Patent Publication Number: US-2013251071-A1

Title: Receiver

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2012-064036, filed Mar. 21, 2012; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate to a receiver. 
     BACKGROUND 
     Detection methods in conventional receivers include delayed detection, pulse count detection, quadrature detection, etc. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates demodulation characteristics of delayed detection, pulse count detection, and quadrature detection methods. 
         FIG. 2  shows an interference wave characteristic, an input signal frequency offset resistance, and an out-of-band detection characteristic of a delayed detection method and pulse count detection and quadrature detection methods. 
         FIG. 3  shows an example configuration of a receiver according to a first embodiment. 
         FIG. 4  shows an example configuration of a receiver according to a second embodiment. 
         FIG. 5  shows an example configuration of a receiver according to a third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments disclosed herein provide a receiver that can improve an interference wave characteristic, an input frequency offset resistance, and an out-of-band detection characteristic of its output signals. 
     A receiver according to one embodiment is provided with a channel selection filter that receives an IF signal and outputs a filtered IF signal as a first signal, an IF amplifier that receives the first signal from the channel selection filter and outputs an amplified first signal as a second signal, a first detector that receives the second signal from the IF amplifier and outputs a third signal after the second signal is delayed and detected, a second detector that receives the second signal from the IF amplifier and outputs a fourth signal after the second signal undergoes pulse count detection or quadrature detection, a switching circuit that selects one of the third signal and the fourth signal and outputs the selected signal as a demodulated signal through an output terminal, and a control circuit that controls the switching circuit to select either the third signal or the fourth signal. 
       FIG. 1  illustrates demodulation characteristics of delayed detection, pulse count detection, and quadrature detection methods. 
     As shown in  FIG. 1 , the demodulation characteristics of the delayed detection, pulse count detection, and quadrature detection methods are similar from zero frequency to a certain frequency (e.g., 400 kHz in  FIG. 1 ). However, the delayed detection method exhibits a characteristic where the output voltage response in relation to the input frequency is folded back (reverses slope) above the certain frequency as shown. In contrast, in the pulse count detection method and the quadrature detection method, the output voltage response in relation to an input frequency is constant above the certain frequency. 
       FIG. 2  shows the interference wave characteristic, input signal frequency offset resistance, and out-of-band detection characteristic of the delayed detection, pulse count detection, and quadrature detection methods. 
     As shown in  FIG. 1 , with the delayed detection method, the demodulation characteristic (e.g., output voltage response to input frequency) is folded back (reverses slope) near the band of interference waves (for example 400-1,600 kHz). As a result, demodulation voltage is suppressed, causing a high resistance. In the pulse count detection and the quadrature detection, by contrast, the demodulation characteristic is not folded back. As a result, a large demodulation voltage is output in response to interference waves, causing a low resistance. 
     As for the input signal frequency offset resistance, in the delayed detection, the output voltage is folded back at 400 kHz or higher (in the example given in  FIG. 1 ), making demodulation of offsets in input signal frequency not possible at the higher frequency ranges. On the other hand, in the pulse count detection and quadrature detection methods, although output voltage distortion is caused, the input frequency offsets can be demodulated over a wider frequency range. 
     As for the out-of-band detection characteristic in which signals that are out-of-band are erroneously detected when there is no desired signal, it is disadvantageous to use the delayed detection method because signals are not discriminated from the desired signal in the delayed detection method. Thus, erroneous detection may result. On the other hand, no erroneous detection occurs in the pulse count detection and quadrature detection methods, because the demodulated signal is insignificant. 
     Therefore, there are respective advantages and disadvantages in the delayed detection, the pulse count detection, and the quadrature detection methods. 
     Accordingly, in the following Embodiments, receivers, which select detection methods in consideration of their respective advantages and disadvantages to improve the interference wave characteristic, input signal frequency offset resistance, and out-of-band detection characteristic, are proposed. 
     Next, each embodiment will be explained with reference to the figures. 
     (Embodiment 1) 
       FIG. 3  shows an example configuration of a receiver  100  of Embodiment 1. As shown in  FIG. 3 , the receiver  100  is provided with antenna ANT, low-noise amplifier LNA, local oscillator OSC, mixer M, a channel selection filter F, IF amplifier A, first detector D 1 , second detector D 2 , switching circuit SW, and control circuit CON. In this embodiment, the receiver  100  is an FM receiver. 
