JPS6044849B2 - FM-AM receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In an FM-AM receiver, the FM receiving section thereof is generally provided with a muting circuit.

This is because when the sensitivity of the FM receiving section is increased, the overall gain inevitably increases, so inter-station noise increases during channel selection operations, and this is to prevent the feeling from becoming worse. On the other hand, the AM receiving section is generally not provided with a muting circuit, but for the same reason and to avoid discomfort such as inter-station heat and random noise, it is considered to provide a muting circuit in the AM receiving section as well. It will be done.

However, simply providing a muting circuit for the AM receiving section will cause problems as will be described later when the FM receiving section and the receiving section are integrated into an IC.

The present invention attempts to realize muting of the FM-AM receiving section by taking such points into consideration.

An example of this will be explained below.

In FIG. 1, 10 indicates an FM receiving section, 11 its antenna tuning circuit, 12 a high frequency amplifier, 13 an interstage tuning circuit, 14 a mixer circuit, 15 a local oscillation circuit, and 16
is its resonant circuit.

When receiving FM, the function switch (band changeover switch) 36 switches to the FM side contact F as shown in the figure.
The voltage from the power supply terminal 39 is supplied as the operating voltage to the circuits 12, 14, and 15 through the switch 36, and although not shown, the voltage from the power supply terminal 39 is supplied to the circuits from the next stage onward regardless of the switching of the switch 36. Operating voltage is always supplied. Therefore, the intermediate frequency signal of the received FM wave is taken out from the mixer circuit 14, and this intermediate frequency signal is passed through the band pass filter 17, which has a band pass filter having an intermediate frequency transformer and a ceramic filter, and further outputs the intermediate frequency signal. It is supplied to the FM demodulation circuit 19 through the amplification limiter amplifier 18 and demodulated, and the demodulated signal is sent to the attenuator 2 for level adjustment.
1 → FM side contact F of the function switch 31 → is supplied to the stereo demodulation circuit 33 through a muting switch circuit 32 (described later), and when the demodulated signal is a stereo composite signal, the left and right channels are output from the stereo composite signal. A stereo signal is demodulated and taken out to the output terminals 34L, 34R, while when the demodulated signal is a monaural signal, the monaural signal is taken out as it is to the terminals 34L, 34R.

Further, 40 indicates an AM receiving section, 41 its antenna tuning circuit, 42 a mixer circuit, 43 a local oscillation circuit, and 44
is its resonant circuit.

When receiving W, the switch 36 is switched to the AM side contact A, contrary to the diagram, and the voltage from the terminal 39 is transferred to the circuit 42.
. Therefore, from the mixer circuit 42,
The intermediate frequency signal of the received AM wave is extracted, and
This intermediate frequency signal is supplied to a detection circuit 47 through a bandpass filter 45 having, for example, an intermediate frequency transformer and a ceramic filter, and further through an amplifier 46 for intermediate frequency amplification, and is detected.The detected signal is sent to an attenuator for level adjustment. 48 → AM side contact A of switch 31
-> switch circuit 32 -> stereo demodulation circuit 33 and output to terminals 34L and 34R. At this time, the detection signal from the detection circuit 47 is supplied to the low-pass film 51 to extract the DC component, that is, the AGC voltage at a level corresponding to the input electric field level. The signal is supplied to the mixer circuit 42 and intermediate frequency amplifier 46 through 52, and AGC is performed.

For such FM receiving section 10 and M receiving section 40,
A muting circuit according to the present invention is configured as follows.

That is, at the time of FM reception, the FM intermediate frequency signal obtained by the intermediate frequency amplifier 18 is supplied to the detection circuit 23 and detected, and this detected signal is supplied to the low pass filter 24 to output the signal at a level corresponding to the input electric field level, and , a direct current voltage whose level changes in accordance with the bandwidth, that is, a muting signal is formed, and this muting signal is supplied to the adder circuit (combining circuit) through the switch circuit 25.

