JPH0516695B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to, for example, an amplitude modulation receiver, and more specifically to a so-called receiver that automatically changes the frequency characteristics of an acoustic signal according to the reception level of a received high-frequency signal. This relates to the configuration of a tone control circuit.

BACKGROUND ART FIG. 1 is a prior art electrical circuit diagram. A high frequency signal such as an amplitude modulated broadcast signal is tuned by a tuning circuit 1 and given to a mixing circuit 2 according to a superheterodyne system. A signal from a local oscillation circuit 3 is applied to the mixing circuit 2 . The output from the mixing circuit 2 is given to an intermediate frequency amplification circuit 4. The output from the intermediate frequency amplification circuit 4 is detected from a line 5 by a detection circuit 6, and the acoustic signal is amplified by an amplification circuit 8 via a tone control circuit 7, and made into sound by a speaker 9. . The signal derived from the intermediate frequency amplifier circuit 4 to the line 5 is also applied to a detection circuit 10 having a larger time constant than the detection circuit 6. The signal derived from the detection circuit 10 to the line 11 has a level corresponding to the reception level of the high frequency signal received and tuned by the tuning circuit 1. The signal from the line 11 is applied to a variable resistance circuit 12 included in the tone control circuit 7. The tone control circuit 7 includes a resistor 13 in addition to the variable resistance circuit 12, and is realized by an integrated circuit. A capacitor 14 is externally connected to the tone control circuit 7. The variable resistance circuit 12 receives the signal from the line 11, and when the reception level of the high frequency signal is low, that is, when the electric field of the broadcast frequency signal is weak, the contact 12a is equivalently displaced to the resistance 13 side, that is, downward in FIG. However, when the reception level is high and the electric field of the broadcast frequency signal is strong, contact 1
2a is equivalently displaced upward in FIG. In this manner, when the broadcast frequency signal is in a weak electric field state, the high frequency range of the acoustic signal is attenuated to reduce noise such as beats when an adjacent broadcast frequency signal is present.

In the prior art shown in FIG. 1, the tone control circuit 7 implemented by an integrated circuit has four terminals as indicated by reference numerals 15 to 18, and it is possible to further reduce the number of terminals. desired.

Another problem with the prior art illustrated in FIG. 1 relates to frequency characteristics. When the signal representing the reception level derived from the detection circuit 10 via the line 11 changes, the frequency characteristic of the tone control circuit 7 has such a characteristic that the cutoff frequency does not change as shown in FIG. Therefore, the effect of reducing noise such as beats caused by adjacent broadcast frequency signals in a weak electric field is small.

Purpose An object of the present invention is to provide a receiver in which the number of terminals of a circuit that automatically performs tone control according to the reception level of a high-frequency signal is reduced as much as possible.

Another object of the present invention is to provide a receiver that reduces noise by lowering the cutoff frequency of the high frequency range of an acoustic signal when the reception level of the high frequency signal is low.

Structure of the Invention The present invention has two input terminals, a first detection means for receiving a high frequency signal and deriving an acoustic signal, and a second detection means for detecting the reception level of the high frequency signal, one of which has two input terminals. an adder circuit that receives the acoustic signal at an input terminal thereof; a first multiplier circuit that multiplies the acoustic signal by a value corresponding to the reception level output from the second detection means; a resistor connected in series,
a second multiplication unit that multiplies an integral type capacitor connected to the output side of the resistor, an output at a connection point between the resistor and the capacitor, and a value corresponding to the reception level output from the second detection means; A receiver comprising: a circuit; and a subtraction circuit that calculates the difference between the output of the first multiplication circuit and the output of the second circuit, and supplies a signal representing the difference to the other input terminal of the addition circuit. It is.

Embodiment FIG. 3 is an electrical circuit diagram of an embodiment of the present invention. A high frequency signal such as an amplitude modulated broadcasting frequency signal is received and tuned by a tuning circuit 1 and given to a mixing circuit 2 according to a superheterodyne system. This mixing circuit 2 is given a local oscillation frequency signal from a local oscillation circuit 3 . The output from the mixing circuit 2 is given to an intermediate frequency amplification circuit 4 and amplified. The output from the intermediate frequency amplification circuit 4 is connected to the line 5.
is detected by the detection circuit 6, and an acoustic signal is applied from the line 20 to the terminal 22 of the tone control circuit 21. Tone control circuit 21
The acoustic signal from the terminal 23 is applied to an amplifier circuit 25 via a line 24, where it is amplified and made into sound by a speaker 26.

The signal derived from the intermediate frequency amplification circuit 4 to the line 5 is transferred to another circuit whose time constant is larger than that of the detection circuit 6.
one detection circuit 10. This detection circuit 1
The output from tone control circuit 21 has a value corresponding to the reception level of a high frequency signal, which is a broadcast frequency signal received and tuned by tuning circuit 1, and is applied to terminal 27 of tone control circuit 21. The tone control circuit 21 has the aforementioned three terminals 22, 23, 27.
The number of terminals, three, is smaller than the number of terminals, four, of the tone control circuit 7 in the prior art described in connection with FIG.

