Power amplifying circuit and method

Abstract: An envelope level of an output of a variable gain power amplifier 1 is detected by a detector 5. An envelope level of an output of the variable gain power amplifier 1 detected by the detector 5 and a waveform of a reference signal which is generated from a reference signal generator 7 are compared. A gain of the variable gain power amplifier 1 is controlled in accordance with a comparison output. Upon leading of a transmission output, the reference signal is raised from a ground level to a rest value higher than the rest value of the detector 5. After the reference signal entered a response raised along a cosine square wave. Upon trailing of the transmission output, the reference signal is smoothly reduced to a value near the rest value of the detector 5 along a cosine square wave and is maintained at a value near the rest value of the detector 5. After the negative feedback loop did not respond, the reference signal is reduced to the rest value of the detector 5 or less.

Description: The invention relates to power amplifying circuit and method suitable for use in a power amplification of a digital cellular phone terminal of a time-division multiplex system. In a manner similar to a GSM (Group Special Mobile) system, since a transmission is performed in a burst manner in a digital cellular phone using the time-division multiplex system, if leading and trailing (ramp-up and ramp-down) of a transmission signal are not smoothly performed upon transmission, the transmission signal spectrum is spread, so that a neighboring channel is affected. That is, as shown in Fig. 1A, when the leading and trailing edges of the transmission signal are steep, an envelope of the transmission signal becomes a square wave. Therefore, the spectrum is spread and an influence is exerted on the neighboring channel. As shown in Fig. 1B, a control is performed so that the leading and trailing edges of the transmission signal become gentle. In this manner, the control to make the leading and trailing edges of the transmission signal gentle is realized by a negative feedback loop such that an output level of a variable gain power amplifier is detected, the output level of the variable gain power amplifier is compared with for example, a cosine square waveform, and a gain of the variable gain power amplifier is controlled in accordance with a comparison output. Fig. 2 shows an example of a conventional power amplifying circuit in which the leading and trailing edges of the transmission signal is controlled so as to be gentle in this manner. In Fig. 2, reference numeral 101 denotes a variable gain power amplifier. The variable gain power amplifier 101 power amplifies a transmission output in a digital cellular phone terminal of, for example, the GSM system. A gain of the variable gain power amplifier 101 can be controlled by a control signal from an operational amplifier 106. The transmission signal is supplied from an input terminal 102 to the variable gain power amplifier 101. Since the time-division multiplex system is used in the digital cellular phone of the GSM system, the transmission signal is sent in a burst manner. The transmission signal is power amplified by the variable gain power amplifier 101 and is outputted from an output terminal 103. The output of the variable gain power amplifier 101 is transmitted through a directional coupler 104 and is detected by a detector 105. The detector 105 envelope detects the output of the variable gain power amplifier 101. An output of the detector 105 is supplied to one input terminal of the operational amplifier 106. A reference signal 'from a reference signal generator 107 is supplied to another input terminal of the operational amplifier 106. A resistor 108 and a capacitor 109 are provided for the Operational amplifier 106 to act as an integrator. The reference signal generator 107 generates a reference signal of a cosine square waveform as shown in Fig. 3 so that an envelope level of the transmission output from the variable gain power amplifier 101 is smoothly changed along, for example, a cosine square waveform. An envelope level S12 of the output of the variable gain power amplifier 101 from the detector 105 and a reference signal S11 from the reference signal generator 107 are compared by the operational amplifier 106. A control signal S13 is formed by the comparison output. The gain of the variable gain power amplifier 101 is controlled by the control signal S13. By the negative feedback loop as mentioned above, the leading and trailing edges of the output of the variable gain power amplifier 101 are controlled so as to form, for example, a cosine square curve. Consequently, the leading and trailing edges at the time of the transmission become gentle and it is possible to prevent an obstruction of the neighboring channel due to the spread spectrum upon burst transmission. For instance, in the GSM system, a leakage power of a non-transmission time slot has to be suppressed to a value lower than an electric power of a transmission time slot by about 70 dB. On the other hand, a dynamic range of the detector 105 is equal to about 30 dB and cannot cover a power variable range of the variable gain power amplifier 101. Consequently, even when a signal with the cosine square waveform as shown in Fig. 3 is used as a reference signal, the transmission output is not changed like a reference signal. Fig. 4 shows waveforms in the sections when they are controlled by using the reference signal as shown in Fig. 3 in the conventional power amplifier shown in Fig. 2. As shown in Fig. 4A, when the transmission is finished, the reference signal S11 is reduced at a time point t 14 along, for example, a cosine square curve. When the reference signal S11 is reduced along, for example, the cosine square curve, since the negative feedback loop operates, the output level of the variable gain power amplifier 101 decreases in accordance with a change in reference signal S11. The level of the reference signal S11 is set to the rest voltage V j of the detector 105 at a time point t 15 . At this time, although