Abstract:
A semiconductor chip contains a multi-channel signal-processing circuit for processing signals in different frequency bands (e.g., an AM and an FM receiver). An inductor is coupled via an external terminal on a package for the semiconductor chip to a first signal-processing circuit. A circuit detects when a connection is made between the inductor and a power supply terminal contained in the semiconductor chip. When the inductor is connected to the power supply terminals, the first signal-processing circuit is activated, while the second signal-processing circuit is deactivated. When the inductor is disconnected from the power supply terminal, the second signal-processing circuit is activated, while the first signal-processing circuit is deactivated. The circuit for detecting a connection between the inductor and the power supply terminal is either a circuit for detecting a potential change or a circuit for detecting an oscillating signal. The inductor may be either an oscillator coil or an IF transformer winding.

Description:
The present invention relates to multi-channel signal processing circuits including circuits for processing signals in different frequency bands, formed on a single semiconductor chip, and more particularly to circuits including an AM receiver circuit and an FM receiver circuit formed on a single semiconductor chip. 
     In one prior art integrated FM-AM receiver circuit, an FM signal processing circuit and an AM signal processing circuit were formed on a single semiconductor chip. Outputs of the FM and AM signal processing circuits were switched by means of a transfer switch and applied to an audio-frequency and a power amplifier in the subsequent stages. For such switching, the output terminals of the respective signal processing circuits were provided as different external terminals on an integrated circuit chip. The output terminal, which is to be connected to the subsequent stages, was selectively determined by means of the transfer switch. In another prior art circuit, different power supply terminals were provided on an integrated circuit chip for supplying a power source voltage to the respective signal processing circuits. A transfer switch selectively supplied a power source voltage to the power supply terminal of the signal processing circuit. 
     Here it is to be noted that the term &#34;FM signal processing circuit&#34; generally implies a circuit for electrically processing frequency-modulated signals. However, the art of integrated circuits, it normally implies a signal processing circuit for amplifying an FM-IF signal and for demodulating the amplified FM-IF signal. Or, it could mean a signal processing circuit capable of either amplifying or demodulating. Likewise, the term &#34;AM signal processing circuit&#34; generally implies a circuit for electrically processing amplitude-modulated signals. Again, the art of integrated circuits, it normally implies a signal processing circuit for amplifying an AM-RF signal, producing a local oscillating signal, converting the amplified AM-RF signal into an AM-IF signal, and demodulating the AM-IF signal to become an audio signal. Or, it could mean a signal processing circuit capable of any one of the steps of amplification, of an AM-RF signal, producing a local oscillating signal, frequency-conversion into AM-IF signal and demodulation to an audio signal. 
     In the above-described FM-AM receiver circuits, the prior art required a great many external terminals for an integrated circuit. Such increased numbers of external terminals in an integrated circuit caused the semiconductor chip or a package to become unnecessarily large and complex. It also increased manufacturing costs, and reduced the integration density and yield. 
     Therefore, a major object of the present invention is to form a multi-channel signal processing circuit into an integrated circuit for processing signals in various frequency bands, while using fewer external terminals for channel switching. 
     According to one feature of the present invention, there is provided a multi-channel signal processing circuit, in which first and second signal processing circuits, (which process signals in various frequency bands), are formed on a single semiconductor chip. An inductor is coupled to the first signal processing circuit via an external terminal on the semiconductor chip. Furthermore, a circuit which detects a connection between the inductor and a power supply terminal, is contained in the semiconductor chip. 
     Further, according to the invention, when the inductor is connected to the power supply terminals, the first signal processing circuit is activated the second signal processing circuit is deactivated. On the other hand, when the inductor is disconnected from the power supply terminal, the second signal processing circuit is activated and the first signal processing circuit is deactivated. Typically, an AM signal processing circuit acts as the first signal processing circuit, while an FM signal processing circuit acts as the second signal processing circuit. Since the circuit for detecting a connection between the inductor and the power supply terminal is applicable, the FM signal-processing circuit also detects a potential change or an oscillation. An oscillator coil or an IF transformer is typically employed as the inductor. 
