JPH0510430Y2 - - Google Patents

Description

[Detailed explanation of the invention] (Field of industrial application) This invention is applicable to an AM/FM tuner in which an AM section and an FM section are incorporated as one tuner.
It concerns the AGC circuit.

(Prior Art) Figure 5 shows a block diagram of the main parts of a conventional tuner. As shown in Figure 5, conventionally, an AM tuner 1 and an FM tuner 2 are formed independently. An antenna input from an antenna 3 is separated by a coil 4 and a capacitor 5 into an AM band signal and an FM band signal, which have different frequencies, and the AM band signal is given to the AM tuner 1 via the coil 4, and the FM band signal is given to the FM tuner 2 via the capacitor 5. Here,
The AM tuner 1 and the FM tuner 2 are provided with pin diode attenuation circuits 6 and 7, respectively. The pin diode attenuation circuit 6 of the AM tuner 1 is driven and controlled by an AMAGC signal, and the pin diode attenuation circuit 7 of the FM tuner 2 is driven and controlled by an FMAGC signal.
The pin diode attenuation circuits 6 and 7 are provided to prevent the characteristics of the AM and FM tuners 1 and 2 from being distorted by a strong antenna input.

(Problems to be Solved by the Invention) In the tuner described above, the AM tuner 1 and the FM tuner 2 are provided with independent pin diode attenuation circuits 6 and 7, respectively. The pin diodes included in these pin diode attenuation circuits 6 and 7 are expensive. Therefore, the problem with the conventional one was that the tuner as a whole was expensive.

The purpose of this invention was to solve the problems of the conventional tuner mentioned above. By sharing one pin diode attenuation circuit between the AM section and the FM section, the entire tuner can be constructed at low cost. The purpose of the present invention is to provide an AGC circuit for an AM/FM tuner.

(Means for solving the problem) In order to achieve this purpose, the AM/
The AGC circuit of the FM tuner has a pin diode attenuation circuit interposed between the antenna input signal line and ground before being branched into the AM section and the FM section, and this pin diode attenuation circuit controls the amount of attenuation in parallel. The AMAGC signal output from the AM section is given to one of the control means, the FMAGC signal output from the FM section is given to the other control means, and the AMAGC signal output from the AM section is given to the other control means.
In response to the AMAGC signal, one of the control means controls the attenuation amount, and in response to the FMAGC signal, the other control means operates to make the attenuation amount zero, and when receiving FM, the other control means operates in response to the FMAGC signal. The attenuation amount is controlled by means and the above-mentioned
The AMAGC signal causes one of the control means to operate so as to reduce the amount of attenuation to zero.

(Function) Since a pin diode attenuation circuit is interposed between the antenna input signal line and the ground, the antenna input signal during strong input is attenuated before the RF amplifier circuit, causing distortion in the RF amplifier circuit. Can be prevented.
And when receiving AM, the FM signal is not received.
FMAGC signal is without FM input signal,
The control means to which the FMAGC signal is applied operates to make the attenuation amount zero. Therefore, by using a control means provided in parallel and receiving the AMAGC signal,
The amount of attenuation is controlled according to the AMAGC signal. Also, when receiving FM, the AM signal may not be received.
AMAGC signal is the state without AM input signal,
The control means to which the AMAGC signal is applied operates to make the attenuation amount zero. Therefore, by using control means provided in parallel and receiving FMAGC signals,
The amount of attenuation is controlled according to the FMAGC signal.

(Description of Embodiments) Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2. Figure 1 shows the AM/
2 is a block diagram of a main part of an FM tuner provided with an AGC circuit, and FIG. 2 is a circuit diagram of a specific embodiment of FIG. 1.

In FIG. 1, an antenna 13 is attached to an AM/FM tuner 12 having an AM section 10 and an FM section 11.
The antenna input is given from One pin diode attenuation circuit 15 is interposed between the signal line 14 and the ground before this antenna input is branched into the AM section 10 and the FM section 11. The pin diode attenuation circuit 15 includes two control means for controlling the amount of attenuation in parallel, and the AMAGC signal output from the AM section 10 and the FMAGC signal output from the FM section 11 are respectively The pin diode attenuation circuit 15 is driven and controlled by the respective signals through two control means.