the output level S12 of the detector 105 is set to the rest voltage V d , the dynamic range of the detector 105 doesn't cover the range of the leakage power of the non-transmission time slot and the electric power of the transmission time slot, so that the leakage power at the time of the non-transmission is not always sufficiently reduced. That is, although it is required to reduce the leakage power of the non-transmission time slot to a value which is lower than the electric power of the transmission time slot by about 70 dB, the dynamic range of the detector 105 is equal to about 30 dB. Therefore, since the control to reduce the leakage power of the non-transmission time slot to the value which is lower than the electric power of the transmission time slot by about 70 dB exceeds a range of the system control, whether the leakage power at the time of the non-transmission has sufficiently been reduced cannot be assured. Hitherto, when the power level is low, a variation occurs in the time until the maximum output is derived. Fig. 5 shows a case where the transmission power level is low. As shown in Fig. 5, when the transmission power level is low, a period of time (time points t 21 to t 22 ) until the output level of the variable gain power amplifier 101 enters the dynamic range of the detector 105 becomes long at the start of the transmission. Consequently, a time point t 23A when the output power reaches the maximum value is delayed as compared with a time point t 23B when the reference signal reaches the maximum value. As mentioned above, hitherto, a variation occurs in the time until the output power becomes maximum. Namely, a delay time Δt when the output power becomes maximum is varied due to the output power. For example, a power amplifier circuit is disclosed in JP-A-3, 289805 and EP-A-0,434,294 on which the two part form of claim is based. In these documents there has been proposed an apparatus constructed in a manner such that a rectangular wave pulse is superimposed to the control signal S13 to be sent to the variable gain amplifier at the time of the transmission, and the lack of the dynamic range of the detector is compensated by the rectangular wave pulse. With this construction, however, since the rectangular wave pulse is newly needed, a circuit scale increases. As shown in JP-A-7,015,267 and JP-A-4,355,507, an apparatus having an auxiliary negative feeback loop starts to respond has been provided. However, when such an auxiliary loop is provided, a circuit scale increases. According to a first aspect of the present invention, there is provided a power amplifying circuit comprising: a variable gain power amplifier for amplifying a transmission output; a detector for detecting an envelope level of an output of said variable gain power amplifier; a reference signal generator for generating a reference signal for converting an envelope of the output of said variable gain power amplifier to a cosine square waveform; and a negative feedback loop for comparing the envelope level of the output of said variable gain power amplifier detected by said detector with a waveform of the reference signal which is generated from said reference signal generator, and arranged to control a gain of said variable gain power amplifier in accordance with a comparison output, characterised in that said reference signal generator is arranged to generate the reference signal with a shape which: reduces with a cosine square waveform to a value near the rest value of said detector upon trailing of a transmission output supplied through said variable gain amplifier; after that, remains at said value near the rest value of the said detector; and, after that, reduces to the rest value of said detector or less. According to a second aspect of the present invention, there is provided a power amplifying method comprising: detecting an envelope level of an output of a variable gain power amplifier by a detector; generating a reference signal for converting an envelope of the output of said variable gain power amplifier to a cosine square waveform by a reference signal generator; and comparing the envelope level of the output of said variable gain power amplifier detected by said detector with a waveform of the reference signal which is generated from said reference signal generator, and controlling a gain of said variable gain power amplifier in accordance with a comparison output, and characterised by further comprising: reducing the level of the reference signal with a cosine square waveform from said reference signal generator to a value near the rest value of said detector upon trailing of a transmission output supplied through said variable gain amplifier; after that, maintaining said level at said value near the rest value of said detector; and, after that, reducing said level to the rest value of said detector or less. The hereinafter described and illustrated power amplifying circuit which'is an embodiment of the present invention smooths the trailing edges of a transmission output and can prevent spread of the spectrum. It can control a leakage power at a non-transmission time slot to a small enough value. Also it accomplishes this advantage without causing an increase in circuit scale. When the transmission output trails, the reference signal is smoothly reduced to a value near the rest of the detector along a cosine square wave, and, after that, is maintained at said value near the rest value of the detector. After the negative feedback loop ceases to respond, the reference signal is reduced to the rest value of the detector or less. By using the reference signal, a discontinuity of the transmission level upon leading of the transmission output is extinguished and the generation of a spurious can be prevented. Further, a leakage power in a non-transmission slot can be sufficiently reduced. To assist understanding the following detailed non-limitative description of embodiments of the present invention is given with reference to the accompanying drawings in which: Figs. 1A and 1B are waveform diagrams which are used for explanation of a conventional power amplifying