Modulator and demodulator

Details Modulator and demodulator Modulator and demodulator

2003-07-03

2004-12-21

Mis, David (Department: 2817)

Demodulators

Phase shift keying or quadrature amplitude demodulator

Input signal combined with local oscillator or carrier...

Reexamination Certificate

active

06833755

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a modulator for modulating a carrier wave with an in-phase component (I component) signal and a quadrature component (Q component) and a demodulator for demodulating the in-phase component signal and quadrature component signal, particularly to a technology enabling broadband modulation and demodulation with simple control.
2. Description of the Prior Art
In, for example, intelligent transport systems (ITS) used to increase traffic efficiency through exchange of information among people, vehicles and roads, consideration is being given to use of software radio that uses software to send and receive wireless signals.
Wireless devices such as software radios need to be equipped with modulator and demodulator units for high-frequency and/or broadband wireless communication.
An example configuration of a modulator-demodulator unit conventionally used for analog modulation-demodulation will be explained.
FIG. 5
shows the configuration of an analog quadrature modulator provided downstream of a digital unit D
21
. Although the digital unit D
21
is included in the drawing for convenience of explanation, it should be noted that the digital unit D
21
would not ordinarily be a component of an analog quadrature modulator.
In the analog quadrature modulator shown in the figure, an in-phase component signal output by the digital unit D
21
is input to an in-phase component side mixer (MIX) MI
21
and a quadrature component signal output by the digital unit D
21
is input to a quadrature component side mixer (MIX) MQ
21
.
Further, in this analog quadrature modulator, a local signal generator (OSC) OSC
11
generates a signal having the frequency of, for instance, a carrier wave signal ordinarily used in communication (carrier wave frequency) and the signal having this carrier wave frequency is output as an in-phase component carrier wave signal to the in-phase component side mixer MI
21
without modification and the signal having the carrier wave frequency is also output to a 90-degree (°) phase shifter P
11
. The 90-degree phase shifter P
11
shifts the signal received from the local signal generator OSC
11
90 degrees and outputs the phase-shifted signal to the quadrature component side mixer MQ
21
as a quadrature component carrier wave signal.
The in-phase component side mixer MI
21
mixes the in-phase component carrier wave signal received from the local signal generator OSC
11
and the in-phase component signal received from the digital unit D
21
to modulate the in-phase component carrier wave signal with the in-phase component signal and outputs the resulting in-phase modulated component.
The quadrature component side mixer MQ
21
mixes the quadrature component carrier wave signal received from the 90-degree phase shifter P
11
and the quadrature component signal received from the digital unit D
21
to modulate the quadrature component carrier wave signal with the quadrature component signal and outputs the resulting quadrature modulated component.
In this analog quadrature modulator, the in-phase modulated component output by the in-phase component side mixer MI
21
and the quadrature modulated component output by the quadrature component side mixer MQ
21
are synthesized and synthesized signal is output as a composite signal. The composite signal is a carrier wave frequency signal including, for example, amplitude information and phase information. By controlling the in-phase component signal and the quadrature component signal output by the digital unit D
21
to modify the amplitude information and the phase information, data to be transmitted by frequency modulation, phase modulation and/or amplitude modulation can be transmitted on the carrier wave. In addition, the composite signal output by the analog quadrature modulator can be wirelessly transmitted to another party's wireless device as a wireless signal via an antenna or the like (not shown).
The configuration of an analog quadrature demodulator will now be explained with reference to FIG.
6
.
The analog quadrature demodulator illustrated in the drawing is input with a carrier wave frequency composite signal including amplitude information or phase information, specifically with a signal transmitted wirelessly from, for example, a wireless device with which communication is to be conducted and received wirelessly via an antenna (not shown). The received composite signal is divided and input to an in-phase component side mixer MI
22
and a quadrature component side mixer MQ
22
.
Similarly to the case of the analog quadrature modulator shown in
FIG. 5
, in this analog quadrature demodulator, a local signal generator (OSC) OSC
12
generates a signal of, for instance, a carrier wave frequency and the signal having this carrier wave frequency is output as an in-phase component carrier wave signal to the in-phase component side mixer MI
22
without modification and the signal having the carrier wave frequency is also output to a 90-degree phase shifter P
12
, which shifts it 90 degrees and outputs the phase-shifted signal to the quadrature component side mixer MQ
22
as a quadrature component carrier wave signal.
The in-phase component side mixer MI
22
mixes the in-phase component carrier wave signal received from the local signal generator OSC
12
and the composite signal to demodulate the in-phase modulated component contained in the composite signal with the in-phase component carrier wave signal and outputs the in-phase component signal produced by the demodulation.
The quadrature component side mixer MQ
22
mixes the quadrature component carrier wave signal received from the 90-degree phase shifter P
12
and the composite signal to demodulate the quadrature modulated component contained in composite signal with the quadrature component carrier wave signal and outputs the quadrature component signal produced by the demodulation.
The in-phase component signal and the quadrature component signal output by the analog quadrature demodulator are, for example, output to a downstream digital unit (not shown) to acquire receive data based on to the in-phase component signal and the quadrature component signal.
There will now be explained a configuration for changing the carrier wave frequency used in modulation and demodulation in the analog quadrature modulator shown in FIG.
5
and the analog quadrature demodulator shown in FIG.
6
.
Carrier wave frequency change is required, for example, in a wireless device or the like that sends and receives wireless signals by switching among and using carriers of different frequencies spread over a broad band.
In the analog quadrature modulator shown in FIG.
5
and the analog quadrature demodulator shown in
FIG. 6
, a configuration enabling carrier wave frequency change can conceivably be implemented, for instance, by installing voltage-controlled oscillators (VCOs) in place of the local signal generators OSC
11
and OSC
12
and controlling the voltage applied to the voltage-controlled oscillators to change the frequency of the signals (local signals) output from the voltage-controlled oscillator to the in-phase component side mixers MI
21
, MI
22
and the 90-degree phase shifters P
11
, P
12
. With this configuration, however, the fact that the devices constituting the 90-degree phase shifters P
11
, P
12
have frequency characteristics would make it possible to achieve accurate 90-degree phase shift only in a relatively narrow band, i.e., frequencies would be present in the required broad band at which a phase shift greater than 90 degrees or less than 90 degrees arose, making modulation-demodulation impossible over a broad band.
While it is conceivable to overcome this problem by providing multiple 90-degree phase shifters associated with different frequencies and using a switch or the like to switch to the one to be used at each frequency, this configuration would complicate the control, raise cost and increase circuit size, because it would require provision of phase shifters for the individual fr

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