Process and apparatus for changing frequency in a multichannel radio system

0001The invention relates to a method and apparatus the frequency change in a multi-channel radio system according to the preamble of claim 1.

0002Wireless alarm systems include detection systems, which in the case a detected hazard (fire, intrusion) a danger message via a radio link to a hazard warning center transmit, in the other to eliminate the risk measures initiated (alerting the fire brigade or the police) will. The alarm sensors comprise, a transmitting and Receiving device and are for use on inadequate Locations as independent as possible, ie with a battery and not operated by a cable connection to a power grid will. For all components of the signaling sensor possible power saving interpreted, and the components should also be switched on only at certain times and not constantly be in operation.

0003In the conventional method, signals with different Frequencies for the transmission between the hazard warning center provide and alarm sensor generates a voltage controlled Oscillator (VCO) signals with a high frequency as Carrier frequency using a phase locked loop (PLL). there generates a reference oscillator such as a quartz oscillator, Signals with a very stable frequency. On downstream reference divider produces from digital one Reference frequency. Here are the reference frequency and the Frequency of the reference oscillator in an integer division ratio to each other. The from the voltage controlled oscillator High frequency is generated by a high frequency divider digitally divided down to a reduced frequency. The high frequency and the reduced frequency are doing also in an integer division ratio. In a phase detector reference frequency with compared to the reduced frequency, and it is a function the deviation of the frequencies of each other, an error voltage generated. This error voltage is a so-called Loop filter for alternating voltage suppression on the voltage controlled oscillator placed, which thereby its High frequency changes. This change causes at fixed Dividing ratio of the high frequency divider, a change the reduced frequency, thus increasing the error voltage decreased until the reference frequency and the divided down Frequency are the same and then the desired RF is generated by the voltage controlled oscillator. Of the Phase-locked loop is "locked". A change in the high frequency now takes place by changing the division ratio of the high frequency divider. A change in the division ratio the high frequency divider by one causes Shift of the high frequency to the reference frequency. Therefore is at herkömmmlichen method for generating different High frequencies with a predetermined channel spacing the reference frequency selected equal to the channel spacing. are completely analogous to carrier frequencies beat frequencies generated for use in superheterodyne receivers. at combined transmitting and receiving devices (transceivers) are thereby cost saving some components both to generate of the transmission signals as well as for receiving the emitted Signals.

0004A disadvantage of this method is the size of Regelungseinschwingzeit with small channel spacing. So does a channel spacing 25 KHz, as described for example for radio alarm systems is provided, which at high frequencies work to 869 MHz, that only every 40 microseconds, a new control value is available. An estimated 100 necessary control values the correct frequency setting is thus the Settling 4 ms. In connection with the use as battery-powered radio fire alarm disturbs the in this time operating current flowing. Another disadvantage of the low Reference frequency is that higher-frequency instabilities the voltage controlled oscillator insufficiently are corrected, whereby the spectrum of a high frequency undesirably high noise floor created.

0005From an application note (Philips Semiconductors SA8025 Fractional-N synthesizer for 2GHz band-applications TO 1891 Djen WS) is a method known to the settling time and to reduce the noise floor. Here, the high frequencies not divided by an integer, and then with the reference frequency is compared in the phase detector, but it is also a division by a rational number. this results disadvantageously undesired spurious frequencies.

0006It is therefore the object of the invention to provide a method and an Device with good noise characteristics for power saving ends Changing the frequency in a multi-channel radio system specify a small channel spacing.

0007The object is inventively achieved by a method of the mentioned type with the characterizing features of claim 1 dissolved.

0008According to the invention the disturbing low reference frequency avoided because the frequency of the reference oscillator is readily varied when the high frequency over some channels is changed. This higher reference frequencies arise with the advantageous result of lower transient and lower power consumption by sending Claim 1, and when receiving according to the superposition principle according to claim 2nd

0009In an advantageous embodiment of the method according to claim 3, the frequency of the reference oscillator is additionally varied so that a temperature dependent frequency deviation the reference oscillator is compensated.

0010A further advantageous embodiment of the method Claim 4 provides that the frequency of the reference oscillator also taking into account existing circuit tolerances of the reference oscillator is varied.

