CN111200469A

CN111200469A - FM channel detection circuit and related method

Info

Publication number: CN111200469A
Application number: CN201811373925.5A
Authority: CN
Inventors: 倪成武; 苏裕哲
Original assignee: MediaTek Inc
Current assignee: MediaTek Inc
Priority date: 2018-11-19
Filing date: 2018-11-19
Publication date: 2020-05-26

Abstract

The invention discloses a frequency modulation channel detection circuit, which comprises a demodulation circuit, a direct current component acquisition circuit and a judgment circuit. In operation of the FM channel detection circuit, the demodulation circuit is configured to receive a plurality of input signals to generate a plurality of frequency components, respectively, wherein the plurality of input signals are generated by a tuner using a plurality of oscillation signals to mix a received signal, respectively; the direct current component acquisition circuit is used for acquiring a direct current component in the frequency components; and the judging circuit is used for judging the channel frequency corresponding to at least one frequency modulation channel according to the acquired direct current components.

Description

Frequency modulation channel detection circuit and related method

Technical Field

The present invention relates to a frequency modulation channel, and more particularly, to a frequency modulation channel detection circuit and related method.

Background

In current Frequency Modulation (FM) channel detection, a tuner (tuner) is used to scan channels with different frequencies, and the center frequencies of multiple FM channels are determined according to the signal strength (e.g., amplitude) of the scanned channels. However, such channel detection is easily interfered by noise and is misjudged, which causes the user to be confused when listening to the fm channel broadcast.

Disclosure of Invention

Therefore, an objective of the present invention is to provide a frequency modulation channel detection circuit and a related method, which acquire a dc frequency component in a signal through a simple circuit architecture to accurately determine a frequency corresponding to a frequency modulation channel, so as to solve the problem of erroneous determination caused by using signal strength or amplitude as a determination reference in the prior art.

In one embodiment of the present invention, a frequency modulation channel detection circuit is disclosed, which comprises a demodulation circuit, a dc component obtaining circuit and a determining circuit. In operation of the FM channel detection circuit, the demodulation circuit is configured to receive a plurality of input signals to generate a plurality of frequency components, respectively, wherein the plurality of input signals are generated by a tuner using a plurality of oscillation signals to mix a received signal, respectively; the direct current component acquisition circuit is used for acquiring a direct current component in the frequency components; and the judging circuit is used for judging the channel frequency corresponding to at least one frequency modulation channel according to the acquired direct current components.

In another embodiment of the present invention, a method for detecting a frequency modulated channel is disclosed, which comprises the following steps: receiving a plurality of input signals to respectively generate a plurality of frequency components, wherein the plurality of input signals are generated by a tuner respectively mixing a received signal by using a plurality of oscillation signals; acquiring a direct current component in the plurality of frequency components; and judging the channel frequency corresponding to at least one frequency modulation channel according to the acquired direct current components.

Drawings

Fig. 1 is a block diagram of a receiver according to an embodiment of the invention.

Fig. 2 is a block diagram of a frequency modulated channel detection circuit according to an embodiment of the present invention.

Fig. 3 is a schematic diagram showing the dc component obtained by the dc component obtaining circuit when the tuner adopts different frequency values without noise interference.

Fig. 4 is a schematic diagram showing the dc component obtained by the dc component obtaining circuit when the tuner adopts different frequency values under the noise interference.

Fig. 5 is a flowchart of a frequency modulation channel detection method according to an embodiment of the invention.

Reference numerals

100 FM channel detection circuit

102 tuner

104 filter

106 mixer

110 demodulation circuit

112 low pass filter

120 DC component acquisition circuit

122 high pass filter

124 calculation circuit

130 judging circuit

500 to 506 steps

OS1 and OS2 oscillation signals

Vin input signal

Detailed Description

Fig. 1 is a block diagram of a receiver according to an embodiment of the invention. As shown in fig. 1, the receiver includes a tuner 102, a filter 104, a mixer 106, and a frequency modulation channel detection circuit 100. In the present embodiment, the receiver is applied to a television.

