CN1398092A - Frequency shift keying/Gaussian frequency shift keying signal receiver and its receiving method - Google Patents

Abstract

The invention discloses a frequency shift keying/Gaussian frequency shift keying (FSK/GFSK) signal receiver and a receiving method thereof, wherein the signal receiver comprises: a FSK/GFSK signal demodulator for receiving the transmission signal received from the antenna, amplifying and filtering the transmission signal and generating an intermediate frequency (baseband) signal; an analog-to-digital converter for receiving the intermediate frequency (baseband) signal and converting the signal into a digital signal; a digital frequency discriminator for receiving the digital signal and generating a discriminating signal; a digital band-pass filter for filtering the high frequency component and the DC component of the identification signal and generating a demodulation signal; and a level judger for receiving the demodulated signal and generating a received signal; the invention uses the digital filter circuit to filter the DC offset of the identification signal, and generates a demodulation signal which is not affected by the frequency offset DC component, so that the post-stage level judger can correctly judge the demodulation signal without the need of the DC level of the signal.

Description

Frequency shift keying/Gaussian frequency shift keying signal receiver and its receiving method

technical field

The invention relates to an automatic frequency offset compensator, in particular to a digital filter to filter out frequency offset in a Frequency Shift Keying (FSK)/Gaussian Frequency Shift Keying (GFSK) demodulator. A frequency shift keying/Gaussian frequency shift keying (FSK/GFSK) signal receiver of a DC voltage caused by a frequency offset and a receiving method thereof.

Background technique

Due to limitations of size, cost, etc., in many occasions, frequency synthesizers (synthesizers), quartz oscillators (quartz oscillators) or other devices with high-precision oscillation frequencies cannot be used to generate radio frequency (radio frequency). Therefore, a general radio unit performs frequency offset between the transmission side and the reception side by automatic frequency control.

Figure 1 shows a block diagram of a typical receiver for receiving FSK/GFSK signals. As shown in the figure, the receiver 10 includes an antenna 11 , a signal demodulator (signal demodulator) 12 , a frequency discriminator (Frequency Discriminator) 13 , and a data output unit 14 . The signal demodulator 12 filters and amplifies the signal received by the antenna 11, including a band-pass filter 121 (band-pass filter), a first amplifier (Amplifier) 122, a mixer (Mixer) 123, and an oscillator 124 , a second amplifier 125 , and an amplitude limiter (Limiter) 126 . The antenna 11 receives a radio frequency signal transmitted from a transmitter (not shown), generates a received signal and transmits it to a signal demodulator 12 . The signal demodulator 12 extracts the desired frequency range from the received signal and amplifies it for output. Finally, the received signal is demodulated by the frequency discriminator 13 , and the demodulated signal is output through the output unit 14 . However, in this communication system, due to the carrier frequency offset between the transmitting end and the receiving end, the output signal of the frequency discriminator will contain a DC offset value, resulting in misjudgment by the output unit.

Generally, the FSK/GFSK receiver output unit 14 adopts an analog low-pass filter composed of a resistor 142 and a capacitor 144 to obtain the DC level of the output signal of the frequency discriminator 13, and then compares the output signal of the frequency discriminator 13 through the comparator 15 A demodulated signal is generated by combining with the direct current level. The output signal of the frequency discriminator 13 charges the capacitor 144 through the buffer 141 and the resistor 142 , and the charging time is controlled by the control switch 143 to obtain the DC level of the frequency discriminator 13 . Then, the control switch 143 is turned on (Turn off), and the voltage stored in the capacitor 144 is used as the level basis of the comparator 15, so as to generate a correct demodulation signal.

However, there are several problems in the above-mentioned output unit 14 that will affect the correctness of the demodulated signal. Firstly, the switching time of the control switch 143 has a great influence on the accuracy of the obtained DC level. The second is that the size of resistors and capacitors must be evaluated individually according to the system being designed. Third, the switch 143 must be controlled by a subsequent control unit (not shown), which increases manufacturing costs.

Contents of the invention

In view of the above problems, the object of the present invention is to propose a frequency shift keying/Gaussian frequency shift keying (FSK/GFSK) signal receiver and receiving method thereof using a digital filter unit to filter the DC component caused by the frequency offset value .