     Since inductors, such as the IF transformer and an oscillator coil, cannot be formed in a semiconductor integrated circuit, external terminals are required for connecting these inductors to a semiconductor integrated circuit. The connections between these inductors and the power supply terminal are unnecessary when the signal processing circuit including these inductors is not in use. 
     The present invention makes use of this feature of the signal processing circuit. The selection of either the first or second signal processing circuit is thus effected depending upon whether or not the power supply terminal is connected to the intermediate frequency transformer or another inductor. Additional external terminals are unnecessary for selecting the signal processing circuits. Further, a single power supply terminal and a single output terminal can be commonly used for all the signal processing circuits, thus saving external terminals. Such a saving of external terminals results in a small-sized semiconductor chip and a package thereof, and it reduces manufacturing costs. Also, further circuit functions can be incorporated in the integrated circuit, extra external terminals can be used for the semiconductor chip and package. Hence, the commercial value of the integrated circuit can be enhanced by reducing the number of terminals used for non-signal processing functions. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     The above and further objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a circuit diagram showing a first preferred embodiment of the present invention; 
     FIG. 2 is a circuit diagram showing a second preferred embodiment of the present invention; 
     FIG. 3 is a circuit diagram showing a third preferred embodiment of the present invention; 
     FIG. 4 is a circuit diagram showing a fourth preferred embodiment of the present invention; and 
     FIG. 5 is a circuit diagram showing a fifth preferred embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1 of the drawings, in the first preferred embodiment of the present invention the portion encircled by a dash-dot line frame 100 is an integrated circuit formed on a semiconductor chip. The integrated circuit comprises an FM signal processing circuit which includes an FM intermediate-frequency (FM IF) amplifier 210 and an FM demodulator 220, an AM signal processing circuit including a radio-frequency (RF) amplifier 310, a frequency converter 320, local oscillator 330, an AM intermediate-frequency (AM IF) amplifier 340, an AM demodulator 350, and a switching circuit 400. Moreover, the integrated circuit comprises an FM signal input terminal 4, an AM signal input terminal 5, a power supply terminal 1, a ground terminal 2, and an output terminal 3. It also comprises a tuning circuit connection terminal 15 for the frequency converter 320, an oscillator coil connection terminal 16 for the local oscillator 330, an AM IF signal input terminal 17 for the AM IF amplifier 340, a tuning circuit connection terminal 18 for the AM IF amplifier 340 and an input terminal 19 for the AM demodulator 350. 
     Each of the tuning circuits 20, 30 and 40 has an inductor and capacitor parallel circuit. One end of each of the tuning circuits 20, 30 and 40 is connected to the connection terminals 15, 16 and 18, respectively. A power supply voltage Vcc is connected directly to the power supply terminal 1 and to the other ends of the tuning circuits 20 and 30, and is supplied through a channel selection switch 50 to the other end of the tuning circuit 40. 
     An AM IF signal of 455 KHz is derived from the terminal 15, and is applied to the terminal 17 through a capacitor 301. Similarly, the amplified AM IF signal is transferred from the terminal 18 to the terminal 19 by way of a capacitor 302. The FM signal input terminal 4 is connected to an input end of the FM IF amplifier 210, and an output end 214 of the FM IF amplifier 210 is connected to an input end 221 of the FM demodulator 220. Two output ends, that of the FM demodulator 220 and end 354 of the AM demodulator 350, are connected to the output terminal 3 of the integrated circuit. 
