Device operable with an excellent spectrum suppression

Abstract: In a device for use in processing a baseband input signal and a carrier signal into an envelope output signal, a processing unit (3) is supplied with the baseband input signal and the carrier signal and produces, as a produced signal, a modulated signal and a non-modulated signal one at a time in response to a burst control signal. A waveform generating unit (2) is supplied with the burst control signal and generates a control signal. An amplifying unit (4) is supplied with the produced signal and the control signal and amplifies the produced signal to make the envelope output signal represent an envelope of the produced signal and to produce the envelope output signal with an excellent spectrum suppression. Alternatively, the processing unit may be supplied with the control signal instead of the burst control signal.

Description: This invention relates to a device for use in processing a baseband input signal and a carrier signal into an envelope output signal and, more particularly, to an improvement in spectrum suppression under a burst switching condition used in a TDMA type radio communication apparatus in which a modulated signal has an envelope. In general, a device of the type described is supplied with a baseband input signal and a carrier signal to produce an envelope output signal. The device comprises a modulating unit responsive to the baseband input signal and the carrier signal for producing a modulated signal variable within a power range. A waveform generating unit is supplied with a burst control signal and generates a control signal for controlling the power range into a controlled region. An amplifying unit is connected to the modulating unit and the waveform generating unit and amplifies the modulated signal having the controlled region to make the envelope output signal represent an envelope of the modulated signal and to produce the envelope output signal. A conventional device is disclosed in EP-A-0 110 368 (US-A-4,592,073) and comprises a waveform generating unit for receiving the burst control signal having a rectangular waveform and for generating the control signal for controlling the power range into the controlled region. The control signal has a controlled shape comprising sloping leading and trailing edges and a plateau between the sloping leading and trailing edges. The modulating unit always modulates the baseband input signal and the carrier signal into the modulated signal with no consideration given to the burst control signal. The amplifying unit amplifies the modulated signal having the controlled region to make the envelope output signal represent the envelope of the modulated signal. As a result, the envelope output signal has a shape which is similar to the controlled shape. Therefore, the modulated signal is amplified throughout the sloping leading and trailing edges and the plateau. EP-A-0 156 398 discloses an FSK or FM burst signal generating apparatus which controls a burst signal having leading and trailing edges subjected to ramp control. The carrier signal, however, is modulated at the leading and trailing edges. However, it has now been found by the present inventor that it is impossible to suppress a spectrum divergence of the envelope output signal within a predetermined guard mask which is a permitted limit of the spectrum divergence in the envelope output signal. When the spectrum divergence overrun the guard mask, a jamming occurs as a result of the envelope output signal. Therefore, a transmission interference occurs. This is because the modulated signal inevitably has an inherent band. Even if the amplifying unit tries to amplify the modulated signal in due consideration of the inherent band in order to avoid such a trouble, a very delicate adjustment is required in the amplifying unit. It is therefore an object of the present invention to provide a device for improving a spectrum suppression under a burst switching condition and which can suppress a spectrum divergence within a predetermined guard mask and with no need for delicate adjustment. This object is solved with the features of the claims. Fig. 1 is a block diagram of a device according to a first embodiment of the instant invention; Fig. 2(a) shows one example of a burst control signal which is used in the device illustrated in Fig. 1 and has a rectangular waveform; Fig. 2(b) shows one example of a control signal which is used in the device illustrated in Fig. 1 and has a controlled shape comprising sloping leading and trailing edges and the plateau between the leading and trailing edges; Fig. 2(c) shows an envelope of a produced signal which is used in the device illustrated in Fig. 1; Fig. 2(d) is a time chart of modulation by a switching unit which is used in the device illustrated in Fig. 1; Fig. 3(a) is a graph illustrative of a line spectrum of a non-modulated signal; Fig. 3(b) is a graph showing the spectrum divergence of the modulated signal; and Fig. 4 is a block diagram of a device according to a second embodiment of the instant invention. A device in accordance with the present invention is supplied with a baseband input signal and a carrier signal and produces an envelope output signal. Referring to Fig. 1, the device comprises a producing unit 3 for producing a produced signal which has a variable power range. A waveform generating unit 2 is for generating a control signal for controlling the power range into a controlled region. An amplifying unit 4 is for anplifying the produced signal having a controlled region. The producing unit 3 includes a modulating circuit 5 and a switching circuit 6. The modulating circuit 5 is for modulating the baseband signal and the carrier signal into the produced signal. The switching circuit 6 is supplied with a burst control signal from a burst control signal input terminal 1 and switches on and off the modulating circuit 5 to produce a modulated signal and a non-modulated signal one at a time as the produced signal. The waveform generating unit 2 is supplied with the burst control signal from the burst control signal input terminal 1 and generates the control signal for controlling the power range into the controlled region. Referring to Figs. 2(a) and (b), the burst control signal has a shape comprising a rectangular waveform which has an inherent characteristic and is shown in Fig. 2(a). The waveform generating unit 2 generates the control signal having a controlled shape from the burst control signal, as shown in Fig. 2(b). The controlled shape comprises sloping leading and trailing edges and a plateau between the leading and trailing edges. Each of the sloping leading and trailing edges has a sloping time interval. The plateau has a plateau time interval. The sloping time and the plateau time interval can be predetermined from the inherent characteristic of the burst control signal. Returning to Figs. 1 and 2(c) and (d), the switching circuit 6 is for switching off the modulating unit 5 during each of the sloping time intervals to produce the non-modulated signal and is to switch on during the plateau time interval to produce the modulated signal, as shown in Fig. 2(d). Thus, the switching circuit 6 acts to produce a switching signal as shown in Fig 2(d). The amplifying unit 4 is connected to the producing unit 3 and the waveform generating unit 2 and amplifies the produced signal having the controlled region to make the envelope output signal represent an envelope of the produced signal and to produce the envelope output signal, as shown in Fig. 2(c). In this event, when the switching circuit 6 switches off the modulating unit 3, the non-modulated signal is produced from the modulating circuit 5 without modulating the carrier signal by the baseband signal. Figs. 1 and 3(a) will be referred to. The amplifying unit 4 amplifies the non-modulated signal to produce the envelope output signal having line spectrum, as shown in Fig. 3(a). On the other hand, when the switching circuit 6 switches on the modulating unit 3 to produce the modulated signal, the amplifying unit 4 amplifies the modulated signal to produce the envelope output signal having spectrum divergence, as shown in Fig. 3(b). In Fig. 2(c), the envelope output signal could have the line spectrum at the sloping leading and trailing edges and the spectrum divergence at the plateau. Therefore, it is possible to suppress the spectrum divergence to be within a predetermined guard mask which is a permitted limit of the spectrum divergence. This is because the line spectrum of the envelope output signal corresponds to the leading and trailing edges. Referring to Fig. 4, the description will be made as regards a device where the first switching circuit 6 is supplied with the control signal instead of the burst control signal illustrated in Fig.1. In this connection, such a signal given to the switching circuit 6 may be collectively called a production control signal. The waveform generating unit 2 is connected to the switching circuit 6 and generates the control signal. The control signal comprises a sloping signal and a plateau signal collectively representative of the controlled shape. In the manner depicted in Fig. 2(b), the sloping signal represents the sloping leading and trailing edges. The plateau signal represents the plateau between the sloping leading and trailing edges. Returning to Fig. 4, the switching circuit 6 is to switch off the modulating circuit 5 in response to the sloping signal to produce the non-modulated signal and is to switch on in response to the plateau signal to produce the modulated signal in the same manner of the above description.