0011In one embodiment of the invention according to claim 5 are both beat frequencies of a receiver according the double conversion principle by the variable reference frequency generated. By using only one reference oscillator are thereby cut costs in an advantageous manner.

0012By means of the targeted generation of beat frequencies according to claim 6 it is ensured in an advantageous manner, that for all channels on receipt of the same Band filter is working.

0013Particularly suitable method for the carrier frequency range is 868-870 MHz claim 7.

0014In claim 8 is advantageously an inventive Apparatus for applying the method in a transmitter and in claim 9 is a device for use in a Receiver described.

0015In claim 10, an apparatus is described with which the The method according to the invention used in a transceiver becomes.

0016The device described in claim 11 has the advantage that for both beat frequencies of a receiver after the double conversion principle requires only one reference oscillator becomes.

0017In the embodiment of claim 12 a is easy to realized frequency changing device provided.

0018The apparatus of claim 13 comprising advantageously a temperature sensing device, if necessary a temperature-dependent adjustment of the frequency of reference oscillator perform.

0019Particularly advantageously, the device is in the carrier frequency range used 868-870 MHz claim 14th

0020Using an embodiment of the invention, with the Figures of the drawings explained. show case<sl><li>Fig.1: a schematic block diagram of an inventive Apparatus for frequency hopping,</li><li>Fig.2: is a schematic block diagram of an inventive Broadcast reception apparatus,</li><li>Fig.3: a schematic block diagram for frequency change of two different beat frequencies.</li></sl>

0021In Fig.1, a first voltage controlled oscillator (VCO) 3 shown, with a first high-frequency HF1 swings, which is stabilized by a first phase locked loop 2 becomes. The first high-frequency HF 1 is connected to the input a first high frequency divider 4 and provides a framework by the first high-frequency divider 4 digitally on a first reduced FT1 frequency divided down, wherein the first high-frequency HF1 and the first reduced frequency FT1 in a first are mutually fixed division ratio N1, which is set by the first high frequency divider 4th The first reduced frequency FT1 located at a first input a first phase detector 5. In this first phase detector 5 is the first reduced frequency FT1 with a first Reference frequency FR1 compared. The first reference frequency FR1 created digitally by a reference divider 8 from the first Frequency FQ1 a reference oscillator 7 (for example, a crystal oscillator). Here are the first reference frequency FR1 and the first frequency of the reference oscillator FQ1 7 in a second integer division ratio N2 to each other, that is predetermined by the reference divider eighth give way the first reference frequency FR 1 and the first reduced frequency FT1 from each other, produced the first phase detector 5 an error voltage, via a first loop filter 6 for suppressing AC voltages to the input of first voltage-controlled oscillator 3 is placed, whereby the first high frequency HF1 the first voltage controlled is controlled oscillator. 3 Does the first reference frequency FR1 with the first reduced frequency FT1 agree is thus no error voltage to the first voltage-controlled Oscillator 3 is applied, and the desired first RF HF1 is generated. A known method of Changing the first high-frequency HF1 to a second high-frequency HF2 is the division ratio N1 of the first High frequency divider 4 at constant first reference frequency FR1 vary. In a variation of the first division ratio N1 by one differ first (HF1) and the second (HF 2) RF to the first reference frequency FR1. Therefore, the first reference frequency FR1 is in this process equal to the channel spacing. In a radio alarm system the 870 MHz band with a channel spacing of 25 kHz is only once every 40 microseconds, a new control value is available. at estimated 100 necessary control values ​​to correct Frequency adjustment is thus the settling time 4 ms.

