This application is based upon and claims the benefit of the priority of Japanese patent application No. 2008-168852, filed on Jun. 27, 2008, the disclosure of which is incorporated herein in its entirety by reference thereto.
This invention relates to a receiver and to a method of reducing operating current of the receiver. More particularly, the invention relates to a receiver having a start circuit for detecting a radio-frequency signal and starting the receiver proper.
The spread of mobile wireless communication devices has been accompanied by the proposal of various techniques for lengthening battery drive time. One promising technique among these is to reduce power consumption using an RF signal detection and start circuit.
Japanese Patent Kokai Publication No. JP-P2005-184175A
Japanese Patent Kokai Publication No. JP-A-10-28078
However, with the radio-frequency-detection start circuit described in Patent Document 1, if another wireless communication device whose frequency band is the same as that of the desired signal and whose protocol is the same exists in an area reached by radio waves, the circuit will detect the radio waves and output the start signal even if the transceiver to which the circuit belongs is not communicating. Owing to the start signal, there are instances where the transceiver starts up and consumes power despite the fact that communication is not being carried out.
With the wireless communication device described in Patent Document 2, whether or not it is necessary for the main arithmetic unit 704 to start requires FSK demodulation by the receiving circuit 701 and a determination by the auxiliary arithmetic unit 703. Accordingly, even if absence of a signal continues, it is necessary to periodically actuate the auxiliary arithmetic unit 703 in order to verify whether there is a signal or not, a demodulation operation must be performed by the receiving circuit 701 and whether there is a signal or not must be checked by the auxiliary arithmetic unit 703. Further, in order to activate the auxiliary arithmetic unit 703 periodically, it is required that the internal blocks of the wireless communication device operate at all times. The result is an increase in power consumption.
Thus there is demand for a receiver which will stand by with little power consumption if absence of a signal continues and which will not undergo a large increase in power consumption even if an unwanted signal is received, as in a case where the receiver receives a signal intended for another wireless communication device of the same frequency band and communication protocol.
According to a first aspect of the present invention, there is provided a receiver comprising; a start circuit that detects a radio-frequency signal and outputting a start signal if a level of the detected radio-frequency signal is no less than a fixed level, and a receive-signal processor that receives the start signal and starts a demodulating operation for demodulating the radio-frequency signal. The receive-signal processor includes: a demodulator that reconstructs a demodulated signal from the radio-frequency signal; and a restart-inhibit controller that determines whether the demodulated signal is a desired signal and, if the demodulated signal is not a desired signal, outputs a restart-inhibit signal to the start circuit and causes the start circuit to inhibit output of the start signal for a fixed period of time.
According to a second aspect of the present invention, there is provided a method of reducing operating current of a receiver having a start circuit and a receive-signal processor, the method comprising: the start circuit operating and the receive-signal processor ceasing operation in a standby state; when the start circuit detecting a radio-frequency signal and a level of the detected radio-frequency signal is no less than a fixed level, starting the receive-signal processor to perform a demodulating operation for reconstructing a demodulated signal from the radio-frequency signal and suspending operation of the start circuit; when the demodulated signal is a desired signal, continuing signal-receive processing until end of communication and returning to the standby state following end of communication; and when the demodulated signal is not a desired signal, setting the start circuit in such a manner that it will not start the receive-signal processor for a fixed period of time, and returning to the standby state after the setting is made.
The meritorious effects of the present invention are summarized as follows.
In accordance with the present invention, there is obtained a receiver which stands by with little consumption of power if absence of a signal continues, and which makes reduces an increase in power consumption even if an unwanted signal is received.
In accordance with the method of reducing operating current in a receiver according to the present invention, the operating current of a receiver when an unwanted signal has been received can be reduced.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.
Exemplary modes of the present invention will now be described with reference to the drawings as necessary.
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Exemplary embodiments of the present invention will now be described in detail with reference to the drawings.
The start circuit 115 includes a matching circuit 102 for receiving only a signal of a desired frequency band contained in the signal that has entered from the RF signal input terminal 101; a detecting circuit 103 for detecting the signal of the desired frequency band; an amplifying circuit 104 for amplifying the output of the detecting circuit 103; and a binarizing circuit 105 for comparing the amplified analog signal with a fixed reference value and converting the signal to a digital value. The start circuit 115 further includes a capacitor 108 charged to a restart-inhibit signal 141 that is output by the receive-signal processor 114; a resistor 107 for constantly discharging the charge that has been charged in the capacitor 108; a binarizing circuit 109 for comparing the voltage level of the restart-inhibit signal 141 with a fixed reference voltage and converting the level to an inverted digital value; and an AND gate 106 for outputting a start signal 113 if the outputs of the binarizing circuits 105 and 109 are both at the high level.