     In more detail, the power supply terminal 1 is connected to a cathode of a Zener diode 121 via a resistor 120. The anode of the Zener diode 121 is connected to the ground terminal 2. The cathode of the Zener diode 121 is connected to the respective bases of npn-transistors 114, 122 and 141. The transistors 114,122 are a power switch for the FM IF amplifier 210 and for the FM demodulator 220. The emitter of the transistor 114 is connected to a first power supply end 212 of the FM IF amplifier 210, and, via a resistor 117, to an anode of a diode 119. The cathode of the diode 119 is connected to the ground terminal 2 through a resistor 118, while the anode of that diode 119 is connected to a base of an npn-transistor 115. The collector of the transistor 115 is connected to a second power supply terminal 213 of the FM IF amplifier 210. The emitter of the transistor 115 is connected to the ground terminal 2 via a resistor 116. The collector of the transistor 114 is connected to a first collector 112 of a npn-transistor 111. This npn transistor has a first collector 112, which is connected to its own base and it also has a second collector 113. The emitter of transistor 111 is connected to the power supply terminal 1, and the second collector 113 is connected to a base of an npn-transistor 131. The collector of the transistor 131 is connected to the anode of the diode 119, and the emitter of transistor 131 is connected to the ground terminal 2 via a resistor 132. 
     The collector and emitter of the transistor 122 are connected respectively to the power supply terminal 1 and to a first power supply terminal 222 of the FM demodulator 220. A second power supply terminal 223 of the FM demodulator 220 is connected to the ground terminal 2. 
     The AM signal input terminal 5 is connected to an input end 311 of the RF amplifier 310. The output end 314 of the RF amplifier 310 is connected to an input end 321 of the frequency converter 320, and the output end 324 of the frequency converter 320 is connected through the tuning circuit connection terminal 15 to a tuning circuit 20. The tuning circuit connection terminal 15 is connected via an external capacitor 301 to the input terminal 17 for the AM IF amplifier 340, and the input terminal 17 is connected to an input end 341 of the AM IF amplifier 340. An output end 344 of the AM IF amplifier 340 is connected to a base of an npn-transistor 345 having an emitter connected through a resistor 346 to the ground terminal 2, and a collector connected to the tuning circuit connection terminal 18. The tuning circuit connection terminal 18 is coupled via an external capacitor 302 to the input end 351 of the AM demodulator 350, and to the input terminal 19. An output end 354 of the AM demodulator 350 is connected to the output terminal 2 of the integrated circuit 100. 
     The power supply terminal 1 is connected to respective collectors of npn-transistors 151, 152, 153, 154 and 155. The respective bases of the npn-transistors 151, 152, 153, 154 and 155 are connected to a cathode of a Zener diode 157 having an anode connected to the ground terminal 2. The emitter of the npn-transistor 151 is connected to a first power supply end 312 of the RF amplifier 310. The emitter of the npn-transistor 152 is connected to a first power supply end 322 of the frequency converter 320, and the emitter of the npn-transistor 153 is connected to a first power supply end 332 of the local oscillator 330. Second power supply ends 313, 323 and 333 of the RF amplifier 310, the frequency converter 320 and the local oscillator 330 are each connected to the ground terminal 2. An end 334 of the local oscillator 330 is connected to the terminal 16 on the integrated circuit 100, which terminal is also used for making a connection to the tuning circuit 30. An output signal at the output end 331 of the local oscillator 330 is supplied to an input end 325 of the frequency converter 320. The emitter of the npn-transistor 154 is connected to a first power supply end 342 of the AM IF amplifier 340. A second power supply end 343 of the AM IF amplifier circuit 340 is connected to the ground terminal 2. In the same way, the emitter of the npn-transistor 155 is connected to a first power supply end 352 of the AM demodulator 350, and a second power supply end 353 of the AM demodulator 350 is connected to the ground terminal 2. 
     The tuning circuit connection terminal 15, for the frequency converter 320, is connected to an external power supply Vcc through a tuning circuit 20. The terminal 16 is also connected to the external power supply through an oscillator circuit 30. The tuning circuit connection terminal 18 is connected to a tuning circuit 40, and the tuning coil is in turn connected to the external power supply Vcc via an ON-OFF switch 50. 