0022In the novel process is now provided for changing from a first RF HF1 to a second high-frequency HF2 using an adjustable frequency changing device 10, which is driven via a control processor 11 is the first frequency of the reference oscillator FQ1 7 a second frequency FQ2 to change the reference oscillator. In the following Table 1, the high frequencies generated HF, the first division ratios N1 of the first High frequency divider 4, the frequencies of the reference oscillator FQ 7 and the reference frequency FR at a constant second division ratio N2 of 111 indicated (all frequencies in kHz) as the frequency of the reference oscillator FQ 7 is varied for each of four channels. In this example oscillates the reference oscillator nominally at 11.135649 MHz.<tables><table><tgroup cols="4"><tbody><row><entry align="center">High-frequency RF in kHz</entry><entry align="center">Division ratio N1 of the high frequency divider</entry><entry align="center">Frequency FQ of the reference oscillator in kHz</entry><entry align="center">Reference frequency FR in kHz</entry></row><row><entry align="right">869000</entry><entry align="right">8690</entry><entry align="center">11100.0000</entry><entry align="center">100.0000000</entry></row><row><entry align="right">869 025</entry><entry align="right">8690</entry><entry align="center">11100.31933</entry><entry align="center">100.0028769</entry></row><row><entry align="right">869050</entry><entry align="right">8690</entry><entry align="center">11100.3867</entry><entry align="center">100.0057537</entry></row><row><entry align="right">869 075</entry><entry align="right">8690</entry><entry align="center">11100.95800</entry><entry align="center">100.0086306</entry></row><row><entry align="right">869 100</entry><entry align="right">8691</entry><entry align="center">11100.0000</entry><entry align="center">100.0000000</entry></row><row><entry align="right">869 125</entry><entry align="right">8691</entry><entry align="center">11100.31933</entry><entry align="center">100.0028769</entry></row><row><entry align="right">869 150</entry><entry align="right">8691</entry><entry align="center">11100.63867</entry><entry align="center">100.0057537</entry></row><row><entry align="right">869 175</entry><entry align="right">8691</entry><entry align="center">11100.95800</entry><entry align="center">100.0086306</entry></row><row><entry align="right">869 200</entry><entry align="right">8692</entry><entry align="center">11100.0000</entry><entry align="center">100.0000000</entry></row></tbody></tgroup></table></tables>

0023At a relative change in frequency FQ of the reference oscillator 7 to 86 ppm can be increased by a factor of 4 Reference frequency FR to adjust the high frequencies HF accomplish at 869 MHz and a channel spacing of 25 kHz. This reduces the settling time to 1 ms, thereby the current flowing during the transient current to the Factor Four is reduced.

0024The measure described must practice with great care will be realized. They will do it first the essence lost the Frequenzsynthetisierung, namely the digital Connecting the required to generating high-frequency HF at constant possible reference frequency FR. The variation the frequency FQ of the reference oscillator 7 is circuitry for example, by a voltage-controlled capacitance diode (Varactor) as a frequency changing device 10 generated, the control voltage to by a DA converter on Control processor 11 is set. It is, of course, it to ensure that this variation stable reproducibly Manner is done so that the high stability of the reference oscillator 7 is not impaired. For this reason, limited Also, the above example to a variation of the high frequency HF through four channels and thus a limited to 86 ppm necessary variation of the frequency FQ of the reference oscillator. This pull-in range can be at the fundamental wave quartz as reference oscillator 7 without appreciable loss of stability realize.

0025The high frequencies generated by the process are both as a carrier frequency for a transmitter as well as a superposition of frequencies for a receiver according to the heterodyne principle.

0026In Figure 2 is schematically illustrates a combined transceiver (Transceiver) shown that a battery powered transceiver is used in wireless alarm systems.

0027When sending is thereby connected to a first voltage-controlled Oscillator 3, the first high-frequency RF 1 as the first carrier frequency produced and stabilized with a first phase locked loop. 2 The selected first carrier frequency is in digital Form from the control processor 11 to the first phase locked loop 2 transfer. Serves to stabilize a crystal oscillator as a reference oscillator 8, which via a varactor diode as frequency changing means 10 via a digital-to-analog converter 21 for temperature compensation and / or to Frequency change is connected to the control processor eleventh to Reduction of settling time is via a digital-to-analog converter 19 for channel preset by the control processor 11 shows a default setting of the first voltage-controlled Oscillator 3 made. The data transfer to the recipient occurs with narrowband FM modulation realized by a Frequency modulation of the frequency FQ of the reference oscillator 8 via a control processor 11 operated by the digital-to-analog converter 16 for transmission modulation. The output of the first voltage-controlled oscillator 3 is in a transmit amplifier 12 amplified and a transmission filter 13 for suppressing of harmonics and a transmit-receive switch 14 transmitted to an antenna 15 for sending.

