CN102938747B - A kind of digital interphone signal demodulation device - Google Patents
A kind of digital interphone signal demodulation device Download PDFInfo
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- CN102938747B CN102938747B CN201210473532.8A CN201210473532A CN102938747B CN 102938747 B CN102938747 B CN 102938747B CN 201210473532 A CN201210473532 A CN 201210473532A CN 102938747 B CN102938747 B CN 102938747B
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Abstract
A kind of digital interphone signal demodulation device, relate to signal receiving field, solve because device aging and variations in temperature make the problem that the distortion factor of the poor stability of restituted signal, restituted signal is high, demodulating equipment comprises voltage controlled oscillator, frequency mixer, frequency discriminator and voltage output module, and the control level that voltage controlled oscillator exports according to voltage output module produces local oscillated signal; The radiofrequency signal that local oscillated signal and antenna receive by frequency mixer carries out mixing, obtains intermediate-freuqncy signal; Frequency discriminator through demodulation of frequency discriminator, exports restituted signal to intermediate-freuqncy signal; Voltage output module exports control level according to restituted signal, calculate the DC component in restituted signal, result of calculation is compared, if deviation is greater than direct current threshold value with reference to DC component, then change the control level outputting to described voltage controlled oscillator, until deviation is less than direct current threshold value.For improving the stability of restituted signal, reducing the distortion factor of restituted signal.
Description
Technical field
The present invention relates to signal receiving field, be specifically related to a kind of digital interphone signal demodulation device.
Background technology
For ground specialty wireless intercom system, it it within 2008 to 2013, is the conversion period that simulation transfers numeral to.Will turn to the digital intercom of low cost in this one-phase major part market, and DPMR is current business intercommunication best solution of generally acknowledging.Because DPMR have employed 4FSK (Frequency-shiftkeying, frequency shift keying) digital modulation and demodulation replaces traditional FM modulation /demodulation, receiver in partial solution adopts secondary down-conversion, first local oscillated signal and the second local oscillated signal are all the signals produced from reference crystal, so the stability of reference crystal output signal frequency, just directly have influence on the performance of whole receiver.But the frequency of oscillation of reference crystal corresponding change can occur along with the change of the objective condition such as time and temperature, cause the signal DC level after demodulation unstable, may produce saturated under extreme conditions, cause restituted signal distortion, improve the error rate.
Existing general processing mode is: reference crystal oscillator adopts temperature complement voltage-control crystal oscillator, and this crystal can compensate the frequency change that a part of Yin Wendu causes, but compensation range is limited.The reference level being supplied to reference crystal oscillator is about 1.5V, thus reference crystal oscillator produces corresponding frequency, this frequency inputs to phase-locked loop circuit (or phase-locked loop chip), as the reference frequency point of phase-locked loop, this reference frequency point and voltage controlled oscillator feed back frequency and compare, produce phase difference between the two, thus make the phase discriminator in phase-locked loop create corresponding pump current/voltage, pump current/voltage changes voltage controlled oscillator frequency through loop low pass filter, thus formation feedback loop, obtain the first local oscillation frequency point required for us.The radiofrequency signal that this local oscillations frequency and antenna receive carries out mixing, obtains intermediate-freuqncy signal, and intermediate-freuqncy signal, through frequency discriminator demodulation, finally exports to the restituted signal required for software decode.
Because reference crystal adopts temperature complement voltage-control crystal oscillator, when temperature changes between-30 DEG C to 75 DEG C, crystal oscillator frequency is changed to 5ppm, and every aging one-year age, and crystal oscillator frequency is changed to 2ppm.If used for a long time, again in different environment, frequency may be caused to change 7ppm.Because reference crystal oscillator frequency changes, so local oscillations frequency is with regard to respective change 7ppm, finally cause, the signal DC level after demodulation changes, and too increases the distortion factor of restituted signal simultaneously.
The change of temperature and the aging of device, belong to objective fact, is unavoidable.And use at different temperatures for a long time, can the problems referred to above be caused again.So compensate the reference crystal frequency change because device aging and variations in temperature produce, just seem especially important.
Summary of the invention
In order to compensate the reference crystal frequency change because device aging and variations in temperature produce, improve the stability of restituted signal, reduce the distortion factor of restituted signal, the present invention proposes a kind of digital interphone signal demodulation device.
