MXPA06004353A - Wideband phase shift device - Google Patents

Abstract

The invention relates to a wideband phase shift device. A phase shift f is introduced on the fixed frequency local oscillator. The principle of the invention is to realise a double translation of the input signals. The phase variation introduced at the level of the local oscillator has a positive value on one of the translated signals and a negative value on the other. The signals are recombined at the reception frequency with a phase difference of 2 f so as to maximise the amplitude of the signal at the output of the summator.

Description

DISPLACEMENT DEVICE OF BAND PHASE NCHA The present invention relates to a broadband phase shift device, more particularly to a phase shift device for a receiver used in the framework of digital terrestrial television, such as a QFD receiver. l (by division ultiplex áe orthogonal frequency by its acronym in English). In a standard signal reception system for digital terrestrial television DVB-T (Digital Video Broadcasting -Terrestre for its acronym in English), an OFD type modulation is most frequently used. This is a particularly robust modulapion and makes it possible to retransmit the isafrequence of a DVB-T channel in a domestic environment. The DVB-T signals can thus be captured at a point in the environment where they are at a sufficient level, then amplified and retransmitted in the environment to be captured identically, from this relay by "portable" digital receivers such as televisions. digital or analog televisions equipped with digital terrestrial decoders. This is the principle retained for Digital Terrestrial Television (DTT for its acronym in English). However, despite the robustness of the modulation, notable reception problems occur for portable reception.

Currently, the favored solution for more robust reception consists in the use of more than one antenna (usually 2). The two antennas are therefore physically positioned to receive two received de-correlated signals corresponding to the same transmitted signal. The distance to allow the signals in the two antenna accesses to be de-correlated and approximately equal to 0.7 times the wavelength of the received signal, a difference between antennas in the order of 45 cm is obtained for the UHF band (470- 860 MHz.} Thus, it seems unrealistic to consider this type of concept relatively difficult to handle due to the dimension of the radiating elements.Another technique is to implement an intelligent antenna device constituted by the two radio accesses.

(Radio frequency) separated with a broadband phase shifter that can be controlled over one of the channels and a combination of the received signals, as shown in the Figure 1 a. However, the implementation of these two techniques is not easy, in the frequency band considered, due to the congestion of the function in the relatively low frequencies considered here [470-860 MHz] since they do not allow an octave to be covered. On the other hand, they can not be integrated into a single component.

Another integrable approach consists of generating two quadrature signals (sine and cosine) from a single signal. Such an integrable circuit is shown in Figure 1 b. Each of these signals thus manages a variable gain amplifier LNA1 and LNA2, controlled by voltage by a polarization CP circuit. The peculiarity of this polarization circuit is that since the resultant output is constant in amplitude, the phase of the resulting signal at the output varies according to the control voltage. However, this integrable technique in one component does not allow an octave to be covered either. The invention aims to overcome these disadvantages. It proposes a new concept based on the use of two separate antennas and the introduction of a fixed frequency variable phase shift controlled on each of the channels by an electrical control that introduces a gradual phase shift in the signals before the sum . It also allows the destructive effect of combining the received signals to be prevented and the signal energy to be maximized. The object of the invention is a broadband phase shift device, more particularly for a digital signal receiver. It comprises translation means formed by a plurality of mixers for translating the first input signals received by the two antennas into two signals. It also comprises oscillation means for sending a local oscillation signal on each of the mixers.

The oscillation means: comprise a local fixed frequency oscillator connected by means of a phase shifter to a first series of mixers and directly connected to a second series of mixers to compensate for the phase shift between the different input signals during a double frequency translation. The invention has the advantage of introducing a phase shift on each of the channels. This phase shift is controlled very high above a very wide frequency band since it is of a phase shift introduced on the fixed frequency local oscillator. The invention also has the advantage that the phase shredder is simple to manufacture due to the fact that it first operates at a fixed frequency and secondly that the required phase variation is at least divided by two. In one embodiment, the phase shifter introduces a positive phase shift on one of the input signals and a negative phase shift on the other input signal parq doubles the phase shift introduced by the phase shifter between intermediate frequency signals . In another embodiment, the mixers are subharmonic mixers that can quadruple the phase shift introduced by the phase shifter between the intermediate frequency signals.

