JPH0124991Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a receiver that receives both AM and FM.

Conventionally, automatic gain control devices (hereinafter abbreviated as AGC in this specification), as already well known,
Transistors, field effect transistors, PIN diodes, etc. were controlled by the AGC voltage.

Figure 1 is a block diagram of a device that controls the gain of a high-frequency amplifier using the AGC voltage. In the figure, 1 is an antenna terminal, 2 is an antenna tuning circuit, 3 is a high-frequency amplifier, 4 is a high-frequency tuning circuit, and 5 is a mixer/ A local oscillator, 6 a first intermediate frequency amplification stage, 7 an AGC detection circuit, a voltage doubler rectifier circuit, and a DC amplifier are all collectively represented, and 8 represents the next stage. Figure 2 is
This is a block diagram of a device that controls the amount of attenuation of a PIN attenuator using an AGC voltage. In the figure, reference numbers common to those in FIG. 1 represent the same parts as in FIG. 1, and 9 represents the PIN attenuator.

Since these systems are designed with a weak input level optimum bias, as the AGC works, the optimum bias is lost and the distortion component of the device increases. This situation is shown in FIG. In FIG. 3, 10 represents a change in attenuation as a function of input level, and 11 is a curve representing a change in distortion. As seen in Figure 3, as the input level increases, the AGC
Although the effect appears, the distortion component increases and the effect of AGC weakens. These are the drawbacks of device control.

Furthermore, even if AGC is applied to the high-frequency amplifier as shown in FIG. 1, if the antenna input level increases further, the tuner itself will reach a saturation level, so the strong input characteristics will not be improved much.

The situation is shown in Figure 4. In a tuner without AGC, the output level changes from A to B to C to D as the input level increases, but reaches a saturation level at _X2 . If you attach AGC to Chiyuna, A → B
It shows the change in output level from →E→D, and it can be seen that the saturation level has increased to _X4 . Furthermore, in order to measure the increase in X ₄ , it is sufficient to increase the effect of AGC, but if the AGC operation level is set above X ₁ , the distortion increases as it approaches the saturation level point C.
Setting it below X ₁ increases the gain of the AGC amplifier,
It may become unstable or the distortion component of AGC double voltage detection may become unstable.
It wraps around the AGC loop. That is, in both cases, distortion components are generated due to device control. Moreover, there is a drawback that the distortion occurs during strong input when the effect should be exhibited most.

Furthermore, since these circuits extract the detection signal from the load of the mixer, even if a mixer with a somewhat low load Q is used, the signal is dominated by the desired input signal in most cases. Therefore, there are many interference signals,
Even if intermodulation or cross modulation occurs in the tuner section,
There is a drawback that it is difficult to facilitate the operation of AGC in a wide band. On the other hand, it is better to completely eliminate the interfering signal by increasing the mixer load Q and apply AGC only to the desired signal, but it is difficult to obtain an ideal mixer load Q (high Q).

The object of the present invention is to provide a receiver of the type mentioned at the beginning, in which the interference characteristics such as cross-modulation distortion and intermodulation distortion of the FM tuner circuit are improved by a simple method.

In order to achieve the above object, the receiver according to the present invention includes a noise prevention coil between the branch point of the input signal to the AM tuner section and the FM tuner section and the antenna, and a PIN diode in parallel with the coil. and a capacitor in series with each other, and the above
The PIN diode control circuit, which is activated by the AGC voltage output from the FM tuner section, turns on the PIN diode when there is a weak FM input,
The gist is that the PIN diode is configured to be turned off during strong input.

Hereinafter, the present invention will be explained in more detail using examples with reference to the drawings, but these are merely illustrative and it is understood that various modifications and improvements may be made without going beyond the scope of the present invention. Of course.

Figure 5 is a circuit diagram of a high frequency signal attenuation circuit, a tuning circuit, a high frequency amplification circuit, and an intermediate frequency amplification circuit according to the present invention.
Represents the same part as in the figure, 12 is AM
A tuner 13 is an FM tuner including a mixer and a first intermediate frequency amplification section, and 14 is an FM tuner leading to an audio section. Dx is a PIN diode added according to the present invention, Cx ₁ and Cx ₂ are capacitors,
Lx is AM noise prevention coil, Qx ₁ and Qx ₂ are NPN
The transistors Rx ₁ , Rx ₂ , and Rx ₃ are resistors.

Here, the coil Lx has an inductance of 100μH to 200μH, and together with the antenna capacitance, it forms a reduction pass filter to cut out the frequency band where car electrical noise, such as remote control mirror noise and blower noise, is likely to occur. There is. Here, the response decreases rapidly above 2.0MHz. L ₁₀₁ is
It has an impedance of about 5 μH and is used to prevent FM band signals from being mixed in, and is also a noise prevention coil.

Also, Vcc is the power supply for FM, V'cc is the power supply for AM,
_Q1 is a dual gate FET, and 13a is an AGC terminal of the FM tuner section 13.

