WO1997031465A2 - Frequency control in an fsk receiver - Google Patents
Frequency control in an fsk receiver Download PDFInfo
- Publication number
- WO1997031465A2 WO1997031465A2 PCT/GB1997/000478 GB9700478W WO9731465A2 WO 1997031465 A2 WO1997031465 A2 WO 1997031465A2 GB 9700478 W GB9700478 W GB 9700478W WO 9731465 A2 WO9731465 A2 WO 9731465A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- signal
- frequency
- receiver
- representing
- electrical signal
- Prior art date
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/10—Frequency-modulated carrier systems, i.e. using frequency-shift keying
- H04L27/14—Demodulator circuits; Receiver circuits
- H04L27/144—Demodulator circuits; Receiver circuits with demodulation using spectral properties of the received signal, e.g. by using frequency selective- or frequency sensitive elements
- H04L27/152—Demodulator circuits; Receiver circuits with demodulation using spectral properties of the received signal, e.g. by using frequency selective- or frequency sensitive elements using controlled oscillators, e.g. PLL arrangements
Definitions
- the present invention relates to a frequency modulated (FM) detection apparatus and method, and relates particularly to an apparatus and method for detection of digitised FM data.
- FM frequency modulated
- Radio frequency transmission of digital signals is usually achieved by means of frequency-shift keying (FSK) , in which an RF carrier signal is shifted in frequency between two closely spaced frequencies, respectively above and below the carrier frequency representing the l*s and O's of digital serial bits transmitted.
- FSK frequency-shift keying
- a received FSK signal is detected by providing an electrical signal lowered in frequency from the carrier frequency of the signal by a fixed frequency interval, and providing an output electrical signal having an amplitude representing the frequency deviation of the frequency shifted signal so that the output electrical signal represents the frequency modulating signal.
- One of the limitations of existing digital FM detection techniques is that limitations to the rate at which the output electrical signal representing the serial data bits can be generated in turn limit the rate at which transmitted data can be received and processed.
- a receiver for digitised frequency modulated signals comprising mixer means for receiving a first electrical signal representing the signal at a carrier frequency and frequency modulated to carry power at first and second frequencies representing respective first and second signal logic levels, wherein the mixer means is controlled by a local oscillator and in use provides a second electrical signal representing the first signal lowered in frequency by a substantially fixed amount; detector means for receiving said signal and providing a third electrical signal having an amplitude representing an instantaneous logic level of the digital frequency modulating signa l ; and feedback means for adjusting the frequency of the local oscillator to adjust the carrier frequency corresponding to the second electrical signal within a range between said first and second frequencies in dependence upon the amplitude of the third electrical signal.
- the sensitivity of the receiver is enhanced as far as detection of the instantaneous logic level is concerned. This in turn increases the speed at which the instantaneous logic level of the incoming signal can be identified which has the advantage of increasing the rate at which incoming data can be received and processed.
- the receiver is adapted to receive digitised frequency modulated radio frequency signals.
- the feedback means adjusts the frequency of the local oscillator away from the first or second frequency representing the instantaneous logic level of the signal output by the receiver.
- the mixer means includes a voltage influenced oscillator.
- the feedback means preferably comprises an impedance connected between an output terminal of the detector means and an input terminal of the voltage influenced oscillator.
- the receiver preferably further comprises at least one further mixer means arranged between the mixer means and said detector means for lowering the frequency of the second signal output signal by a substantially fixed interval.
- a method of demodulating digitised frequency modulated signals comprising converting an incoming signal into a first electrical signal having a carrier frequency modulated by a transmitted signal to carry power at first and second frequencies representing first and second logic levels of the frequency modulating signal; mixing the first electrical signal with a signal at a reference frequency to provide a second electrical signal representing said first signal lowered in frequency by substantially fixed interval; detecting said second signal to provide a third electrical signal having an amplitude representing the instantaneous logic level of the frequency modulating signal; and adjusting the carrier frequency corresponding to the second signal within a range between said first and second signals in dependence upon the amplitude of the third signal.
- the carrier freguency corresponding to the second signal is preferably adjusted away from the first or second frequency representing the instantaneous logic level of the third signal output by the receiver.
- the signal to be demodulated falls within the radio frequency band.
- the method preferably further comprises the step of adjusting a voltage influenced oscillator in dependence upon the amplitude of the third signal.
- FIG. 1 is a schematic diagram of a digitised FM receiver embodying the present invention
- FIG. 2 is a schematic block diagram of the FM receiver of Figure 1.
- an RF receiver 1 comprises an antenna 2 for receiving radiated RF signals and providing an FSK electrical signal along an input lead 3 at a carrier frequency.
- the signal along lead 3 then passes to an input terminal of an input amplifier 4, the output signal from which passes via an LC network 5 to pin 1 of an FM receiver integrated circuit 6, such as an MC3363 FM receiver manufactured by Motorola.
- the signal input at pin 1 of the integrated circuit 6 is input to a first mixer 31 in which a signal from a local oscillator is mixed with the input signal to provide an output signal at pin 23 of the integrated circuit 6 at an intermediate frequency of 10.7 MHZ.
- the local oscillator 32 of the first mixer 31 includes a voltage influenced oscillator 7 wherein adjustment of the frequency of the voltage controlled oscillator adjusts the point at which the expected incoming frequency should be so that the frequency of the input signal on lead 3 which is mixed with the local oscillator signal and input to the integrated circuit 6 is adjusted.
- the output from the first mixer is a version of the signal on lead 3, but at 10.7 MHZ.
- the output signal of the first mixer 31 passes from pin 23 of the integrated circuit 6 via a ceramic filter 8 and is input via pin 21 of the circuit 6 to a second mixer 33 where it is mixed with the output signal of an oscillator 34 having a reference frequency controlled by a clock signal input via clock terminal 9 to pin 6 of the receiver circuit 6.
