WO1996007234A1 - Dispositif de communications a generateur de passage a zero - Google Patents

Dispositif de communications a generateur de passage a zero Download PDF

Info

Publication number
WO1996007234A1
WO1996007234A1 PCT/US1995/010565 US9510565W WO9607234A1 WO 1996007234 A1 WO1996007234 A1 WO 1996007234A1 US 9510565 W US9510565 W US 9510565W WO 9607234 A1 WO9607234 A1 WO 9607234A1
Authority
WO
WIPO (PCT)
Prior art keywords
phase
zero
quadrature
components
communication device
Prior art date
Application number
PCT/US1995/010565
Other languages
English (en)
Inventor
Edward K. B. Lee
Joseph P. Heck
Original Assignee
Motorola Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Motorola Inc. filed Critical Motorola Inc.
Publication of WO1996007234A1 publication Critical patent/WO1996007234A1/fr

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K9/00—Demodulating pulses which have been modulated with a continuously-variable signal
    • H03K9/06—Demodulating pulses which have been modulated with a continuously-variable signal of frequency- or rate-modulated pulses
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
    • H03D3/00—Demodulation of angle-, frequency- or phase- modulated oscillations
    • H03D3/007—Demodulation of angle-, frequency- or phase- modulated oscillations by converting the oscillations into two quadrature related signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
    • H04L27/22—Demodulator circuits; Receiver circuits
    • H04L27/233—Demodulator circuits; Receiver circuits using non-coherent demodulation
    • H04L27/2332—Demodulator circuits; Receiver circuits using non-coherent demodulation using a non-coherent carrier

