JP2009147500A - Radio receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a high-cut function of a radio receiver in an electric field area in which high-band noise is comparatively small while powerfully removing the high-band noise in a weak electric field. <P>SOLUTION: A received electric field intensity discrimination circuit 84 discriminates which area includes received electric field intensity, an area more than an intermediate electric field, a first weak electric field area adjacent to the intermediate electric field area, or a second weak electric field area lower than the first electric field area on the basis of a received electric field intensity signal output from an S meter circuit to control a mixing ratio of an output from a bypass circuit 114 and an output from an RC filter 112 in a mixer 110 in an HCC filter circuit 94. In an area of lower electric field intensity, much output of the RC filter 112 is mixed to remove a high frequency component more powerfully from a detected modulation signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a radio receiver having a high-cut circuit that removes high-frequency noise when a received signal is a weak electric field.

  In a radio receiver such as an FM radio receiver, when the received electric field strength is a weak electric field, the high frequency component of noise included in the demodulated signal obtained by detection increases compared to the medium electric field or higher, and the reproduced sound is harsh. Sound quality. For example, an FM radio receiver uses a method of detecting an FM signal after making it a rectangular wave with a limiter amplifier, but a weak electric field signal is not converted into a rectangular wave, resulting in pulse noise, This can be weak electric field noise.

  In order to remove the weak electric field noise, high cut control (HCC) is performed. In order to realize the HCC function, an HCC filter circuit having a low pass filter (LPF) function capable of removing weak electric field noise from a demodulated signal, and selectively causing the HCC filter circuit to function in a weak electric field And a reception electric field strength determination circuit.

FIG. 5 is a circuit diagram of the HCC filter circuit 2 and the received electric field strength discriminating circuit 4 for realizing the conventional HCC function. The demodulated signal is input to the HCC filter circuit 2 as the input signal _SH-IN . The HCC filter circuit 2 includes a mixer 6, an RC filter 8 that constitutes an LPF, and a bypass circuit 10 that bypasses the RC filter 8 and inputs _SH-IN directly to the mixer 6. Is done. Mixer 6, and _{S H-IN} from the bypass circuit 10 is inputted and _{S H-IN} passed through an RC filter 8, respectively, in response to the signal _{S HCC} from the reception field strength judgment circuit 4, mixtures thereof The output signal _SH-OUT is generated by changing the ratio. The received electric field strength discriminating circuit 4 has a comparator 12 and compares the received electric field strength signal S _M-DC from the S meter circuit (not shown) with the reference voltage V _ref1 to determine whether the weak electric field state is higher than the middle electric field. Determine. When S _M-DC ≧ V _ref1 , that is, when the electric field is equal to or higher than the medium electric field, the reception electric field strength determination circuit 4 controls the mixer 6 so that _{SH -IN} from the bypass circuit 10 becomes _SH-OUT . On the other hand, when S _M-DC <V _ref1 , that is, in the weak electric field state, the reception electric field strength determination circuit 4 controls the mixer 6 so that the output of the RC filter 8 becomes _SH-OUT . The RC filter 8 is designed such that a high frequency band component of about 10 kHz can be suitably removed in a weak electric field state.
JP 2004-040169 A

The above-described HCC filter circuit 2 selectively functions as an LPF in a weak electric field state. However, the characteristics of the LPF are constant in the range of the received electric field strength that satisfies S _M-DC <V _ref1 . For this reason, for example, the removal of high frequency components in the weak electric field region close to the middle electric field region is conservative, while the removal of high frequency components is strong in regions where weak electric field noise increases and the received electric field strength is weaker. There was a problem that it was not easy to satisfy the demand to do. That is, if the characteristics of the RC filter 8 are set so that the removal of high frequency components is conservative in a portion close to the middle electric field region, the weak electric field noise cannot be sufficiently removed, and conversely, the weak electric field noise should be sufficiently removed. Then, there is a problem that the high frequency characteristics of the reproduced sound in the portion close to the middle electric field region are greatly deteriorated compared with the characteristics at the middle electric field or higher.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a radio receiver in which a suitable HCC function is realized over a medium electric field or more and a weak electric field state.

