Modulators – Phase shift keying modulator or quadrature amplitude modulator
Patent
1999-10-18
2000-08-08
Mis, David
Modulators
Phase shift keying modulator or quadrature amplitude modulator
332119, 332151, 455 674, 455103, 455104, 375224, H03C 300, H04B 1700, H04L 2700
Patent
active
061007714
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a multi-signal generator used for testing receivers of mobile communication systems.
BACKGROUND ART
An example of conventional technology is explained with reference to FIGS. 5 and 6.
A multi-signal generator used for testing receivers of mobile communication systems outputs signals having multiple frequencies by adding a plurality of signals corresponding to the requirements of testing.
The configuration and its function of such a conventional technology are explained in the case where a multi-signal generator of three channels generates signals having three different frequencies.
As shown in FIG. 5, a multi-signal generator 1 in the conventional technology has a three-channel configuration and includes frequency synthesizers 11, 12, and 13, modulators 21, 22, and 23, amplifiers 71, 72, and 73, and attenuators 81, 82, and 83. The multi-signal generator 1 also includes an adder 90.
Each of the components and functions is explained in the following:
The frequency synthesizer 11 in the channel 1 is a variable frequency synthesizer in the frequency range of 0-2 GHz, and generates a frequency f1 as a carrier signal.
The modulator 21 is a mobile communication modulator used in a mobile communication system such as a quadrature modulator.
The quadrature modulator modulates an amplitude and phase of a carrier signal by an I channel and an Q channel of the base band signal.
Namely, the same phase (I: In Phase) components of the carrier signal is modulated by the binary data of an I channel base band signal, and the 90-degree phase shifted (Q : Quadrature Phase) components is modulated by the binary data of a Q channel base band signal, and then both modulated components are combined with one another to be output as a modulated carrier signal.
The modulated carrier signal is amplified by the amplifier 71 and is attenuated to a desired power level by the attenuator 81. Thus, the signal frequency f1 which is in the range of 0-2 GHz with a desired power level is output to the adder 90 as an output signal of the channel 1.
In the similar manner, an output signal of channel 2 and an output signal of channel 3 are provided to the adder 90.
These signals of three channels are combined by the adder 90 which outputs a signal having frequencies f1, f2, and f3 in the frequency range of 0-2 GHz.
In this example, however, when frequency variable synthesizers of wide frequency range and quadrature modulators are used, depending on frequency settings in the output signals, calibration processes become necessary to suppress spurious responses at the output of quadrature modulators by fine adjusting amplitudes and phases of the base band signals to modulate the carrier signals or several additional quadrature modulators must be provided.
In other words, in this method, the circuit configuration needs to be complex because the wide range frequencies are applied to the quadrature modulators.
Moreover, in the multi-signal generator using this method, the production cost needs to be high because the frequency synthesizers with wide variable frequency range and the modulators of wide frequency range are needed for the number of channels of the multi-signals.
To solve this problem, it may be possible to limit the variable frequency range of the frequency synthesizers 11, 12 and 13 to a narrower range of, for instance, 800 MHz.
However, it is difficult to deal with different test situations where frequency bands of the communication devices to be tested are changed, for example to 1.5 GHz or 1.7 GHz.
Another conventional example of multi-signal generator using frequency conversion method is explained with reference to FIG. 6.
This example has a 3-channel configuration having fixed frequency synthesizers 16, 17, 28, 36, 37 and 38, modulators 21, 22 and 23, mixers 61, 62, 63, 66, 67 and 68, variable frequency synthesizers 41, 42 and 43, band pass filters 51, 52 and 53, amplifiers 71, 72 and 73, attenuators 81, 82 and 83, and an adder 90.
The operation of this generator is explained for an exampl
REFERENCES:
patent: 5659891 (1997-08-01), Hays et al.
Advantest Corp.
Mis David
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