     A portion of the integrated circuit 100, which is encircled by a dotted line frame 400, operates as an FM-AM switching circuit. A collector of an npn-transistor 141 is connected to the power supply terminal 1, the base to a cathode of a Zener diode 121, and the emitter to an emitter of a pnp-transistor 9 through a resistor 8. The transistor 9 has two collectors. A first collector 10 is connected to a base of an npn-transistor 7, and a second collector 11 is connected to an anode of a diode 12 and a base of an npn-transistor 13. The cathode of the diode 12 is connected to the ground terminal 2. The emitter of the transistor 7 is directly connected to the ground terminal 2. The collector of the transistor 7 is connected to bases of both an npn-transistor 131, and an npn-transistor 6. Transistor 6 has a grounded emitter. The junction between the collector of the transistor 7 and the base of the transistor 6 forms a first output end 401 of the FM-AM switching circuit 400. The collector of the transistor 6 is connected to a base of a pnp-transistor 161, and forms a second output end 402 of the FM-AM switching circuit 400. The emitter of the transistor 161 is connected to the power supply terminal 1, and the transistor&#39;s collector is connected through a resistor 162 to the cathode of the Zener diode 157. 
     The base of the pnp-transistor 9 is connected to a collector of an npn-transistor 13. The base of the transistor 13 is connected to both the anode of the diode 12, and to the second collector 11 of the pnp-transistor 9. The emitter of the transistor 13 is connected to the ground terminal 2 through a resistor 14. The junction between the base of the transistor 9 and the collector of the transistor 13 is connected to the collector of the transistor 345 through an input end 403 of the FM-AM switching circuit 400. 
     According to the invention, the FM signal processing circuit is made operative by the voltage potential at the first output end 401 of the FM-AM switching circuit 400. The AM circuit is activated due to the voltage potential at the second output end 402 of the same switching circuit 400. These voltage potentials are charged by the voltage potential at the input end 403 of the FM-AM switching circuit 400. This potential at end 403 depends on whether switch 50 is on or off. Thus the integrated circuit 100 does not need an additional external lead-out terminal for switching between the FM and AM signal-processing circuits. On the contrary, power supply terminals 1 and the output terminal 3 are each formed as a single terminal for both processing circuits, thereby reducing the number of external lead out terminals which are required. 
     Next, the switching operation will be explained. When integrated circuit 100 is operated with the switch 50 turned ON, the sum of AC and DC voltages at the collector of the npn-transistor 345 is applied to the input end 403 of the switching circuit 400 and to the base of the transistor 9. Then, the emitter-base voltage of the transistor 9 becomes inversely biased, thereby cutting off transistor 9. In this state, since no current is fed to the base of the transistor 7, it is cut off. Then, the cut-off state of the transistor 9 is enhanced by the transistor 13, so that the junction between the base of the transistor 9 and the collector of the transistor 13 has a high impedance as viewed from the collector of the transistor 345. Hence, the signal switching circuit 400 does not influence operation of the AM signal processing circuit. At this time, a current is fed from the second collector 113 of the transistor 111 to the base of the transistor 131. Transistor 131 becomes saturated and depletes the base current of the transistor 115, to cut off that transistor. Consequently the second power supply end 213 of the FM IF amplifier 210 cannot be fed with electric power, and the FM IF amplifier circuit 210 is deactivated. Accordingly, the FM signal processing circuit derives no FM signal processed output at the output terminal 3. 
