Modulators – Phase shift keying modulator or quadrature amplitude modulator
Reexamination Certificate
1999-06-16
2001-06-05
Kinkead, Arnold (Department: 2817)
Modulators
Phase shift keying modulator or quadrature amplitude modulator
C332S146000, C333S164000, C375S308000, C455S111000, C455S042000
Reexamination Certificate
active
06242990
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to high frequency (microwave and mm-wave) modulators, and more specifically to a modulator, for communications applications, for producing a high frequency carrier signal so as to have one of four possible quadrature phase states in response to a simple modulation control voltage.
BACKGROUND OF THE INVENTION
Phase modulation of a carrier signal is, of course, well known for transmitting information onto a carrier signal. A common practice in communications is to employ bi-phase shift keyed (BPSK) or quadrature phase shift keyed (QPSK) modulation of the carrier signal to impart information thereon. That is, a receiver may detect variations in phase of a received carrier signal for obtaining information on the carrier signal. Applications for such phase shift keyed modulators include, among others, satellite communications and terrestrial digital radio systems.
High frequency phase modulators, as used herein, refer to those associated with microwave and mm-wave phase shift keyed applications. High frequency phase modulators are particularly difficult to construct economically to meet the performance requirements of having essentially constant amplitude for all phase states, and substantially constant phase states over a narrow bandwidth. A common practice for constructing such phase modulators is the employment of modulation techniques at low frequencies, and then to up-convert or frequency translate the resulting modulation waveform to the higher frequency. Such practices involve extra mixing circuitry and necessitate complex circuitry. For microwave and mm-wave applications, such complex circuitry adds to the degradation of performance due to, among others, signal insertion loss and signal degradation.
A phase shift keyed modulator is illustrated in a paper entitled, “Embedded Transmission Line (ETL) MMIC for Low Cost, High-Density Wireless Communication Applications,” by H. Q. Tserng, et.al., in 1997 IEEE Radio Frequency Integrated Circuits Symposium (0-7803-4603-9/97), incorporated herein by reference. In this paper, four pairs of transmission line segments are fabricated by way of MMIC technology. These line segments are switched in and out to provide a 16-state phase modulator for phased array radar applications. For radar applications, it is desired to a have a multi-bit phase shifter in which each phase state the phase is intended to be a linear function of frequency.
The phase shift keyed modulator of Tserng, et.al., although acceptable for radar applications, it is unacceptable for communication applications. This is so, since ideally it is not acceptable in communication applications for the phase to change with input frequency.
Therefore, there is a need for phase modulator for high frequency communication applications that is simple to construct, simple in structure, and provides good performance.
There is a need for a high frequency phase modulator which provides a quadrature-phase or bi-phase change which is substantially constant with frequency over a narrow bandwidth and which is simple to implement using MMIC integrated circuit fabrication technology.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a simple phase modulator for communication applications, which is easily fabricated in accordance with hybrid or MMIC fabrication techniques.
An object of the present invention is to provide a phase modulator where the amplitude remains substantially constant.
Another object of the invention is to provide a phase modulator which imparts directly onto a microwave or mm-wave carrier signal one of two or four possible phase states and to switch them by way of a simple control voltage.
In accordance with the present invention, a high frequency phase modulator for communication applications is constructed for discretely varying the phase of an input carrier signal between two possible phase states, where the imparted phase change is substantially constant over a narrow frequency bandwidth. The phase modulator includes a phase modulator section followed by a saturated power amplifier. The phase modulator section includes a phase bit circuit combination of at least a first pair of first and second transmission line segments and a pair of switches, where each switch serves as a single-pole double-throw switch. The phase bit combination of components are arranged for operatively connecting one of the pair of transmission line segments between an input associated with the first switch, and an output associated with the second switch. The length of the transmission line segment of each of the first and second line segments differs by a first selected difference value, in terms of desired radian phase delay determined at a desired operating carrier signal. A control means is provided to control the gate voltages of each of the field effect transistors of each of the switches so as to provide Bi-phase switching of the carrier signal. The output of the phase modulator section is provided as an input to a saturated power amplifier whose output is the intended communications signal.
In another embodiment of the invention, the phase modulator section includes a second phase bit circuit combination including an additional pair of switches and an additional pair of transmission line segments of predetermined length difference value are employed to provide phase quadrature switching of the carrier signal between 4 possible phase states.
REFERENCES:
patent: 5424696 (1995-06-01), Nakara et al.
Embedded Transmission Line (ETL) MMIC for Low-Cost, High-Density Wireless Communication Applications by H.Q. Tserng, et al., 1997 IEEE Radio Frequency Integrated Circuits Symposium (0-7803-4603-9/97).
Embodded Transmission Line (ETL) MMIC for Low-Cost, High-Density Wireless Communication Applications by H.Q. Tseng, et al., 1997 IEEE Radio Frequency Integrated Circuits Symposium (0-7803-4603-9/97).
A Ka-Band GaAs Monolithic Phase Shifter by V. Sokolov, et al., IEEE Transactions on Microwave Theory and Techniques, vol. MTT-31, No. 12, Dec. 1983, pp. 1077-1083.
Resonated GaAs FET Devices for Microwave Switching, by W. McLevige, et al, IEEE Transactions on Electron Devices, vol. ED028, No. 2, Feb. 1981, pp. 198-204.
Jensen Roger W.
Kinkead Arnold
TLC Precision Wafer Technology Inc.
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