JP2003218672A - Receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a seek sensitivity difference small based upon a reception frequency in local mode. <P>SOLUTION: A receiver equipped with a function of attenuating a receive signal inputted to an RF amplifier 3 by an attenuating circuit 10 and detecting a frequency band wherein the electric field intensity of the signal having been attenuated is larger than a specified level attenuates the receive signal by using the tuning voltage of a local oscillation circuit 5 which increases in value as the reception frequency becomes higher and decreases as the reception frequency becomes lower. In a high-frequency range, larger currents are supplied to diodes D1 and D2 to make the on-resistances small and the receive signal is so corrected as to decrease in attenuation quantity. In a low frequency range, smaller currents are supplied to the diodes D1 and D2 to make the on-resistances large and the receive signal is so corrected as to decrease in attenuation quantity, thereby reducing the difference in signal attenuation quantity with the reception frequency. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver, and is particularly suitable for use in a receiver having a function of automatically searching for frequency bands of various broadcasting stations.

[0002]

2. Description of the Related Art Many radio receivers are provided with a function of automatically searching for frequency bands of various broadcasting stations (so-called seek function). In the seek function, the reception frequency band in which the reception sensitivity (electric field strength) becomes equal to or higher than a predetermined level is regarded as the frequency band of the broadcasting station, and this is automatically detected. This seek function is a DX that searches for all available broadcasting stations.
There is a mode and a local mode in which only stations with strong received radio waves are searched.

The DX mode is a mode in which all frequency bands in which the received electric field strength is a predetermined level or higher (for example, 20 dB or higher) are detected. The local mode is a mode in which the level of the received signal is attenuated to some extent before the received signal enters the electric field strength detection circuit, and all frequency bands in which the electric field strength of the attenuated signal is equal to or higher than a predetermined level are detected. For example, when the level of the received signal is attenuated by 10 dB, only the frequency band in which the received electric field strength is 30 (= 20 + 10) dB or more is detected.

FIG. 3 is a diagram showing the configuration of a conventional receiver having a seek function. In FIG. 3, 1 is a receiving antenna, 2 is a filter, 3 is an RF amplifier, 4 is a mixer, 5 is a local oscillation circuit, 6 is an IF amplifier, 7 is a comparator as an electric field strength detection circuit, and 8 is an attenuation circuit.

The filter 2 extracts a signal in a target reception frequency band from the broadcast signal received by the reception antenna 1 and outputs the RF signal.
Output to the amplifier 3. The RF amplifier 3 performs high frequency amplification on the broadcast signal output from the filter 2 and outputs the amplified broadcast signal. The mixer 4 mixes the amplified broadcast signal output from the RF amplifier 3 with an oscillation signal of a predetermined frequency output from the local oscillation circuit 5 to output an intermediate frequency signal obtained by converting the frequency of the broadcast signal. To do.

The IF amplifier 6 amplifies the intermediate frequency signal output from the mixer 4 and performs a tuning operation. The comparator 7 receives the intermediate frequency signal output from the IF amplifier 6 and a preset predetermined level (for example, 20
The signal of dB) is compared, and when the level of the intermediate frequency signal is higher, a pulse signal is output to notify that there is a broadcast signal in the frequency band.

The attenuation circuit 8 includes a filter 2 and an RF amplifier 3.
It is connected in parallel between and. The attenuation circuit 8 includes capacitors C1 and C2, diodes D1 and D2, a resistor R,
A local switch SW and a power supply voltage V are provided. When the DX mode is selected, the local switch SW is in the cutoff state, and the signal attenuation operation is not performed. On the other hand, when the local mode is selected,
The local switch SW becomes conductive, and the RF amplifier 3
The broadcast signal input to is attenuated.

That is, in the local mode, a constant voltage V is output through the local switch SW, the resistor R converts the current, and the current flows through the diodes D1 and D2. The on-resistance of the diodes D1 and D2 generated at this time attenuates the broadcast signal input to the RF amplifier 3 through the capacitors C1 and C2.

