JP2013225806A - Radio tuner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio tuner capable of accurately detecting a signal level.SOLUTION: A radio tuner comprises an S meter 102 detecting electric field that includes an auto gain controller 44 automatically adjusting a gain, an RF amplifier 30 dividing an input signal by the gain set by the auto gain controller 44, a post-stage circuit (a mixer 32, an IF amplifier 34, and an IF band-pass filter 36) processing an output signal from the RF amplifier 30, a gain control level detector 46 detecting the gain set by the auto gain controller 44, and a multiplier 50 multiplying a signal processed by the post-stage circuit by the gain detected by the gain control level detector 46.

Description

  The present invention relates to a radio tuner.

  Conventionally, S meter detection is applied to detect the electric field strength of an RF signal received by a radio tuner or the like. As shown in FIGS. 11 and 12, the input RF signal is amplified by the RF amplifier 10, the amplified RF signal is frequency-converted to an intermediate frequency band (IF) by the mixer (MIX) 12, and the frequency is converted. The signal level is detected by a signal level detector (S meter) 18 via an IF amplifier 14 for amplifying the converted IF signal and a filter (BPF) 16 for selecting a desired frequency band. Thereby, the signal level of the desired frequency band included in the RF signal can be detected. That is, since each gain of RF amplification, mixing, IF amplification, and BPF is known, the signal level (electric field strength) of the selected frequency band included in the RF signal is detected by detecting the signal level after passing through the BPF. Can be detected.

  Further, as shown in FIG. 13, a configuration in which an auto gain controller (AGC) 20 is provided in the RF amplifier 10 may be employed. In this case, when a strong electric field RF signal is input, the gain of the RF amplifier 10 is changed so that the signal level does not exceed the dynamic range of the circuit.

  For example, as shown in FIG. 14, when there are two or more disturbing signals and the disturbing signal exceeds the dynamic range of the circuit, intermodulation occurs. By adding the AGC 20 to the RF amplifier 10, even if a strong electric field interference signal is input, the input signal is controlled so as not to exceed the dynamic range of the circuit, and the occurrence of intermodulation can be prevented.

  By the way, if AGC 20 or the like is added to the previous stage of the signal level detector 18 and the gain of the previous stage changes from a known value, an error may occur in the electric field strength detection value by the signal level detector 18. For example, as shown in FIG. 15, the signal level is output according to the input electric field strength in the weak electric field where the AGC 20 does not operate, but the gain control by the AGC 20 (the first stage of the signal level detector 18 is performed in the strong electric field where the AGC 20 operates. (Gain control) prevents the signal level from being output according to the input electric field strength.

  One aspect of the present invention divides the input signal by an auto gain controller that automatically adjusts the gain so as to maintain the intensity of the input signal below the operation start point, and the gain set by the auto gain controller. An amplification circuit; a post-stage circuit that processes an output signal from the amplification circuit; a gain control level detection circuit that detects a gain set by the auto gain controller; and a gain detected by the gain control level detection circuit A radio tuner comprising: an S meter circuit that detects an electric field, and a multiplier that multiplies a signal that has been processed by a post-stage circuit.

  Another aspect of the present invention divides the input signal by an auto gain controller that automatically adjusts the gain so as to maintain the intensity of the input signal below the operation start point, and the gain set by the auto gain controller. An amplifier circuit, a post-stage circuit for processing an output signal from the amplifier circuit, a first logarithmic converter circuit for logarithmically converting the signal output from the post-stage circuit, and a gain for detecting a gain set by the auto gain controller A control level detection circuit; a second logarithmic conversion circuit for detecting a logarithmically converted value of the signal level adjusted in the amplifier circuit according to the gain detected by the gain control level detection circuit; and the first logarithmic conversion circuit. An S meter circuit for detecting an electric field, comprising: an adder that adds the signal after processing in the second logarithmic conversion circuit to the signal after processing in It is a radio tuner and said Rukoto.

  Here, the auto gain controller determines the number of steps, and the amplifier circuit divides the input signal by a gain obtained by multiplying a predetermined step value and the number of steps, and the gain control level It is preferable that the detection circuit detects the number of steps and detects the gain by multiplying the step value and the number of steps.

  A main tuner that extracts a sound signal by selecting one frequency band in a radio broadcast frequency band; and the S meter circuit, and selects one frequency band in the frequency band of the radio broadcast to select a sound. A sub-tuner for extracting a signal, and the main tuner is used to actually output sound, and the sub-tuner scans the frequency band of the radio broadcast and is based on the value of the S meter. It is preferably used to confirm the reception status.

