JPS58119236A - Fm-am reception circuit - Google Patents

Abstract

PURPOSE:To obtain a reception circuit which can receives AM, FM electromagnetic waves stably, by attaining stable amplification and detection of intermediate frequencies by using a special low-pass filter operated only at the reception of AM signals. CONSTITUTION:An FM high-frequency circuit 1 is connected to a contact (b) of an FM/AM changeover switch S1, an AM high-frequency circuit 2 is connected to a contact (a) and IF amplifier circuits X, Y in common use of FM and AM are connected to the circuits 1, 2 via IF filters F1, F2. An FM signal from a circuit Y is amplified at an FM-IF amplifier circuit F and an AM signal from the circuit Y is amplified at an AM-IF amplifier circuit A. The circuit A is provided with low-pass filters L1, L2 comprising capacitors 25, 28 and resistors 26, 27, and the output of the circuit A is detected at an AM detection circuit D. The output of the circuit F is detected at an FM detection circuit 42. In receiving the AM signal, signals more than IF of AM pass through at the filters L1, L2 to make the IF amplification and detection stable.

Description

[Detailed description of the invention] The present invention relates to an FM-AM receiving circuit.

In general, most types of receiver-resistant receivers are known to have a circuit configuration in which the amplifying element of the intermediate frequency amplifying circuit is shared, for example, in common use with the store-7M.

However, such a circuit has the following drawbacks.

In other words, 1. The local oscillation frequency t/ in the tree high frequency [11 paths is higher than the receiving frequency by the intermediate frequency; instead, if the receiving frequency is 1000 KHz, the local oscillating frequency is 100 KHz.
0 + 455 = 1455 KHz.

When this local oscillation frequency (1455KHz J or AM) leaks from the frequency circuit to the base of the transistor in the intermediate frequency amplifier circuit, the local oscillation frequency is amplified by a large amplifier in the intermediate frequency amplifier and is transmitted to the next stage detection circuit. Added.

For this reason, even if there is no input signal, a DC voltage is output as the detection output, which causes the inconvenience that this output operates as an automatic gain control signal (AGO signal).

In addition, when operating the receiver in a large transfer, for example, 1,000 wires should be connected to the input lead wire of the intermediate frequency amplifier circuit
A directly received signal of KHz may appear, and in such a case, this directly received signal (that is, input signal) is amplified by an intermediate frequency amplifier circuit, α-detected by the next stage α-detecting circuit, and the Fi store detected signal is generated. The disadvantage is that the signal output can always be heard even if the local oscillation frequency is not adjusted and tuned.

In order to eliminate this drawback, if a low-pass filter is simply incorporated into the intermediate frequency amplification circuit, the intermediate frequency song of the rooster is 10.7 MEfx, and the frequency between α9 (455 KHz) is
Since the frequency is higher than that of the filter, a disadvantage arises in that the intermediate frequency signal is attenuated by the capacitor constituting the filter and then applied to the half-wave detection circuit or the α-detection circuit, making it impossible to perform stable operation.

The present invention has been made in view of these circumstances, and by using a special low-pass filter that operates only when receiving an AM signal, it is possible to perform each operation of intermediate frequency amplification and detection stably. Its purpose is to provide an FM-AM receiving circuit.

The configuration of the present invention includes: (1) a suspicious reception changeover switch, (2) an intermediate frequency amplification circuit, an illness intermediate frequency amplification circuit, and an α detection circuit;
In the eight-channel reception I circuit comprising a y-detection circuit,
A first signal system that applies a signal from the intermediate frequency amplification circuit to the inspection circuit and performs α detection; a $22 signal system that applies a signal from the intermediate frequency amplification circuit to the α detection circuit and performs α detection;
A third signal system that adds a signal from the intermediate frequency amplification circuit to the y detection circuit to perform y detection, and a low pass filter that attenuates signals higher than the intermediate frequency only when receiving an AM signal are provided, and the filter is connected to the second It is installed in the signal system, and when the reception signal is received, it is determined by the switching operation of the reception selector switch.
It operates by passing through a low-pass filter that reduces signals above the intermediate frequency, and passes through the filter when receiving strong signals.
I tried not to do that.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

Fig. 1 shows the electrical circuit of the FM-AM receiving circuit according to the present invention, where (81) is a reception selector switch (81); when the switch (Sl) is turned to the a side, the reception operation is performed; When inserted into the side, it performs N reception operation.

(1) is a y high frequency circuit connected to the b side of the switch (Sl), (2) is an AM high frequency circuit connected to the a side of the switch (81), and each of these high frequency circuits 11 f2
1 is connected to the next stage circuit through intermediate frequency filters (Fl) (Fs) % respectively.

Do(Y)ti sotL sotL ) 5 y shi xri (61
(71, Q41CIS color fj AM-7M common intermediate frequency amplification circuit, (to) is the west intermediate frequency amplification circuit consisting of transistor AS (2I, (4) is transistor (21C
This is an intermediate frequency amplification circuit consisting of II.

