (MOD) 180 . Further in FIG. 1 a TDD Control signal S 100 is shown connected to the demodulator (DEM) 120 and modulator (MOD) 180 of the baseband signal S 190 and information carrying signal S 180 , respectively. TDD Control signal S 100 is also connected to the switch 160 , which controls the switch 160 to switch between the receive and transmit mode in correspondence to the rate of the TDD frame. The TDD Control signal S 100 here, symbolizes the synchronization between receive mode and the demodulator (DEM) 120 working and synchronization between transmit mode and modulator (MOD) 180 working. FIG. 2 illustrates a part of an exemplary transceiver 200 in a Time Division Duplex (TDD) system similar to the transceiver in FIG. 1 . The main difference is how the mixer 250 is placed in the transceiver; directly next to the front-end filter 260 , corresponding to the front-end filter 140 in FIG. 1 . The result of placing the mixer 250 there next to the front-end filter and after the modulator (MOD) 230 is that the information carrying baseband signal S 280 , modulated by the modulator (MOD) 230 into another signal S 250 with another application specific modulated bandwidth and center frequency f 250 , e.g. preferably can be up-converted by the mixer 250 , which is not the case for the modulated signal S 170 in FIG. 1 . Another difference of FIG. 2 is the placement of the switch 240 , here in FIG. 2 the switch in transmit mode receive the modulated signal S 250 into the mixer 250 and in receive mode the received IF signal S 220 from the mixer 250 is passed through the switch 240 and further inputted into the demodulator (DEM) 220 . The demodulated signal S 290 in FIG. 2 is corresponding to the demodulated signal S 190 in FIG. 1 . By this arrangement switches in the RF-frequency path is avoided. As further signals and components in FIG. 1 correspond to: S 100 &rlarr;S 200 , 110 &rlarr; 210 , 180 &rlarr; 230 , 120 &rlarr; 220 , 140 &rlarr; 260 , 150 &rlarr; 270 , S 180 &rlarr;S 280 , S 170 &rlarr;S 250 , S 160 &rlarr;S 270 , S 150 &rlarr;S 280 , S 130 &rlarr;S 230 , S 120 &rlarr;S 220 , in FIG. 2 . In FIG. 3 a block diagram 300 is shown of a mixer 330 with its first S 300 , second S 310 , and third S 320 input signals and its output signal S 330 . In a general mixer 330 , the second S 310 and third S 320 input signals are multiplied, S 330 &equals;S 310 · S 320 resulting in the product output signal S 330 . If the mixer 330 is ideal no spurious signals is produced by the mixer 330 and no intermodulation products will be found in the output signal S 330 . The first input signal S 300 symbolizes the TDD Control signal S 400 , S 500 , S 600 in FIG. 4 - 6 that is further explained below where for example the mode of the mixer can be changed according to the invention. It should be noted that the realization of the TDD Control signal S 300 need not be by a separate input signal of the mixer 330 , e.g. it may be connected to any of the other two input signals S 310 or S 320 , or the TDD Control signal S 300 may just change the use of an input port to an output port. When the second S 310 and third S 320 input signals are two sinusoidal signals described as, S 310 &equals; &Scirc; 320 ·sin(w 310 t) and S 320 &equals; &Scirc; 320 ·sin(w 320 t), as the corresponding frequencies for the second signal S 310 is f 310 and third signal S 320 is f 320 (w 310 &equals;2&pgr;f 310 , w 320 &equals;2&pgr;f 320 ), the signal product S 330 is mathematically described as, 1 S330 = 1 2 &it; &Sum; m , n &it; S ^ 310 &it; m , n &CenterDot; S ^ 320 &it; m , n &af; ( cos &af; ( m &it; &it; w 310 - n &it; &it; w 320 ) - cos &af; ( m &it; &it; w 310 + n &it; &it; w 320 ) ) , where &Scirc; 310 and &Scirc; 320 are top amplitude of the input signals, and m and n is the order of the harmonics. In FIG. 1 and FIG. 2 the TDD Control signal S 100 and S 200 control a switch, which is switching between transmit and receive mode. At high RF frequencies a switch with high performance and with low disturbance properties is expensive. In FIG. 1 , with a switch so close to the antenna, affect the linearity of the transceiver. For both the prior art transceivers