Definitions

  • This invention is generally related to communication devices and more particularly to digital communication devices.
  • This patent uses four mixers to produce four signal components, i.e. two in- phase and two Quadrature components.
  • two more mixers are used to produce additional zero- crossings.
  • the additional mixers provide additional in-phase and quadrature components at 45° and 135°. These two components will be used with phase components at 0° (in-phase) and 90° (quadrature phase) to decode the transmitted signal.
  • a significant problem with this approach is the need for two additional mixers. As is known in the art, mixers generally draw much supply current or may require significant power from the local oscillate signal.
  • the addition of two more mixers is therefore particularly troubling in portable communication devices which use battery power. It is one goal of this invention to conserve energy particularly in portable radio applications.
  • two more phase shifters and filters are needed at the local oscillator and the output of the mixer, respectively.
  • the phase shifters produce appropriate local oscillator signals to produce mixed signals at 45° and 135° away.
  • the added filters remove undesired high frequency signals from the output of the two additional mixers.
  • the problem of added current drain is exacerbated by the filters and phase shifters.
  • the prior art is therefore inefficient in recovering digitally modulated signals.
  • a scheme is desired to recover digitally modulated communication signals without a significant demand on current drain and/or unnecessarily additional circuit components..
  • FIG. 1 is a block diagram of a communication device with an efficient zero-crossing generator/detector in accordance with the present invention.
  • FIG. 2 shows the vector relationship of the four vectors as generated by the block diagram of FIG. 1.
  • FIG. 3 shows a block diagram of a summer and subtracter in accordance with the present invention.
  • FIG. 4 shows the vector relationship of the vectors of the block diagram of FIG. 5.
  • FIG. 5 shows a block diagram for producing additional zero crossings in accordance with the present invention.
  • Some digital demodulation schemes (such as Frequency Shift Keying (FSK)) estimate transmitted data by estimating a phase rotation direction at zero-crossing points.
  • the performance of such demodulation schemes varies with the number of zero crossing points.
  • An increase in the number of measurements of a phase rotation direction at zero-crossing points improves the performance of the demodulator, and increases the maximum transmit bit rate with acceptable performance.
  • a received signal is converted to zero IF either directly or via multiple conversion stages.
  • a zero IF signal may be acquired either by directly converting the received signal to zero IF or first going through an intermediate conversion stage.
  • the conversion is accomplished via two mixers which produce the in-phase (i(t)) and the quadrature phase (q(t)).
  • the i and q signals are used in the recovery of the transmitted information signal using methods known in the art.
  • One technique determines the polarity of the bit by estimating the phase rotation direction.
  • a phase rotation direction may be determined by sampling q waveforms at i zero crossings and i waveforms at q zero-crossing points.
  • the number of zero crossings formed by the in-phase and quadrature components are insufficient to recover an information signal transmitted via narrowband FM and/or under noisy conditions. Indeed, in narrowband FM some bits may be missed (wrongly estimated) due to the lack of a sufficient number of zero crossings. Noise could similarly affect the detection of the signal.
  • the present invention proposes the use of summers and subtractors at the outputs of only two mixers to increase the number of i and q components, hence increasing the number of zero crossings.
  • FIG. 1 shows relevant portions of a communication device 100 having a zero IF demodulator including an efficient zero-crossing generator.
  • a radio frequency signal such as FSK
  • received at the antenna 102 is converted to zero IF via two mixers 104 and 108
  • An oscillator 112 provides the local oscillator (LO) signal for 104.
  • the local oscillator signal for the mixer 108 is supplied through a 90° phase shifter 106.
  • the radio frequency signal may be converted down to a non-zero IF before a final conversion to zero IF.
  • the output signals of the mixers 104 and 108 are filtered at LPFs 110 and 114 to produce the i(t) and q(t) signals. These signals are added in the summer 116 and subtracted in the subtractor 118 to produce additional in-phase and quadrature signals, i ⁇ (t)) and q ⁇ (t), respectively. As will be shown mathematically, these additional channels are 45° and 135° away from i(t).
  • a received RF signal coupled from the antenna 102 is mixed with cos (w c t) and -sin (w c t) to generate i and q signals at the outputs of mixers 104 and 108, respectively.
  • the mixing operation may be mathematically described as:
  • This signal is filtered via filters 110 and 114.
  • the filtered signals are represented as:
  • the filtered signals are applied to limiters 120 and 122 before being coupled to a zero-crossing detector 128. These limiters provide zero crossing information on the i and q channels.
  • the filtered signals are added and subtracted at 116 and 118, respectively to produce:
  • Equation 9 may be expressed in terms of i (t) and q (t) using
  • q. (t) may be generated using the following equation:
  • Equations 10 and 11 indicate that L (t) and q. (t) may be generated by summing and subtracting i (t) and q (t).
  • the second in-phase ii (t) and quadrature q ⁇ (t) components result in additional zero crossings.
  • the outputs of the summer 116 and the subtracter 118 are coupled to the zero-crossing detector 128 via limiters 124 and 126, respectively. These limiters work in conjunction with limiters 120 and 122 to provide the detector 128 with additional zero crossings which are detected therein.
  • the detection of zero crossings may be accomplished via D flip flops with edge triggered clock inputs.
  • q values at i zero crossings indicate the direction of phase rotation.
  • the zero crossings of i and q waveforms may be viewed as the phase crossings of i and q axes in the phase diagram 200.
  • a positive phase axis-crossing means that the phase trajectory crosses i or q axis in a positive direction (counter-clockwise).
  • a negative phase axis-crossing means that the phase trajectory crosses i or q axis in a negative direction (clockwise).
  • the zero-crossing detector 128 sets its output high if the phase trajectory crosses i or q axis in a positive direction. A low output is produced when the phase trajectory crosses i or q axes in the negative direction.
  • the detection of zero crossings is translated to information signal at a controller 130.
  • the controller 130 may be any micro-controller or microcomputer available from various semiconductor manufacturers.
  • the audio portions of the decoded information signal is coupled to a speaker 134.
  • the data portion is displayed on a display 132 automatically or upon request or otherwise used or processed.
  • a significant feature of this invention is the fact that demodulation can be done digitally without the use of conventional A D converters. In other words, only simple limiters or compactors are needed to convert the baseband signals into a 0 and 1 representation. The need for A/D converters is eliminated by performing the addition and subtraction functions in the analog domain. Consequently, the additional i and q signals are generated in the summer 116 and subtractor 118 before application to the limiters.
  • an efficient zero-crossing generator utilizes a summer and a subtractor to generate additional zero crossings.
  • zero crossings provide vital information on the phase of the signal. Indeed, by generating zero crossings one could readily recover the transmitted information signal. Additional zero crossings are highly desired in systems particularly those having low modulation indices.
  • the present invention Instead of mixing a received signal with a local oscillator utilizing additional mixers and phase shifters, the present invention generates the additional zero crossings by adding and subtracting the initial in-phase and quadrature components. This manipulation of the mixer signal is highly efficient and may be accomplished with minimum additional components. It is known that the summation or the subtraction of unit quadrature vectors results in a coefficient (amplitude) other than one (i.e. V ⁇ ). Due to this change in the amplitude, it is required to scale the components to a point where the resultant vector has an amplitude of one.
  • FIG. 3 shows an analog circuit technique using operational amplifiers which can be used to accomplish the needed inversions, summations and magnitude scaling.
  • the i and q components are inverted via inverters 302 and 304.
  • the inverted signals are then added and scaled at the summer 306.
  • the output of this summer is the second quadrature signal q ⁇ (t).
  • a second summer 308 adds and scales the inverted i and q signals to produce the first in-phase component ii (t) (scaled).
  • devices 306 and 308 are both adders they provide summing and subtracting functions, respectively by inversion actions that take place on the signals before they are applied thereto.
  • some scaling is necessary, particularly if additional in-phase and quadrature signals are desired beyond ii (t) and q ⁇ (t).
  • additional in- phase and quadrature signals may be generated to improve the performance of the demodulator by the generation of more zero crossings. Additional signals are particularly helpful in systems having a small modulation index. These additional signals are generated by continuing the progression of the summer/subtractor circuit.
  • FIG. 4 shows a specific case where four additional vectors, i2(t), q2(t), i3(t), q 3 (t) are generated. These vectors are used in the phase domain to represent the additional in- phase and quadrature signals.
  • FIG. 5 shows the circuit implementation for the additional vectors.
  • the differing values of resistors used in the circuits are for the purpose of scaling the input phase components. As mentioned, this scaling is necessary to produce vectors with uniform amplitudes. Obviously, the progression could be continued indefinitely to generate ever more vectors. Generally, it is desirable to progress the number of i and q vectors by powers of 2 so that the vectors are all equally spaced.
  • a significant benefit of the present invention is the elimination of additional mixers, phase shifters and filters as suggested by the prior art.
  • the elimination of these additional components results in significant current savings which is highly desired in portable communication devices.
  • the summer and the subtractor which provide the additional in- phase and quadrature components are traditionally low current consuming devices as compared to mixers.
  • An additional benefit of the present invention is the ease with which the number of in-phase and quadrature components may be increased beyond those suggested by the prior art. By adding and subtracting the original in-phase and quadrature components from the output signal of the summer and subtractor one could generate additional i and q signals with significant ease. These additional components produce even more zero- crossing points which would in turn provide for very narrowband communication.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Abstract