Preferably, the broadband phase shift device can be integrated into a component. The invention will be better understood and other specific aspects and advantages will emerge from reading the following description, the description with reference to the appended drawings, wherein: Figures 1a and 1b show diagrams of blocks of phase shifts according to the previous technique. Figure 2 is a block diagram of a broadband phase shift device according to the present invention. Figure 3 illustrates the different frequency translation and filtering operations implemented. Figure 2 corresponds to a modality of a broadband phase shift device according to the present invention. The broadband phase shift device 10 is part of a system for receiving signals received by the antennas A1 and A2. A description is given for an antenna number equal to 2. However, a larger number of antennas can be considered. This receiving system comprises the amplifiers of LNA (Lpw Moíse Amplifier or Noise Low Level Amplifier) 1 and 2 connected respectively with the antennas A1 and A2, a phase shift device 10 to which the filters 3 and 4 are connected. step band, an adder 5 connected to the outputs of the phase shifting device, a tuner 6 for selection of the reception channel, a demodulator 7 for demodulating the signal of the selected channel. It also comprises a phase shift control block 8 which allows the phase shift of the phase shift device 10 to be controlled. The phase shift device 10 basically comprises oscillation means which are constituted by u? fixed frequency local oscillator 16 which supplies an OL signal for example at 1.98 GHz and a phase shifter 15 voltage controlled by the signal of the phase shift control block 8. It also comprises a first series of mixers 11 and 12 connected by filters to a second series of mixers 13 and 14, to perform a double frequency translation. It should be noted that the filters are not part of the device. The device includes connections to make the connection of these filters easier. Hence, on the first channel the Vantl input signal, received by the antenna A1 and amplified by the amplifier 1, is applied to the bandwidth phase shift device 10 as claimed. This Vantl signal applied to one of the inputs of the mixer 11 is multiplied with the fixed frequency local oscillation signal of the local oscillator 16 and phase shunted by the phase shifter 15. This phase shifter 15 is voltage controlled by the signal of the control block 8, thus translating to the intermediate frequency. The sum and difference of the frequencies are thus generated. By means of the filtering performed by the filter 3, the high band 2270-2660 MHz is selected, thus allowing a translation in supradino mode. The translated IF1 signal is displaced from fa ^ e by + with respect to the input signal. It will be shown later that this phase shift + <; p introduced by the phase shifter over the translated signal allows half of the phase shift 2? be compensated between the input signals. This phase shifted signal, translated into a high frequency after being filtered by the filter 3, is applied over an input of the mixer 13. This is mixed with the fixed frequency signal of the local oscillator 16, allowing a new frequency translation of this offset signal of intermediate frequency phase in a second Voutl signal in the initial frequency band. In parallel, on the second channel the input signal Vant2, received by the antenna A2 and amplified by the amplifier 2, is applied to the broadband phase shift device 10 as claimed. This Vant2 signal applied to one of the inputs of the mixer 12 is multiplied with the fixed frequency local oscillation signal of the local oscillator 16 and phase shifted by the phase shifter 15 controlled by voltage by the signal of the control block 8, translating so to the intermediate frequency. The sum and difference of the frequencies are thus generated. By means of the filtering performed by the filter 4, the low band 940-1339 MHz is selected for example, thus allowing a translation in infradino mode. The translated IF1 signal is shifted by -f with respect to the input signal. This phase shift -f introduced by the phase shifter over the translated signal allows half of the phase shift 2f to be compensated between the input signals. This shifted phase signal, translated into a low frequency after being filtered by the filter 4, is applied on an input of the mixer 14. This is mixed with the fixed frequency signal of the locator oscillator 16, allowing a new frequency translation of this intermediate frequency phase shifted signal in a second signal in the initial frequency band. This device resets the input signals on the two channels of this device. As the phase shift of these input signals 2f, the control circuit will introduce on the first channel, by phase shifter 15, a phase shift of + f and on the second channel a phase shift of -f. The phase shift of 2f between the input signals will therefore be compensated and the output signals of the 2 channels of the phase shift device will therefore be in phase. The phase shift introduced on each channel is controlled well above a very wide frequency band since it is of a phase shift introduced on the fixed frequency local oscillator. The two output signals Voutl and Vout2 will then be added by the adder 6 to provide an IF3 signal at the output which is the sum of the signals Voutl and Vout2, in phase, thus maximizing the amplitude of the restored signal IF3. The control means of the phase shifter 8 provides a control signal of the phase shifter. This signal is, for example, a measurement of the signal energy in the channel eh output of the tuner 6. The control signal can also be, in another embodiment, information of the reception quality of the demodulator 7 to optimize the quality of reception. Consequently, phase displacement will be gradual since it always depends on the signal of perception. To clarify the understanding of this device, we can consider the extreme case for which the signals at the output of the two antennas are in phase opposition. The difference of phase 2f between the input signals therefore equals%. The phase shift device allows the signal on one of the channels to be shifted by + f = +? R / 2 and the other channel by -f = -t¿ / 2, phase shift introduced by the shifter 15 of phase. The 2 signals Voutl and Vout2 will therefore be in phase. The signal of the adder 6 will therefore be maximized.