     In addition, a current flows from the second collector 113 of the transistor 111 to the base of the transistor 6, thereby enabling transistor 6 to conduct current. Then, since there is a base current for the pnp-transistor 161, the transistor 161 can also conduct current. In this way, a current is fed to the Zener diode 157 through the transistor 161 and the resistor 162. Consequently, currents are fed to the bases of the respective transistors 151, 152, 153, 154 and 155, enabling each of these transistors to conduct current and feed a power supply voltage to the AM signal processing circuit. Hence, the AM signal processing circuit is activated. Accordingly, the AM signal processed output is derived at the output terminal 3. Therefore, in cases where switch 50 is turned ON, the integrated circuit 100 derives an output of the AM signal processing circuit at the output terminal 3. On the other hand, if the switch 50 is turned OFF, the sum of the AC and DC voltages is lowered and applied to the input end 403 of the FM-AM switching circuit 400. This enables transistor 9 to conduct current, and raises the voltage at the base of the transistor 13 which switches on. The current conduction of transistor 9 is enhanced by the collector current of the transistor 13. A current from the first collector 10 of the transistor 9 is fed to the base of the transistor 7, enabling transistor 7 to conduct, and prevent transistor 6 from conducting. When transistor 7 begins to conduct, the current fed to the base of the transistor 131 is decreased. This cuts off transistor 131. Simultaneously, a current is fed to the base of the transistor 115 from the resistor 117, so that the transistor 115 conducts. This transistor is fed with a current from the second power supply end 213 of the FM IF amplifier circuit 210. This causes the FM signal processing circuit to deliver an FM signal processed output at the output terminal 3. 
     While cut off, transistor 6 does not feed a current to the pnp transistor 161, thereby cutting off pnp transistor 161. The pnp transistor 161 is then unable to feed currents to the respective bases of the transistors 151, 152, 153, 154 and 155, so that the AM signal processing circuit is deactivated and cannot deliver an AM signal processed output at the output terminal 3. Accordingly, when the switch 502 is turned OFF, the integrated circuit 100 delivers an output of the FM signal processing circuit at the output terminal 3. 
     As described above, by providing the FM-AM switch terminal in common with the tuning coil or circuit connection terminal, an FM-AM receiver circuit can be provided which has a reduced number of external lead out terminals. 
     In the preferred embodiment (FIG. 1) the tuning circuit connection terminal 18 for the AM IF amplifier 340, and the FM-AM switch terminal are provided in common. An alternative embodiment provides the oscillator coil connection terminal 16, and the FM-AM switch terminal in common. 
     This modification is applied to the second embodiment shown in FIG. 2. The same reference numerals are employed in FIG. 2 for denoting the same part or circuit as in FIG. 1. The basic circuit construction is the same as that of FIG. 1, except that one end of the tuning circuit 40 is directly connected to the power supply line Vcc. The collector of the transistor 345 is disconnected from the input end 403 of the FM-AM switching circuit 400. The FM-AM switch 502 is inserted between the tuning coil circuit 30 and the power supply line Vcc. The local oscillator 330 includes both a differential circuit of npn transistors 335 and 336, and a resistor 337. The base of the transistor 335 is connected to the collector of the transistor 336 and delivers an oscillation output to the frequency converter 320. The base of the transistor 336 is connected to the collector of the transistor 335 and the emitter of the transistor 153. The collector of transistor 336 is also connected to the terminal 16 and the input end 403 of the FM-AM switching circuit 400. 
     When the switch 502 is ON, the high voltage at the collector of the transistor 336 is applied to the input end 403 of the FM-AM switching circuit 400. The transistors 9 and 7 are cut off; the transistors 131 and 115 turn ON and are cut off, respectively, and then the FM-IF amplifier 210 is deactivated. On the contrary, the transistors 6 and 161 turn ON and enable the transistors 151, 152, 153, 154 and 155 to conduct current. Thus, the AM RF amplifier 310, the frequency converter 320, the local oscillator 330, the AM IF amplifier 340 and the AM demodulator 350 are activated, thereby providing the AM demodulated output at the output terminal 3. 
     When the switch 502 is cutt off, the lower voltage is applied to the input end 403 of the FM-AM switching circuit 400, and the transistor 9 begins conducting current. The transistor 7 also begins conducting current, causing transistors 131 and 115 to become non-conductive and conductive, respectively. The FM IF amplifier is activated so that the FM demodulated output may be delivered from the output terminal 3. On the contrary, the transistors 6 and 161 become non-conductive, and the transistors 151 to 155 can no longer supply power from their emitters. Consequently, the AM signal processing circuit is deactivated. 