in FIG. 1 and FIG. 2 the conversion losses for the mixers 130 and 250 are high. Normally, in the prior art both the transmitted and received signal need to be amplified. In FIG. 1 it is illustrated by the amplifier 170 next to the modulator (MOD) 180 . In receive mode an amplifier placed in FIG. 1 after the switch 160 (in between the switch 160 and mixer 130 ) could help to amplify an often weak received RF signal S 150 . An amplifier and a switch increase the size of the transceiver, affect the linearity and are a costly pieces of a radio equipment at high frequencies. A general overview of one exemplary transceiver 400 according to the invention is illustrated in FIG. 4 . In FIG. 5 and 6 is this general overview divided up into two parts 500 , 600 to separately illustrate when the transceiver 400 in FIG. 4 is in its transmit ( FIG. 5 ) and receive ( FIG. 6 ) mode. The block diagrams of the exemplary embodiment in FIG. 4 - 6 is a part of a transceiver 400 , 500 , 600 used in a TDD system. The block diagram in FIG. 4 show an oscillating means block 410 , a mixer 430 , a front-end filter 440 , antenna 450 and demodulator 420 . The oscillating means block 410 and mixer 430 and demodulator (DEM) 420 are all controlled by the TDD Control signal S 400 . It has a rate of a TDD frame, thus in the exemplary transceiver 400 according to the invention, the TDD Control signal S 400 switches mode (functionality) of the mixer 430 and the oscillating means block 410 . As described above the TDD Control signal S 400 connected to the demodulator (DEM) 420 is just symbolizing the synchronization between the receive mode and demodulator (DEM) 420 working. The change of mode (functionality change) is coordinated with receive and transmit mode. With the TDD Control signal S 400 connected to the mixer 430 in FIG. 4 the TDD Control signal S 400 may interfere with the other incoming signals to the mixer, but as the TDD Control signal S 400 consists of a direct current (DC) signal, its value does not affect the mixer product output S 420 . However, one skilled in the art will recognize that another solution is not to give the TDD Control signal S 400 a value that is mixed with the other incoming signals to the mixer. Instead, a value is given that only implies controlling the functionality of the mixer, i.e. shifting the mixer function between amplifier (attenuator mode depending on the implementation) and mixer mode. Another solution is to switch direction of at least one signal into the ports of the mixer, e.g. change direction of a signal such as an input port in transmit mode change into an output port in receive mode. The oscillating means block 410 in FIG. 4 , is symbolizing the modulator (MOD) 510 in FIG. 5 in transmit mode, and the local oscillator (LO) 610 in FIG. 6 in receive mode. In transmit mode, illustrated in more detail in FIG. 5 , the same oscillating means block 410 and information carrying baseband signal S 480 into the oscillating means block 410 in FIG. 4 , is illustrated in FIG. 5 as an information carrying baseband signal S 580 . The modulator 510 in FIG. 5 , modulates the incomming information carrying baseband signal S 580 into a first RF signal S 510 (in transmit mode, corresponding to first RF signal S 410 in FIG. 4 ) with another application specific modulated bandwidth and center frequency f 510 defined by the carrier frequency. In transmit mode the mixer 530 transfers the first RF signal S 510 with or without amplification (amplify the first RF signal S 510 with an amplification factor greater, or equal, or less than one) resulting in the transmitted RF signal S 540 (S 540 &equals;K·S 510 when −∞&lE;K&lE;∞). If first RF signal S 510 is a sinusoidal signal, S 510 &equals; &Scirc; 510 ·sin(w 510 t) when w 510 &equals;2&pgr;f 510 and m is the order of an harmonic and K m (−∞&lE;K m &lE;∞) symbolizes an amplification or attenuating factor connected to each harmonics m, the output signal of the mixer will be, S 540 &equals;K m ·&Scirc; 510 ·sin(mw 510 t) By transferring the first RF signal S 510 with or without amplification through the mixer 530 , the mixer 530 will not cause any conversion