  It is preferable that a plurality of the main tuners are provided, the plurality of main tuners are switched and selected, and the selected main tuner is used for actual sound output.

  ADVANTAGE OF THE INVENTION According to this invention, while providing an auto gain controller in the front | former stage, the radio tuner which can detect a signal level correctly can be provided.

It is a figure which shows the structure of the S meter circuit in embodiment of this invention. It is a figure explaining gain adjustment with RF amplifier in an embodiment of the invention. It is a figure which shows the structural example of RF amplifier in embodiment of this invention. It is a figure explaining the calculation method of the gain control level in embodiment of this invention. It is a figure which shows the structural example of the S meter circuit in embodiment of this invention. It is a figure explaining gain compensation in an embodiment of the invention. It is a figure which shows the structural example of RF amplifier in embodiment of this invention. It is a figure which shows the structural example of the S meter circuit in embodiment of this invention. It is a figure which shows the modification of a structure of the S meter circuit in embodiment of this invention. It is a figure which shows the structure of the radio tuner in embodiment of this invention. It is a figure which shows the structure of the S meter circuit in a prior art. It is a figure which shows the structure of the S meter circuit in a prior art. It is a figure which shows the structure of the S meter circuit in a prior art. It is a figure explaining the intermodulation of broadcast. It is a figure explaining the effect | action of an auto gain controller.

<Basic configuration>
As shown in FIG. 1, the S meter circuit 100 according to the embodiment of the present invention includes an RF amplifier 30, a mixer (MIX) 32, an IF amplifier 34, an IF bandpass filter (BPF) 36, a signal level detector 38, A logarithmic conversion unit 40, an adder 42, an auto gain controller (AGC) 44, a gain control level detector 46, and a second logarithmic conversion unit 48 are included.

  The RF amplifier 30 is a circuit that amplifies a radio frequency band signal received by an antenna with a predetermined gain. The output of the RF amplifier 30 is input to the mixer 32. The gain of the RF amplifier 30 is adjusted by the AGC 44. The AGC 44 adjusts the gain of the RF amplifier 30 so that the level of the output signal from the RF amplifier 30 is equal to or lower than a predetermined operation start point.

  For example, as shown in FIG. 2, every time the level of the output signal of the RF amplifier 30 reaches the operation start point REF, the level of the output signal from the RF amplifier 30 is decreased by a predetermined step value A (for example, −6 dB). Let The AGC 44 detects the level of the output signal of the RF amplifier 30, determines the number of steps N for making the operation start point REF or less, and outputs it to the RF amplifier 30. The RF amplifier 30 receives the step number N, divides (attenuates) the input RF signal by a gain of step value A × step number N, and outputs the result.

  The RF amplifier 30 can be configured by a circuit as shown in FIG. 3, for example. In this example, the gain can be adjusted by inserting a resistor into the differential input emitter and setting the transconductance (gm). For example, the resistance R0 is fixed, and the gm is changed by controlling each of the switches SW1,. At this time, gm in the state where only the switches SW1 to SWn are turned on to the state where only the switch SW1 is turned off is lowered by a step value (for example, −6 dB), and when the switch SW2 is further turned off, the gm is further lowered by a step value (for example, −6 dB). Each time the switch is turned off in order, the gm is decreased by a step value (for example, −6 dB). By controlling this switch according to the number of steps N from the AGC 44, the gain can be lowered by the step value A × the number of steps N.

  The mixer 32 mixes a local signal having a frequency in the intermediate frequency band (IF) and an output signal from the RF amplifier 30, thereby down-converting and outputting the input signal. The output of the mixer 32 is input to the IF amplifier 34.

  The IF amplifier 34 amplifies or attenuates the signal down-converted to the intermediate frequency with a predetermined gain and outputs the amplified signal. The output of the IF amplifier 34 is input to the BPF 36.

  The BPF 36 filters the signal and outputs it. For example, the BPF 36 transmits only a signal in a preset frequency band of a desired station. The RF amplifier 30 to the BPF 36 constitute a front stage portion of the S meter circuit 100.

  The signal level detector 38 detects the signal level (electric field strength) of the signal processed by the BPF 36. The signal level detected by the signal level detector 38 is output to the first logarithmic conversion unit 40. The first logarithmic conversion unit 40 logarithmically converts the signal level detected by the signal level detector 38. The logarithmically converted signal level is output to the adder 42.

