Abstract:
A microwave frequency converting receiver of an RF unit should be generally used in wireless/mobile communications systems such as cellular, PCS, WLL and IMT2000 systems and also have low power consumption, low-noise characteristic, high gain and small size. In order to produce the above frequency converting receiver, a multi-band and multi-mode frequency converting receiver for use in a wireless mobile communications system comprises a wideband low-noise amplifier for amplifying a radio frequency input signal, a frequency mixer for generating an intermediate frequency signal having a relatively high linearity by mixing a local oscillator frequency signal and the amplified radio frequency signal outputted from the wideband low noise amplifier, an intermediate frequency amplifier for producing a final intermediate frequency signal by amplifying the intermediate frequency signal derived from the frequency mixer and an input matching circuit for receiving a microwave signal within a frequency band of the wireless mobile communications system, impedance-matching the received microwave signal to the radio frequency input signal of the wideband low-noise amplifier and determining an operating frequency band of the frequency converting receiver.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a frequency converting receiver; and, more particularly, to a monolithic microwave integrated circuit(MMIC) frequency converting receiver which employs field effect transistors(FETs) and is used in wireless/mobile communication systems. 
     DESCRIPTION OF THE PRIOR ART 
     Recently, to accommodate the tremendously increasing wireless communications demand, the need of a large capacity communication method is increasing. As a result, there has been proposed a digital scheme capable of accommodating a lot of users compared to a conventional analog scheme and there are being developed mobile communications systems providing services in various frequency bands. As examples, there are a cellular at about 900 MHz and a personal communications services(PCS) at about 1.9 GHz which is presently providing communications services, and international mobile telecommunications 2000 (IMT2000) at about 2.1 GHz and a wireless local loop(WLL) at about 2.4 GHz which will be served sooner or later. 
     Further, portable terminals used in the above various communications services have been developed depending on the communications systems. And the down converter IC chips used in the potable terminals of various communications services have own specific purpose and operating frequency. 
     At this time, there is increasing the demand of a multi-band, multi-mode portable terminal capable of serving all kinds of communications services by using one portable terminal and, thereafter, it is necessary to develop a wideband microwave frequency converting receiver so as to develop the multi-band, multi-mode portable terminal. 
     In general, the microwave frequency converting receiver comprises a low-noise amplifier(LNA) for detecting and amplifying weak radio frequency signals(referred to as “RF signals” hereinafter), a frequency mixer for modulating or mixing small RF signals and large local oscillator signals(referred to as “LO signals” hereinafter) to thereby produce signals having sum, difference(intermediate frequency signal referred to as “IF signal” hereinafter) or multiple frequencies of the RF signals and the LO signals and a balun and IF signal amplifier for producing complementary signals based on a single signal. 
     The conventional frequency converting receiver shown above is produced according to a hybrid scheme manufacturing a whole receiver by assembling its components. Therefore, although the frequency converting receiver is made as an MMIC, it is only applicable to one system whose operating frequency is within a narrow frequency band and corresponds to that of the receiver. This type of conventional frequency converting receiver for the hand held phone application is disclosed in an article published by A. Brunel et al., entitled “A DOWNCONVERTER FOR USE IN A DUAL-MODE AMPS/CDMA CHIP SET”,  Microwave journal,  pp20˜42, February 1996. A down converter IC, which operates in frequency range of 500˜1900 MHz, is disclosed in an article by L.Reynolds, “Downconverter IC processes Signals From 500 To 1900 MHz,  Microwaves &amp; RF,  pp134˜140, July, 1997”, where this chip set is employed in PCS application. Another type of the conventional frequency converting receiver is demonstrated in an article by Mark William et al., entitled “GaAs RF ICs TARGET 2.4 GHz FREQUENCY BAND”,  Microwaves &amp; RF,  pp111˜118, July, 1994, which may have potential of application in WLL system. Another type of down converters for satellite communication is disclosed in U.S. Pat. Nos. 5,528,769 and 5,649,312 issued on Jun. 18, 1996 and Jul. 15, 1997. Like above down converter ICs, most developed down converter had the specific operating frequency depending on the communication system. And there is no a down converter MMIC which can be applied to a multi band, multi mode portable terminal. Thereafter, it is difficult to apply the receiver to a receiving end of an RF unit of all of communications systems. 