  A radio receiver according to the present invention includes a demodulating circuit that demodulates a received signal and generates a demodulated signal, an intensity signal generating circuit that generates an electric field strength signal corresponding to the received electric field strength based on the received signal, Based on the electric field strength signal, the received electric field strength is a region above the middle electric field that is greater than or equal to a predetermined first threshold, a first weak electric field region that is less than the first threshold and greater than or equal to the predetermined second threshold, and the second A received electric field strength discriminating circuit for discriminating which one of the second weak electric field regions is less than the threshold, and a high frequency which operates in the first weak electric field region and the second weak electric field region and is included in the demodulated signal A high-cut circuit for attenuating a noise component in a region, and the high-cut circuit changes an attenuation characteristic according to a determination result by the reception electric field strength determination circuit, and sets the attenuation in a predetermined target high-frequency region. First weak electric It is for larger at the second weak electric field area than.

  According to the present invention, the attenuation characteristics of high frequency components can be switched to a plurality of stages in a weak electric field state. Thereby, in the first weak electric field region close to the middle electric field region, the removal of the high frequency component is conservative, while the second weak electric field region in which the received electric field intensity is lower than that of the first weak electric field region and the weak electric field noise can be increased. In this case, it is possible to enhance the removal of high-frequency components and to suitably remove weak electric field noise, and a suitable HCC function can be realized over the intermediate electric field and the entire weak electric field state.

  Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

  FIG. 1 is a schematic block diagram of an FM radio receiver 50 according to the embodiment. The main part of the FM radio receiver 50 is formed on a common circuit board while being integrated into an integrated circuit (IC), and is basically configured as an integral module. For example, the module is incorporated as a part in an in-vehicle audio device of an automobile.

  The FM radio receiver 50 includes an antenna 52, an RF amplifier 54, a first local oscillation circuit 56, a first mixing circuit 58, BPFs 60 and 64, an amplifier 62, a second local oscillation circuit 66, a second mixing circuit 68, an IFBPF 70, a limiter. An amplifier 72, a detection circuit 74, a stereo demodulator 76, an S meter circuit 82, and a received electric field strength determination circuit 84 are configured.

The RF signal S _RF received by the antenna 52 is amplified by the RF amplifier 54 and then input to the first mixing circuit 58. The first mixing circuit 58 mixes the input RF signal S _RF with the first local oscillation signal S _LO1 input from the first local oscillation circuit 56 to generate a first intermediate signal S _IF1 . Frequency of S _{LO1 f LO1 is} such that the signal of interest received station of the frequency _{f R} included in the _{S RF} is converted to a first intermediate frequency _{f IF1} predetermined by the frequency conversion to _{S IF1} by the first mixing circuit 58 Adjusted to The first intermediate frequency _{f IF1} is set to, for example, 10.7 MHz.

S _IF1 is input to the second mixing circuit 68 through the BPF 60, the amplifier 62 and the BPF 64. The second mixing circuit 68 mixes the input first intermediate signal S _IF1 with the second local oscillation signal S _LO2 input from the second local oscillation circuit 66, and the second intermediate frequency f _IF2 has a second intermediate frequency f _IF2 . A signal _SIF2 is generated. The frequency f _{LO2 of} S _LO2 is set to (f _IF1 −f _IF2 ), and the target reception signal of the frequency f _IF1 included in S _IF1 is converted into the frequency f _IF2 in the second mixing circuit 68. The second intermediate frequency f _IF2 is set to 450 kHz, for example.

S _IF2 is input to the detection circuit 74 via the IFBPF 70 and the limiter amplifier 72. The detection circuit 74 is an FM detection circuit, and is composed of, for example, a quadrature detection circuit. The detection circuit 74 performs FM detection on S _IF2 input from the limiter amplifier 72 and extracts a detection signal _SDET that is a composite signal.