A specific embodiment of this pin diode attenuation circuit 15 will be described with reference to FIG. In Figure 2,
The signal line 14 is connected to the anode of a first pin diode 17 via a DC blocking capacitor 16. Also, this first pin diode 1
The cathode of a second pin diode 18 is connected to the anode of 7, and the anode of the second pin diode 18 is grounded through a capacitor 19 and a resistor 20 in parallel, and is connected to a positive voltage through a resistor 21. A bias voltage is applied. The cathode of the first pin diode 17 is grounded through a resistor 22 and an NPN transistor 23 as one control means in series, and a resistor 24 and a PNP transistor 25 as the other control means in series. , and a bias voltage is applied via a resistor 26. The base of the NPN transistor 23 is given the AMAGC signal output from the AM section 10, and the base of the PNP transistor 25 is given the AMAGC signal output from the FM section 11.
FMAGC signal is given. Note that when a strong antenna input comes in, the AMAGC signal changes to a higher level, and the FMAGC signal changes to a lower level.

In such a configuration, the NPN transistor 23
Since the PNP transistor 25 and the PNP transistor 25 are connected in parallel, the current flowing through the first pin diode 17 is controlled in parallel. Therefore, first, during AM reception, the FMAGC signal is at a high level, making the transistor 25 non-conductive, and the AMAGC signal changes depending on the strength of the antenna input. And when the antenna input is weak, the AMAGC signal is low and the first and second
The pin diodes 17 and 18 are both non-conducting and the antenna input is not attenuated in any way. Also, when a strong antenna input comes in, the AMAGC signal changes to a high level, causing transistor 23 to conduct. Then, a forward current flows through the first and second pin diodes 17 and 18 due to the bias voltage, and the impedance decreases. Therefore, the antenna input is attenuated by a path via the DC blocking capacitor 16 and the first pin diode 17, and a path via the DC blocking capacitor 16, the second pin diode 18, and the capacitor 19.

Next, when receiving FM, the AMAGC signal is at a low level, making the transistor 23 non-conductive, and the FMAGC signal changes depending on the strength of the antenna input. Then, when the antenna input is weak, the FMAGC signal is high and the transistor 25 is non-conducting, and the first
and the second pin diodes 17 and 18 are both non-conducting and the antenna input is not attenuated in any way. Also,
When a strong antenna input occurs, the FMAGC signal changes to a low level, causing transistor 25 to conduct and attenuate the antenna input via the first and second pin diodes 17,18.

Therefore, one pin diode attenuation circuit 1
5 is shared by the attenuation circuit of the AM section 10 and the FM section 11, and both are driven and controlled by the AMAGC signal and the FMAGC signal.

Note that in the embodiment shown in Figure 2, when the antenna input is weak, the AMAGC signal has a low level;
I explained that the FMAGC signal is set to have a high level, but if the antenna input is weak,
If the levels of the AMAGC signal and FMAGC signal are both low, and if the antenna input is strong, the levels of both become high, then the PNP in Figure 2
Transistor 25 may be replaced with an NPN transistor. Conversely, if the antenna input is weak,
If the levels of the AMAGC signal and FMAGC signal are both high, and the antenna input is strong and the level is low, then the NPN in Figure 2
It is sufficient to replace the transistor 23 with a PNP transistor.

Figure 3 shows the AGC of the AM/FM tuner of this invention.
FIG. 7 is a specific circuit diagram of another embodiment of the circuit.

In FIG. 3, the signal line 14 is connected to a first pin diode 17 via a DC blocking capacitor 16.
is connected to the anode, and the cathode is grounded. Further, the anode of the first pin diode 17 is connected to the cathodes of third and fourth pin diodes 30 and 31, which serve as two control means provided in parallel. The anode of the third pin diode 30 is grounded via a capacitor 32 and connected to the AM section 1 via a resistor 33.
The AMAGC signal output from 0 is given. Further, the anode of the fourth pin diode 31 is grounded via a capacitor 34, and is supplied with the FMAGC signal output from the FM section 11 via a resistor 35. In addition, the third
The AMAGC signal and FMAGC signal in the figure are
The level is set so that when the antenna input is weak, the level is as low as zero, and when the antenna input is strong, the level is high.

In such a configuration, first, when receiving AM,
When the FMAGC signal is at zero level, the fourth pin diode 31 is non-conductive. Then, the AMAGC signal changes according to the antenna input, and a forward current flows through the third pin diode 30 and the first pin diode 17 according to the level of this AMAGC signal, lowering the impedance and attenuating the antenna input. will be done.