  The gain control level detector 46 detects the number of steps N output from the AGC 44. The detected number of steps N is output to the second logarithmic conversion unit 48. The second logarithmic conversion unit 48 generates a logarithmically converted gain control level according to the step number N received from the gain control level detector 46 and outputs the gain control level to the adder 42. In the second logarithmic conversion unit 48, a step value A used in the RF amplifier 30 is set and stored in advance. As shown in FIG. 4, the second logarithmic conversion unit 48 multiplies the step value A by the step number N, performs logarithmic conversion on the multiplication value, and outputs the result. If the step value A is already set in logarithm (for example, −6 dB), it is only necessary to multiply the step value A by the step number N as shown in FIG.

  The adder 42 adds the output signal from the first logarithmic conversion unit 40 and the output signal from the second logarithmic conversion unit 48 and outputs the result. The output signal from the first logarithmic conversion unit 40 has a value obtained by logarithmically converting the signal subjected to gain adjustment at the RF amplifier 30, and the output signal from the second logarithmic conversion unit 48 is the amount of gain adjustment at the RF amplifier 30. Has a logarithmically converted value. Therefore, as shown in FIG. 6, the output signal of the adder 42, which is the sum of these values, is compensated for the gain adjustment in the RF amplifier 30, and has a value that accurately corresponds to the input signal level.

  Therefore, if the gain of each of the mixer 32, IF amplifier 34, and BPF 36 is known, the signal level (electric field) of the selected frequency band included in the RF signal is detected by detecting the signal level of the output signal from the adder 42. (Strength) can be known accurately. On the other hand, even when a signal having a dynamic range in which intermodulation occurs is input, the dynamic range in the mixer 32, IF amplifier 34, and BPF 36 is not exceeded by adjusting the signal level in the RF amplifier 30. Controlled. Thereby, the occurrence of intermodulation can be prevented.

Note that the RF amplifier 30 does not have to be configured to adjust the gain stepwise, but may be configured to adjust the gain linearly. For example, as shown in FIG. 7, the transconductance (gm) can be changed by the current source I1 of the differential amplifier. That is, the gm of this circuit is expressed by Equation (1), and gm can be changed in proportion to the current source I1. Here, q is an electron charge amount, k is a Boltzmann constant, and t is an absolute temperature.

  When the RF amplifier 30 is configured in this way, as shown in FIG. 8, the same current as the current source I1 for controlling the gain is output from the AGC 44, and the current I1 is logarithmically converted. The logarithmically transformed output is multiplied by a constant K and output to the adder 42. At this time, the change amount of the signal in the RF amplifier 30, the signal level detector 38, and the first logarithmic conversion unit 40 and the change amount obtained by multiplying the value obtained by logarithmically converting the current I1 by the constant K are in reverse phase. Set a constant K to. By setting the constant K in this manner, the adder 42 cancels the change in the RF amplifier 30.

<Modification>
FIG. 9 shows an S meter circuit 102 in a modification of the present embodiment. As shown in FIG. 9, the S meter circuit 102 does not include the first logarithmic conversion unit 40 and the second logarithmic conversion unit 48, and includes a multiplier 50 instead of the adder 42.

  In this modification, the gain control level detector 46 detects the step number N output from the AGC 44, calculates a multiplication value of the step value A and the step number N that are set and stored in advance, and the multiplier 50 Output to.

  The multiplier 50 multiplies the output signal of the signal level detector 38 and the output signal of the gain control level detector 46 and outputs the result. In the present modification, since the logarithmic conversion is not performed in the first logarithmic conversion unit 40 and the second logarithmic conversion unit 48, the gain control level detector is added to the output signal of the signal level detector 38 subjected to the gain adjustment in the RF amplifier 30. By multiplying the gain adjustment value detected at 46, the gain adjustment in the RF amplifier 30 can be compensated.

  Therefore, if the gains of mixer 32, IF amplifier 34, and BPF 36 are known, the signal level (electric field) of the selected frequency band included in the RF signal is detected by detecting the signal level of the output signal from multiplier 50. (Strength) can be known accurately. On the other hand, even when a signal having a dynamic range in which intermodulation occurs is input, control is performed so as not to exceed the dynamic range of the circuit as in the above embodiment. Thereby, the occurrence of intermodulation can be prevented.

<Application to radio tuner>
The S meter circuits 100 and 102 in this embodiment can be applied to a radio tuner. As shown in the background art, when receiving a radio broadcast, it is necessary to accurately detect the signal level of each broadcast station (desired station or adjacent interfering station) in order to determine which channel is received.

  The radio tuner 200 includes a first main tuner 60, a second main tuner 62, and a sub tuner 64 as shown in FIG.

  The first main tuner 60 and the second main tuner 62 are tuners used for actual audio output, and either one of the received signals is converted into an audio signal and output. For example, when the same content is broadcast on a plurality of channels, the first main tuner 60 and the second main tuner 62 are tuned to the frequency bands of different channels on which the same content is being broadcast, The stronger signal is converted into an audio signal and output. Thereby, a radio broadcast can be received by selecting a channel having a better reception state.