The receiver shown in fig. 1 is swept when the television is turned on to determine a center frequency of at least one fm channel for a user to subsequently listen to the fm channel. Specifically, in the operation of the receiver shown in fig. 1, the tuner 102 first receives a received signal from an antenna, and performs a mixing operation on the received signal by using a plurality of oscillation signals OS1 with different frequencies to generate an intermediate frequency signal, and the intermediate frequency signal is processed by the filter 104 and then performs a mixing operation by using the oscillation signal OS2 through the mixer 106 to generate an input signal Vin to the fm channel detection circuit 100. In a preferred embodiment, the tuner 102 sequentially uses the oscillation signals OS1 with increasing or decreasing frequencies to perform the mixing operation on the received signals, so that the frequency-modulated channel detection circuit 100 can be regarded as sequentially receiving the input signals corresponding to the oscillation signals OS1 with increasing or decreasing frequencies. The fm channel detection circuit 100 includes a demodulation circuit 110, a dc component acquisition circuit 120, and a determination circuit 130. In operation of the fm channel detection circuit 100, the demodulation circuit 110 receives the plurality of input signals sequentially for demodulation to generate a plurality of frequency components, the dc component obtaining circuit 120 obtains the dc component of the plurality of frequency components, and the determining circuit 130 determines a frequency corresponding to at least one fm channel according to the obtained plurality of dc components.

In detail, referring to the block diagram of the frequency modulation channel detection circuit 100 shown in fig. 2, wherein the frequency modulation channel detection circuit 100 further includes a low pass filter 112, the dc component obtaining circuit 120 includes a high pass filter 122 and a calculating circuit 124, and in the embodiment, the calculating circuit 124 is a subtracting circuit. In the embodiment shown in fig. 1 and 2, assuming that the received signal received by the tuner 102 currently has a frequency modulation signal as follows, a × (2 π ft + φ (t)) + n (t), where "f" is the center frequency of the frequency modulation signal, φ (t) is the phase information actually carrying the content of the frequency modulation channel, and n (t) is noise, the input signal Vin received by the demodulation circuit 110 is a × (a τ) cos (2 π Δ ft + φ (t)) + n (t), where Δ f is the difference between the frequency of the oscillation signal OS1 used by the tuner 102 and "f". The demodulation circuit 110 performs demodulation operations on the input signals to obtain frequency components of the input signals Vin, i.e. frequency components of the input signals Vin

Then, the low pass filter 112 performs low pass filtering on the frequency components of the plurality of input signals to filter out the noise component n' (t) therein. The high-pass filter 122 then performs a high-pass filtering operation on the frequency components of the plurality of input signals to generate a plurality of filtered frequency componentsFrequency component

Then, the calculating circuit 124 calculates the difference between the frequency components of the input signals Vin and the filtered frequency components to generate the dc component 2 pi Δ f of the frequency components.

Fig. 3 is a schematic diagram showing the dc component 2 pi Δ f obtained by the dc component obtaining circuit when the tuner 102 adopts different frequency values f _ OS1 without noise interference. As shown in fig. 3, the dc component 2 pi Δ f of the plurality of frequency components reflects the difference between the frequency of the oscillating signal OS1 used by the tuner 102 and the frequency of the frequency modulation signal (e.g., "f" in the above formula), i.e., when the frequency of the oscillating signal OS1 used by the tuner 102 is exactly equal to the frequency of the frequency modulation signal, the dc component thereof is equal to 0. Therefore, the determining circuit 130 may find at least one specific dc component having a relatively small value among the dc components, and determine the frequency corresponding to the frequency modulation channel according to the frequency of the oscillating signal OS1 used by the tuner 102 corresponding to the at least one specific dc component. Taking fig. 3 as an example, since the frequencies f1, f2 and f3 of the oscillation signal OS1 have relatively small dc components 2 pi Δ f, the determining circuit 130 determines that f1, f2 and f3 correspond to the center frequencies of three fm channels, and the subsequent tuner 102 can process the received signal by using the oscillation signal OS1 with three frequencies f1, f2 and f3, respectively, so as to obtain the content of the fm channel.