     Consequently, there is required to develop a wideband microwave frequency converting receiver applicable to the RF unit which can be used in all of the wireless/mobile communications systems and the wideband microwave frequency converting receiver should have low-noise, high conversion gain and high linearity characteristics over a wide frequency band. 
     In addition, the portable terminal is continuously developed to have smaller size and lighter weight. Since a capacitor having a low capacity in order to reduce the weight of the portable terminal, it is necessary for the portable terminal to use components operating with low power consumption so as to extend its operating time. And, in order to manufacture the portable terminal having smaller size and lighter weight, it is also necessary to reduce the sizes of the components constituting the portable terminal. Further, as the number of subscribers of the mobile telephone system increases, a portable terminal having an advanced transmitting and receiving characteristic(specially, low-noise and high linearity characteristics) is required. Therefore, the performances of the components constituting the portable terminals should be also improved. In particular, microwave components which are core components of the portable terminal are being developed to the smallization through the use of an MMIC scheme, low-cost by a chip smallization scheme and low power by the improvement of a circuit structure. 
     Herein, the MMIC is referred to as a circuit employing active and passive devices integrated in a single semiconductor wafer. Compared with a conventional circuit employing individual devices therein, it is possible to reduce the size and weight of a circuit integrated in the MMIC since the pitches of devices constituting the circuit can be reduced. Further, since parasitic components due to the packaging of individual devices are originally eliminated, the availability of a frequency bandwidth can be substantially improved. Therefore, the trend is that the RF components of the wireless/mobile communications system are integrated into the MMIC in order to mass-produce a low cost, small size and light weight wireless/mobile communications equipment(e.g., mobile communications terminal) with low cost and good reproduction characteristics. The most important subject is to reduce the size of the MMIC since the manufacturing cost of the MMIC increases proportional to its size. 
     Therefore, it is required to develop a wideband frequency converting receiver which can be used in all of the wireless/mobile communication systems such as the cellular, PCS, WLL and IMT2000 and, further, integrated into the MMIC which results in mass-producing a low cost microwave frequency converting receiver applicable to the RF unit with low cost and good reproduction characteristics, which has low power consumption, low-noise, high gain and small size characteristics. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of the present invention to provide a microwave frequency converting receiver applicable to an RF unit, which can be used in all of wireless/mobile communications systems such as cellular, PCS, WLL and IMT2000 systems and, further, has low power consumption, low-noise, high gain and small size characteristics. 
     In accordance with the present invention, there is provided a multi-band and multi-mode frequency converting receiver for use in a wireless mobile communications system, comprising: a wideband low-noise amplifier for amplifying a radio frequency input signal; a frequency mixer for producing an intermediate frequency signal having a relatively high linearity by mixing a local oscillator frequency signal and the amplified radio frequency signal outputted from the wideband low-noise amplifier; an intermediate frequency amplifier for producing a final intermediate frequency signal by amplifying the intermediate frequency signal derived from the frequency mixer; and an input matching circuit for receiving a microwave signal within a frequency band of the wireless mobile communications system, impedance-matching the received microwave signal to the radio frequency input signal of the wideband low-noise amplifier and determining an operating frequency band of the frequency converting receiver. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments of the invention with reference to the accompanying drawings, in which: 
     FIG. 1 represents a block diagram of a frequency converting receiver in accordance with the present invention; 
     FIG. 2 shows an internal circuit diagram of the frequency converting receiver in accordance with an embodiment of the present invention; 
     FIG. 3 provides a characteristic diagram of a conversion gain and output standing-wave ratio of the wideband low-noise amplifier in FIG. 2; and 
     FIG. 4 illustrates a noise characteristic diagram of the wideband low-noise amplifier in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is illustrated a block diagram of a frequency converting receiver in accordance with the present invention. In this diagram, reference numerals  100 ,  101 ,  102 ,  103 ,  104 ,  105  denote a frequency converting receiver, an input matching circuit, a wideband low-noise amplifier, an image signal eliminating filter, a frequency mixer and an intermediate frequency amplifier, respectively. 