[0009]

In the case of the conventional example shown in FIG. 3, the diodes D1 and D2 are in the local mode in which the local switch SW of the attenuation circuit 8 is ON.
Since the current flowing through is constant regardless of the reception frequency, the on resistances of the diodes D1 and D2 have constant values. On the other hand, there is a capacitive component between the antenna 1 and the filter 2, and the resistance value between them varies depending on the reception frequency.

The capacitance between the antenna 1 and the filter 2 and the on resistance of the diodes D1 and D2 form a high pass filter. Therefore, at a low reception frequency, the resistance value between the antenna 1 and the filter 2 increases and the signal attenuation increases, and at a high reception frequency, the resistance value decreases and the signal attenuation decreases. . Therefore, in the local mode, there is a problem in that there is a large difference in sensitivity in that the receiving sensitivity required for detection by the seek function is higher in the low frequency region than in the high frequency region.

The present invention has been made to solve such a problem, and an object thereof is to make it possible to reduce the seek sensitivity difference due to the reception frequency in the local mode.

[0012]

A receiver of the present invention is a receiver having a function of attenuating a received signal and detecting a frequency band of a broadcasting station in which the electric field strength of the attenuated signal becomes a predetermined level or more. And a high-frequency amplifier circuit for high-frequency amplifying the received signal, and an attenuator circuit for attenuating the signal input to the high-frequency amplifier circuit.The attenuator circuit utilizes a tuning voltage that fluctuates according to the received frequency. And a signal input to the high frequency amplifier circuit is attenuated.

The tuning voltage used by the attenuator circuit is, for example, the tuning voltage of the local oscillator circuit. This local oscillation circuit is originally provided in the receiver in order to output an oscillation signal of a predetermined frequency to a frequency conversion circuit that performs frequency conversion of the signal output from the high frequency amplification circuit. The attenuator circuit may include an amplifier circuit that amplifies the tuning voltage of the local oscillator circuit with a predetermined gain and outputs the amplified voltage.

According to the present invention configured as described above, since the tuning voltage increases as the reception frequency increases, a large amount of current flows in the attenuating circuit, and the on-resistance decreases,
It is corrected so that the amount of signal attenuation is greater than when a constant voltage is supplied to the attenuation circuit. On the contrary, since the tuning voltage becomes smaller when the reception frequency becomes lower, a small amount of current flows in the attenuator circuit to increase the on-resistance, and the amount of signal attenuation becomes smaller than when a constant voltage is supplied to the attenuator circuit. Is corrected as follows. This makes it possible to prevent the amount of signal attenuation from changing so much over the entire reception frequency band.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of a receiver having a seek function according to the present embodiment, for example, AM
Shows a radio receiver. In FIG. 1, 1 is a receiving antenna, 2 is a filter, 3 is an RF amplifier (high frequency amplification circuit), 4 is a mixer (frequency conversion circuit), 5 is a local oscillation circuit, 6 is an IF amplifier, and 7 is an electric field strength detection circuit. Comparator 10 is an attenuation circuit.

The filter 2 extracts a signal in the target reception frequency band from the broadcast signal received by the receiving antenna 1 and outputs the RF signal.
Output to the amplifier 3. The RF amplifier 3 performs high frequency amplification on the broadcast signal output from the filter 2 and outputs the amplified broadcast signal. The mixer 4 mixes the amplified broadcast signal output from the RF amplifier 3 with an oscillation signal of a predetermined frequency output from the local oscillation circuit 5 to output an intermediate frequency signal obtained by converting the frequency of the broadcast signal. To do.

The IF amplifier 6 amplifies the intermediate frequency signal output from the mixer 4 and performs a tuning operation. The comparator 7 receives the intermediate frequency signal output from the IF amplifier 6 and a preset predetermined level (for example, 20
The signal of dB) is compared, and when the level of the intermediate frequency signal is higher, a pulse signal is output to notify that there is a broadcast signal in the frequency band.