losses. Dependant on how the filter bandwidth is set the signal after the filter 540 can be changed, thus here, the signal input to the filter S 540 equals the signal after the filter S 560 (S 540 &equals;S 560 ). The amplification factor (−∞&lE;K m &lE;∞) is dependent on how well the mixer is performing as an amplifier. In a mixer with passive components there will be an attenuation for the first RF signal S 510 , while in a mixer with active components, an amplification factor greater than one can be expected. In receive mode, illustrated in more detail in FIG. 6 , the oscillating means 610 , a Local Oscillator (LO) 610 , produces a second RF signal S 610 so the received RF signal S 650 (in air from the antenna 650 ), after being filtered S 630 , is e.g. down-converted by the mixer 630 . The change of frequency (i.e. the frequency change of the signal between first RF signal f 510 and second RF signal f 610 ) for the signal produced by the oscillating means 610 is controlled as said above by the TDD Control signal S 600 . In FIG. 6 , also the Local Oscillator (LO) 610 can be symbolized with the same modulator block (MOD) 510 as in FIG. 5 , with the information baseband carrying signal S 580 equal to zero. The modulator would then produce a local oscillating (LO) signal, a second RF signal S 610 . However, one skilled in the art will recognize that the second RF signal S 610 described above to be a local ocillating (LO) signal, may also be a modulated information signal with a modulated bandwith. The result after mixing the second RF signal when the second RF signal S 610 has a modulated bandwith with a certain center frequency f 610 , with the receiving RF signal S 630 (which has another modulated bandwith and center frequency) will be a signal with two modulated information signals. In a further step the information signal comming from the oscillating means 610 can be removed since it is a known signal and the information signal from the receiving RF signal S 630 can be obtained. One skilled in the art will recognize further that a filter may be placed before the demodulator (DEM) 620 or/and after the oscillating means 510 , 610 to filter out frequencies of interest. Further in the receive mode, a direct demodulating mode can be implemented, in which the second RF signal S 610 from the oscillating means 610 is mixed in the mixer 630 with the received RF signal S 650 (in air from the antenna 650 ) in such a way so the resulting signal S 620 out of the mixer 630 is equal to the demodulated signal S 690 out of the demodulator (DEM) 620 , which is the same function as if the demodulator (DEM) 620 is included in the mixer 630 . In receive mode, illustrated in FIG. 6 , the mixer 630 is mixing the second RF signal S 610 from the oscillating means 610 with the filtered received RF signal S 630 i.e., S 620 &equals; S 610 · S 630 resulting in the frequency product, f 620 &equals;&verbar;± f 610 &mnplus; f 630 &verbar; &verbar;f 610 &plus;f 630 &verbar;, &verbar;f 610 −f 630 &verbar;, &verbar;−f 610 −f 630 &verbar;, &verbar;−f 610 &plus;f 630 &verbar;) if the corresponding frequency for each signal is, S 620 &rlarr;f 620 , S 610 &rlarr;f 610 , S 630 &rlarr;f 630 . The frequency of the RF signal S 560 to be transmitted (after it has first been modulated, then amplified with an amplification factor greater or less than one, and lastly filtered) and the receiving RF signal S 650 from air is normally the same (f 560 &equals;f 650 , if the corresponding frequency for each signal is S 560 &rlarr;f 560 and S 650 &rlarr;f 650 ), but different frequencies (f 560 ≠f 650 ) can also be used. The function of the filter 440 , 540 , 640 in general for the receive and transmit mode is to select the frequency band in use. In receive mode, according to FIG. 6 the frequency f 610 of the second RF signal S 610 is selected so that together with the filter 640 the resulting IF signal S 620 out of the mixer 630 into the demodulator (DEM) 620 is chosen so that when f 610 &gE;f 650 only the frequency of the second RF signal f 610 minus the frequency f 650 of receiving RF signal S 650 from air (f 610 -f 650 ), or when f 610 &lE;f 650 the