Demodulators – Phase shift keying or quadrature amplitude demodulator – Input signal combined with local oscillator or carrier...
Reexamination Certificate
2000-02-11
2004-10-12
Tse, Young T. (Department: 2634)
Demodulators
Phase shift keying or quadrature amplitude demodulator
Input signal combined with local oscillator or carrier...
C375S340000
Reexamination Certificate
active
06803814
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates generally on demodulators for modulated RF signals, mobile communications devices comprising such a demodulator as well as the method for demodulating modulated RF signals on the basis of a four port structure. It is particularly suitable for the demodulation of signals having a finite number of different magnitude states, such as f.e. (n)QAM.
(2) Description of Related Art
six-port receiver is known acting in the direct conversion manner and allowing conversion from mm-wave range and microwave range directly to the base band. At the same time a classic I/Q-demodulation chip (digital or analogue) can be avoided. By using suitable calibration procedures the influences of the non-ideal passive RF-components including manufacturing tolerances can be minimised. The six-port receiver detects the relative phase and relative magnitude of two incoming RF-signals. The circuitry of the six-port receiver is realised using only passive components in combination with power sensors for the detection of the relative phase and the relative magnitude of the RF-signals. An important feature of six-port receivers is that fabrication tolerances can be calibrated, which inherently allows low-cost production.
In Bossisio, Wu “A six-port direct digital millimeter wave receiver”, Digest of 1994 IEEE MTT Symposium, vol. 3, page 1659-1662, San Diego, May 1994, a structure for a six-port receiver is proposed.
The six-port technique has been known for its ability to accurately measure the scattering parameters, both amplitude and phase, of microwave networks. Instead of using heterodyne receivers a six-port receiver accomplishes direct measurements at microwave and mm-wave frequencies by extracting power levels at at least three and particularly four of the 6 ports. The imperfections of the hardware can be readily eliminated by an appropriate calibration procedure. Six-port junction receivers consist of passive microwave components such as directional couplers and power dividers as well as diode detectors. The circuit can be easily integrated as MHMIC or MMIC. The known receiver performs direct phase/amplitude demodulation at microwave and mm-wave frequencies.
By performing a calibration procedure the hardware imperfections can be readily eliminated. This significantly eases the requirement of the hardware implementation and enables the six-port receiver to operate over a wide band up to mm-wave frequencies.
According to the above cited document of Bossisio et. al. a six-port receiver concept with power dividers and 90 degrees hybrid circuits realized in distributed technology is used. The application of that known structure lies mainly in the frequency bands above 10 GHz, however, it suffers from an insufficient band width of the operation due to the inherently frequency selective nature of the 90 degrees hybrid circuits.
FIG. 11
shows the structure of a six-port receiver known from Bossisio, Wu “A six-port direct digital millimeter wave receiver”, Digest of 1994 IEEE MTT Symposium, vol. 3, page 1659-1662, San Diego, May 1994.
The incoming digitally modulated RF-signal is compared with the output of a digital controlled local oscillator
218
. Carrier recovery is first performed. The DSP-unit
217
detects-the frequency difference of the signals and then controls the local oscillator
218
to track the incoming signal. Once the carrier is recovered the instantaneous phase of the received signal is detected and decoded so as to recover the original modulated data. The maximum data transmission rate is determined mainly by the sampling rate of the A/D-converters
216
and the processing speed of DSP-unit
217
.
From D. Maurin, Y. Xu, B. Huyart, K. Wu,M. Cuhaci, R. Bossisio “CPW Millimeter-Wave Six-Port Reflectometers using MHMIC and MMIC technologies”, European Microwave Conference 1994, pp. 911-915, a wide-band topology for reflectometer used is known which is based on a distributing element approach featuring coplanar wave guide applications in the frequency range from 11 to 25 GHz.
From V. Bilik, et al. “A new extremely wideband lumped six-port reflectometer” European Microwave Conference 1991, pp. 1473-1477 and the idea of using Wheatstone Bridges and resistive structures for reflectometer applications is known.
From j:Li, G. Bossisio, K. Wu, “Dual tone Calibration of Six-Port Junction and its application to the six-port direct digital receiver”, IEEE Transactions on Microwave Theory and Techniques, vol. 40, January 1996 a six-port reflectometer topology based on four 3 dB hybrid circuits, power dividers and attenuators is known.
From U.S. Pat. No. 5,498,969 an asymmetrical topology for a reflectometer structure featuring matched detectors and one unmatched detector is known.
From U.S. Pat. No. 4,521,728 with the title “Method and six-port network for use in determining complex reflection coefficients of microwave networks” a reflectometer six-port topology is known comprising two different quadrate hybrids, phase shifter, two power dividers and one directional coupler for which the realization by a microstrip line technology is disclosed.
From EP-A-0 805 561 a method for implementing a direct conversion receiver with a six-port junction is known. According to this known technique, modulated transmitted modulation is received by a direct conversion receiver which comprises a six-port junction. The demodulation is carried out analogically.
From EP-A- 0 841 756 a correlator circuit for a six-port receiver is known. In this correlator circuit the received signal is summed up with a local oscillator signal at various phase angles, wherein the phase rotation between the local oscillator and RF signals is carried out separately from the summing of the correlator outputs.
In the following a four-port junction device (N=4) as a first example for the N-port junction technology will be explained with reference to FIG.
4
. Such a four-port receiver is known from the post-published application PCT/EP 98/08329 in the name of SONY INTERNATIONAL (EUROPE) GMBH.
FIG. 10
shows the use of said known four-port junction device in a I/Q demodulator or QPSK demodulator. A signal is received by means of an antenna
426
and is then either supplied directly to a bandpass filter
428
or first downconverted optionally in a first stage downconverter
427
. The output signal of the bandpass filter
428
is amplified by a gain controlled LNA block
429
. The gain of the gain controlled LNA block
429
is controlled by a control unit
430
. The amplified output signal of the gain controlled LNA block
429
is fed to the RF input
404
of the four-port junction device
401
.
A RF switch
451
is connected to the second RF input port
405
of the four-port junction device
401
. Depending on the switching position of the RF switch
451
the RF input port
405
of the four-port junction device
401
is either connected to ground potential by means of a resistor
450
with a resistance value of 50 &OHgr; (impedance matching) or a RF output signal of a local oscillator
420
is fed to the RF input
405
of the four—port junction device
401
. The frequency and the phase of the local oscillator
420
is also controlled by the control unit
430
. Furthermore, the control unit
430
controls the switching effected by the RF switch
451
.
The four-port junction device
401
comprises a first passive three-port structure and a second passive three-port structure. The first and the second passive three-port structure are connected with each other by means of a phase shifter. At a RF input port of the first passive three-port structure a RF signal to be processed is supplied. The first passive three-port structure has an output connected to a power sensor P
1
.
The second passive three-port structure of the four-port junction device according to the embodiment has a RF input port to which a second RF signal is fed wherein the second RF signal can e.g. originate from a local oscillator. The second passive three-port structure has an output port conn
Abe Masayoshi
Brankovic Veselin
Dölle Thomas
Konschak Tino
Krupezevic Dragan
Frommer William S.
Frommer & Lawrence & Haug LLP
Lugo David B.
Sony International (Europe) GmbH
Tse Young T.
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