FIG _. 7 is _a block diagram used to facilitate understanding of the operation of the circuit shown in FIG.
Tuner section, FM consists of FM tuner 13, capacitor C ₁ , FETQ ₁ , PIN CL
is a PIN diode control circuit consisting of a portion from point X _A to resistor Rx ₃ , including transistors Qx ₂ and Qx ₁ , etc.

In the circuit shown in Figure 5, first, when receiving AM,
Power is supplied from the AM power supply V'cc, and the FM power supply
Since power is not supplied from Vcc, no voltage is applied to the PIN diode Dx, which turns it off. . Therefore, the signal from the antenna 1 passes through the capacitor Cx ₂ , passes through the noise prevention coil Lx, reaches the coil L ₁₀₁ , and is supplied to the AM tuner 12.

Next, when receiving FM, the power supply from the AM power supply V'cc is cut off, so the AM tuner 12 does not operate.
Instead, power is supplied from the FM power supply Vcc.

Now, when FM weak input is applied, FM tuner 13
The voltage at the AGC terminal 13a becomes 6 to 7V, so the point _XA also becomes 6 to 7V, and the dual gate FETQ ₁
is in optimal operation, working at maximum gain and having the lowest S/N. At this time, the transistor Qx ₂ is turned on, the transistor Qx ₁ is turned off, and the voltage of the FM power supply Vcc is applied to the PIN diode Dx, which turns on. Therefore, the signal from antenna 1 is
FM tuner 13 via Cx ₂ , Dx, Cx ₁ , C ₁
is supplied to

Also, when FM strong input is applied, the voltage of AGC terminal 13a
Since it drops to about 0.5V, the voltage at point _XA also becomes 0.5V. Then, the operation of FETQ ₁ is cut off, transistor Qx ₂ is turned off, and transistor
Since Qx ₁ is turned on and the power supply from the FM power supply Vcc is grounded, the PIN diode Dx is turned off. Therefore, at this time, the signal from antenna 1 is sent to FM tuner 13 via Cx ₂ , Lx, and C ₁ .
, and the signal is significantly attenuated. If these operations are expressed in an equivalent diagram,
It will look like Figure 6.

In FIG. 6, a represents an equivalent circuit at a weak input, b at a medium input, c at a large input, and d at an even higher input, R>>r, and the lower end is connected to the tuner.

As shown in Figure 6, when inputting weaker than these, the PIN
Diode Dx is short-circuited, and coil Lx does not participate in the receiving state, but it has a small resistance r at medium input.
Lx operates in parallel. When it comes to even larger inputs,
The voltage applied to the PIN diode Dx becomes smaller,
Its operating resistance increases and as the input level increases further, the circuit opens and the signal inevitably passes only through the coil Lx and is fed to the FM tuner circuit. . Therefore, the received signal is sufficiently attenuated.

As explained above, according to the present invention, by simply adding a small number of parts, the received signal during strong FM input can be attenuated in the antenna circuit, thereby reducing intermodulation distortion and interference during FM reception in AM/FM receivers. Modulation distortion can be significantly reduced.

[Brief explanation of the drawing]

Figures 1 and 2 are block diagrams showing the configurations of two different conventional devices that control gain by AGC voltage, Figure 3 is a graph showing the relationship between input level, attenuation, and distortion, and Figure 4 is a graph showing the relationship between input level, attenuation, and distortion. The figure is a graph showing the relationship between antenna input level and tuner output level, Figure 5 is a circuit diagram of a high frequency signal attenuation circuit according to the present invention, and Figures 6 a, b, c and d are according to the present invention at various receiving input levels. FIG. 7, an equivalent circuit diagram of the antenna circuit, is a block diagram for explaining the operation of the circuit of FIG. 5. 1... Antenna terminal, 2... Antenna tuning circuit, 3... High frequency amplifier, 4... High frequency tuning circuit, 5... Mixer/local oscillator, 6... First high frequency amplification stage, 7... AGC detection circuit , 8...An arrow indicating reaching the next stage, 9...PIN attenuator, 10...A curve expressing a change in attenuation as a function of the input level, 11...A curve expressing a change in distortion as a function of the input level. 12...AM tuner section, 13...mixer and first intermediate frequency amplification section,
14...An arrow indicating that it leads to the audio section,
Dx...PIN diode, Cx ₁ , Cx ₂ ...Capacitor, Lx...AM noise prevention coil, Qx ₁ , Qx ₂ ...
...NPN transistor, Rx ₁ , Rx ₂ , Rx ₃ ...Resistor.

Claims (1)

[Claims for Utility Model Registration] An AM tuner section, an FM tuner section, a noise prevention coil provided between the branch point of the input signal to both tuner sections and the antenna, and a coil connected in parallel with the above coil. It is operated by a PIN diode and a capacitor connected in series with each other and the AGC voltage output from the FM tuner section, turning on the above PIN diode when there is a weak FM input, and turning off the above PIN diode when there is a strong FM input. An AM/FM radio receiver comprising: a PIN diode control circuit;