This detection signal _SDET is input to the stereo demodulator 76. Stereo demodulation unit 76, at the time of a stereo broadcast, (L + R) signal _S L + R, the (L-R) signal _{S L-R} is a composite signal which is superimposed, and outputs to separate the L signal _{S L} and R signals _{S R} be able to. Stereo demodulation unit 76, a main demodulator circuit 90, the sub-demodulation circuit 92, HCC filter circuit 94, configured to include a matrix circuit 96, a main demodulator circuit 90 _extracts from the _{S DET} the (L + R) signal _{S L + R,} the sub demodulation circuit 92 extracts from the _{S DET} the (L-R) signal _{S L-R.} The (L + R) signal S _{L + R} is input to the matrix circuit 96 via the HCC filter circuit 94. Matrix circuit 96 is inputted to _{S L + R} from HCC filter circuit 94 is input to _{S L-R} from the sub-demodulation circuit 92 separates the L signal _{S L} and R signal _{S R} from the two signals by matrix processing . These S _L and S _R are output to an output circuit comprising a speaker or the like (not shown).

The S meter circuit 82 generates a received electric field strength signal S _M-DC based on S _IF1 . The received electric field strength determination circuit 84 compares the S _M-DC input from the S meter circuit 82 with two threshold voltages V _ref1 and V _ref2 set in advance, and generates a control signal for the HCC filter circuit 94.

FIG. 2 is a circuit diagram showing a schematic configuration of the HCC filter circuit 94 and the received electric field strength discriminating circuit 84. S _{L + R} is input from the main demodulation circuit 90 to the HCC filter circuit 94 as the input signal _SH-IN . The HCC filter circuit 94 includes a mixer 110, an RC filter 112 that constitutes an LPF, a bypass circuit 114 that bypasses the RC filter 112 and inputs _SH-IN to the mixer 110 basically with the original frequency characteristics, And outputs a signal _SH-OUT . Incidentally, the resistor inserted in series with the bypass circuit 114 serves to maintain the base bias voltage of the input transistor of the mixer 110 at an appropriate value.

The reception electric field strength determination circuit 84 includes comparators 130 and 132 and an addition circuit 134. The comparators 130 and 132 respectively compare the received electric field strength signal S _M-DC from the S meter circuit 82 shown in FIG. 1 with the threshold voltages V _ref1 and V _ref2 generated by the reference power supply, respectively, and according to the comparison result. Voltage signals S _HCC1 and S _HCC2 are output. Here, V _ref1 is a threshold voltage that determines the upper limit value of the first weak electric field region, while V _ref2 is a threshold voltage that determines the lower limit value of the first weak electric field region and the upper limit value of the second weak electric field region, V _ref1 > V _ref2 is set. Output _{S HCC2} output _{S HCC1} and comparator 132 of the comparator 130 is input to the adder circuit 134. The adder circuit 134 generates a voltage signal S _HCC corresponding to the total value of S _HCC1 and S _HCC2 and outputs it to the HCC filter circuit 94 as a control signal. Specifically, the output S _HCC of the adder circuit 134 is supplied to the mixer 110 of the HCC filter circuit 94, and the mixing ratio between the input signal from the bypass circuit 114 of the mixer 110 and the input signal from the RC filter 112. To control.

Next, the operation of HCC performed by the HCC filter circuit 94 and the received electric field strength determination circuit 84 will be described. Based on the _SM-DC from the S meter circuit 82, the received electric field strength discriminating circuit 84 determines whether the current received electric field strength is any of the region above the middle electric field, the first weak electric field region, and the second weak electric field region. Determine if it belongs. When the electric field is equal to or higher than the medium electric field, that is, when S _M−DC ≧ V _ref1 , the comparators 130 and 132 both output a predetermined high voltage (H level), and the adder circuit 134 outputs the voltage V H as the output signal S _HCC accordingly. ₁ is output. In the case of the first weak electric field region where V _ref1 > S _M-DC ≧ V _ref2 , the comparator 130 outputs a predetermined low voltage (L level) lower than the H level, while the comparator 132 outputs the H level. addition circuit 134 outputs a voltage _{V 2} as the output signal _{S HCC} according to. In the case of the second weak electric field region where V _ref2 > S _M-DC , both the comparators 130 and 132 output the L level, and in response thereto, the adder circuit 134 outputs the voltage V ₃ as the output signal S _HCC . Here, V ₁ , V ₂ , and V ₃ are voltages having a relationship of V ₁ > V ₂ > V ₃ , for example. Thus, the combination of the output signals of the comparators 130 and 132 differs depending on the region to which the received electric field strength belongs, and the voltage of the output signal _SHCC of the adder circuit 134 also changes stepwise based on this output signal. The mixer 110 changes the mixing ratio in accordance with the S _HCC , whereby the HCC filter circuit 94 is controlled to have different filter characteristics for each region.