  The sub-tuner 64 includes the S meter circuit 100 or 102 in the present embodiment, and scans over the frequency band of the radio broadcast independently of the first main tuner 60 and the second main tuner 62. Detect a good channel. The sub-tuner 64 changes the frequency characteristics of the BPF 36 so as to scan the entire frequency band of radio broadcasting, and checks the signal level between the desired station and the adjacent interfering station to detect a channel with a good reception state. For example, it is a channel that broadcasts the same content as the channel received by the first main tuner 60 and the second main tuner 62, and the channel is received by the first main tuner 60 or the second main tuner 62. In addition, a channel having a high signal level and a low signal level of adjacent interfering stations is searched from the entire frequency band of radio broadcasting. If such a channel exists, one of the first main tuner 60 and the second main tuner 62 that is not currently used for audio output is tuned to the frequency band of that channel.

  At this time, by applying the S meter circuit 100 or 102 according to the present embodiment to the sub-tuner 64, the signal level of the received signal of each channel can be accurately detected. Even if the reception state of one of the first main tuner 60 and the second main tuner 62 deteriorates by configuring the radio tuner in this way, the desired broadcast content can be changed by immediately switching to the other tuner. Output can be made without interruption. Further, by providing the sub tuner 64 including the S meter circuit 100 or 102 in the present embodiment, a channel having a good reception state is detected from among a plurality of channels transmitting desired broadcast contents, and the first main tuner 60 and Any one of the second main tuners 62 can be tuned to the frequency band of the channel.

  Note that the radio tuner 200 according to the present embodiment is configured to include the two first main tuners 60 and the second main tuner 62, but may be a single tuner. In this case as well, by providing the sub-tuner 64, a channel having a good reception state is detected in advance, and the frequency band of the channel detected when the reception state of the main tuner deteriorates may be tuned. .

  10 RF amplifier, 12 mixer, 14 IF amplifier, 16 filter, 18 signal level detector, 30 RF amplifier, 32 mixer, 34 IF amplifier, 36 IF bandpass filter, 38 signal level detector, 40 first logarithmic conversion unit, 42 adder, 44 auto gain controller, 46 gain control level detector, 48 second logarithmic conversion unit, 50 multiplier, 60 main tuner, 62 main tuner, 64 sub tuner, 100, 102 S meter circuit, 200 radio tuner.

Claims (5)

An auto gain controller that automatically adjusts the gain so as to maintain the intensity of the input signal below the operation start point;
An amplifier circuit that divides the input signal by a gain set by the auto gain controller;
A subsequent circuit for processing an output signal from the amplifier circuit;
A gain control level detection circuit for detecting a gain set by the auto gain controller;
A multiplier that multiplies the signal detected by the gain control level detection circuit by the signal processed by the subsequent circuit;
An S meter circuit for detecting an electric field including
A radio tuner characterized by comprising: An auto gain controller that automatically adjusts the gain so as to maintain the intensity of the input signal below the operation start point;
An amplifier circuit that divides the input signal by a gain set by the auto gain controller;
A subsequent circuit for processing an output signal from the amplifier circuit;
A first logarithmic conversion circuit for logarithmically converting the signal output from the subsequent circuit;
A gain control level detection circuit for detecting a gain set by the auto gain controller;
A second logarithmic conversion circuit that detects a value obtained by logarithmically converting the signal level adjusted in the amplification circuit in accordance with the gain detected by the gain control level detection circuit; and a signal that is processed by the first logarithmic conversion circuit. An adder for adding signals after processing in the second logarithmic conversion circuit;
An S meter circuit for detecting an electric field including
A radio tuner characterized by comprising: The radio tuner according to claim 1 or 2,
The auto gain controller determines the number of steps,
The amplifier circuit divides the input signal by a gain obtained by multiplying a predetermined step value and the number of steps.
The gain control level detection circuit detects the number of steps and multiplies the step value by the number of steps to detect a gain. The radio tuner according to any one of claims 1 to 3,
A main tuner for extracting an audio signal by selecting one frequency band in a radio broadcast frequency band;
A sub-tuner that includes the S meter circuit and extracts a sound signal by selecting one of the frequency bands of the radio broadcast;
With
The main tuner is used to actually output sound,
The sub-tuner is used to scan a frequency band of the radio broadcast and confirm reception status based on a value of the S meter. The radio tuner according to claim 4,
A plurality of the main tuners;
A radio tuner characterized in that the plurality of main tuners are switched and selected, and the selected main tuner is used for actual sound output.

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