The attenuation circuit 10 is connected in parallel between the filter 2 and the RF amplifier 3. This attenuation circuit 10
Includes capacitors C1 and C2, diodes D1 and D2, a resistor R, a local switch SW, and an amplifier 11. The amplifier 11 amplifies the tuning voltage of the local oscillation circuit 5 with a predetermined gain and outputs it.

The tuning voltage required for the local oscillator circuit 5 is LC
It is applied to a resonating varactor (not shown).
This tuning voltage requires a high voltage when increasing the oscillation frequency of the local oscillation circuit 5. On the contrary, the local oscillation circuit 5
When the oscillation frequency of is lowered, the tuning voltage is lowered.

When the DX mode is selected, the local switch SW is in the cutoff state, and the attenuation circuit 10 does not perform the signal attenuation operation. On the other hand, when the local mode is selected, the local switch SW is turned on, and the attenuation operation of the broadcast signal input to the RF amplifier 3 is performed.

That is, in the local mode, a voltage amplified based on the tuning voltage of the local oscillation circuit 5 is output from the amplifier 11 through the local switch SW, and the resistor R performs current conversion to the diodes D1 and D2. Apply current. The on-resistance of the diodes D1 and D2 generated at this time attenuates the broadcast signal input to the RF amplifier 3 through the capacitors C1 and C2.

When the reception frequency becomes high, the tuning voltage becomes large and a large amount of current flows through the diodes D1 and D2, so that the ON resistance of the diodes D1 and D2 becomes small. As a result, the amount of signal attenuation is corrected to be larger than when a constant voltage is supplied to the attenuation circuit. On the contrary, when the reception frequency becomes low, the tuning voltage becomes small and a small current flows through the diodes D1 and D2, so that the diode D
The on resistances of 1 and D2 become large. As a result, the amount of signal attenuation is corrected to be smaller than when a constant voltage is supplied to the attenuation circuit. This makes it possible to prevent the amount of signal attenuation from changing so much over the entire reception frequency band.

FIG. 2 is a diagram for explaining the operation of the receiver according to the present embodiment. As in the conventional example shown in FIG. 3, when the voltage used in the attenuation circuit 8 is a constant voltage V,
As shown in Graph A, many seek sensitivity differences occur depending on the reception frequency band. That is, since there is a large amount of signal attenuation in a region where the reception frequency is low, unless the reception sensitivity is considerably high, the frequency band of the broadcasting station cannot be detected (high reception sensitivity is required). On the other hand, since the amount of signal attenuation is small in a region where the reception frequency is high, it is possible to detect a frequency band of a broadcasting station whose reception sensitivity is low (reception sensitivity may be low).

On the other hand, when the tuning voltage of the local oscillation circuit 5 is used in the attenuation circuit 10 as in the present embodiment, as shown in graph B, the tuning voltage becomes lower as the frequency becomes lower, and the diode D1, It is corrected so that the on-resistance of D2 increases and the amount of signal attenuation decreases.
Further, as the frequency becomes higher, the tuning voltage becomes higher, the ON resistance of the diodes D1 and D2 becomes smaller, and the amount of signal attenuation is corrected. As a result, the reception sensitivity required for the seek detection in the local mode is corrected as shown in graph C, and the seek sensitivity difference due to the reception frequency is reduced.

The diode D1, depending on the tuning voltage,
How much the ON resistance of D2 is variable depends on the amplifier 11
It is possible to adjust by the gain of. That is, by providing the amplifier 11, the attenuation correction amount can be arbitrarily adjusted.