To achieve the above object, a frequency shift keying/Gaussian frequency shift keying (FSK/GFSK) signal receiver of the present invention includes: a FSK/GFSK signal demodulator, which receives the transmission signal received from the antenna, After amplification and filtering, an intermediate frequency (base frequency) signal is generated; an analog-to-digital converter receives the intermediate frequency (base frequency) signal of the FSK/GFSK signal demodulator and converts it into a digital signal; a digital frequency discriminator receives analog-digital The digital signal of the converter, and generates a discrimination signal; a digital bandpass filter, filters the high frequency component and the DC component of the discrimination signal, and generates a demodulation signal; and, a level judger, receives the demodulation signal and generates a reception signal Signal. The digital band-pass filter can be formed by connecting a digital low-pass filter and a digital high-pass filter in series. Therefore, the frequency shift keying/Gaussian frequency shift keying (FSK/GFSK) signal receiver of the present invention uses a digital filter circuit to filter the DC offset of the identification signal to generate a solution that is not affected by the frequency offset DC component. Modulate the signal, so that the level judger in the subsequent stage can correctly judge the demodulated signal without relying on the DC level of the signal.

Description of drawings

Fig. 1 is the block diagram of receiving FSK/GFSK signal receiver of prior art;

Fig. 2 is the block diagram of FSK/GFSK signal receiver of the present invention;

Fig. 3 is the embodiment of the partial unit of Fig. 2;

Fig. 4 is among Fig. 3, the output signal of low-pass filter has not passed through the wave form of the signal B of digital filter circuit;

Fig. 5 is among Fig. 3, the output signal of low-pass filter passes through the waveform of the signal A of digital filtering circuit;

FIG. 6 is a flowchart of the FSK/GFSK signal receiver of the present invention.

Description of component parameter symbols in the figure:

12 signal demodulator

20FSK/GFSK signal receiver

21 Analog to Digital Converter

22 digit frequency discriminator

23 Finite Impulse Response Digital Low Pass Filter

24 infinite impulse response digital filter circuit

25 level judge

Detailed ways

The frequency shift keying/Gaussian frequency shift keying (FSK/GFSK) signal receiver of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 2 is a block diagram of the FSK/GFSK signal receiver of the present invention. As shown in the figure, the FSK/GFSK signal receiver 20 of the present invention is similar to the general FSK/GFSK signal receiver (refer to FIG. 1 ), and both include an antenna 11 and a signal demodulator 12 . Moreover, the structures and functions of these units are similar to those of a general signal receiver (refer to FIG. 1 ), and will not be repeated here.

In addition to the above-mentioned units, the FSK/GFSK signal receiver 20 of the present invention also includes an analog-to-digital converter (Analog/Digital Converter, ADC) 21, a digital frequency discriminator (Digital Frequency Discriminator) 22, a finite impulse response digital low-pass filter A device (Finite Impulse Response Digital Low Pass Filter) 23, an infinite impulse response digital filter (Infinite Impulse Response Digital Filter) 24, and a level judger (slicer) 25. The analog-to-digital converter 21 receives the signal from the signal demodulator 12 and converts the signal into a digital signal DS. After the digital signal DS passes through the digital frequency discriminator 22 to identify the desired frequency signal, the digital low-pass filter 23 allows the desired low-frequency signal to pass through to generate the first demodulated signal. Next, the DC component is filtered out by an infinite impulse response digital filter 24 to generate a second demodulated signal without DC component. The second demodulated signal is converted into a received signal via the level determiner 25 . Since the second demodulated signal generated by the infinite impulse response digital filter 24 does not have a DC component, the level determiner 25 only needs a comparator 251, and the output demodulated signal will not be affected by the DC offset value And misjudgment.