Also, when receiving AM, the detection signal obtained by the detection circuit 47 is
The muting signal supplied to the low-pass filter 54 is supplied to the adder circuit 65 through the switch circuit 55.

Then, the output signal of the adder circuit 65 is sent to the switch circuit 32 through the attenuator 64 for setting the muting level, the muting switch 66, and the Schmitt circuit 67.
is supplied as its control signal.

Furthermore, the presence or absence of voltage at contact A of the switch 36 is detected by the detection circuit 61, and the detection signal is transmitted to the switch circuit 2.
5, 55 as the control signal, and when receiving FM (
As shown in the figure, when voltage is not being supplied to contact A, the switch circuit 25 is on and switch circuit 55 is off, and when receiving data (when voltage is being supplied to contact A), , contrary to the figure, the switch circuit 25 is turned off and the switch circuit 55 is turned on.

A display circuit for input electric field level is also configured.

That is, the DC voltage from the filter 24 is supplied to the adder circuit (combining circuit) 68 through the switch circuit 28. Furthermore, the DC voltage from the filter 54 is applied to the switch circuit 5.
8 to an adder circuit 68. The output signal of the adder circuit 68 is then supplied to an input level meter 69. Further, the detection signal from the detection circuit 61 is transmitted to the switch circuit 2.
8 and 58 as their control signals, and the switch circuits 28 and 58 are controlled in the same manner as the switch circuits 25 and 55.

Furthermore, in order to ensure the operation of the muting circuit and the electric field level display circuit, the structure is as follows.

That is, contact A of the switch 36 is connected to, for example, a bias circuit of an amplification transistor of the intermediate frequency amplifier 18 through a resistor 71.

Further, the DC power supply 73 is connected to the adder circuit 52 through the switch circuit 74, and the detection signal of the detection circuit 61 is supplied to the switch circuit 74 as its control signal. It is turned on, and turned off when receiving AM.

Note that the portion surrounded by the chain line in the figure is integrated into one IC.

According to such a configuration, the switches 31 and 36 are connected to the contact point F.
When the mode is switched to FM broadcast reception mode, the switch circuits 25, 55, 28, 58, and 74 are switched to the state shown in the figure by the detection signal from the detection circuit 61.

Therefore, the muting signal from the filter 24 is sent to the switch circuit 3 through the switch circuit 25 → addition circuit 65 → attenuator 64 → switch 66 → Schmitt circuit 67.
2, and muting is performed during FM reception. Also, at this time, a voltage indicating the input electric field level from the filter 24 is supplied to the meter 69 via the switch circuit 28→addition circuit 68, and the input electric field level of the FM wave is displayed.

During FM reception, the DC voltage from the power supply 73 is supplied as an N°C voltage to the mixer circuit 42 and intermediate frequency amplifier 46 through the switch circuit 74 and the adder circuit 52, so the gains of these circuits 42 and 46 decrease. , the detection circuit 47 cannot obtain a detection signal, and the switch circuit 55
, 58 are also off.

Therefore, the muting operation during FM reception and the display of the input electric field level are not influenced by the AM receiving section 40. On the other hand, when the switches 31 and 36 are switched to contact A, the mode is AM broadcast reception mode. At this time, the detection signal of the detection circuit 61 causes the switch circuit 2
5, 55, 28, and 74 are switched to states opposite to those shown in the figure.

Therefore, the muting signal from the filter 54 is transmitted to the switch circuit 3 through the switch circuit 55 → adder circuit 65 → attenuator 64 → switch 66 → Schmitt circuit 67.
2, and muting is performed during AM reception. At this time, a voltage indicating the input electric field level from the filter 54 is supplied to the meter 69 via the switch circuit 58→addition circuit 68, and the input electric field level of the AM wave is displayed.

When receiving this AM, the DC voltage at the terminal 39 is supplied to the bias circuit of the intermediate frequency amplifier 18 through the contact A of the switch 36 and the resistor 71, so that the bias of the intermediate frequency amplifying transistor is shifted and the amplifying operation is performed. is stopped, no detection signal is obtained in the detection circuit 23, and the switch circuits 25 and 28 are also off.

