Radio receiver and intermediate frequency selection method

Patent metadata

Field	Value
Publication number	US-10263654-B2
Application number	US-201815889945-A
Country	US
Kind code	B2
Filing date	Feb 6, 2018
Priority date	Apr 5, 2017
Publication date	Apr 16, 2019
Grant date	Apr 16, 2019

Abstract

A radio frequency signal can be received in an intermediate frequency mode suitable for radio wave reception conditions. An oscillator has a variable oscillation frequency. A quadrature demodulator includes a frequency mixer and generates an intermediate frequency signal having an intermediate frequency lower than the frequency of the radio frequency signal. An ADC receives the intermediate frequency signal passed through an analog filter and converts the received intermediate frequency signal to a digital signal. A channel selection signal processing section generates a demodulated signal from the intermediate frequency signal converted to the digital signal. A mode control section switches the operating mode of the quadrature demodulator between a zero intermediate frequency mode and a low intermediate frequency mode in accordance with the radio wave reception conditions.

First claim

What is claimed is:

1. A radio receiver, comprising:
an oscillator that has a variable oscillation frequency;
a quadrature demodulator that includes a frequency mixer and generates an intermediate frequency signal having an intermediate frequency lower than a frequency of a radio frequency signal, the frequency mixer mixing the radio frequency signal with an oscillation signal outputted from the oscillator;
an analog filter that bandlimits the intermediate frequency signal;
an analog-to-digital converter that receives an intermediate frequency signal inputted through the analog filter and converts the received intermediate frequency signal to a digital signal;
a received signal processing section that generates a demodulated signal from the intermediate frequency signal converted to the digital signal; and
a mode control section that switches the operating mode of the quadrature demodulator between a zero intermediate frequency mode and a low intermediate frequency mode in accordance with radio wave reception conditions, the zero intermediate frequency mode providing the intermediate frequency signal having a zero intermediate frequency, the low intermediate frequency mode providing the intermediate frequency signal having a low intermediate frequency higher than the zero intermediate frequency,
wherein, in the zero intermediate frequency mode, the analog filter passes frequency components of the intermediate frequency signal that are not higher than a predetermined frequency, and in the low intermediate frequency mode, the analog filter passes signal components of the intermediate frequency signal that have a frequency band including a frequency of the intermediate frequency signal.

2. The radio receiver according to claim 1 , wherein the mode control section selects the zero intermediate frequency mode or the low intermediate frequency mode in accordance with a signal level of a selected wave frequency band including the demodulated signal and with a signal level of a frequency band other than the selected wave frequency band.

3. The radio receiver according to claim 2 , wherein the mode control section determines whether the signal level of the selected wave frequency band is lower than a first threshold value, and
wherein, if the signal level of the selected wave frequency band is determined to be not lower than the first threshold value, the mode control section selects the zero intermediate frequency mode.

4. The radio receiver according to claim 3 , wherein, if the signal level of the selected wave frequency band is determined to be not lower than the first threshold value, the mode control section further determines whether a ratio between the signal level of the selected wave frequency band and the signal level of an upper adjacent frequency band is greater than a second threshold value, the upper adjacent frequency band being higher than and adjacent to the selected wave frequency band of the intermediate frequency signal,
wherein, if the ratio between the signal level of the selected wave frequency band and the signal level of the upper adjacent frequency band is determined to be greater than the second threshold value, the mode control section selects the zero intermediate frequency mode, and
wherein, if the ratio between the signal level of the selected wave frequency band and the signal level of the upper adjacent frequency band is determined to be not greater than the second threshold value, the mode control section selects the low intermediate frequency mode.

5. The radio receiver according to claim 3 , wherein, if the signal level of the selected wave frequency band is determined to be lower than the first threshold value, the mode control section further determines whether a ratio between the signal level of the selected wave frequency band and the signal level of a lower adjacent frequency band is greater than a third threshold value, the lower adjacent frequency band being lower than and adjacent to the selected wave frequency band of the intermediate frequency signal,
wherein, if the ratio between the signal level of the selected wave frequency band and the signal level of the lower adjacent frequency band is determined to be greater than the third threshold value, the mode control section selects the low intermediate frequency mode, and
wherein, if the ratio between the signal level of the selected wave frequency band and the signal level of the lower adjacent frequency band is determined to be not greater than the third threshold value, the mode control section selects the zero intermediate frequency mode.

6. The radio receiver according to claim 1 , wherein the received signal processing section includes:
a zero intermediate frequency signal processing section that generates a demodulated signal from an intermediate frequency signal having the zero intermediate frequency, the intermediate frequency signal being converted to a digital signal by the analog-to-digital converter; and
a low intermediate frequency signal processing section that generates a demodulated signal from an intermediate frequency signal having the low intermediate frequency, the intermediate frequency signal being converted to a digital signal by the analog-to-digital converter.

7. The radio receiver according to claim 6 , wherein the zero intermediate frequency signal processing section includes:
a first low-pass filter that passes frequency components not higher than the frequency of the selected wave frequency band including the demodulated signal of the intermediate frequency signal, and generates the demodulated signal;
a complex multiplier that shifts a frequency spectrum of the intermediate frequency signal to a lower frequency side or a higher frequency side by the predetermined frequency; and
a second low-pass filter that passes frequency components of the intermediate frequency signal that are subjected to frequency spectrum shift by the complex multiplier and not higher than the predetermined frequency.

8. The radio receiver according to claim 7 , wherein, in the zero intermediate frequency mode, the mode control section selects the zero intermediate frequency mode or the low intermediate frequency mode in accordance with a signal level of the intermediate frequency signal, a signal level of the demodulated signal outputted from the first low-pass filter, and a signal level of a signal outputted from the second low-pass filter.

9. The radio receiver according to claim 6 , wherein the low intermediate frequency signal processing section includes:
a complex multiplier that shifts a frequency spectrum of the intermediate frequency signal to a lower frequency side by the intermediate frequency;
a third low-pass filter that passes frequency components not higher than the frequency of the selected wave frequency band including the demodulated signal of the intermediate frequency signal that subjected to frequency spectrum shift by the complex multiplier, and generates the demodulated signal, and generates the demodulated signal; and
a band-pass filter that attenuates frequency components outside a frequency band different from the selected wave frequency band of the intermediate frequency signal, and passes frequency components in the frequency band different from the selected wave frequency band of the intermediate frequency signal.

10. The radio receiver according to claim 9 , wherein, in the zero intermediate frequency mode, the mode control section selects the zero intermediate frequency mode or the low intermediate frequency mode in accordance with a signal level of the intermediate frequency signal, a signal level of the demodulated signal outputted from the third low-pass filter, and a signal level

Assignees

• Renesas Electronics Corp

Inventors

• Matsui Naohiro
• Okada Hiroyuki
• Kim Kichung
• Hirota Tomoaki
• Sato Takahiro
• Inagawa Osamu

Classifications

• H04W4/80

  Services using short range communication, e.g. near-field communication [NFC], radio-frequency identification [RFID] or low energy communication · CPC title

• H04B1/0007

  wherein the AD/DA conversion occurs at radiofrequency or intermediate frequency stage · CPC title

• H04B1/1638 Primary

  Special circuits to enhance selectivity of receivers not otherwise provided for (resonant circuits H03H) · CPC title

• H04B1/16 Primary

  Circuits · CPC title

• H04B1/30

  for homodyne or synchrodyne receivers (demodulator circuits H03D1/22) · CPC title