     Referring now to FIG. 3, illustrating the third embodiment, the switching between the operations of FM and AM signal processing circuit is achieved responsive to detection of the oscillation output from the local oscillator by means of the oscillation detector 410 which is inserted between the collector of the transistor 336 in the local oscillator 330 and the input end 403 of the FM-AM switching circuit 400. The other construction is similar to that of FIG. 2. 
     In this embodiment, the oscillation of the local oscillator 330 is provided by closing the switch 502, which makes the voltage at the output end of the oscillation detector 410 high and the transistor 9 conductive. Hence, the AM signal processing circuit begins operating, but the FM signal processing circuit becomes inoperative, as mentioned above. When the oscillation of the local oscillator 330 stops by turning off the switch 502, a lower voltage is provided at the output end of the oscillation detector 410 and applied to the input end 403 of the FM-AM switching circuit 400. The transistor 9 becomes non-conductive. The FM signal processing circuit is deactivated but the AM signal processing circuit is deactivated, as also mentioned above. 
     Referring now to FIG. 4, the fourth embodiment has an FM-AM switch 504 positioned between the tuning circuit 20 and the power supply line Vcc. The frequency converter 320 is formed by cascade connection of two differential amplifier stages. The lower stage comprises two transistors 328 and 329 and a resistor 3210, and the upper stage comprises two transistors 326 and 327. The AM RF amplifier 310 delivers two outputs having different phases. These outputs are applied to the bases of the transistors 328 and 329. The collector of the transistor 328 is connected to the common emitter of the transistors 326 and 327. Two outputs of the local oscillator 330, which have different phases with respect to each other, are applied to the bases of the transistors 326 and 327. The collectors of the transistors 326 and 329 are commonly connected to the emitter of the transistor 152. The collector of the transistor 329 is connected to the terminal 15 and the input end 403 of the FM-AM switching circuit. The amount of voltage at the input end 403 is regulated by turning switch 504 on and off. The FM-AM switching circuit controls the operation of the FM and AM signal processing circuits (see FIGS. 1 and 2). 
     With reference to FIG. 5, the fifth embodiment has additional terminals 61 and 62 for connecting turning circuit 60 and the switch 505. The tuning circuit 60 is connected through terminal 61 to both the FM IF amplifier 210 and to the input end 403 of the FM-AM switching circuit 400. The circuit&#39;s tuned frequency is 10.7 MHz. The output of the FM IF amplifier 210 is provided at the terminal 61 and is applied to the following FM IF amplifier 230 by way of a capacitor 303 and the terminal 62. The power supply to the FM IF amplifier 230 is controlled by transistors 231 and 232 and by resistor 233. The switch 505 is inserted between the tuning circuit 60 and the power supply line Vcc. It is noted that the additional transistor 404 is inserted between the transistors 9 and 7 of the FM-AM switch circuit 400 to convert the output states at the output ends 401 and 402 with respect to another embodiment. 
     When the switch 505 is turned on, a raised voltage is applied to the input end 403. The potentials at the output ends 401 and 402 become low and high, respectively. The transistor 131 becomes non-conductive and the transistors 115 and 232 become conductive. In this state, the FM IF amplifiers 210 and 230 are activated and the FM demodulated output is delivered from the output terminal. However the AM RF amplifier 310, the frequency converter 320, the local oscillator 330, the AM IF amplifier 340 and the AM demodulator 350 are deactivated. 
     When the switch 505 is turned off, a lowered voltage is applied to the input end 403. The potentials at the output ends 401 and 402 become high and low, respectively. Consequently the FM signal processing circuit becomes inoperative and the AM signal processing circuit is activated. 
     Thus, according to the present invention, a semiconductor integrated circuit does not require special terminals to be used exclusively for switching between circuits. Further, a single output terminal and a single power supply terminal are both required to selectively derive an output signal in a semiconductor integrated circuit. Therefore, the semiconductor integrated circuit requires fewer terminals. This reduces cost and increases production yield. In addition, since the unused terminals can be combined in a semiconductor integrated circuit which is used for another operation, such as noise cancellation, the commercial value of the integrated circuit is enhanced.