Therefore, the muting operation and the display of the input electric field level during AM reception are not affected by the FM receiving section 10. Thus, according to the present invention, not only FM broadcasting but also AM broadcasting can be performed.
You can also apply mutating to broadcasts,
Therefore, AM broadcasting can be selected with good feeling. Moreover, in that case, according to the invention, in particular the switch circuits 55, 5
8, when the switches 31 and 36 are switched from the AM mode to the FM mode, the muting will not malfunction or the meter 69 will not go overboard.

That is, during FM reception, the voltage from the power supply 73 lowers the gains of the mixer circuit 42 and the intermediate frequency amplifier 46, making it impossible to obtain a detection signal from the detection circuit 47, so that a mutating signal (DC voltage) from the filter 54 is also obtained. I won't be able to do it.

Therefore, even if the switch circuit 55 is not provided, muting should be performed during FM reception. However,
Since the filter 54 must extract only the DC component not included in the output signal of the detection circuit 47, its time constant must be sufficiently large. Therefore, even if the switches 31 and 36 are switched from the AM mode to the FM mode, a DC voltage, that is, a muting signal, is still obtained from the filter 54 for a short time after the switch is switched. Therefore, if the switch circuit 55 is not provided, when the switches 31 and 36 are switched to the FM mode, the muting signal from the filter 54 is supplied to the switch circuit 32 through the adder circuit 65, turning it on.

Therefore, when switches 31 and 36 are switched to FM mode, muting is canceled, so at this time,
If the FM is out of tune, or even if it is in tune, the electric field level is not suitable for canceling the muting, noise will be extracted to the terminals 34L and 34R as the muting is canceled. This makes the listener feel uncomfortable. Similarly, when the switch circuit 58 is not provided, when the switches 31 and 36 are switched to FM mode, the DC voltage remaining in the filter 54 is added to the DC voltage from the filter 24, so the meter 69 ends up being thrown off.

However, in the present invention, switch circuits 55 and 58 are provided, and when the switches 31 and 36 are switched to FM mode, the DC voltage remaining in the filter 54 is cut off. The meter 69 never goes over. In addition,
Since the output signal of the detection circuit 23 does not include an AM component, the time constant of the filter 24 is small, so the switch 31
, 36 to AM mode, almost no DC voltage remains in the filter 24, so the switch circuits 25, 36 are switched to AM mode.
28 may not be provided, but if provided, it will be even more effective.

Figure 2 shows an example of the connection of the main parts, with transistors Qll, Q
The emitter of l2 is connected to a constant current source Xll to form a differential amplifier 81, and the transistors Ql3 and Ql4 are differentially connected using the transistor Qll as a constant current source. , Ql6 are differentially connected.

Transistors Q3l and Q32 forming a current mirror circuit 82 are connected to the collectors of the transistors Ql4 and Ql6 as loads. In addition, the transistor Q
33 is for biasing transistors Q3l and Q32. In this case, transistors Ql4 and Ql6 correspond to switch circuits 55, 58, and 74, and switch circuits 25,
There is no transistor corresponding to 28.

Also, are 83 to 87 current mirror circuits? be. During AM reception, the voltage at the terminal 39 is transferred from the contact A of the switch 36 to the transistor Ql through the resistor 77.
4, supplied to the base of Ql6, transistor Ql4,
Ql6 is turned on, and transistors Ql3 and Ql5 are turned off.

Therefore, the transistor Q2l of the current mirror circuit 83,
Q22 is turned off, which also turns off transistor Q1. Then, the DC voltage from the filter 54 is supplied to the transistor Ql2 to be converted into a current, and the current is amplified by the differential amplifier 81, and the output current is changed from the current mirror circuit 82 to the current mirror circuit 84 (the transistor Q44 is for bias). Transistor Q4l→Same transistor Q43→Transistors Q7l and Q72 of current mirror circuit 87 to be supplied to variable resistor 64 for voltage conversion, and this voltage is passed through mute switch 66→Schmitt circuit 67 to switch circuit 32
, and muting is performed during AM reception.