In order to solve the problems of the technologies described above, the invention provides a kind of digital interphone signal demodulation device, described demodulating equipment comprises voltage controlled oscillator, frequency mixer, frequency discriminator and voltage output module,
Described voltage controlled oscillator, produces local oscillated signal for the control level exported according to voltage output module;
Described frequency mixer, carries out mixing for radiofrequency signal local oscillated signal and antenna received, obtains intermediate-freuqncy signal;
Described frequency discriminator, for described intermediate-freuqncy signal through demodulation of frequency discriminator, export restituted signal;
Described voltage output module, for exporting control level according to described restituted signal, calculate the DC component in described restituted signal, result of calculation is compared with reference to DC component, if deviation is greater than direct current threshold value, then change the control level outputting to described voltage controlled oscillator, until the restituted signal received is less than direct current threshold value with the deviation with reference to DC component.
Further, described voltage output module comprises DC component computing module and voltage control module,
Described DC component computing module, for calculating the DC component in described restituted signal;
Described voltage control module, DC component for being exported by DC component computing module compares with reference to DC component, if deviation is greater than direct current threshold value, according to the relation of DC component with the frequency departure with reference to DC component deviation and voltage controlled oscillator, to the direction regulation output with reference to DC component to the level of described voltage controlled oscillator, until the restituted signal received is less than direct current threshold value with the deviation with reference to DC component, output level is now input to voltage controlled oscillator as control level; If described deviation is less than direct current threshold value, then keep the control level being input to voltage controlled oscillator constant.
Further, described voltage output module also comprises reference crystal oscillator and phase discriminator,
Described reference crystal oscillator, produces reference frequency point for the level exported according to described voltage control module;
Described phase discriminator, for being compared by the feedback frequency of described reference frequency point and described voltage controlled oscillator, according to phase difference between the two, producing pump current/voltage, and described pump current/voltage is input to voltage controlled oscillator as control level.
Further, voltage output module also comprises low pass filter,
Described low pass filter, for producing filtering level according to described pump current/voltage, and is input to voltage controlled oscillator using described filtering level as control level.
Further, described low pass filter is loop low pass filter.
Further, described reference crystal oscillator is temperature complement voltage-control crystal oscillator.
Further, the process producing pump current/voltage is: the phase difference calculating described reference frequency point and described feedback frequency, if described phase difference is greater than phase threshold, according to the relation of described reference frequency point and the described phase difference of feedback frequency and the frequency departure of voltage controlled oscillator, produce pump current/voltage, until the phase difference of described reference frequency point and described feedback frequency is less than phase threshold, pump current/voltage is now input to voltage controlled oscillator as control level; If described phase difference is less than phase threshold, then keep the control level being input to voltage controlled oscillator constant.。
Compared with prior art, the present invention is by detecting the DC level of the signal after demodulation in real time, the corresponding frequencies change of computing reference crystal oscillator, by adjustment reference crystal oscillator control voltage after radio frequency exports, compensate for reference crystal oscillator is because the frequency shift (FS) of environmental change generation, finally obtain the DC level of stable restituted signal, reduce the distortion factor of restituted signal simultaneously.
Accompanying drawing explanation
Fig. 1 is the structural representation of the digital interphone signal demodulation device of the embodiment of the present invention.
Embodiment
For making the object, technical solutions and advantages of the present invention clearly understand, hereinafter will be described in detail to embodiments of the invention by reference to the accompanying drawings.It should be noted that, when not conflicting, the embodiment in the application and the feature in embodiment can combination in any mutually.
The embodiment of the present invention proposes a kind of digital interphone signal demodulation device, by following the tracks of the radiofrequency signal received, detect the change of the restituted signal received, dynamic realtime regulates the control voltage of voltage controlled oscillator 4, makes the signal after demodulation remain on galvanic current and puts down.Specific implementation is as follows:
Described voltage controlled oscillator 4, produces local oscillated signal for the control level exported according to voltage output module 7;
Described frequency mixer 5, carries out mixing for radiofrequency signal local oscillated signal and antenna received, obtains intermediate-freuqncy signal;
Described frequency discriminator 6, for described intermediate-freuqncy signal through demodulation of frequency discriminator, export restituted signal;
Described voltage output module 7, for exporting control level according to described restituted signal, calculate the DC component in described restituted signal, result of calculation is compared with reference to DC component, if deviation is greater than direct current threshold value, then change the control level outputting to described voltage controlled oscillator 4, until the restituted signal received is less than direct current threshold value with the deviation with reference to DC component.
Wherein, described voltage output module 7 comprises DC component computing module 7-1 and voltage control module 7-2,
Described DC component computing module 7-1, for calculating the DC component in described restituted signal;
Described voltage control module 7-2, DC component for being exported by DC component computing module 7-1 compares with reference to DC component, if deviation is greater than direct current threshold value, according to the relation of DC component with the frequency departure with reference to DC component deviation and voltage controlled oscillator 4, to the direction regulation output with reference to DC component to the level of described voltage controlled oscillator 4, until the restituted signal received is less than direct current threshold value with the deviation with reference to DC component, output level is now input to voltage controlled oscillator 4 as control level; If described deviation is less than direct current threshold value, then keep the control level being input to voltage controlled oscillator 4 constant.