     In FIG. 1, the frequency converting receiver  100  comprises the input matching circuit  101  receiving a radio frequency(RF) signal, the wideband low-noise amplifier  102  amplifying the RF signal coupled from the input matching circuit  101 , an MMIC chip  110  including the frequency mixer  104  having a high linearity and the intermediate frequency amplifier  105 , and the image signal eliminating filter  103  which is positioned outside of the MMIC chip  110 . The image signal eliminating filter  103  eliminates an image signal from the output signal of the wideband low-noise amplifier  102  and provides it to the frequency mixer  104 . 
     More specifically, the RF signal is inputted to the wideband low-noise amplifier  102  via the input matching circuit  101  and then amplified. The amplified signal from which the image signal eliminating filter  105  eliminates the image signal is inputted into the frequency mixer  104  together with an LO signal and mixed to thereby produce an IF signal whose frequency is the difference between the RF and LO frequencies. The IF signal is re-amplified at the intermediate frequency amplifier  105  and outputted as a final IF signal. 
     Referring to FIG. 2, there is shown an internal circuit diagram of the frequency converting receiver in accordance with an embodiment of the present invention and, herein, a gate bias circuit is omitted for the simplicity of configuration. In this drawing, the frequency mixer is illustrated to incorporate therein a balun in order to clarify the connection between the frequency mixer and the balun. 
     Hereinafter, the internal circuit configuration of the components constituting the frequency converting receiver will be explained in detail. 
     First of all, an input matching circuit  201  positioned outside of an MMIC chip  210  is made of a chip inductor Lc and a chip capacitor Cc so as to perform the impedance matching at an input terminal of a wideband low-noise amplifier  202  in each frequency band, e.g., a cellular band, a PCS band and so on. As a result, an operating frequency band of the frequency converting receiver is determined depending on the input matching circuit  201 . 
     The wideband low-noise amplifier  202  is constituted to have a low-noise characteristic in the frequency band determined by the input matching circuit  201  and have a low output standing-wave ratio and a high linearity in a wide frequency band. Specifically, the wideband low-noise amplifier  202  comprises an inductor L 1  whose one side is connected to a ground voltage terminal, a source-coupled input transistor Q 1  whose gate receives a small-sized RF input signal from the input matching circuit  201  and source is connected to the other side of the inductor L 1 , a capacitor C 1  whose one side is connected to the drain of the input transistor Q 1 , a transistor Q 2  whose gate is connected to the other side of the capacitor C 1  and source is coupled to the ground voltage terminal and which outputs an RF signal whose phase is opposite to that of the RF signal amplified by the input transistor Q 1 , a capacitor C 3  whose one side is connected to an output terminal, actively matched output transistors Q 5  and Q 6  which are of a push-pull structure and commonly connected to the other side of the capacitor C 3 , a capacitor C 2  whose one side is coupled to the ground voltage terminal, gate-coupled amplification transistors Q 3  and Q 4  whose sources are connected to the drain of the transistor Q 2  and the drain of the input transistor Q 1 , respectively, and gates are commonly coupled to the other side of the capacitor C 2  to thereby provide complementary signals to the output transistors Q 5  and Q 6 , and capacitors C 4  and C 5  connected between the drains of the amplification transistors Q 3  and Q 4  and the gates of the output transistors Q 5  and Q 6 , respectively. 
     Characteristically, the wideband low-noise amplifier  202  includes the gate-coupled amplification transistors Q 3  and Q 4  so as to provide complementary signals to the push-pull structural output transistors Q 5  and Q 6  employed between the input terminal and the output terminal. As a result, the amplifier  202  can have low-noise and linearity characteristics in a wide frequency band. In general, a source-coupled amplifier is known to have a low-noise characteristic. A gate-coupled amplifier is used as a wideband amplifier. The push-pull structural amplifier is usually used at an output matching terminal of an amplifier requiring high linearity since it can generate a higher output power than that of a drain-coupled amplifier. 