FIG. 3 shows an embodiment of some units of FIG. 2 . In this embodiment, the frequency of the input IF (Inter-medium frequency) signal IF is 1 MHz, and has a frequency offset value of 150 KHz. The symbol rate of the signal is 1 Mbps, and the sampling rate of the ADC 21 is fs=32 MHz. In addition, the transfer function of the finite impulse response digital low-pass filter 23 is h(z)=h ₀ +h ₁ z ^-1 +...+h ₆₃ z ^-63 , and the pass-band is 0-0.2MHz , the stop frequency band (stop-band) is more than 2M. The design of the coefficients of the h(z) function is an existing technology in the field of digital signal processing (Digital Signal Processing), and the design method can refer to relevant literature, or use relevant computer software to aid design (such as the Signal Processing Toolbox of MATLAB ^R ). At the same time, the Gaussian BT Product of the finite impulse response digital low-pass filter 23 is 0.5. In addition, the transfer function of the infinite impulse response digital filter 24 is $g\left(z\right)=\frac{{1-z}^{-2}}{1-{(1-2^{-8})}^{z^{-2}}}.$

Since the frequency response of the digital filter $G\left(g\right)=g\left[e^{j\frac{2\mathrm{nf}}{f_0}}\right],$ It can be known that the frequency response of the digital filter is 0 when the frequency f=0 Hz and f=16 MHz (ie g(z) is when z=1 and z=-1). Because the first demodulation signal of inputting this filter has filtered out the frequency components above 2MHZ in the finite impulse response digital low-pass filter 23 of previous stage, so the actual function of the infinite impulse response digital filter 24 is to convert the first The DC component of the demodulated signal is filtered out. In addition, the order of the finite impulse response digital low-pass filter 23 and the infinite impulse response digital filter 24 for filtering out the DC component can also be exchanged. Or use the prior art of digital signal processing to design an appropriate band-pass filter to replace two series-connected digital low-pass filters and digital high-pass filters, so as to simultaneously filter out high-frequency components and DC components in the identification signal .

Fig. 4 is in the embodiment of Fig. 3, the output signal of the finite impulse response digital low-pass filter 23 has not passed through the waveform of the signal B of the infinite impulse response digital filter circuit 24, Fig. 5 is in Fig. 3 embodiment, the finite impulse response digital low The output signal of the pass filter 23 passes through the waveform of the signal A of the infinite impulse response digital filter circuit 24 . As the waveform shown in FIG. 4 , the output signal of the finite impulse response digital low-pass filter 23 is affected by a frequency offset of 150KHz, so a DC offset voltage (DC offset) of about 0.4V is generated. The offset voltage of 0.4V will cause misjudgment by the output unit (the level determiner 25 ). However, as shown in FIG. 5 , after the output signal of the finite impulse response digital low-pass filter 23 passes through the infinite impulse response digital filter circuit 24 , the DC offset voltage has been eliminated. Therefore, the level determiner 25 will not generate misjudgment.

FIG. 6 shows a flow chart of the frequency shift keying/Gaussian frequency shift keying (FSK/GFSK) signal receiving method of the present invention. As shown in the figure, the receiving method of the present invention is roughly divided into five steps. The following describes the actions of each step according to the flow chart:

Step S600: start.

Step H602: Signal receiving step, receiving the transmission signal received from the antenna, amplifying and filtering to generate an intermediate frequency (base frequency) signal.

Step S604: a signal conversion step, converting the intermediate frequency (base frequency) signal into a digital signal.

Step S606: a signal frequency identification step, identifying the frequency of the digital signal and generating an identification signal.

Step S608: a signal filtering step, filtering the high-frequency components and low-frequency components of the identification signal, and generating a demodulated signal.

Step S610: Determine the level step, determine the level of the demodulated signal and generate a received signal.

Step S612: end.

In step S608, the method of the present invention uses a band-pass filter to filter the high-frequency component and the DC component of the discrimination signal. Therefore, the generated demodulated signal will not contain a DC component, so in the step of determining the level in step S610, a level determiner such as a comparator can be used to correctly generate the received signal. And as mentioned above, the band-pass filter can be composed of a finite impulse response digital low-pass filter connected in series with an infinite impulse response digital filter.

Although the present invention has been described above with examples, the scope of the present invention is not limited thereto. Those in the industry can make various modifications or changes as long as they do not depart from the gist of the present invention.

Claims (11)

1. a frequency-shift keying/Gauss frequency-shift keying (FSK/GFSK) signal receiver, it is characterized in that: it comprises:

One receives the transmission signal received from antenna and through amplifying and filter the FSK/GFSK signal demodulator of back generation intermediate frequency (fundamental frequency) signal;

One receives intermediate frequency (fundamental frequency) signal of aforementioned FSK/GFSK signal demodulator and converts the analog-digital converter of digital signal to;

One receives the digital signal of aforementioned analog-digital converter and produces the digital frequency discriminator of distinguishing signal;

One filters the radio-frequency component and the low-frequency component of aforementioned distinguishing signal and produces the digital band-pass filter of restituted signal; And,

One receives aforementioned restituted signal and produces the accurate position determining device of received signal.