0028In the operation of the transceiver as a receiver, the transmit-receive switch 14 is switched and the received signal with the first carrier frequency via an input filter 22 (869 MHz SAW filter for suppressing Außerbandstörfrequenzen) directed to the preamplifier 23rd In a first Mixer 24 is the received signal with a first mixed beat frequency, the first high-frequency HF1 provided by the first voltage-controlled oscillator 3 becomes. The generation of the first local frequency takes place analogous to the generation of the carrier frequencies in the Transmission case. The change from a first beat frequency for a first received carrier frequency to a second Beat frequency for a second received carrier frequency also takes place by switching from the first Frequency FQ1 of the reference oscillator 8 to the second frequency FQ2 the reference oscillator 8. When mixing between first carrier frequency and the first local frequency arises In this case, a first intermediate frequency in the range of 45 MHz, during the mixing of the second carrier frequency with the second beat frequency, a second intermediate frequency produced in the region of 45 MHz.

0029As a first mixer for example, a dual-gate field effect transistor are used, the output signal with the first or second intermediate frequency in a first amplified intermediate frequency amplifier 25, and the first in a is filtered band filter 26th In a subsequent second Mixer 27 is the first or second intermediate frequency by a third heterodyne frequency of a second voltage-controlled Oscillator 28 to a third intermediate frequency implemented in the range of 455 kHz.

0030In Fig. 3 is illustrated that the second voltage-controlled Oscillator 28 in a second phase locked loop 29 the third beat frequency as the third high-frequency HF3 is stabilized. In the second phase locked loop 29 is the RF digital by a second high-frequency divider 30 divided down to a third reduced frequency FT3, in a second phase detector 31 first with the reference frequency is compared FR1 from the reference divider 7, with also the first phase locked loop 2 the first voltage-controlled Oscillator 2 stabilized. The third reduced Frequency FT3 stands in a third integer Division ratio N3 for the third high-frequency HF3. Dependent on of the difference between the third divided-down FT3 frequency and the first reference frequency FR1 is a second loop filter 32 a voltage to the second voltage controlled oscillator 28 is applied to this the desired third RF HF3 generates. At a Change from the first received carrier frequency on the second carrier frequency, as already described, the first Reference frequency FR1 on the second reference frequency FR2 by the controlled by the control processor 11 Frequency changing device 10 changed. This changes with constant held division ratio N3 the third high-frequency HF3 of the voltage controlled oscillator 28 to a fourth RF HF4 that a fourth local frequency equivalent. Thereby, the third intermediate frequency changed in a fourth intermediate frequency.

0031In Fig.2 it is shown that the third or fourth intermediate frequency then filtered in a second bandpass filter 33 becomes. This second band-pass filter 33 determines the selectivity the recipient and must therefore be interpreted narrowband. The filtered signal is then in a limiter 34 limited and demodulated in an FM demodulator 35th The FM demodulator 35 provides an analog receive data signal based and an analog signal level to assess the reception quality via an analog-to-digital converter 36 to the control processor 11th

0032In conventional receivers after the dual-conversion principle without variable reference frequency fr, the first and the second local frequency in response to the first and the second carrier frequency is generated so that the first intermediate frequency equal to the second intermediate frequency. For example is at a first carrier frequency of 868,300 MHz and a second carrier frequency of 868.400 MHz, the first Beat frequency equal to 913.300 MHz and the second Beat frequency equal to 913.400 MHz generated to both to obtain cases an intermediate frequency of 45 MHz. at these known receivers is the third beat frequency does not vary, but for example, equal to 44.545 selected MHz, so that after the second mixer, the common third intermediate frequency, in this example 455 kHz, arises.

0033In case of direct application of the inventive method with Stabilizing the second voltage-controlled oscillator 28 by the variable reference frequency FR would the third beat frequency to a fourth local frequency change so that a fourth intermediate frequency arise would, outside the passband of the narrow-band second band-pass filter could be 33rd For example would be a difference of 100 kHz between first and second Beat frequency in the 913 MHz band, a difference of 5 kHz between the third and fourth local frequency in cause 45 MHz range, since the relative changes (Factor 20) of the beat frequencies by the variable Reference frequency will remain the same. The third intermediate frequency would thus, for example, from 455 kHz to Change fourth intermediate frequency of 450 kHz. Since the passband the narrow second band-pass filter 33 at 455 ± 3.5 kHz, this fourth intermediate frequency would already no longer are allowed through.