Further, as shown in the graph A, the case where the seek sensitivity is lowered as the reception frequency is increased (the slope of the graph is a negative value) has been described as an example. In some cases, the seek sensitivity decreases as the frequency decreases (the slope of the graph is a positive value). The graph indicating the sensitivity difference is determined depending on the characteristics of the filter 2, and for example, in a circuit having many inductor components, the slope of the graph may be a positive value. In this case, by using an inverting amplifier as the amplifier 11, it is possible to effectively reduce the sensitivity difference due to the reception frequency.

As described in detail above, according to the present embodiment, the tuning voltage that fluctuates depending on the frequency is used as the voltage applied to the diodes D1 and D2 of the attenuation circuit 10, so that the attenuation of the signal is performed. The amount can be appropriately corrected, and the seek sensitivity difference due to the reception frequency in the local mode can be reduced.

Further, since the tuning voltage of the local oscillation circuit 5 which is usually provided in the receiver is used as the tuning voltage,
There is also an advantage that it is not necessary to provide a special circuit for generating the tuning voltage. Also regarding the amplifier 11, AM
In the case of a receiver for both / FM radio, by adding the one provided for FM radio tracking to AM, no additional parts are required. This makes it possible to reduce the seek sensitivity difference without adding a special circuit.

Further, it is possible to provide a microcomputer, a D / A converter, etc. for generating the tuning voltage, but in this case, it is necessary to have a program for that purpose in the memory to perform a predetermined control. There is. For this reason, the circuit configuration becomes large correspondingly, and the load on the microcomputer becomes necessary. On the other hand, in the present embodiment, since the signal attenuation amount is corrected in an analog manner by using the tuning voltage of the local oscillation circuit 5, there is also an advantage that no special control is required.

The above embodiment is merely an example of the implementation of the present invention, and the technical scope of the present invention should not be limitedly interpreted by this. That is, the present invention can be implemented in various forms without departing from the spirit or the main features thereof.

[0031]

As described above, the present invention provides a receiver having a function of attenuating a received signal and detecting a frequency band in which the electric field strength of the attenuated signal is equal to or higher than a predetermined level.
Since the received signal is attenuated by using the tuning voltage that fluctuates according to the received frequency, the difference in the attenuation due to the received frequency that occurs when the voltage used in the attenuator circuit is constant should be corrected. It becomes possible to call,
It is possible to reduce the sensitivity difference due to the reception frequency in the local mode.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a receiver according to an embodiment having a seek function.

FIG. 2 is a diagram for explaining the operation of the receiver according to the present embodiment.

FIG. 3 is a diagram showing a configuration of a conventional receiver having a seek function.

[Explanation of symbols]

1 antenna 2 filters 3 RF amplifier 4 mixer 5 Local oscillator circuit 6 IF amplifier 7 comparator 10 Attenuation circuit 11 amplifier C1, C2 capacitors D1, D2 diode R resistance SW local switch

Claims (3)

[Claims] 1. A receiver having a function of attenuating a received signal and detecting a frequency band of a broadcasting station in which the electric field strength of the attenuated signal is equal to or higher than a predetermined level, the high frequency amplifying the received signal at high frequency An amplifier circuit and an attenuator circuit for attenuating a signal input to the high frequency amplifier circuit are provided. The attenuator circuit utilizes a tuning voltage that fluctuates according to a reception frequency, and a signal input to the high frequency amplifier circuit. A receiver characterized in that it is configured to attenuate. 2. A frequency conversion circuit that performs frequency conversion by mixing a signal after high frequency amplification output from the high frequency amplification circuit and an oscillation signal of a predetermined frequency, and a local oscillation that outputs the oscillation signal of the predetermined frequency. 2. The reception circuit according to claim 1, further comprising a circuit, wherein the attenuation circuit is configured to attenuate a signal input to the high frequency amplification circuit by utilizing a tuning voltage of the local oscillation circuit. Machine. 3. The receiver according to claim 2, wherein the attenuation circuit includes an amplifier circuit that amplifies the tuning voltage of the local oscillation circuit with a predetermined gain and outputs the amplified tuning voltage.