Also, the peak is an α detection circuit consisting of a transistor C141 (to), and an anti-wavelength circuit made by Co., Ltd., which performs α detection by adding a signal from the intermediate frequency amplification circuit to the α detection circuit.
1 signal system and 1. ■A second signal system that adds a signal from the intermediate frequency amplification circuit (4) to the α detection circuit (G) and performs α detection, and Jγ
1. A third signal system that adds a signal from the intermediate frequency amplification circuit to the west detection circuit and performs detection. A low-pass filter (L) that reduces signals above the intermediate frequency only when receiving AM signals.
l) (Ls) is interposed in the second signal system.

Here, the -10,000 low-pass filter CLl)' is composed of four capacitors and a resistor, and the other low-pass filter (
I4) It is composed of an H capacitor (support) and a resistor (to), and these q3 filters (Ll) (Ls) Fi
It is designed to attenuate signals above the AM intermediate frequency (455 KHz).

Next, the operation of the above configuration will be described.

First, let's talk about the N reception operation.

Now, when the switch (Sl) is turned to the b side, power (10 B) is applied to the FM high frequency circuit (1), the high frequency circuit (1) operates, and when it receives a high frequency signal, it converts the frequency and outputs an intermediate signal. The frequency signal (10.7MHz signal) is connected to the terminal (O
The transistor (6) which configures the intermediate frequency filter (FIJ) and the intermediate station and amplifier (3) via the
) is added to the base of the intermediate frequency signal.

This signal is the transistor +61 +71α4) t15
After being amplified by 1 (till tn), it appears at the resistor (28@). This signal is applied to the oscillator detection circuit (421) for west detection, and is taken out from the terminal throat as an FM detection output.

At this time, the power supply (10B) is connected to the a side of the switch (Sl).
is not supplied, so the transistor is off and the transistor is on.

Therefore, although the bias voltage of the diodes (4) and (5) is applied to the transistor (II (lIc211 (1B)) 143, the base of the transistor (to) is negatively biased when the transistor is turned on, and the transistor is off, so the differential amplifier does not operate.

Further, the collector signal of this bottle base transistor am is applied to the base of the detection transistor c141eB, and can be detected at the emitters of these transistors to obtain a DC signal.

Since there is almost no positive signal component when the image signal is input, a DC voltage is extracted from the industrial ivy of the transistor rMJ (!il), and a DC signal that changes depending on the magnitude of the FM input signal can be extracted.

This DC signal is taken out to a terminal, and can be used as a drive signal for a level meter that displays the magnitude of the input signal level, or as a tuning instruction signal.

Next, the store receiving operation will be explained.

Now, when the switch (81) is turned to side a, power (10 B) is applied to the high frequency circuit (2) and the AM high frequency circuit (
2) is brought into operation.

When a high frequency signal is received, the frequency is converted to 9 and medium! The Vl harmonic harmonic signal (signal of 55 KHz) is outputted from the terminal (d) and applied to the intermediate frequency filter (FsJ) and the base of the transistor (6) constituting the intermediate frequency amplifier (2) via two points.

This signal is transmitted through transistor f61 +71α41 (151
resistor 1, which roughly constitutes a low-pass filter.
231(2) and is amplified by the transistor@en.

The signal of the collector of each of these transistors is added to the base of the detection transistor (to) (to), and the anti-wavelength output is taken out to the emitter of the transistor 31W+.
The signal obtained by detecting the erroneous modulation component can be taken out from the terminal.

On the other hand, the DC voltage at the emitter of the transistor also changes depending on the change in the input signal, and this DC signal is used to display the input level in the same way as when receiving a signal, or as a tuning instruction, and also used as a tuning instruction. It can also be used as a signal (automatic gain control signal).

Here, we will add an additional note regarding automatic gain control.

In FIG. 1, a control signal is applied to the base of the previous transistor 041cl through the resistor ■, and when the input signal becomes large, the transistor 041cl! The emitter voltage of 9 becomes high, turns on the transistor, and current begins to flow, so the current in transistor αG decreases, and the transistor (
The gain of 61 (71) is reduced to allow AGO operation.

In addition, this pre-signal can be added to the direct frequency circuit (2) to lower the gain in the case of a large input and perform AGO operation.

By the way, when the above-mentioned question was received, the switch (81) was turned on to the a side, and the transistor 511641 was turned on.
Transistor ■ turns off.

For this reason, a diode +41 is connected to the transistor (2).
Since the bias voltage of f51 is not applied, the transistor 12t+ u as eA does not operate. Also, when the transistor throat is off, the attached detection circuit (42) does not operate, so the attached detection circuit i4z also does not operate.When receiving this signal, the capacitor 2!51@ is connected to the resistor +231.
Together with 0241, it functions as a low-pass filter and attenuates signals above the AM intermediate frequency (455 KHz).