     The antenna ANT receives a RF (radio frequency) signal. The low-noise amplifier LNA amplifies and outputs the RF signal received by the antenna ANT. The local oscillator OSC generates and outputs a local oscillating signal Lo. The mixer M outputs an IF (intermediate frequency) signal obtained by mixing the signal output from the low-noise amplifier LNA and the local oscillating signal Lo. The channel selection filter F receives the input of the IF signal, filters the IF signal, and outputs the filtered IF signal as a first signal S 1  or a desired signal. The channel selection filter F may be a band pass filter or a low-pass filter. 
     The IF amplifier A receives the first signal S 1  from the channel selection filter F, amplifies the first signal S 1 , and outputs the amplified first signal S 1  as a second signal S 2 . The first detector D 1  receives the second signal S 2  from the IF amplifier A and outputs a third signal S 3  after it has delayed and detected the second signal S 2 . The second detector D 2  receives the second signal S 2  from the IF amplifier A and outputs a fourth signal S 4  after it has performed pulse count detection or quadrature detection on the second signal S 2 . The switching circuit SW selects one of the third signal S 3  and the fourth signal S 4  and outputs the selected signal as a demodulated signal Sout through an output terminal Tout. 
     The control circuit CON controls the switching circuit SW with a control signal Sc to detect either the third signal S 3  or the fourth signal S 4 . In one embodiment, the control circuit CON controls the switching circuit SW in accordance with an external signal Sin that causes either the signal S 3  or the fourth signal S 4  to be selected. The external signal Sin is generated based on any of the following: interference wave characteristic, input signal frequency offset resistance, or out-of-band detection characteristic shown in  FIG. 2 , and supplied to the control circuit CON, which selects either the third signal S 3  or the fourth signal S 4  in accordance with the external signal Sin. 
     For example, when the input frequency offset resistance and the out-of-band detection characteristic are considered important as determined according to techniques known in the art, the control circuit CON as directed by the external signal Sin controls the switching circuit SW to select the third signal S 3 . On the other hand, when the interference wave characteristic is considered important as determined according to techniques known in the art, the control circuit CON as directed by the external signal Sin controls the switching circuit SW to select the fourth signal S 4 . Therefore, the receiver  100  changes the detection method in accordance with characteristics that are considered to be important. 
     With the receiver of Embodiment 1, the interference wave characteristic, the input signal frequency offset resistance, and the out-of-band detection characteristic can be improved. 
     (Embodiment 2) 
     Embodiment 2 provides an example in which the switching circuit is automatically controlled. 
       FIG. 4  shows an example configuration of a receiver  200  of Embodiment 2. In  FIG. 4 , the symbols of  FIG. 3  are used to identify elements that are common between Embodiment 1 and Embodiment 2. 
     As shown in  FIG. 4 , as compared to Embodiment 1, the receiver  200  is further provided with a first signal level detecting circuit L 1 , a second signal level detecting circuit L 2 , and a comparator COMP. 
     The first signal level detecting circuit L 1  detects a signal level (voltage level) of an IF signal. Then, the first signal level detecting circuit L 1  outputs a first detected signal SV 1  based on the detected signal level (referred to as a first level) of the IF signal. The second signal level detecting circuit L 2  detects a signal level (voltage level) of a first signal S 1 . Then, the second signal level detecting circuit L 2  outputs a second detected signal SV 2  based on the detected signal level (referred to as a second level) of the first signal S 1 . The comparator COMP compares the first detected signal SV 1 , which has been output based on the first level by the first signal level detecting circuit L 1 , with the second detected signal SV 2  output based on the second level by the second signal level detecting circuit L 2 , and outputs a comparison result signal SCOMP based on the comparison result. 
     The control circuit CON receives the comparison result signal SCOMP (instead of the signal Sin as in Embodiment 1) and obtains the comparison result of the first detected signal SV 1  and the second detected signal SV 2 , that is, information on the size relation between the first level and the second level. Then, the control circuit CON controls the switching circuit SW based on this information. In other words, based on the first level, which is the signal level of the IF signal detected by the first signal level detecting circuit L 1  and the second level, which is the signal level of the first signal S 1  detected by the second signal level detecting circuit L 2 , the control circuit CON controls the switching circuit SW to select either the third signal S 3  or the fourth signal S 4 . 