Un dispositif de communications (100) comporte un premier (104) et un second (108) mélangeurs conçus pour produire respectivement une première composante en phase et une composante en quadrature. Des points de passage à zéro supplémentaires sont générés efficacement par addition et soustraction des composantes en phase et en quadrature dans, respectivement, un sommateur (118) et un organe de soustraction (118). Les points de passage à zéro supplémentaires sont générés par la formation de secondes composantes en phase et en quadrature. Un détecteur de passage à zéro (128) est utilisé pour détecter le passage à zéro au moyen de la première et seconde composantes en phase et de la première et seconde composantes en quadrature.
PCT/US1995/010565 1994-08-26 1995-08-18 Dispositif de communications a generateur de passage a zero WO1996007234A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US29613994A 1994-08-26 1994-08-26
US08/296,139 1994-08-26

Publications (1)

Publication Number Publication Date
WO1996007234A1 true WO1996007234A1 (fr) 1996-03-07

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PCT/US1995/010565 WO1996007234A1 (fr) 1994-08-26 1995-08-18 Dispositif de communications a generateur de passage a zero

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4254503A (en) * 1978-10-24 1981-03-03 International Standard Electric Corporation Radio receiver for tone modulated signals
US4498050A (en) * 1982-05-07 1985-02-05 Nec Corporation Demodulation device for composite PSK-PSK modulated waves
US4540948A (en) * 1982-09-14 1985-09-10 Nec Corporation 8-Phase phase-shift keying demodulator
US4577157A (en) * 1983-12-12 1986-03-18 International Telephone And Telegraph Corporation Zero IF receiver AM/FM/PM demodulator using sampling techniques
US4605903A (en) * 1985-11-07 1986-08-12 Motorola, Inc. FSK demodulator with high noise immunity digital phase detector
US4752742A (en) * 1983-11-08 1988-06-21 Nec Corporation Frequency demodulator for recovering digital signals
US4795986A (en) * 1986-12-05 1989-01-03 Gte Telecommunicazioni, S.P.A. Method and circuit for carrier synchronism recovery in PSK coherent demodulators

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4254503A (en) * 1978-10-24 1981-03-03 International Standard Electric Corporation Radio receiver for tone modulated signals
US4498050A (en) * 1982-05-07 1985-02-05 Nec Corporation Demodulation device for composite PSK-PSK modulated waves
US4540948A (en) * 1982-09-14 1985-09-10 Nec Corporation 8-Phase phase-shift keying demodulator
US4752742A (en) * 1983-11-08 1988-06-21 Nec Corporation Frequency demodulator for recovering digital signals
US4577157A (en) * 1983-12-12 1986-03-18 International Telephone And Telegraph Corporation Zero IF receiver AM/FM/PM demodulator using sampling techniques
US4605903A (en) * 1985-11-07 1986-08-12 Motorola, Inc. FSK demodulator with high noise immunity digital phase detector
US4795986A (en) * 1986-12-05 1989-01-03 Gte Telecommunicazioni, S.P.A. Method and circuit for carrier synchronism recovery in PSK coherent demodulators

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