frequency f 650 of receiving RF signal S 650 from air minus the frequency f 610 of second RF signal S 610 (f 650 -f 610 ) is the used product of the mixer 630 . But this all depends on which IF signal S 620 is of interest in the application. In FIG. 7 is illustrated a circuit diagram 700 of a practical realization of the mixer 430 , 530 , 630 in FIG. 4 - 6 according to the invention. The circuit diagram in FIG. 7 shows a transistor circuit 700 which is on one hand a power amplifier (or a low loss attenuator depending on the implementation) and on the other hand a converting mixer. This design combines cost efficiency and predictability with good RF performance. In transmit mode the transistor circuit 700 is working as a common source amplifier with the first RF signal S 510 , fed into S 510 /S 610 port P 750 . An appropriate voltage for the drain (D) bias Vd is fed into Vd/Ground port P 710 , approximately &plus;3 VDC (i.e. the TDD Control signal S 400 , S 500 , S 600 in synchronization with the TDD frame). With the TDD control signal S 500 connected to the drain (D) the channel of the FET transistor T 710 will be switched between interruption and short circuit. S 540 /S 630 port P 720 is the output from power amplifier, which is connected to the front-end filter 540 . Disable Output/S 620 port P 730 is disabled. An appropriate voltage for the gate (G) bias Vg, is approximately 0 VDC, which is fed to the amplifying transistor T 710 through Vg port P 740 . Circuit elements C 720 , L 710 , C 730 , L 720 , C 740 and L 730 are all elements performing matching and band pass filtering with corresponding ports P 720 , P 730 , and P 750 . In the receive mode the local oscillator (LO) signal, the second RF signal S 610 , is fed to S 510 /S 610 port P 750 . The second RF signal S 610 input power switches the transistor channel S 510 /S 610 port P 750 between interruption and short-circuit (ideal), i.e. the mixer 630 , 700 acts as a resistive mixer. Vd/Ground port P 710 is connected to ground as the transistor T 710 is working with 0 VDC on the drain (D) in receive mode (i.e. mixer mode) . A big frequency gap between the receiving RF signal frequency f 630 (the corresponding frequency f 630 for receiving RF signal S 630 ) and the receiving IF signal frequency f 620 (the corresponding frequency f 620 for signal S 620 ) may result in interference, thereby these signals are fed into separate transistor channels S 540 /S 630 port P 720 and Disable Output/S 620 port P 730 . The filtered receiving RF signal S 630 is fed into the transistor channel S 540 /S 630 P 720 and the receiving IF signal S 620 is outputted from Disable Output/S 620 port P 730 . S 540 /S 630 port P 720 and Disable Output/S 620 port P 730 is filtering (works as a short-circuit) unwanted frequency signals produced by the oscillating means 610 . For best performances in receive mode is the mixing transistor T 710 working near pinch-off; it is realized by feeding the gate (G) bias a correct voltage through connection Vg port P 740 . Circuit elements C 720 , L 710 , C 740 and L 730 are all elements performing matching and band-pass filtering with corresponding ports P 720 and P 750 . Further is circuit element C 730 with L 720 and G 720 filtering the frequency produced by the oscillating means 610 . Decoupling of the voltage supply Vd, and Vg, Vd/Ground port P 710 and Vg port P 740 are performed through the circuit elements C 710 with G 710 and C 750 with G 720 . The transistor T 710 with G-gate, S-source, and D-drain is of PHEMT (pseudomorphic) type. The S 510 /S 610 port P 750 and Disable Output/S 620 port P 730 can be connected to the same drain (D) terminal and the source (S) terminal connected to ground. The noise factor is increasing almost only with increased loss when mixing. There is no gain factor in receive mode. As a person skilled in the art appreciates, application of the invention is in no way limited to only TDD system networks. As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a wide range of applications. Accordingly, the scope of patented subject matter should not be limited to any of the specific exemplary teachings discussed.