- the second mixer outputs a signal of frequency 455 KHZ from pin 7 of the circuit 6 which is a frequency - shifted version of the signal on lead 3.
- the output of the second mixer 34 is then passed via a further ceramic filter 10 and pin 8 of the circuit 6 to a limiter amplifier 35, the output of which is input to a detector circuit 36 comprising a quaderature detector.
- the detector circuit provides an output signal 37 such that amplitude of the output signal represents the instantaneous logic level of the frequency modulating signal received on lead 3 from antenna 2.
- the output of the detector is amplified and input to an FSK comparator 38, the output of which is taken from pin 18 of the integrated circuit 6 to an output terminal 11 of the receiver 1.
- a feedback resistor 12 is connected between output terminal 11 and pin 27 of circuit 6 to provide a tuning voltage to the voltage controlled oscillator 7 of the first mixer in dependence upon the amplitude of the signal output at terminal 11.
- Digitised serial data to be transmitted is frequency odulated onto an RF carrier signal by a FSK technique as will be known to persons skilled in the art.
- the RF signal at the carrier frequency is frequency modulated to carry power at first and second closely spaced FSK frequencies, slightly separated from the carrier frequency and respectively higher and lower in frequency.
- the antenna 2 detects the RF signal and outputs an electrical signal at the carrier frequency along line 3 having the same frequency modulation as the transmitted signal.
- the input signal After amplification by the input amplifier 4, the input signal is mixed with the signal produced by the first mixer 31, and the input voltage of the voltage controlled oscillator 7 is selected so that the 10.7 MHZ output signal of the first mixer 31 is a frequency-shi ted version of the signal at the carrier frequency of interest.
- the output signal of the first mixer is input to the second mixer 33 to provide a 455 KHZ output signal which is also a frequency shifted version of the signal at the carrier frequency of interest.
- the output signal of the second mixer 33 is input to the limiter 35 and detector 36, and the amplified output of the detector circuit provided at output terminal 11 of the receiver 1 is high or low, depending upon the logic level of the detected frequency modulating signal.
- the carrier frequency processed by the integrated circuit 6 is shifted in the direction of the power carrying frequency representing logic level 1 of the frequency modulating signal.
- the local oscillator frequency shift caused by a slight shift in incoming frequency will emphasise the change in incoming frequency, thus causing the sensitivity of the final detector stage is increased, which in turn enhances the speed at which the logic level corresponding to the output of the detector stage can be determined.
- the passed carrier frequency is slightly shifted towards the power - carrying frequency representing logic level 0, with the result that the sensitivity of the detector is increased.
- this action will emphasize the data. If on the other hand the decoding of the signal was incorrect, this action will attenuate the data.
- the action may be viewed as "Intelligent Hysteresis”.
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- Physics & Mathematics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
- Superheterodyne Receivers (AREA)
- Circuits Of Receivers In General (AREA)
Abstract
Description
Claims
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AU18059/97A AU1805997A (en) | 1996-02-21 | 1997-02-20 | Frequency control in an fsk receiver |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9603660.3 | 1996-02-21 | ||
GBGB9603660.3A GB9603660D0 (en) | 1996-02-21 | 1996-02-21 | Fm detection apparatus and method |
Publications (2)
Publication Number | Publication Date |
---|---|
WO1997031465A2 true WO1997031465A2 (en) | 1997-08-28 |
WO1997031465A3 WO1997031465A3 (en) | 1997-10-23 |
Family
ID=10789150
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/GB1997/000478 WO1997031465A2 (en) | 1996-02-21 | 1997-02-20 | Frequency control in an fsk receiver |
Country Status (3)
Country | Link |
---|---|
AU (1) | AU1805997A (en) |
GB (1) | GB9603660D0 (en) |
WO (1) | WO1997031465A2 (en) |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR2482804A1 (en) * | 1980-05-16 | 1981-11-20 | Plessey Overseas | RADIO RECEIVER WITH FREQUENCY MODULATION |
GB2120052A (en) * | 1982-04-30 | 1983-11-23 | Philips Electronic Associated | Receiver |
GB2146876A (en) * | 1983-09-14 | 1985-04-24 | Plessey Co Plc | FSK radio receiver |
US4628518A (en) * | 1981-08-20 | 1986-12-09 | Plessey Overseas Limited | Radio receiver |
EP0527469A2 (en) * | 1991-08-12 | 1993-02-17 | Matsushita Electric Industrial Co., Ltd. | FSK data receiving system |
-
1996
- 1996-02-21 GB GBGB9603660.3A patent/GB9603660D0/en active Pending
-
1997
- 1997-02-20 AU AU18059/97A patent/AU1805997A/en not_active Abandoned
- 1997-02-20 WO PCT/GB1997/000478 patent/WO1997031465A2/en active Application Filing
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR2482804A1 (en) * | 1980-05-16 | 1981-11-20 | Plessey Overseas | RADIO RECEIVER WITH FREQUENCY MODULATION |
US4628518A (en) * | 1981-08-20 | 1986-12-09 | Plessey Overseas Limited | Radio receiver |
GB2120052A (en) * | 1982-04-30 | 1983-11-23 | Philips Electronic Associated | Receiver |
GB2146876A (en) * | 1983-09-14 | 1985-04-24 | Plessey Co Plc | FSK radio receiver |
EP0527469A2 (en) * | 1991-08-12 | 1993-02-17 | Matsushita Electric Industrial Co., Ltd. | FSK data receiving system |
Also Published As
Publication number | Publication date |
---|---|
AU1805997A (en) | 1997-09-10 |
WO1997031465A3 (en) | 1997-10-23 |
GB9603660D0 (en) | 1996-04-17 |
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