     As shown above, the RF signal fed to the gate of the input transistor Q 1  is amplified and coupled to the gate of the transistor Q 2  which outputs through its drain a signal whose phase is opposite to the RF signal. Herein, the signal outputted from the drain of the transistor Q 2  and the RF signal outputted from the drain of the input transistor Q 1  which are complementary are provided to the sources of the amplification transistors Q 3  and Q 4 , respectively, and amplified to thereby being inputted to the gates of the transistors Q 5  and Q 6 , respectively. 
     The output of the wideband low-noise amplifier  202  is provided through a common node of the source of the output transistor Q 5  and the drain of the output transistor Q 6 . The output RF signal of the wideband low-noise amplifier  202  is coupled to an image eliminating band filter  203  which eliminates an image signal from the output RF signal to thereby provide it to an RF input terminal of a frequency mixer  204 . 
     Meanwhile, the frequency mixer  204  comprises an internal input matching unit receiving the RF signal from the image eliminating band filter  203 , a cascaded mixer core unit and a balun unit having low-noise and high amplification characteristics. Herein, the internal input matching unit includes a transistor Q 8  receiving the RF signal from the image eliminating band filter  203  through its source and a transistor Q 7  receiving the LO signal through its source, thereby constituting a gate-coupled active matching unit. The mixer core unit includes a transistor Q 9  receiving the drain output of the transistor Q 7  through its gate and a transistor Q 10  receiving the drain output of the transistor Q 8  through its gate, wherein the transistors Q 9  and Q 10  are connected in series between a source voltage terminal and the ground voltage terminal, an inductor L 2  which is connected between the source voltage terminal and the source of the transistor Q 9  and used as an output resistive component to provide a high output power without distortion, a capacitor CF and a resistor RF which are connected in series between the source of the transistor Q 9  and the gate of the transistor Q 10  to thereby form a feedback structure and a capacitor C 6  which is connected between the drain of the transistor Q 9  and the ground voltage terminal to thereby operate as a low pass filter. The balun unit comprises a transistor Q 11  whose gate receives the output signal of the mixer core unit and source is connected to the ground voltage terminal, a transistor Q 12  whose gate is joint to the drain of the transistor Q 11  and source is connected to the ground voltage terminal and which outputs a signal having an opposite phase to the signal outputted from the drain of the transistor Q 11 , gate-coupled amplification transistors Q 13  and Q 14  whose gates are commonly connected to the ground voltage terminal, wherein the transistor Q 13  is connected between the drain of the transistor Q 12  and a first output terminal of the frequency mixer  204  and the transistor Q 14  is joint between the drain of the transistor Q 11  and a second output terminal of the frequency mixer  204 , and a capacitor C 7  which is connected between the drain of the transistor Q 13  and the drain of the transistor Q 14  and operates as a low pass filter. 
     The frequency mixer constituted as illustrated above has low-noise, low power consumption and high linearity characteristics since the mixer has the cascaded structure, low-noise and high conversion gain characteristics. 
     Specifically, the mixer core unit having the cascaded structure improves the linearity by using the inductor L 2  as an output resistor so as to provide the high output power without distortion. Further, the mixer core unit enhances its stability and linearity by using the feedback from the source of the transistor Q 9  to the gate of the transistor Q 10  through the use of the resistor RF and the capacitor CF. 
     With reference to the drawings, the detailed operation of the frequency mixer  204  is described hereinafter. 