circuit; Fig. 2 is a block diagram of an example of the conventional power amplifying circuit; Fig. 3 is a waveform diagram of a reference signal of a cosine square waveform; Figs. 4A and 4B are control waveform diagrams which are used for explanation of an example of the conventional power amplifying circuit; Figs. 5A and 5B are control waveform diagrams in case of a low power level which are used for explanation of the example of the conventional power amplifying circuit; Fig. 6 is a block diagram of another example of a conventional power amplifying circuit; Fig. 7 is a block diagram of an example of a power amplifying circuit to which the invention is applied; Fig. 8 is a waveform diagram of a reference signal which is used for explanation of the example of the power amplifying circuit to which the invention is applied; Figs. 9A and 9B are waveform diagrams which are used for explanation of the example of the power amplifying circuit to which the invention is applied; Fig. 10 is a block diagram of an example of a reference signal generator in the power amplifying circuit to which the invention is applied; Figs. 11A, 11B, and 11C are leading waveform diagrams which are used for explanation of the reference signal generator in the power amplifying circuit to which the invention is applied; Figs. 12A, 12B, and 12C are leading waveform diagrams which are used for explanation of the reference signal generator in the power amplifying circuit to which the invention is applied; Fig. 13 is a connection diagram of a resistor synthesizing circuit which is used for explanation of the reference signal generator in the power amplifying circuit to which the invention is applied; and Figs. 14A, 14B, and 14C are leading and trailing waveform diagrams which are used for explanation of the reference signal generator in the power amplifying circuit to which the invention is applied. An embodiment of the invention will now be described hereinbelow with reference to the drawings. Fig. 7 shows an embodiment of the invention. In Fig. 7, reference numeral 1 denotes a variable gain power amplifier. The variable gain power amplifier 1 power amplifies a transmission output in, for example, a digital cellular phone terminal of a GSM system. A gain of the variable gain power amplifier 1 can be controlled by a control signal from an operational amplifier 6. A transmission signal is supplied from an input terminal 2 to the variable gain power amplifier 1. In the digital cellular phone of the GSM system, since a time-division multiplex system is used, the transmission signal is sent in a burst-like manner. The transmission signal is power amplified by the variable gain power amplifier 1 and is outputted from an output terminal 3. An output of the variable gain power amplifier 1 is detected by a detector 5 through a directional coupler 4. The detector 5 detects an envelope of the output of the variable gain power amplifier 1. An output of the detector 5 is supplied to one input terminal of the operational amplifier 6. A reference signal from a reference signal generator 7 is supplied to another input terminal of the operational amplifier 6. A resistor 8 and a capacitor 9 are provided for the operational amplifier 6, thereby adding integrating characteristics. The reference signal generator 7 generates the reference signal so that an envelope level of the transmission output from the variable gain power amplifier 1 smoothly changes along a cosine square waveform. The reference signal from the reference signal generator 7 rises from a grounding level to a rest voltage or more of the detector 5 at the time of the leading of the transmission output so that the envelope level of the output signal can be controlled within a response range of a negative feedback loop. The reference signal is maintained to a value higher than the rest voltage of the detector 5. After the reference signal rose to a value that is equal to or larger than the detection rest value and entered a response range of the negative feedback loop, it is smoothly allowed to rise along a cosine square wave. At the time of trailing of the transmission output, the reference signal is allowed to smoothly drop by a cosine square wave to a level near the rest voltage of the detector and is maintained at a level near the rest voltage of the detector 5. After a response of the negative feedback loop was extinguished, the reference signal is trailed to the grounding level. Namely, Fig. 8 shows an example of the reference signal from the reference signal generator 7. As shown in Fig. 8, upon trailing, the reference signal is gradually dropped along a cosine square curve and is reduced to a level V2 that is almost equal to the rest voltage of the detector 5 and is maintained at the level V2. When the response of the negative feedback loop is extinguished, the reference signal is dropped to the grounding level. An envelope output level S2 of the output of the variable gain power amplifier 1 from the detector 5 and a reference signal S1 from the reference signal generator 7 are compared by the operational amplifier 6. A control signal S3 is formed by a comparison output. The gain of the variable gain power amplifier 1 is controlled by the control signal S3. By such a negative feedback loop, the leading edge and trailing edge of the envelope level of the output of the variable gain power amplifier 1 are controlled to a cosine square curve. Thus, the leading edge and trailing edge upon transmission become smooth and an interference of the adjacent channel due to a spread spectrum at the time of the burst transmission can be prevented. According to the embodiment of the invention, the reference signal as shown in Fig. 8 is used. When the transmission is finished, as shown in Fig. 9A, the reference signal S1 is reduced along a cosine square curve at a time point t4. When the reference signal S1 is dropped along the cosine square curve, the control signal S3 is formed by a comparison output between the envelope level S2 of the detector 5 and the reference signal S1 and the negative feedback loop operates. Therefore, the output level of the