The proposed variable phase device introduces a controlled phase shift at the level of the first and second mixers to maximize the amplitude of the signal recovered at the adder output. This allows the reception capacity to be improved significantly. The concept can be fully integrated into a component (excluding filtering) on the basis, for example, of a phase shifter implementation described above. Figure 3 illustrates the different frequency translation and filtering operations that will be implemented. The band of RF1 and the input signal of the first antenna A1 is translated into high band by the signal of local oscillator 16 and shifts phase (+ f) to obtain the IF1 band of intermediate frequency with a phase shift + F. The band RF2 of the input signal of the second antenna A1 is translated into a low band by the signal of the local oscillator 16 and shifted phase (-f) to obtain the intermediate frequency band IF2 with a phase shift -f. The IF1 and IF2 bands of intermediate frequency are again translated by the signal of the local oscillator 16 and then added to obtain the resulting IF3 frequency. The resulting displacement 2f of the phase between the two channels is thus doubled with respect to the phase shift f introduced either positively or negatively by the phase shifter.

If the mixers are subharmonic, the phase shift between the two channels is quadrupled. Rely, the harmonics in the frequency 2f will have a phase shift of 2 and will be applied to the fishers 11 and 12 positiv ment on one channel and negatively on the other, thus allowing a phase displacement of 4f between the signals translated. IF1 and IF2.

Claims (5)

1. CLAIMS 1. Broadband phase shifting device comprising: translation means formed by a plurality of mixers for transposing the first input signals received by the two antennas (A1, A1) into two signals; oscillation means, to send a local oscillation signal on each of the mixers; characterized in that the oscillating means comprise a single fixed frequency local oscillator connected by means of u? phase shifter to a first series of mixers and directly connected to a second series of mixers to compensate for the phase shifting between the different input signals during a double frequency translation.
2. 2. Broadband phase shifting device according to claim 1, wherein the phase shifter is voltage controlled by a signal of a control means that allows the fixed frequency signal of the local oscillator to be gradually shifted phase and applied to the first series of mixers.
3. 3. Wideband phase shift device according to claim 2, wherein the phase shift introduces a positive phase shift on one of the signals and a negative phase shift on the other input signal to duplicate the phase shift introduced by the phase shifter between the intermediate frequency signals.
4. 4, Broadband phase shift device according to any of claims 1 or 2, wherein the mixers are subharmonic mixers that quadruple the phase shift introduced by the phase shifter between the inter-frequency signals.
5. 5. Wideband phase shift device according to any of claims 1 to 4, characterized in that it is integrable.