Specifically, the mixer 110 increases the component ratio from the bypass circuit 114 as S _HCC is higher with respect to the mixing ratio of the two input signals in the output signal S _H-MID , while the S _HCC is lower as The component ratio from the RC filter 112 is increased.

With this configuration, the HCC filter circuit 94 outputs _SH-OUT that has not been subjected to the removal of the high-frequency component of the RC filter 112 with respect to the input signal _SH-IN above the medium electric field. That is, S _{L + R} output from the HCC filter circuit 94 is basically a signal that has not been subjected to high frequency component removal by the HCC filter circuit 94.

On the other hand, in the first weak electric field region, S _{L + R} subjected to the high frequency component removal action by the RC filter 112 is generated, and in the second weak electric field region, the high frequency component removal action by the RC filter 112 is further strongly received. S _{L + R} is generated.

FIG. 3 is a schematic graph illustrating input / output characteristics of the FM radio receiver 50. The horizontal axis represents the input level _VIN to the antenna 52 in decibel scale, while the vertical axis represents the output level _VOUT in decibel scale. For example, the characteristic 150 represents an output audio signal characteristic curve with respect to a frequency component of 1 kHz, and the characteristic 152 is an output audio signal characteristic curve with respect to a frequency component of 10 kHz, for example, and represents an HCC characteristic. A characteristic 154 represents an output noise characteristic curve. Furthermore, the figure also shows a characteristic 156 representing the relationship between the voltage level of the _SM-DC output from the S meter circuit 82 and the received electric field strength. Note that the characteristic 156 is represented not by the decibel scale shown by the left vertical axis but by the linear scale (arbitrary unit) shown by the right vertical axis. The input levels _VIN corresponding to the threshold _values V _ref1 and V _ref2 for the S _M-DC are points ξ ₁ and ξ ₂ shown on the horizontal axis. According to the circuit configuration of the HCC of the present embodiment, when ξ ₁ > V _IN ≧ ξ ₂ corresponding to the first weak electric field region, high frequency components are removed conservatively, while corresponding to the second weak electric field region. When ξ ₂ > V _IN , the high-frequency component is strongly removed, as shown by the fact that the 10 kHz component (characteristic 152) is greatly reduced compared to the 1 kHz component (characteristic 150). Incidentally, the dotted line shown close to the characteristic 152 in the second weak electric field region represents the characteristic when it is assumed that the mixing ratio in the first weak electric field region is maintained for comparison.

By setting the second weak electric field region that removes high frequency components more strongly than the first weak electric field region in accordance with the target range for removing pulse noise in the weak electric field, the noise can be suitably removed. In the first weak electric field region close to the medium electric field or higher region, it is possible to prevent the high frequency range of the reproduced sound from being suppressed unnecessarily. The relative strength of HCC in the second weak electric field region with respect to HCC in the first weak electric field region can be adjusted by the control voltages V ₂ and V ₃ described above.

Here, the HCC filter circuit 94 is constituted by a single-stage filter circuit. However, as shown in FIG. 4, the HCC filter circuit 94 may be constituted by connecting similar filter circuits 100 and 102 in two stages in series. it can. The filter circuit 100 includes a mixer 110, an RC filter 112, and a bypass circuit 114, and outputs a signal _SH-MID . On the other hand, the basic configuration of the filter circuit 102 is the same as that of the filter circuit 100, and includes a mixer 120, an RC filter 122, and a bypass circuit 124. The mixing ratio of the mixer 110 is controlled by the output S _HCC1 of the comparator 130, and the mixing ratio of the mixer 120 is controlled by the output S _HCC2 of the comparator 132. Regarding the mixing ratio of the two input signals in the output signal _{SH -MID} , the mixer 110 _basically has the _{SH -MID as} a component from the bypass circuit 114 when the output signal _SHCC1 of the comparator 130 is at the H level. On the other hand, when _SHCC1 is at the L level, the _{SH -MID} is basically configured to be occupied by the component from the RC filter 112. Similarly, with respect to the mixing ratio of two input signals in the output signal _{SH -OUT} , the mixer 120 _basically outputs _{SH -OUT} from the bypass circuit 124 when the output signal _SHHC2 of the comparator 132 is at the H level. On the other hand, when _SHCC2 is at the L level, _{SH -OUT} is basically occupied by the component from the RC filter 122.