Described voltage output module 7 can further include reference crystal oscillator 1 and phase discriminator 2, low pass filter 3,
Described reference crystal oscillator 1, produces reference frequency point for the level exported according to described voltage control module 7-2;
Described phase discriminator 2, for being compared by the feedback frequency of described reference frequency point and described voltage controlled oscillator 4, according to phase difference between the two, produces pump current/voltage.
The process producing pump current/voltage is: the phase difference calculating described reference frequency point and described feedback frequency, if described phase difference is greater than phase threshold, according to the relation of described reference frequency point and the phase difference of described feedback frequency and the frequency departure of voltage controlled oscillator 4, produce pump current/voltage, until the phase difference of described reference frequency point and described feedback frequency is less than phase threshold, pump current/voltage is now input to voltage controlled oscillator 4 as control level; If described phase difference is less than phase threshold, then keep the control level being input to voltage controlled oscillator 4 constant.
Described low pass filter 3, for producing filtering level according to described pump current/voltage, and exports described filtering level to described voltage controlled oscillator 4;
Wherein reference crystal oscillator 1 and phase discriminator 2, low pass filter 3 compensate the change of the voltage controlled oscillator 4 local oscillated signal frequency produced due to device aging and variations in temperature to a certain extent by the mode of feedback.
Described low pass filter 3 can be loop low pass filter, and described reference crystal oscillator 1 is temperature complement voltage-control crystal oscillator.
Before carrying out signal receiving, need to demarcate digital handset, first frequency is exported by voltage-regulation reference crystal oscillator 1, adjust to the frequency required for output always, this frequency inputs to phase discriminator 2 as with reference to frequency, the signal fed back with voltage controlled oscillator 4 carries out phase compare, because phase place has deviation, so phase discriminator 2 produces pump current/voltage, voltage controlled oscillator 4 is regulated, until the frequency that voltage controlled oscillator 4 exports is stabilized in the frequency pre-set by the low low pass filter of loop.This frequency is when receiving, and the radiofrequency signal received as local oscillator signal and antenna utilizes frequency mixer 5 to carry out mixing, obtains intermediate-freuqncy signal after mixing, and intermediate-freuqncy signal by frequency discriminator 6, demodulates required restituted signal again.
The setting of voltage control module 7-2 threshold value, depends on hardware environment, and such as adopt 10 D/A, input voltage interval is the hardware platform of 2V, then minimum direct current threshold value can be set as 2mV, and threshold value setting is less, and DC component is with less with reference to DC component deviation.DC component and the deviation with reference to DC component, also change the size exporting to the voltage of voltage controlled oscillator 4 simultaneously, proportionate relationship also depends on external hardware environment, such as detection DC component and reference component deviation are 10mV, the frequency departure of corresponding voltage controlled oscillator 4 is 150Hz, the frequency of reference crystal oscillator 1 and the frequency proportions of voltage controlled oscillator 4 are 1: 10, then the frequency change of reference crystal oscillator 1 is 15Hz, so the change in voltage inputing to reference crystal oscillator 1 is 15mV, by this rule adjustment, until the restituted signal received is less than direct current threshold value with the deviation with reference to DC component.
This rule is also followed in adjustment for pump current/voltage.
Specify in individual digital intercom agreement, there is the sine wave of 9 600Hz above as each frame head setting up communication, so at receiving terminal, the initially signal received is the sine wave of 9 600Hz, can by receiving the sine wave of 9 600Hz, calculate the DC component of current restituted signal, record this DC component as reference DC component.
The process that embodiment of the present invention adjustment is input to the input voltage of voltage controlled oscillator 4 is:
Due to the change of the environmental factor such as variations in temperature and device aging, cause local oscillations frequency to change, or the frequency of the radiofrequency signal received offset.After local oscillated signal and the radiofrequency signal received carry out mixing, the intermediate-freuqncy signal obtained also can offset, just there is respective change through the DC level of the restituted signal that frequency discriminator demodulation exports in intermediate-freuqncy signal, the DC level of the sine wave of 9 600Hz now received changes too.In time receiving the primary sinusoid, calculate DC component now, result of calculation compares with reference to DC component, if there is deviation, then by changing the control level of reference crystal oscillator 1, regulate local oscillating frequency, until the restituted signal received and the deviation with reference to DC component are within the scope set, regulate and terminate.Now whole receiver circuit just forms negative feedback loop, and each call can compensate the change of local oscillated signal and received RF signal.Finally obtain stable restituted signal.