In one embodiment, the frequency of the oscillating signal OS1 is gradually increased or decreased at a frequency interval less than 200KHz to perform the frequency sweep, for example, at 50KHz intervals to gradually increase the frequency of the oscillating signal OS1 in a preferred embodiment, in consideration of the efficiency of the tuner 102 performing the frequency sweep. Therefore, the determining circuit 130 may find at least one specific dc component having a relatively small value among the plurality of dc components, and directly use the frequency of the oscillation signal OS1 used by the tuner 102 corresponding to the at least one specific dc component as the center frequency corresponding to the frequency modulation channel. Note that, when there is noise interference, even if the frequency of the oscillation signal OS1 used by the tuner 102 is exactly equal to the frequency of the frequency modulation signal, the dc component 2 pi Δ f obtained by the dc component obtaining circuit is not 0, but still has a relatively small value, where the relatively small value refers to the minimum value of the dc components corresponding to the oscillation signals OS1 (e.g., 5 oscillation signals that are continuously increased).

As described above, the frequency modulation channel detection circuit 100 of the present embodiment determines the center frequency of the frequency modulation channel according to the dc component 2 pi Δ f of the input signal Vin, rather than the strength (e.g., amplitude) of the reference signal, so that the influence of noise can be avoided in the determination and a more accurate determination result can be obtained.

In one embodiment, since the pitch of the frequency modulation channels is generally 200KHz, if the frequency difference between the oscillation signals OS1 used by the tuners 102 corresponding to two specific dc components with relatively small values among the plurality of dc components 2 pi Δ f is smaller than a threshold value, for example, the frequency difference is smaller than 100KHz, the determining circuit 130 may determine that the frequency of the oscillation signal OS1 used by the tuners 102 corresponding to the two specific dc components is not the frequency corresponding to the at least one frequency modulation channel. Taking fig. 4 as an example for illustration, assuming that the difference between the frequencies f4 and f5 corresponding to the dc component 2 pi Δ f with a relatively small value is smaller than 100KHz, the determining circuit 130 can determine that the relatively low point of the frequencies f4 and f5 is affected by noise or other invalid signals, so that the frequencies f4 and f5 are not determined as the center frequency of the fm channel.

Fig. 5 is a flowchart illustrating a method for detecting a channel in a frequency band according to an embodiment of the invention. The process flow is as follows with reference to the disclosure of the above embodiments.

Step 500: the process begins.

Step 502: the method comprises the steps of receiving a plurality of input signals to respectively generate a plurality of frequency components, wherein the input signals are generated by a tuner through mixing a received signal by using a plurality of oscillation signals.

Step 504: a DC component among the plurality of frequency components is obtained.

Step 506: and judging the channel frequency corresponding to at least one frequency modulation channel according to the acquired direct current components.

Briefly summarized, in the frequency-modulated channel detection circuit and method of the present invention, a dc component of a plurality of frequency components of an input signal is obtained, at least one specific dc component having a relatively small value among the plurality of dc components is found, and a frequency of an oscillation signal used by a tuner corresponding to the at least one specific dc component is used as a center frequency corresponding to at least one frequency-modulated channel. Therefore, the present embodiment can avoid the influence of noise in the determination and have a more accurate determination result.

The above-mentioned embodiments are merely preferred embodiments of the present invention, and all equivalent changes and modifications made by the claims of the present invention should be covered by the scope of the present invention.

Claims

1. An FM channel detection circuit, comprising:

a demodulation circuit for receiving a plurality of input signals to respectively generate a plurality of frequency components, wherein the plurality of input signals are respectively generated by mixing a received signal with a plurality of oscillating signals by a tuner;

a DC component acquisition circuit, coupled to the demodulation circuit, for acquiring the DC component in the plurality of frequency components; and

A judging circuit, coupled to the DC component obtaining circuit, is used for judging the channel frequency corresponding to at least one FM channel according to the obtained plurality of DC components.

2 . The FM channel detection circuit of claim 1 , wherein the oscillating signals have increasing or decreasing frequencies in sequence. 3 .

3. The FM channel detection circuit as claimed in claim 2, wherein the frequency interval of the oscillating signals is less than 200KHz.

4 . The FM channel detection circuit of claim 1 , wherein the DC components are respectively corresponding to frequency differences between the oscillating signals and the received signal. 5 .