variable gain power amplifier 1 decreases in accordance with a change in reference signal. The level S1 of the reference signal is maintained to the rest voltage Vd for a period of time from t5 to t6. Thus, as shown in Fig. 9B, the level of the control signal S3 from the operational amplifier 6 drops to V A . As shown in Fig. 9A, the reference signal S1 is reduced to the grounding level at the time point t6. When the reference signal S1 decreases to the rest voltage Vd or less, the control system enters the open loop state. As shown in Fig. 9B, the level S3 of the control voltage from the operational amplifier 6 decreases in accordance with the time constant which is determined by the resistor 8 and capacitor 9. The output of the variable gain power amplifier 1 also decreases. According to the embodiment of the invention as mentioned above, when the transmission is finished, after the reference signal was maintained to a level near the rest voltage Vd, if the negative feedback loop doesn't respond, the reference signal is reduced to the grounding level. Therefore, the output power in the non-transmission slot can be sufficiently reduced. The reference signal generator 7 for generating the reference signal as mentioned above can be constructed by, for example, as shown in Fig. 10. In Fig. 10, data to generate the reference signal as shown in Fig. 8 has been stored in an ROM 11. When a transmission control signal is supplied to a terminal 13, an address is generated from an address generating circuit 12 and the data of the reference signal is read out from the ROM 11. The data of the reference signal is converted into an analog signal by a D/A converter 14 and is outputted. The reference signal which is generated from such a reference signal generator can be also formed by adding a cosine square waveform and a rectangular wave in an analogwise or digital manner. Namely, upon trailing, a waveform which trails along a cosine square waveform as shown in Fig. 12A and a waveform which tails as shown in Fig. 12B are prepared. By a synthesizing circuit comprising resistors R1 and R2 as shown in Fig. 13, a waveform which trails along a cosine square waveform as shown in Fig. 12A and a waveform which trails as shown in Fig. 12B are added. Thus, a trailing waveform of the reference signal as shown in Fig. 12C can be obtained. When the control of the leading edge and the control of the trailing edge are simultaneously executed, a waveform which rises along a cosine square waveform and trails along a cosine square wave as shown in Fig. 14A and a rectangular wave as shown in Fig. 14B are prepared. By adding the waveform as shown in Fig. 14A and the waveform as shown in Fig. 14B are added, a leading waveform of the reference signal as shown in Fig. 14C can be obtained. It is also possible to construct such that as shown by a broken line in Fig. 14B, after the rectangular wave was integrated, it is added and a waveform as shown by a broken line in Fig. 14C is derived. Although the preferred embodiments of the present invention has been described above, the invention is not limited to the foregoing embodiments but many modifications and variations are possible within the scope of the appended claims of the invention.

Claims: A power amplifying circuit comprising: a variable gain power amplifier (1) for amplifying a transmission output; a detector (5) for detecting an envelope level of an output of said variable gain power amplifier; a reference signal generator (7) for generating a reference signal for converting an envelope of the output of said variable gain power amplifier (1) to a cosine square waveform; and a negative feedback loop for comparing the envelope level of the output of said variable gain power amplifier (1) detected by said detector (5) with a waveform of the reference signal which is generated from said reference signal generator (7), and arranged to control a gain of said variable gain power amplifier (1) in accordance with a comparison output, characterised in that said reference signal generator (7) is arranged to generate the reference signal with a shape which: reduces with a cosine square waveform to a value near the rest value of said detector (5) upon trailing of a transmission output supplied through said variable gain amplifier; after that, remains at said value near the rest value of the said detector (5); and, after that, reduces to the rest value of said detector (5) or less. A power amplifying circuit according to claim 1, wherein the level of the reference signal from said reference signal generator (7) is maintained at said value near the rest value of said detector (5) for a period of time until the output of the variable gain amplifier (1) reaches the end of the dynamic range of the detector (5), and, after that, said level is reduced to the rest value of said detector (5) or less. A power amplifying method comprising: detecting an envelope level of an output of a variable gain power amplifier (1) by a detector (5); generating a reference signal for converting an envelope of the output of said variable gain power amplifier (1) to a cosine square waveform by a reference signal generator (7); and comparing the envelope level of the output of said variable gain power amplifier (1) detected by said detector (5) with a waveform of the reference signal which is generated from said reference signal generator (7), and controlling a gain of said variable gain power amplifier (1) in accordance with a comparison output, and characterised by further comprising: reducing the level of the reference signal with a cosine square waveform from said reference signal generator (7) to a value near the rest value of said detector (5) upon trailing of a transmission output supplied through said variable gain amplifier (1); after that, maintaining said level at said value near the rest value of said detector (5); and, after that, reducing said level to the rest value of said detector (5) or less.

Inventors: SATO HIDEAKI, SATO, HIDEAKI
Applicants: SONY CORP, SONY CORPORATION
Application year: 1997
Main classification: H03G3
IPC codes: H03G3, H04B1, H04J14, H03F3