0034According to the invention, this effect is avoided by the fact that the first and already produced the second beat frequency so (in the example: first beat frequency equal to 913.300 MHz, second beat frequency equal to 913.405 MHz), that the first intermediate frequency equal to 45.000 MHz and the second intermediate frequency equal to 45.005 MHz and therefore different are. In the third and the fourth beat frequency from the above example would be a fourth intermediate frequency 455 kHz and therefore equal to the third intermediate frequency arise. Through this additional change around 5 kHz between first and second beat frequency in 913 MHz range, however, is an additional change in the same relative height (factor 20) of about 250 Hz in 45 MHz range between the third and fourth beat frequency generated, so that between the third and fourth intermediate frequency still a difference of 250 Hz is. These However, the difference is so small that the third and fourth intermediate frequency from the common second narrowband are allowed to pass band filter 33rd With the inventive Method result from the same relative change from the first to the second beat frequency and from the third to the fourth different beat frequency absolute change between the beat frequencies, Since the first and the second beat frequency in a different frequency range than are third and fourth beat frequency. This ensures, that the first and the second beat frequency are generated so that the third and fourth intermediate frequency close enough to the common second band-pass filter to be filtered 33.

0035Since the second band-pass filter 33, the selectivity of the receiver determined and therefore designed narrowband than the first Band filter 26, the first and the second beat frequency generated so that the third and then the resulting fourth intermediate frequency as possible both in the middle of the are passband of the second bandpass filter 33rd In order to , the first and the second intermediate frequency slightly from the center of the passband of the first bandpass filter 26 away. The latter, however, does not interfere with reception, since, As already described, the bandwidth of the first bandpass filter 26 is sufficiently large.

0036Through a clever implementation of the reference frequency shift can also temperature transitions or circuit tolerances the reference oscillator 7 are compensated.

0037Normally, the temperature response of a crystal undergoes a through the quartz slice given S-curve to give the Choice has between a wide operating temperature range, coupled with greater maximum frequency deviation and a smaller operating temperature range with smaller maximum Frequency deviation. At an operating frequency of 869 MHz and 25 KHz channel spacing is applied to the stability of the reference frequency FR made high demands. Thus, for a maximum deviation of 10% of the channel spacing, ie ± 2.5 KHz a stability of ± 2.7 ppm at the reference frequency necessary. This problem can now be in the inventive Procedures stored by the control processor 11 Loosen temperature compensation table. For this purpose the Temperature response of a Ouarzes reference oscillator 7 once representative survey to establish the compensation table. The temperature of the reference oscillator 7 can then be in Operating with sufficient accuracy, for example by Threshold voltage of diodes in a temperature measuring Measure 18th With the help of the stored temperature compensation table is calculated from the measured temperatures, a value for from control processor 11 to the frequency variation device determined 10 voltage to be applied and applied, thus the frequency FQ of the reference oscillator back to the desired value is corrected.

0038With conventional reference frequency generation is required for the Frequency accuracy a trimming operation inevitable to compensate for the tolerances of a crystal oscillator circuit as a reference oscillator 7, even if the quartz resonator as Such is selected with extremely tight delivery tolerance. This Frequency adjustment can be in the inventive solution also realized by the frequency changing device 10th Conveniently, therefore, the coming out of the production, stocked with far toleriertem quartz reference oscillator 7 turned on in a test facility and, within the drawing area starting at the lowest voltage limit some Voltage via the digital-to-analog converter 21 to the temperature adjustment created and / or channel adjustment, the resulting Frequency FQ of the reference oscillator 7 and measured the digital-to-analog converter control value and the associated Frequency FQ of the reference oscillator 7 is stored. With a Frequency calculation program can now without difficulty the necessary for each channel first division ratio of High frequency divider 7 and the digital-to-analog converter position determined and stored in the memory of the control processor 11 will. By the method and the apparatus described not just settling times are reduced and the power consumption is reduced, but it will also open additional opportunities temperature transitions and voltage tolerances auszuregeln. A timed monitoring device, for example, a quartz-controlled alarm clock 17 ensures that the transceiver is turned on only at predetermined times, thus the power consumption is minimized.