Above embodiment only in order to technical scheme of the present invention and unrestricted to be described, only with reference to preferred embodiment to invention has been detailed description.Those of ordinary skill in the art should be appreciated that and can modify to technical scheme of the present invention or equivalent replacement, and does not depart from the spirit and scope of technical solution of the present invention, all should be encompassed in the middle of right of the present invention.
Claims (5)
1. a digital interphone signal demodulation device, is characterized in that: described demodulating equipment comprises voltage controlled oscillator (4), frequency mixer (5), frequency discriminator (6) and voltage output module (7),
Described voltage controlled oscillator (4), produces local oscillated signal for the control level exported according to voltage output module (7);
Described frequency mixer (5), carries out mixing for radiofrequency signal local oscillated signal and antenna received, obtains intermediate-freuqncy signal;
Described frequency discriminator (6), for described intermediate-freuqncy signal through demodulation of frequency discriminator, export restituted signal;
Described voltage output module (7), for exporting control level according to described restituted signal, calculate the DC component in described restituted signal, result of calculation is compared with reference to DC component, if deviation is greater than direct current threshold value, then change the control level outputting to described voltage controlled oscillator (4), until the restituted signal received is less than direct current threshold value with the deviation with reference to DC component;
Described voltage output module (7) comprises DC component computing module (7-1), voltage control module (7-2), reference crystal oscillator (1) and phase discriminator (2),
Described DC component computing module (7-1), for calculating the DC component in described restituted signal;
Described voltage control module (7-2), DC component for being exported by DC component computing module (7-1) compares with reference to DC component, if deviation is greater than direct current threshold value, according to the relation of DC component with the frequency departure with reference to DC component deviation and voltage controlled oscillator (4), to the direction regulation output with reference to DC component to the level of described voltage controlled oscillator (4), until the restituted signal received is less than direct current threshold value with the deviation with reference to DC component, output level is now input to voltage controlled oscillator (4) as control level, if described deviation is less than direct current threshold value, then keep the control level being input to voltage controlled oscillator (4) constant,
Described reference crystal oscillator (1), produces reference frequency point for the level exported according to described voltage control module (7-2);
Described phase discriminator (2), for the feedback frequency of described reference frequency point and described voltage controlled oscillator (4) is compared, according to phase difference between the two, produce pump current/voltage, and described pump current/voltage is input to voltage controlled oscillator (4) as control level.
2. digital interphone signal demodulation device as claimed in claim 1, is characterized in that: voltage output module (7) also comprises low pass filter (3),
Described low pass filter (3), for producing filtering level according to described pump current/voltage, and is input to voltage controlled oscillator (4) using described filtering level as control level.
3. digital interphone signal demodulation device as claimed in claim 2, is characterized in that: described low pass filter (3) is loop low pass filter.
4. digital interphone signal demodulation device as claimed in claim 1, is characterized in that: described reference crystal oscillator (1) is temperature complement voltage-control crystal oscillator.
5. digital interphone signal demodulation device as claimed in claim 1, it is characterized in that: the process producing pump current/voltage is: the phase difference calculating described reference frequency point and described feedback frequency, if described phase difference is greater than phase threshold, according to the relation of described reference frequency point and the phase difference of described feedback frequency and the frequency departure of voltage controlled oscillator (4), produce pump current/voltage, until the phase difference of described reference frequency point and described feedback frequency is less than phase threshold, pump current/voltage is now input to voltage controlled oscillator (4) as control level; If described phase difference is less than phase threshold, then keep the control level being input to voltage controlled oscillator (4) constant.
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| CN1845542A (en) * | 2005-04-08 | 2006-10-11 | 美国博通公司 | Signal processing method and system |
| US20070046356A1 (en) * | 2005-08-25 | 2007-03-01 | Integrant Technologies Inc. | Adaptive dc offset compensation apparatus and method thereof |
| CN101697488A (en) * | 2009-10-28 | 2010-04-21 | 上海宏力半导体制造有限公司 | Delay-locked loop circuit |
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| US20050052261A1 (en) * | 2003-09-09 | 2005-03-10 | Samsung Electronics Co., Ltd. | Thin film resonator, method for making thin film resonator and filter having thin film resonators |
| CN1845542A (en) * | 2005-04-08 | 2006-10-11 | 美国博通公司 | Signal processing method and system |
| US20070046356A1 (en) * | 2005-08-25 | 2007-03-01 | Integrant Technologies Inc. | Adaptive dc offset compensation apparatus and method thereof |
| CN101697488A (en) * | 2009-10-28 | 2010-04-21 | 上海宏力半导体制造有限公司 | Delay-locked loop circuit |
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