5 . The FM channel detection circuit of claim 4 , wherein the determination circuit searches for a specific DC component with a relatively small value among the plurality of DC components, and determines the corresponding DC component according to the specific DC component. 6 . The frequency of the oscillating signal used by the tuner to determine the channel frequency corresponding to the at least one FM channel.

6 . The FM channel detection circuit of claim 5 , wherein the judging circuit uses the frequency of the oscillation signal used by the tuner corresponding to the specific DC component as one of the at least one FM channel. 7 . one of the corresponding center frequencies.

7 . The FM channel detection circuit as claimed in claim 5 , wherein if two specific DC components with relatively minimum values among the plurality of DC components correspond to the frequencies of the oscillating signal used by the tuner. 8 . When the difference is smaller than a threshold, the determination circuit determines that the frequencies of the oscillation signals used by the tuner corresponding to the two specific DC components are not the channel frequencies corresponding to the at least one FM channel.

8. The FM channel detection circuit of claim 4, wherein the DC component acquisition circuit comprises:

a high-pass filter for performing high-pass filtering on the plurality of frequency components to filter out DC components in the plurality of frequency components, so as to generate a plurality of filtered frequency components respectively; and

A calculation circuit, coupled to the high-pass filter and the demodulation circuit, is used for calculating the plurality of frequency components and the difference between the plurality of filtered frequency components, respectively, to generate the plurality of DC components.

9. The FM channel detection circuit of claim 8, further comprising:

A low-pass filter, coupled between the demodulation circuit and the DC component acquisition circuit, is used for performing a low-pass filtering operation on the plurality of frequency components to filter out noise components in the plurality of frequency components.

10. The FM channel detection circuit as claimed in claim 1, wherein the FM channel detection circuit is arranged in a television.

11. An FM channel detection method, comprising:

receiving a plurality of input signals to respectively generate a plurality of frequency components, wherein the plurality of input signals are respectively generated by mixing a received signal with a plurality of oscillating signals by a tuner;

obtaining a direct current component of the plurality of frequency components; and

The channel frequency corresponding to at least one FM channel is determined according to the obtained multiple DC components.

12 . The FM channel detection method of claim 11 , wherein the oscillating signals have increasing or decreasing frequencies in sequence. 13 .

13. The method of claim 12, wherein the frequency interval of the oscillating signals is less than 200KHz.

14 . The FM channel detection method of claim 11 , wherein the DC components are respectively corresponding to frequency differences between the oscillating signals and the received signal. 15 .

15. The FM channel detection method of claim 14, wherein the step of judging the channel frequency corresponding to the at least one FM channel according to the plurality of acquired DC components comprises:

Find a specific DC component with a relatively small value among the plurality of DC components, and determine the corresponding frequency of the at least one FM channel according to the frequency of the oscillation signal used by the tuner corresponding to the specific DC component channel frequency.

16 . The method of claim 15 , wherein the frequency of the oscillating signal used by the tuner corresponding to the specific DC component is used to determine the frequency of the at least one FM channel corresponding to 16 . 16 . The steps for channel frequency include:

The frequency of the oscillation signal used by the tuner corresponding to the specific DC component is taken as the center frequency corresponding to one of the at least one FM channel.

17. The FM channel detection method of claim 15, wherein one of the at least one FM channel is determined according to the frequency of the oscillating signal used by the tuner corresponding to the specific DC component The steps of a corresponding channel frequency include:

If the frequency difference of the oscillation signal used by the tuner corresponding to two specific DC components with relatively small values among the plurality of DC components is smaller than a critical value, then determine the corresponding frequency of the two specific DC components. The frequencies of the oscillating signals used by the tuner are not the channel frequencies corresponding to the at least one FM channel.

18. The FM channel detection method of claim 14, wherein the step of acquiring the DC component of the plurality of frequency components comprises:

performing high-pass filtering on the plurality of frequency components to filter out DC components in the plurality of frequency components to generate a plurality of filtered frequency components respectively; and

Differences between the plurality of frequency components and the plurality of filtered frequency components are calculated respectively to generate the plurality of DC components.

19. The FM channel detection method of claim 18, further comprising:

A low-pass filtering operation is performed on the plurality of frequency components to filter out noise components in the plurality of frequency components.

20. The FM channel detection method of claim 11, wherein the method is applied in a TV.