The receive-signal processor 114 includes a demodulating circuit 110 for digitally demodulating the RF signal that has entered from the RF signal input terminal 101; a main CPU 121 for data-processing the receive signal reconstructed by the demodulating circuit 110; and a restart-inhibit controller 130 for outputting a restart-inhibit signal 141 if the reconstructed receive signal is not the desired signal.
The restart-inhibit controller 130 includes an auxiliary CPU 120 and a DA converter 112. The auxiliary CPU 120 determines whether the reconstructed receive signal is the desired signal and decides a time period over which restart of the start circuit 115 is inhibited. The DA converter 112 converts the result of the determination by the auxiliary CPU 120 to a current value and outputs the current value as the restart-inhibit signal 141.
The receive-signal determination unit 302 determines whether the demodulated signal is the desired signal. The reception-result storage unit 303 stores a count value which, if the demodulated signal is not the desired signal, indicates how many times in succession the demodulated signal was not the desired signal. The count value shall be referred to as a successive reception failure count Nfail. On the basis of the successive reception failure count Nfail, the output current controller 304 controls the switch circuit 306, decides the output current value of the restart-inhibit signal 141 and controls the time over which restart is inhibited.
Further, the current source circuit 307 is constituted by an N-bit (where N is a natural number) current source, in which the current value of a kth bit (where k is a natural number less than N) has been weighted by 2(k-1)×Io. That is, the current source circuit 307 is so adapted that currents Io, 2×Io, 4×Io, 8×Io, . . . are output in order starting from the first bit.
Next, the operation of the receiver according to the first exemplary embodiment will be described with reference to the operation flowchart of
In the standby state (step 502), any charge that accumulated in the capacitor 108 will have been discharged to the clamp(ground) level via the resistor 107 and therefore the restart-inhibit signal 141 will be at the potential of the clamp(ground) level. Accordingly, the output of the binarizing circuit 109 is at the high level (the reverse logic level of the ground level).
In a case where there is no signal at the RF signal input terminal 101 or in a case where there is an input signal but the input signal detected and amplified by the matching circuit 102, detecting circuit 103 and amplifying circuit 104 does not reach the threshold level of the binarizing circuit 105, the output of the binarizing circuit 105 is the low level. Accordingly, the output of the AND gate 106 is the low level and the standby state is maintained (“NO” at step 504).
On the other hand, if an RF signal of the desired frequency band is input to the RF signal input terminal 101 and the signal exceeds the threshold level of the binarizing circuit 105, then the binarizing circuit 105 outputs the high level (“YES” at step 504). In this case, since the restart-inhibit signal 141 is at the low level (“NO” at step 505), the output of the binarizing circuit 109 is the high level, as mentioned above, the AND gate 106 changes state and the start signal 113 is raised to the high level.
The receive-signal processor 114 receives the high level of the start signal 113, quits the sleep state and attains the operating state. When the auxiliary CPU 120 attains the operating state, it places a start-circuit control signal 142 at the low level and places the start circuit 115 in the sleep state (step 506).
The receive-signal processor 114 inputs the RF signal, which has entered from the RF signal input terminal 101, to the demodulating circuit 110 to thereby reconstruct the digital signal. The auxiliary CPU 120 determines whether the demodulated signal is the desired signal (step 507). If the demodulated signal is the desired signal (“YES” at step 507), then the count value of the successive reception failure count Nfail stored by the reception-result storage unit 303 is made zero by the auxiliary CPU 120 (step 508). The main CPU 121 executes receive-data signal processing until communication ends (step 509). When communication ends, the auxiliary CPU 120 places the start-circuit control signal 142 at the high level to thereby place the start circuit 115 in the operating state, after which the receive-signal processor 114 ceases operation and the standby state is restored (step 502).
On the other hand, if the auxiliary CPU 120 determines that the signal is not the desired signal (“NO” at step 507), it increments the successive reception failure count Nfail stored by the reception-result storage unit 303 (step 510). An instance where the signal is not the desired signal corresponds to a case where reception has failed for some reason, e.g., a case where the demodulated signal is not a signal directed to this receiver but is a call signal directed to another communication apparatus, or a case where the demodulating circuit 110 cannot demodulate the input signal to a meaningful signal. Next, the restart-inhibit controller 130 outputs the restart-inhibit signal 141 (step 511) based upon the count value of the successive reception failure count Nfail, and then places the start-circuit control signal 142 at the high level to thereby place the start circuit 115 in the operating state. The receive-signal processor 114 ceases operation and the standby state is stored (step 502).
The relationship between operation of the restart-inhibit controller 130 and the time during which restart is inhibited will now be described in detail.