Further, the output current of the differential amplifier 81 is changed from the current mirror circuit 82 to the transistor Q4l of the current mirror circuit 84 to
Similarly, the signal is supplied to the meter 69 through the transistor Q42 and the transistors Q62 and Q8 of the current mirror circuit 86, and the input electric field level of the AM wave is displayed. On the other hand, F.M.
During reception, switch 36 is switched to contact F, contrary to the diagram, so transistors Ql4 and Ql6 are turned off and transistors Ql3 and Ql5 are turned on.

Therefore, the transistors Q2l and Q22 are turned on, and a predetermined DC voltage is obtained at the emitter of the transistor Q1 by the constant voltage diode D1, that is, a power supply 73 is configured, and this DC voltage is applied through the adding resistor 52. It is supplied as an AGC voltage to mixer circuit 42 and intermediate frequency amplifier 46, and their gains are reduced. Also, at this time, the transistors Ql4, Ql6 are turned off, so even if there is a DC voltage remaining in the filter 54, it is not supplied to the current mirror circuit 82, and therefore the remaining DC voltage is not supplied to the switch. It is not supplied to the circuit 18 or the meter 69.

Then, the DC voltage from the filter 24 is supplied to the transistor Q3 for current amplification, and the output current is supplied to the variable resistor 64 through the transistor Q5l of the current mirror circuit 85 → the transistor Q53 → the current mirror circuit 87. , Therefore, muting is performed during FM reception. Also, the output current of transistor Q3 is
The signal is supplied to the meter 69 through the transistor Q5l of the current mirror circuit 85 → the transistor Q52 → the current mirror circuit 86, and the input electric field level of the FM wave is displayed. FIG. 3 shows an example of how the FM intermediate frequency amplifier 18 is connected.

That is, transistors Q8l, Q82 and constant current source
1 constitutes a differential amplifier 181, and transistors Q85, Q86 and constant current source X2 constitute a differential amplifier 1.
82 are configured. The intermediate frequency signal from the filter 17 is then supplied to the demodulation circuit 19 through the differential amplifier 181→emitter follower transistors Q33, Q84→differential amplifier 182→emitter follower transistors Q87, Q88. During AM reception, the DC voltage at the terminal 39 is supplied to the base of the transistor Q82 through the contact A of the switch 36 and the resistor 71, which turns on the transistor Q82 and turns off the transistor Q8i, stopping the amplification action. It will be done.

In the above description, the switch circuit 32 is provided separately for the sake of explanation, but it may also be used as a switching element for switching demodulation in the stereo demodulation circuit 33.
Further, a similar switch circuit may be provided between the demodulation circuit 33 and the terminals 34L and 34R. Furthermore, the filter 24,
The input 54 may be any input having information regarding the bandwidth or input electric field level of the intermediate frequency stage of the receiving sections 40 and 10. Further, an adder circuit may be used in place of the switch 31, and the switch 66 may be omitted.

[Brief explanation of drawings]

FIG. 1 is a system diagram of an example of the present invention, and FIGS. 2 and 3 are connection diagrams of a part thereof. 10 is an FM receiving section, 40 is a store receiving section, and 33 is a stereo demodulation circuit.

Claims (1)

[Claims] 1. Provided in a signal path between an FM reception section, an AM reception section, a switch for selecting the operation of these FM reception section and AM reception section, and an output terminal common to the FM reception section and AM reception section. A first switch circuit that performs muting, a first low-pass filter that extracts a DC signal related to the input electric field level from the FM receiver, and a time constant that is larger than the time constant of the first low-pass filter. a second low-pass filter for extracting a DC signal related to the input electric field level from the section, and a second switch circuit, and controls the DC signal from the first and second low-pass filters to the first switch circuit. An FM-AM receiver that performs muting by supplying the signal as a signal, and that when receiving FM, the second switch circuit cuts off the output of the second low-pass filter.