In the tone control circuit 21, the addition circuit 2
8 receives the acoustic signal from terminal 22 at one input terminal 29 . The other input terminal 30 has
An output from an amplifier circuit 31 is given. The first multiplication circuit 32 receives the acoustic signal from the terminal 22 and the terminal 27.
Multiply by the value corresponding to the reception level from. An output terminal 33 of the adder circuit 28 is connected in series to the terminal 23 via a resistor 34. The output side of the resistor 34,
That is, the line 24 interposed between the terminal 23 and the amplifier circuit 25 is connected to an integrating capacitor 3.
5 is connected. The output at the connection point between the resistor 34 and the capacitor 35, that is, the output at the connection point 23, is provided to a second multiplier circuit 36. A value corresponding to the reception level from the terminal 27 is also input to the second multiplier circuit 36 . The second multiplication circuit 36 multiplies the output at the connection terminal 23 by a value corresponding to the reception level. A subtraction circuit 37 subtracts the output of the second multiplication circuit 36 from the output of the first multiplication circuit 32 to obtain a difference, and a signal representing this difference is applied to the amplifier circuit 31 from a line 38. The gain of the amplifier circuit 31 is, for example, about 10. Regarding the multiplication coefficient K of the first multiplication circuit 32, K=0 when the reception level represented by the signal applied from the terminal 27 is the lowest, and K=1 when the reception level is the maximum.

The voltage of the acoustic signal at the terminal 22 is Ei, the voltage of the acoustic signal at the terminal 23 is Eo, the gain of the amplifier circuit 31 is A, the multiplication coefficient of the first multiplication circuit 32 is K, and the second multiplication circuit 36 is When it is assumed that it has the same configuration as the 1 multiplication circuit 32,
The first equation holds true.

{(Ei・K−E0・K)A+Ei}
1/1+P・C・R=Eo (1) Therefore, the second formula is established.

Eo=Ei×1/1+P・C・R/(1+K・A) …(2) In the first and second equations, C is the capacitance of the capacitor 35, R is the resistance value of the resistor 34, and P is the resistance of the acoustic signal. The angular frequency (P=jω).

Referring to the second equation, when the reception level of the broadcast frequency signal to be received is high and the value of K is close to 1, the cutoff frequency is:
When the received level is low and the value of K is close to zero, the cutoff frequency becomes a low value. This is also shown in Figure 4, where as the received level decreases, the value of K decreases, and accordingly the cutoff frequency
1, 2, and 3 move to smaller values in this order. Here, the cutoff frequency is as shown in the third equation.

=1+K・A/2π・C・R …(3) In this way, when the reception level is low and the electric field strength is weak, the cutoff frequency becomes a low value, and therefore, the cutoff frequency becomes a low value, so that beats etc. due to adjacent broadcast frequency signals are suppressed. Noise generation can be sufficiently suppressed.

Although the multiplication circuits 32 and 36 had the same configuration in the above embodiment, they may have mutually different configurations according to the present invention. In the example described above,
Although only one tone control circuit 21 is provided, for example, tone control circuits 21 are provided separately for the left channel and right channel for receiving stereo broadcasting, and in such a case, when integrated circuit The effect of reducing the number of terminals becomes significant.

Effects As described above, according to the present invention, it is possible to reduce the number of terminals of the tone control circuit that attenuates the high frequency range of the acoustic signal as the reception level of the high-frequency signal becomes smaller. It is effective for Also, depending on the reception level, the first
Since the output value of the second multiplication circuit is changed, the cutoff frequency of the acoustic signal changes,
This makes it possible to improve the high frequency attenuation effect.

[Brief explanation of the drawing]

Figure 1 is the electrical circuit diagram of the prior art, Figure 2 is the electrical circuit diagram of the prior art.
A graph showing the frequency characteristics of the tone control circuit 7 shown in the figure, FIG. 3 is an electric circuit diagram of an embodiment of the present invention, and FIG. 4 shows the frequency characteristics of the tone control circuit 21 shown in FIG. It is a graph. 1... Tuning circuit, 2... Mixing circuit, 3... Local oscillation circuit, 4... Intermediate frequency amplification circuit, 6, 10...
...Detection circuit, 21...Tone control, 25
... Amplification circuit, 26 ... Speaker, 28 ... Addition circuit, 31 ... Amplification circuit, 32 ... First multiplication circuit, 36 ... Second multiplication circuit, 37 ... Subtraction circuit.

Claims (1)

[Claims] 1. A first detection means for receiving a high frequency signal and deriving an acoustic signal; and a second detection means for detecting a reception level of the high frequency signal; having two input terminals, one of which has two input terminals; an adder circuit that receives the acoustic signal at an input terminal thereof; a first multiplier circuit that multiplies the acoustic signal by a value corresponding to the reception level output from the second detection means; a resistor connected in series,
a second multiplication unit that multiplies an integral type capacitor connected to the output side of the resistor, an output at a connection point between the resistor and the capacitor, and a value corresponding to the reception level output from the second detection means; A receiver comprising: a circuit; and a subtraction circuit that calculates the difference between the output of the first multiplication circuit and the output of the second circuit, and supplies a signal representing the difference to the other input terminal of the addition circuit. .