With this configuration, at a medium electric field or higher, the HCC filter circuit 94 receives the SH _-OUT that has not been subjected to the removal of any high-frequency components of the RC filters 112 and 122 with respect to the input signal SH _-IN . Output.

On the other hand, in the first weak electric field region, the HCC filter circuit 94 outputs SH _-OUT obtained by applying only the RC filter 112 of the RC filters 112 and 122 to the input signal SH _-IN .

Further, in the second weak electric field region, the HCC filter circuit 94 outputs SH _-OUT obtained by applying both the RC filters 112 and 122 to the input signal SH _-IN . Therefore, SH _-OUT is basically a signal that has been subjected to high frequency component removal corresponding to the product of the frequency characteristics of the RC filters 112 and 122. That is, the HCC filter circuit 94 removes the high frequency component more strongly in the second weak electric field region than in the first weak electric field region.

In the above-described configuration, the configuration in which the strength of the HCC changes in two stages is shown, but a configuration in which the number of comparators for determining the level of SM _-DC is increased to change in more stages can be used. Further, in the above-described configuration, a configuration in which a plurality of LPFs configured by RC filters are used is shown as a configuration in which they are connected in series. However, LPFs having different characteristics are arranged in parallel, and any one of them is connected to a switch circuit. It can also be set as the structure selected by.

1 is a schematic block configuration diagram of an FM radio receiver according to an embodiment of the present invention. It is a circuit diagram which shows the schematic structure of the HCC filter circuit and reception electric field strength discrimination | determination circuit in the FM radio receiver of embodiment of this invention. It is a typical graph explaining the input-output characteristic of the FM radio receiver which concerns on embodiment of this invention. It is a circuit diagram which shows the other schematic structure of the HCC filter circuit and reception electric field strength discrimination | determination circuit in the FM radio receiver of embodiment of this invention. It is a circuit diagram of the HCC filter circuit and reception electric field strength discrimination circuit which implement | achieve the conventional HCC function.

Explanation of symbols

  50 FM radio receiver, 52 antenna, 54 RF amplifier, 56 first local oscillation circuit, 58 first mixing circuit, 60, 64 BPF, 62 amplifier, 66 second local oscillation circuit, 68 second mixing circuit, 70 IFBPF, 72 limiter amplifier, 74 detector circuit, 76 stereo demodulator, 82 S meter circuit, 84 reception field strength discriminating circuit, 90 main demodulator circuit, 92 sub demodulator circuit, 94 HCC filter circuit, 96 matrix circuit, 100, 102 filter circuit, 110, 120 Mixer, 112, 122 RC filter, 114, 124 Bypass circuit, 130, 132 Comparator.

Claims (2)

A demodulation circuit that demodulates the received signal and generates a demodulated signal;
An intensity signal generation circuit for generating an electric field strength signal corresponding to the received electric field strength based on the received signal;
Based on the electric field strength signal, the received electric field strength is a region that is equal to or greater than a predetermined first threshold value, a first weak electric field region that is less than the first threshold value and is equal to or greater than a predetermined second threshold value, and the first A received electric field strength discriminating circuit for discriminating which of the second weak electric field regions is less than two threshold values;
A high cut circuit that operates in the first weak electric field region and the second weak electric field region and attenuates a noise component in a high frequency region included in the demodulated signal;
Have
The high cut circuit changes an attenuation characteristic according to a determination result by the reception electric field strength determination circuit, and a degree of attenuation in a predetermined target high frequency region is higher in the second weak electric field region than in the first weak electric field region. Set it larger,
A radio receiver characterized by. The radio receiver according to claim 1,
The radio receiver according to claim 1, wherein the second weak electric field region is set corresponding to an electric field region where weak electric field noise is included in the demodulated signal.

Images