Receiver and transceiver
Provided is a receiver capable of receiving an FM radio wave and an AM radio wave in a same frequency band (same channel). The receiver includes: a detection voltage output unit that outputs FM detection voltage obtained by detecting the FM radio wave when the FM detection voltage is determined to be at or above a first threshold; and a threshold change unit that sets the first threshold to a first value when a noise amount included in the FM detection voltage before threshold determination by the detection voltage output unit is larger than a predetermined value, and that sets the first threshold to a second value smaller than the first value when the noise amount is smaller than the predetermined value.
1 . A receiver capable of receiving an FM radio wave and an AM radio wave in a same frequency band, the receiver comprising:
an FM detector configured to generate an FM detection voltage from a received FM radio wave;
an AM detector configured to generate an AM detection voltage from a received AM radio wave;
a switch configured to output either one of the FM detection voltage or the AM detection voltage;
an A/D converter configured to sample the FM detection voltage at predetermined time intervals;
a comparator configured to determine whether a sampled FM detection voltage is at or above a first threshold;
a threshold change circuit configured to:
set the first threshold to a first value when a noise amount included in the FM detection voltage, the noise amount being derived from sampled FM detection voltages obtained during a predetermined time period before the determination by the comparator, is larger than a predetermined value; and
set the first threshold to a second value smaller than the first value when the noise amount is smaller than the predetermined value; and
a switch judgement circuit configured to control the switch to output the FM detection voltage when the comparator determines that the sampled FM detection voltage is at or above the first threshold.
2 . The receiver according to claim 1 , further comprising:
an FM squelch circuit configured to determine whether the noise amount included in the FM detection voltage is at or above a second threshold; wherein
when the FM squelch circuit determines that the noise amount is at or above the second threshold, the switch judgement circuit controls the switch to output the AM detection voltage generated by the AM detector.
3 . The receiver according to claim 1 , further comprising:
a memory configured to successively store the FM detection voltage every predetermined time interval;
a calculator configured to calculate an average value of a plurality of the sampled FM detection voltages obtained during a predetermined time period before the determination by the comparator, wherein
the threshold change circuit is configured to:
set the first threshold to the first value when the average value is larger than a predetermined value, and set the first threshold to the second value smaller than the first value when the average value is smaller than the predetermined value.
4 . A transceiver comprising:
the receiver according to claim 1 , including an FM squelch circuit configured to determine whether a noise amount included in the FM detection voltage is at or above a second threshold; and
a transmitter configured to: perform FM transmission when the comparator of the receiver determines that the sampled FM detection voltage is at or above the first threshold; and perform AM transmission when the FM squelch circuit determines that the noise amount is at or above the second threshold.
5 . The transceiver according to claim 4 , further comprising a transmitter that performs AM transmission when a momentary switch is pushed once and the pushed state is maintained, and that performs FM transmission when the momentary switch is pushed twice and the pushed state is maintained.
6 . The receiver according to claim 2 , further comprising:
a memory configured to successively store the FM detection voltage every predetermined time interval;
a calculator configured to calculate an average value of a plurality of the sampled FM detection voltages obtained during a predetermined time period before the determination by the comparator, wherein
the threshold change circuit is configured to:
set the first threshold to the first value when the average value is larger than a predetermined value, and set the first threshold to the second value smaller than the first value when the average value is smaller than the predetermined value.
7 . A transceiver comprising:
the receiver according to claim 2 , including the FM squelch circuit configured to determine whether the noise amount included in the FM detection voltage is at or above the second threshold; and
a transmitter configured to: perform FM transmission when the comparator of the receiver determines that the sampled FM detection voltage is at or above the first threshold; and perform AM transmission when the FM squelch circuit determines that the noise amount is at or above the second threshold.
8 . The transceiver according to claim 7 , further comprising a transmitter that performs AM transmission when a momentary switch is pushed once and the pushed state is maintained, and that performs FM transmission when the momentary switch is pushed twice and the pushed state is maintained.
9 . A transceiver comprising:
the receiver according to claim 3 , including an FM squelch circuit configured to determine whether a noise amount included in the FM detection voltage is at or above a second threshold; and
a transmitter configured to: perform FM transmission when the comparator of the receiver determines that the sampled FM detection voltage is at or above the first threshold; and perform AM transmission when the FM squelch circuit determines that the noise amount is at or above the second threshold.
10 . The transceiver according to claim 9 , further comprising a transmitter that performs AM transmission when a momentary switch is pushed once and the pushed state is maintained, and that performs FM transmission when the momentary switch is pushed twice and the pushed state is maintained.