In this way, the low-pass filter (L
l) (Ls) is used to attenuate the local oscillation frequency signal, directly received signal, or signal input to the intermediate frequency circuit, thereby achieving good and stable reception.

Furthermore, if this circuit is integrated, it is also possible to configure the capacitor (2) within the integrated circuit.

This 4-m MO8 capacitor or the reverse bias capacitance between the base and emitter of the transistor can be used to form an integrated circuit, making it simple and low-cost.

Suppose that during the above-mentioned operation, the transistor Ql■ (company) is removed and the transistor (sub)■ (sub) is operated, the N intermediate frequency is 10.7MHz and the oil intermediate frequency (455KH).
Since the frequency is higher than that of the phantom, it is attenuated by the capacitor QS■, causing a drawback that it adds to the N detection circuit and anti-wavelength circuit.
), and the operation of transistors Qli2G and wm of the differential amplifier circuit of the intermediate frequency amplifier circuit is switched so that the signal passes through the low-pass filter (L1 bar Lm) only during reception without passing through It is something. This switching operation is performed by turning on and off the power supply (10 B) applied to the α high frequency circuit (2).

FIG. 2 shows another embodiment of the invention.

@ In Figure 1, whether or not the signal passes through the low-pass filter <Ll) (Ls) is determined by switching the operation of the intermediate frequency amplifier circuit, but in Figure 2, the operation of the intermediate frequency amplifier circuit is switched. +71αaas (2iI circle is always operated, and the detection transistor C34) is added with a second anti-wavelength transistor G@.

The emitter transistor of this transistor
The emitters of the 34 cans are connected in the same way, and the α detection output is the same.

When a signal is received, the transistor CM1m, which constitutes the AM detection circuit (DI), is turned on and the output output is output to the terminal (411). On the other hand, when receiving a question, the transistor 61 is turned on. Kitchen detection circuit (D
The transistors constituting the s) operate,
The signal that has passed through the low-pass filter (La) (Lm) between the resistor flff41 and the capacitor (2) is detected and output to the terminal. At this time, the detection transistor is off and the N detection circuit does not operate.

As described above, signals that do not pass through the low-pass filters (L8) and (Lm) are detected during normal operation, and good reception can be achieved on both sides of the river.

In the embodiment shown in FIG. 2, the anti-wavelength circuit (Dt) (Da
) by switching between ■reception and store reception■
This allows for good reception of both signals and shop signals.

As described in detail above, the present invention consists of the following: 1. FM-1M reception selector switch (Sl); ■In an FM-AIM receiving circuit comprising an intermediate frequency amplification circuit (4), an AM detection circuit, and an FM detection circuit, a signal is added from the intermediate frequency amplification circuit (to) to the detection circuit. The first signal system for wave detection and the AM intermediate frequency amplification circuit (
A second signal system that applies a signal from 2) to the store detection circuit [F] for store detection, and a third signal system that adds a signal from the Jγ intermediate frequency amplifier circuit (7) to the N detection circuit (company) and performs detection. , low tI that attenuates signals above the oil intermediate frequency only when receiving suspicious signals.
Since the IJ1 overfilter CLl) (Ls) is provided and the filters (Lt) (Lm) are interposed in the second signal system, the reception switching switch (81)
For switching: When receiving AM signals, the signals above the oil intermediate frequency (455 KHz) are filtered through a low-pass filter.
On the other hand, when receiving a signal, it does not pass through the filters (Ll) (Ls), which eliminates the conventional drawbacks mentioned in the chairman's meeting and stabilizes each operation of intermediate frequency amplification and detection. There are some effects that can be done.

[Brief explanation of drawings]

Figure $1 is an electrical circuit diagram showing one embodiment of the present invention, IJ! 2
The figure is an electrical circuit diagram showing another embodiment of the present invention. (Al is oil intermediate frequency amplification circuit, CD is anti-wavelength circuit, (
F5 is an intermediate frequency amplification circuit, <Ll) (Ls) (
La) (Lm) is a low-pass filter, <81)
IdFM-1M reception selector switch, +43-digit W detection circuit

Claims (1)

[Claims] In an FM-AM receiving circuit comprising an FM-AM receiving selector switch, a type intermediate frequency amplifying circuit, a second intermediate frequency amplifying circuit, a J-tomoe detection circuit, and an anti-configuration circuit, from the additional intermediate frequency amplifying circuit. A first signal system that adds a signal to the signal detection circuit and performs detection; a second signal system that adds a signal from the intermediate frequency amplifier circuit to the signal detection circuit and performs detection; and an anti-wavelength circuit from the FM intermediate frequency amplifier circuit. A WI3 signal system is provided which performs east detection by adding a signal to the IJ! FM-AM characterized by having two signal stages
receiving circuit.