2. frequency-shift keying/Gauss frequency-shift keying according to claim 1 (FSK/GFSK) signal receiver is characterized in that: wherein aforementioned digital band-pass filter comprises the wave digital lowpass filter and the digital high-pass filter of serial connection.

3. frequency-shift keying/Gauss frequency-shift keying according to claim 2 (FSK/GFSK) signal receiver is characterized in that: wherein aforementioned wave digital lowpass filter is a finite impulse response (FIR) wave digital lowpass filter.

4. frequency-shift keying/Gauss frequency-shift keying according to claim 2 (FSK/GFSK) signal receiver is characterized in that: wherein aforementioned digital high-pass filter is an infinite impulse response digital filter.

5. a frequency-shift keying/Gauss frequency-shift keying (FSK/GFSK) signal receiver, it is characterized in that: it comprises:

One receives the transmission signal received from antenna and through amplifying and filter the FSK/GFSK signal demodulator of back generation intermediate frequency (fundamental frequency) signal;

One receives intermediate frequency (fundamental frequency) signal of aforementioned FSK/GFSK signal demodulator and converts the analog-digital converter of digital signal to;

One receives the digital signal of aforementioned analog-digital converter and produces the digital frequency discriminator of distinguishing signal;

One filters the radio-frequency component of aforementioned distinguishing signal and produces the wave digital lowpass filter of first restituted signal;

One filters the flip-flop of aforementioned first restituted signal and produces the digital high-pass filter of second restituted signal; And,

One receives aforementioned second restituted signal and produces the accurate position determining device of received signal.

6. frequency-shift keying/Gauss frequency-shift keying according to claim 5 (FSK/GFSK) signal receiver is characterized in that: aforementioned wave digital lowpass filter is a finite impulse response (FIR) wave digital lowpass filter.

7. frequency-shift keying/Gauss frequency-shift keying according to claim 5 (FSK/GFSK) signal receiver is characterized in that: aforementioned digital high-pass filter is an infinite impulse response digital filter.

8. a frequency-shift keying/Gauss frequency-shift keying (FSK/GFSK) signal receiver, it is characterized in that: it comprises:

One receives the transmission signal received from antenna and through amplifying and filter the FSK/GFSK signal demodulator of back generation intermediate frequency signal;

One receives the intermediate frequency signal of aforementioned FSK/GFSK signal demodulator and converts the analog-digital converter of digital signal to;

One receives the digital signal of aforementioned analog-digital converter and produces the digital frequency discriminator of distinguishing signal;

One filters the flip-flop of aforementioned distinguishing signal and produces the digital high-pass filter of first restituted signal;

One filters the radio-frequency component of aforementioned first restituted signal and produces the wave digital lowpass filter of second restituted signal; And

One receives aforementioned second restituted signal and produces the accurate position determining device of received signal.

9. frequency-shift keying/Gauss frequency-shift keying according to claim 8 (FSK/GFSK) signal receiver is characterized in that: aforementioned wave digital lowpass filter is a finite impulse response (FIR) wave digital lowpass filter.

10. frequency-shift keying/Gauss frequency-shift keying according to claim 8 (FSK/GFSK) signal receiver is characterized in that: aforementioned digital high-pass filter is an infinite impulse response digital filter.

11. a frequency-shift keying/Gauss frequency-shift keying (FSK/GFSK) signal method of reseptance is characterized in that: comprise the following step:

Receive signal, receive the transmission signal of receiving from antenna, and produce intermediate frequency (fundamental frequency) signal through amplification and after filtering;

The signal conversion converts aforementioned intermediate frequency (fundamental frequency) signal to digital signal;

The signal frequency is differentiated, differentiates the frequency of aforementioned digital signal, and produces distinguishing signal;

Filtering signals filters the radio-frequency component and the low-frequency component of aforementioned distinguishing signal, and produces restituted signal; And

Judge accurate position, judge the accurate position of aforementioned restituted signal and produce received signal.

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