Claims: A device for processing a baseband input signal and a carrier signal into an envelope output signal, said device comprising producing means (3) responsive to said baseband input signal and said carrier signal for producing a produced signal variable within a power range, waveform generating means (2) responsive to a burst control signal for generating a control signal for controlling said power range into a controlled region, and amplifying means (4) connected to said producing means (3) and said waveform generating means (2) for amplifying the produced signal having said controlled region to make said envelope output signal represent an envelope of said produced signal and to produce said envelope output signal, characterized in that said producing means (3) comprises: modulating means (5) for modulating said baseband input signal and said carrier signal into the produced signal; and switching means (6) supplied with said burst control signal or said control signal for switching on and off said modulating means to produce a modulated signal and a non-modulated signal one at a time as the produced signal having said controlled region. A device as claimed in Claim 1, said control signal having a controlled shape comprising sloping leading and trailing edges and a plateau between said leading and trailing edges, each of said sloping leading and trailing edges having a sloping time interval, said plateau having a plateau time interval, wherein said switching means (6) is for switching off said modulating means (5) during each of said sloping time interval to produce said non-modulated signal and is for switching on during said plateau time interval to produce said modulated signal. A device as claimed in Claim 1, said control signal comprising a sloping signal and a plateau signal collectively representative of a controlled shape, said sloping signal representing sloping leading and trailing edges, said plateau signal representing a plateau between said sloping leading and trailing edges, wherein said switching means (6) is for switching off said modulating means in response to said sloping signal to produce said non-modulated signal and is for switching on in response to said plateau signal to produce said modulated signal.

Inventors: WATANABE NOZOMU C O NEC CORPOR, WATANABE, NOZOMU, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1991
Main classification: H04B7
IPC codes: H04B7, H04L27, H04B1, H04J3