On the basis of the information indicated by the successive reception failure count Nfail stored in the reception-result storage unit 303, the output current controller 304 controls the switch circuit 306 in such a manner that the output current value of the restart-inhibit signal 141 in increased to the extent that the successive reception failure count Nfail increases. More specifically, when the value of the successive reception failure count Nfail is k (where k is a natural number less than N and n represents the number of bits of the switch circuit 306 and current source circuit 307), the output current controller 304 controls the switch circuit 306 so as to turn on the switch of the kth bit and turn off the switches of the other bits. As already mentioned, the current value of each bit (kth bit) of the current source circuit 307 has been weighted in such a manner that the current amount Io of the first bit is multiplied by the (k-1)th power of 2. That is, when the value of the successive reception failure count Nfail is k, the output current value of the restart-inhibit signal 141 becomes an output current value that is the (k-1)th power of 2 times the current amount Io of the first bit.
First, in a case where reception has failed for the (Nfail-1)th time in succession, the output current controller 304 turns on the (Nfail-1)th bit of the switch circuit 306 for a fixed period of time Tn to Tn+1. Accordingly, a current that is the result of multiplying lout by the (Nfail-1)th power of 2 is output as the restart-inhibit signal 141 from Tn to Tn+1, as illustrated in
Next, if reception fails one more time in succession, the output current controller 304 turns on the (Nfail)th bit of the switch circuit 306 for a fixed period of time Tn+3 to Tn+4. Since the (Nfail)th bit of the current source circuit 307 passes a current that is twice that of the (Nfail-1)th bit of the current source circuit 307, a current that is the result of multiplying Iout by the (Nfail)th power of 2 is output as the restart-inhibit signal 141 from Tn+3 to Tn+4, as illustrated in
More specifically, as a result of an attempt by the demodulating circuit 110 to perform demodulation, the period of time over which the output of the start signal 113 is inhibited is lengthened to the extent that the signal obtained continues not to be the desired signal. In a case where the demodulated signal is not the desired signal, it is highly likely that another station using the same frequency band as that of this apparatus and employing the same communication protocol is communicating, and it is conceivable that the other station will be communicating for a while longer. In such case there is a high probability that the desired signal will not be obtained even if demodulation is tried continuously without leaving some time idle. Accordingly, instances of erroneous start-up can be reduced by the function of this exemplary embodiment that prolongs restart-inhibit time as the successive reception failure count Nfail increases. Further, even in a case where the start circuit initiates start-up as a result of ambient noise being misrecognized as communication directed to this apparatus, restart is inhibited until such ambient noise diminishes. It is thus possible to suppress consumption of needless operating current.
It should be noted that even if the successive reception failure count Nfail increases, the current value of the restart-inhibit signal 141 will not increase beyond the current value of the most significant bit of the current source circuit 307 or beyond the sum total of the current values of all bits of the current source circuit 307. It goes without saying, therefore, that the time over which start is inhibited will not be prolonged without limit.
Further, in order to further reduce the current that flows when the start circuit 115 and receive-signal processor 114 are not operating (i.e., when they are in the sleep state), the power sources of the start circuit 115 and receive-signal processor 114 may be cut off at such time. However, in a case where the power source of the reception-result storage unit 303 of the determination unit 120 also is cut off, it is required that the reception-result storage unit 303 be made a non-volatile memory. On the other hand, if the leakage current when operation has ceased (i.e., in the sleep state) is so small in comparison with the operating current that it will not pose a problem, it will suffice to suspend operation while this current continues to be passed. Further, in order to hasten restart and reduce leakage current, the power-source voltage at the time of the sleep state may be lowered. In any case, in accordance with this exemplary embodiment, the operating current of the receiver can be reduced and, as a result, so can the power consumption of the receiver.
It should be noted that when the receive-signal processor 114 outputs the restart-inhibit signal 141 in response to reception failure, suspends operation and restores the standby state, the detecting circuit 203, amplifying circuit 204 and binarizing circuit 205 of the start circuit 215 also cease operating simultaneously. That is, the second exemplary embodiment is such that if reception fails, the receive-signal processor 114 and the detecting circuit 203, amplifying circuit 204 and binarizing circuit 205 of the start circuit 215 are placed in the sleep state simultaneously for a fixed period of time. In comparison with the first exemplary embodiment, therefore, operating current can be reduced to a greater degree. Furthermore, when the fixed period of time elapses and the sleep signal 216 attains the high level, the detecting circuit 203, amplifying circuit 204 and binarizing circuit 205 are removed from the sleep state and the normal standby state is restored.
Though the present invention has been described in accordance with the foregoing embodiments, the invention is not limited to these embodiments and it goes without saying that the invention covers various modifications and changes that would be obvious to those skilled in the art within the scope of the claims.
It should be noted that other objects, features and aspects of the present invention will become apparent in the entire disclosure and that modifications may be done without departing the gist and scope of the present invention as disclosed herein and claimed as appended herewith.
Also it should be noted that any combination of the disclosed and/or claimed elements, matters and/or items may fall under the modifications aforementioned.
Number | Date | Country | Kind |
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2008-168852 | Jun 2008 | JP | national |