Next, when receiving FM, the AMAGC signal is at zero level and the third pin diode 30 is non-conductive.
The FMAGC signal changes depending on the antenna input, and the fourth pin diode 31 and the first pin diode 17 change depending on the level of this FMAGC signal.
The impedance of the antenna is reduced and the antenna input is attenuated.

Figure 4 shows the AGC of the AM/FM tuner of this invention.
FIG. 7 is a specific circuit diagram of still another embodiment of the circuit.
In FIG. 4, the same circuits as those in FIG. 3 are given the same reference numerals and redundant explanations will be omitted.

In FIG. 4, the pin diode 17 in FIG.
The anode of is the fourth pin diode 3 in FIG.
1, it is connected to the emitter of a PNP transistor 42 via a chiyoke coil 40 and a resistor 41 in series. The base of this PNP transistor 42 is supplied with the FMAGC signal outputted from the FM section 11 via a resistor 43, and the collector is supplied with a bias voltage via a resistor 44.
The AMAGC signal in Figure 4 is set so that the level is low to zero when the antenna input is weak, and high when the antenna input is strong.
The FMAGC signal is set so that the level is high when the antenna input is weak, and the level is low when the antenna input is strong.

In such a configuration, when receiving AM,
The FMAGC signal is at a high level and the PNP transistor 42 is non-conductive. Then, the antenna input is attenuated in accordance with the AMAGC signal corresponding to the antenna input, similar to the embodiment shown in FIG.

Furthermore, during FM reception, the AMAGC signal is at zero level and the third pin diode 30 is non-conductive.
Then, the impedance of the PNP transistor 42 is controlled by the FMAGC signal corresponding to the antenna input, and a forward current flows through the first pin diode 17 from the bias voltage. By controlling the impedance of this first pin diode 17, the antenna input is attenuated.

(Effects of the invention) As explained above, according to the AGC circuit of the AM/FM tuner of the invention, a pin diode attenuation circuit is interposed between the antenna input signal line and the ground, so the antenna during strong input The input signal is attenuated before the RF amplifier circuit, and distortion in the RF amplifier circuit can be prevented. Moreover, since one pin diode attenuation circuit is shared as an attenuation circuit for the AM section and the FM section, the number of expensive pin diodes required is reduced, and the pin diode attenuation circuit can be switched between AM reception and FM reception. There is no need to switch and connect by etc., and it has an excellent effect that it can be manufactured at a correspondingly low cost.

[Brief explanation of drawings]

Figure 1 shows the AGC of the AM/FM tuner of this invention.
FIG. 2 is a circuit diagram of a specific embodiment of the tuner shown in FIG. 1, and FIG. 3 is a block diagram of the AGC circuit of the AM/FM tuner of the present invention. It is a specific circuit diagram of another embodiment,
FIG. 4 is a specific circuit diagram of still another embodiment of the present invention, and FIG. 5 is a block diagram of the main parts of a conventional tuner. 10...AM section, 11...FM section, 12...
AM/FM tuner, 13... antenna, 14...
...Signal line, 15...Pin diode attenuation circuit,
17, 18, 30, 31...Pin diode, 2
3, 25, 42...transistor.

Claims (1)

[Claims for Utility Model Registration] 1. A pin diode attenuation circuit is interposed between the antenna input signal line and ground before being branched into the AM section and the FM section, and this pin diode attenuation circuit controls the amount of attenuation. The AMAGC signal output from the AM section is given to one of the control means, and the FMAGC signal output from the FM section is given to the other control means, and when receiving AM, In response to the AMAGC signal, one of the control means controls the attenuation amount, and in response to the FMAGC signal, the other control means operates to make the attenuation amount zero, and when receiving FM, the other control means operates to reduce the attenuation amount to zero in response to the FMAGC signal. The attenuation amount is controlled by the control means and the
One of the control means operates to reduce the amount of attenuation to zero in response to the AMAGC signal.
AM/FM tuner AGC circuit. 2. The pin diode attenuation circuit includes a parallel connection of one pin diode and two transistors interposed in series between the signal line and ground,
Claim 1 of the Utility Model Registration Claim, characterized in that the transistor is formed by applying the AMAGC signal and the FMAGC signal to each of the two transistors, and further applying a bias voltage to cause a forward current to flow through the pin diode. AM/FM tuner AGC circuit.