     The LO signal and the RF signal derived from the transistors Q 7  and Q 8 , respectively, through the matching operation of the internal input matching unit are inputted to the gates of the transistors Q 9  and Q 10 , respectively. The RF signal inputted to the gate of the transistor Q 10  is amplified by the transistor Q 10  and outputted through the drain of the transistor Q 10  to be provided to the source of the transistor Q 9 . On the other hand, the LO signal fed to the gate of the transistor Q 9  changes an operating point of the transistor Q 10  connected to the source of the transistor Q 9 . In other words, if the LO signal having a positive period is coupled to the gate of the transistor Q 9 , the operating point of the transistor Q 10  is moved to a saturation region having a large transconductance so that the transistor Q 10  greatly amplifies the RF signal coupled to its gate. On the other hand, if the LO signal having a negative period is coupled to the gate of the transistor Q 9 , the operating point of the transistor Q 10  is moved to a saturation region having a small transconductance so that the transistor Q 10  amplifies the RF signal by a small amount. As described above, the RF signal and the LO signal are mixed. Thereafter, there can be generated, through the drain of the transistor Q 9 , the RF signal, the LO signal and all kinds of signals(including an IF signal) represented by the multiple of the RF signal and the LO signal. In case of a downward frequency mixer, since the frequencies of the LO signal and the RF signal and the frequency of the IF signal are substantially separated, high frequency components are removed by the capacitor C 1  operating as a low pass filter and a relatively large signal whose frequency is close to the frequency of the IF signal is only provided to the gate of the transistor Q 11 . 
     Continuously, a portion of the RF signal outputted from the drain of the transistor Q 11  is inputted to the gate of the transistor Q 12  and a signal having an opposite phase to the inputted RF signal is outputted from the drain of the transistor Q 12 . The signal outputted from the drain of the transistor Q 12  and the RF signal outputted from the drain of the transistor Q 11  which are complementary are provided to the sources of the transistors Q 13  and Q 14 , respectively, and amplified. The high frequency signals except the IF signal among the signals outputted from the drains of the transistors Q 13  and Q 14  are substantially reduced by the capacity C 2  operating as a low pass filter and, thereafter, large-sized complementary IF signals are only detected at the first and second output terminals of the frequency mixer  204 . 
     Finally, an intermediate frequency amplifier  205  is constituted by a two-stage differential amplifier. The first differential amplifier is made of a transistor Q 15  whose gate is connected to the first output terminal of the frequency mixer  204 , and a transistor Q 16  whose gate is joint to the second output terminal of the frequency mixer  204 . On the other hand, the second differential amplifier contains a transistor Q 17  whose gate is connected to the drain of the transistor Q 15 , and a transistor Q 18  whose gate is joint to the drain of the transistor Q 16 . Also, the intermediate frequency amplifier  205  further includes as loads inductors L 3  and L 4  connected between the source voltage terminal and the drains of the transistors Q 17  and Q 18 , respectively, in order to increase the linearity by raising the output power capacity. 
     The complementary IF signals outputted from the first and the second output terminals of the frequency mixer  204  are amplified in the intermediate frequency amplifier  205  employing the two-stage differential amplifiers Q 15 , Q 16 , Q 17  and Q 18  and then outputted through an IF final output terminal of the MMIC  210 . 
     Referring to FIG. 3, there is shown a characteristic diagram of a conversion gain and an output standing-wave ratio of the wideband low-noise amplifier in FIG.  2 . In this drawing, the conversion gain and the output standing-wave ratio of the wideband low-noise amplifier are represented by a frequency function. With reference to FIG. 3, it can be seen that three bands shown in FIG. 3 are frequency bands determined at the input matching circuit  201 ; the conversion gain is more than or equal to 15 dB at all of bands; and the output standing-wave ration is less than or equal to 1.3. 
     Referring to FIG. 4, there is illustrated a noise characteristic diagram of the wideband low-noise amplifier in FIG. 2, which shows the noise characteristic depending on the frequency of the wideband low-noise amplifier. In this drawing, it can be understood that the noise is less than or equal to 1.5 dB at all of wireless/mobile service frequency bands. 
     Therefore, the frequency converting receiver of the present invention can be used in all of the wireless/mobile communications systems such as the cellular, PCS, WLL and IMT2000 and, further, implemented as a wideband frequency converting receiver for use in the MMIC which mass-produces a low cost microwave frequency converting receiver applicable to the RF unit with low cost and good reproduction characteristics, which has low power consumption, low-noise, high gain and small size characteristics. 
     While the present invention has been described with respect to the particular embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.