Phase-shift keying electronic circuit with distributed structure

Details Phase-shift keying electronic circuit with distributed structure Phase-shift keying electronic circuit with distributed structure

1999-08-19

2000-12-19

Mis, David

Modulators

Phase shift keying modulator or quadrature amplitude modulator

332104, 332105, 375308, H03C 300, H03C 702, H04L 2720

Patent

active

061632309

DESCRIPTION:

BRIEF SUMMARY
The invention concerns a phase-shift keying modulator circuit (so-called PSK "phase Shift keying" or MDP "modulation de phase").
Such circuits are used in particular for the transmission of digital signals. For example, the transmission of digital signals between a satellite and earth can be effected by phase modulation of a microwave carrier signal by a digital signal.
Binary phase-shift keying (BPSK/or MDP2) or quadrature phase-shift keying (QPSK/or MDP4) modulator circuits are already known ("HIGH BIT RATE FOUR PHASE MMIC REMODULATION DEMODULATOR AND MODULATOR", A. Primerose et al., Proceedings of GAAS '92, Estec, Nordwich, The Netherlands). A BPSK circuit can thus be formed by a low-pass filter and a high-pass filter mounted in parallel and whose outputs are switched to a common output by an array of two shunted MESFET transistors whose gates receive complementary, two-state signals. This circuit has the advantage of supplying a phase shift between the signals, which of course by design tends towards the theoretical value of 180.degree., despite inevitable manufacturing imperfections. Furthermore, the MESFET transistors used for switching are not biased and the circuit introduces only small losses (of the order of 3 dB). It can be realised in MMIC technology and requires little space (typically 2 mm.times.1 mm for 8 GHz). Nevertheless, such a BPSK circuit has the drawback of a large spectral bandwidth for a given bit timing. Moreover, it does not include any electrical control means and does not allow phase shifts with values other than 180.degree., so that it cannot be used in certain applications when a residual carrier with non-zero amplitude is required(to synchronize a receiver for example).
A QPSK circuit formed from two BPSK circuits allows a smaller spectral bandwidth for the same bit timing, but still has the disadvantages of absence of adjustment means based on an electrical control and only allows phase shifts of a fixed value. Furthermore, these circuits generate larger losses (of the order of 8 dB) and have overall dimensions of the order of 2.5 mm.times.3.5 mm at 8 GHz.
.pi.n/4-QPSK circuits are also known (".pi./4-QPSK MODEMS FOR SATELLITE SOUND/DATA BROADCAST SYSTEMS", Chiu-Liang Liu, Kassilo Feher, IEEE Transactions on broadcasting, vol. 37, No. 1, March 1991, pp 1-8) which are circuits with eight phase states obtained by additional .pi./4 phase shifts at each phase change. These circuits have the same disadvantages as the above-mentioned traditional QPSK circuits. It should also be noted that of the eight possible phase states, only certain phase transitions are allowed, so that the .pi./4-QPSK circuits are only compatible with an appropriate coding system, and in particular cannot be used with certain types of digital signal coding to be transmitted.
The document "A VERSATILE VECTOR MODULATOR DESIGN FOR MMIC", L. M. Devlin, B. J. Minnis, 1990 IEEE MTT-S Digest L-7 pp 519-522, describes a 2.times.four phase state modulator circuit, that is to say producing two vectorial signal structures with different amplitudes. This circuit has overall dimensions of 4 mm.times.3 mm at 8 GHz, and has four variable resistances whose adjustment is complex. Moreover, it is functionally equivalent to a QPSK circuit, since the eight phase states, not having the same amplitude, are not useable for basic phase modulation (without amplitude modulation) with eight phase states.
With the aim of reducing the power during the transmission, an attempt is made to use high-performance digital signal coding such as TCM (trellis-coded modulation). To do this, it is essential to have modulation circuits having a number of phase states greater than four (in particular 8, 16 . . . ).
Now it is not conceivable to combine the architecture of the known BPSK or QPSK arrangements in the same circuit with the aim of improving bit rate performance since the imperfections of each component affect the others and accumulate at the output. Moreover, a crippling loss of power results, particularly for systems on board aircraft and

REFERENCES:
patent: 3867574 (1975-02-01), McIntosh
patent: 5442327 (1995-08-01), Longbrake et al.
patent: 5463355 (1995-10-01), Halloran
patent: 5504461 (1996-04-01), Vaughn et al.
By A. Boveda et al., "A 0.7-3 GHz GaAs QPSK/QAM Direct Modulator", IEEE Journal of Solid-State Circuits, vol. 28, No. 12, Dec. 1993, pp. 1340-1349.
By A. Primerose et al., "High Bit Rate Four Phase MMIC Remodulation Demodulator and Modulator", Proceedings of the GAAS92 European Gallium Arsenide and Related III-V Compounds Applications Symposium, Apr. 1992, 6 pages.
By C.L. Liu, ".pi./4-QSPK Modems for Satellite Sound/Data Broadcast Systems", IEEE Transactions on Broadcasting, vol. 37, No. 1, Mar. 1991, pp. 1-8.
By L.M. Devlin et al., "A Versatile Vector Modulator Design for MMIC", IEEE MTT-S Digest L-7, 1990, pp. 519-522.

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