     In one embodiment, if the first level is higher than the second level, the control circuit CON controls the switching circuit SW so that the third signal S 3  is selected. In some embodiments, the control circuit CON controls the switching circuit SW to select the third signal S 3  only if the first level is higher than the second level by more than a preset threshold Vth. 
     In this case, the receiver  200  outputs the third signal S 3 , which has been delayed and detected by the first detector D 1 , as the demodulated signal Sout through the output terminal Tout. 
     Therefore, if the first level is higher than the second level, that is, if the level of interference waves is high, the receiver  200  automatically applies delayed detection to produce an output signal with excellent interference wave characteristics. On the other hand, if the first level is at the second level or lower, the control circuit CON controls the switching circuit SW to select the fourth signal S 4 . In some embodiments, if the first level is higher than the second level by the threshold Vth or lower, the control circuit CON controls the switching circuit SW to select the fourth signal S 4 . Thereafter, the receiver  200  outputs the fourth signal S 4 , which has undergone the pulse count detection or quadrature detection in the second detector D 2 , as the demodulated signal Sout through the output terminal Tout. 
     Therefore, if the first level is at the second level or lower, that is, if the level of interference waves is low, the receiver  200  automatically applies pulse count detection or quadrature detection to produce a signal with an excel lent input frequency offset resistance and out-of-band detection characteristics. 
     The control circuit CON controls the switching circuit based on the comparison result signal SCOMP to select either the third signal S 3  or the fourth signal S 4 . 
     In Embodiment 2, other configurations and functions of the receiver  200  are similar to those of Embodiment 1. According to the receiver of Embodiment 2, the interference wave characteristic, the input signal frequency offset resistance, and the out-of-band detection characteristic can be improved similarly to Embodiment 1. 
     (Embodiment 3) 
     Embodiment 3 provides another example in which the switching circuit is automatically controlled. 
       FIG. 5  shows an example configuration of a receiver  300  of Embodiment 3. In  FIG. 5 , the symbols of  FIG. 3  are used to identify elements that are common between Embodiment 1 and Embodiment 3. 
     As shown in  FIG. 5 , as compared to Embodiment 1, the receiver  300  is further provided with a signal level detecting circuit L. 
     The signal level detecting circuit L detects a signal level (voltage level) of the first signal (desired signal) S 1 . Then, the signal level detecting circuit L outputs a detected signal SV based on the detected signal level of the first signal S 1 . 
     The control circuit CON receives the detected signal SV (instead of the signal Sin as in Embodiment 1) and obtains information on the detected signal level. Next, the control circuit CON controls the switching circuit SW based on this information. In other words, based on the detected signal level of the first signal S 1 , the control circuit CON controls the switching circuit SW to select either the third signal S 3  or the fourth signal S 4 . For example, if the detected signal level is higher than a preset threshold Vth, the control circuit CON controls the switching circuit SW to select the third signal S 3 . Thereafter, the receiver  300  outputs the third signal S 3 , which has been delayed and detected by the first detector D 1 , as a demodulated signal Sout through the output terminal Tout. 
     Therefore, if the first level is higher than the threshold Vth, that is, the signal level of the desired signal is higher than the threshold Vth, the receiver  300  automatically applies delayed detection to produce an output signal with excellent interference wave characteristics. 
     On the other hand, if the detected signal level is equal to the threshold Vth or lower, the control circuit CON controls the switching circuit SW to select the fourth signal S 4 . Thereafter, the receiver  200  outputs the fourth signal S 4 , which has undergone the pulse count detection or quadrature detection in the second detector D 2 , as the demodulated signal Sout through the output terminal Tout. 
     Therefore, if the detected signal level is at the threshold Vth or lower, the receiver  300  automatically applies the pulse count detection or quadrature detection to produce an output signal with excellent input frequency offset resistance and out-of-band detection characteristics. 
     According to the receiver of Embodiment 3, the interference wave characteristic, the input signal frequency offset resistance, and the out-of-band detection characteristic can be improved similarly to Embodiment 1. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.