JPH05300043A - Attenuator circuit - Google Patents

Abstract

PURPOSE:To prevent deterioration in an IM and to reduce the adverse effect of it onto an antenna line. CONSTITUTION:When a passing quantity of an input signal is reduced by a PIN diode D2, the impedance at the input side is decreased up to a prescribed value by a PIN diode D1 whose operating resistor changes with a control voltage from a control voltage generating circuit 7A. Thus, when the electric field strength in an input signal is very high, the attenuation of the input signal is increased without incurring the deterioration in the IM and even in the case of a community receiving antenna employed, the adverse effect on other receiver is relieved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an attenuator for eliminating intermodulation interference or the like by attenuating the level of an RF signal which is an input signal when the electric field strength is too strong and excessive input occurs. Regarding the circuit.

[0002]

2. Description of the Related Art Conventionally, the electric field strength of an RF signal, which is an input signal from an antenna in a radio receiver, is constantly changing depending on the place, time, etc. If the electric field strength is too strong, intermodulation due to excessive input ( IM) and intermodulation may occur.

FIG. 1 schematically shows a radio receiver in which a signal passing amount is controlled by an operating resistance of a pin diode in order to eliminate such a bad effect. When the electric field strength is strong, the level of the RF signal is attenuated by the attenuator circuit 2a, and then the antenna circuit 3 for tuning and impedance matching is performed.
Is taken into the high-frequency amplifier circuit 4 via. The RF signal tuned by the high frequency amplifier circuit 4 and amplified to a predetermined level is mixed with the local oscillator signal from the local oscillator circuit 6 by the MIX circuit 5 to have an intermediate frequency of 10.7 MHz.

The attenuator circuit 2a is provided with a pin diode D2 inserted in series in the path of the RF signal. Anode side of pin diode D2 and capacitor C
A control voltage generating circuit 7a controlled by the CPU 8 is connected to a connection point with 1 through a coil L1 for blocking an RF signal.

The connection point between the cathode side of the pin diode D2 and the capacitor C2 is grounded via the resistor R1. Here, the pin diode D2 has a characteristic that its operating resistance decreases as the forward current increases.
The capacitors C1 and C2 are for blocking direct current.

When the attenuation of the level of the RF signal is increased, the value of the control voltage from the control voltage generation circuit 7a is decreased, and conversely when the attenuation is decreased, the value of the control voltage is increased. It is supposed to be done.

Further, FIG. 2 schematically shows a radio receiver in which an RF signal is shunted and attenuated by an operating resistance of a pin diode in order to eliminate the above-mentioned harmful effects. The pin diode D2 has its anode side connected to the RF signal path and its cathode side grounded. A current controlled by the control voltage generation circuit 7a controlled by the CPU 8 is supplied to the anode side of the pin diode D2 via the coil L1 for blocking the RF signal.

The RF signal is attenuated by the operating resistance of the pin diode D1 corresponding to the forward current value flowing in the pin diode D1.

[0009]

FIG. 3 shows the attenuation amount in the attenuator circuit 2b of FIG. 1 from 0 dB to 10 dB.
IM when variable in 3 steps of B, 15 dB, 20 dB
It is an example of actual measurement of characteristics.

In the figure, the horizontal axis represents the difference (Δf) in the interference frequency with respect to the reception frequency. For example, a curve of 0 dB means that the allowable level is higher as the interference wave is separated.

Generally, when the interference frequency is far from the reception frequency, the allowable level of the interference wave is high, and when the interference frequency is close to the reception frequency, the allowable level of the interference wave is low, which is the antenna of the radio receiver. This is due to the tuning characteristics of the circuit.
In the case of an ideal attenuator circuit, this curve should move parallel in parallel with the attenuation amount, but in FIG. 3, the allowable level when the attenuation amount is large decreases and Δ
Reverse rotation occurs on the plus side of f.

In the attenuator circuit 2a of the radio receiver shown in FIG. 1, even if the input voltage of the pin diode D2 is increased by lowering the control voltage from the control voltage generating circuit 7a in order to increase the attenuation amount. The stray C between the anode and the cathode of the pin diode D2 or electromagnetic coupling in the air causes interference radio waves to fly in, and the impedance of the pin diode D2 rises, resulting in impedance mismatch with the antenna circuit 3. This is because IM is likely to occur due to the occurrence of a standing wave due to the reflection of the RF signal.

Therefore, in this type of attenuator circuit, even if the nominal amount of attenuation is about 20 dB, the improvement in IM is limited to about 10 dB. On the other hand, in the attenuator circuit 2b shown in FIG. 2, the pin diode D1
Even if the operating resistance of is sufficiently reduced, it cannot be zero. Therefore, the attenuation amount itself remains at about 10 dB, and the IM improvement is about 10 dB.

In the attenuator circuit 2b of FIG. 2, the RF signal is attenuated by pulling it to the ground side through the pin diode D1. Therefore, the antenna 1 is shared with other receivers (co-listening). When the antenna is used, there is a problem that the signal system is adversely affected by mismatching and the RF signal to the other receiver side is also attenuated.

The present invention has been made in consideration of such circumstances, and when the electric field strength of the input signal is extremely high, the attenuation amount of the input signal can be increased without deteriorating the IM. Moreover, it is an object of the present invention to provide an attenuator circuit that can reduce adverse effects on other receivers even when a co-listening antenna is used.

[0016]

In order to achieve the above object, the present invention provides a first attenuator circuit for attenuating a level of an input signal input to a radio receiver by a predetermined amount. And a signal passage amount control means for controlling the impedance at the input side of the signal passage amount control means when the passage amount of the input signal is reduced by the signal passage amount control means. And impedance control means for reducing the impedance to a predetermined value in accordance with the above.

[0017]

In the attenuator circuit of the present invention, when the attenuation amount is increased, the impedance control unit adjusts the impedance on the input side to the second control voltage when the signal passage amount control unit reduces the passage amount of the input signal. Since it is lowered to a predetermined value by the above, jumping to the output side can be prevented without deteriorating the impedance matching.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the drawings described below, parts common to those in FIGS. 1 and 2 are designated by the same reference numerals, and overlapping description will be omitted.

FIG. 4 shows an embodiment of the attenuator circuit of the present invention. The RF signal from the antenna 1 is a local signal from the attenuator circuit 2A, the antenna circuit 3, the high frequency amplifier circuit 4 and the local oscillator circuit 6. An intermediate frequency of 10.7 MHz is set via the MIX circuit 5 for mixing with.

Pin diode D of attenuator circuit 2A
On the anode side and the cathode side of 2, a capacitor C1,
C2 is connected. A control voltage generating circuit 7B is connected to a connection point between the anode side of the pin diode D2 and the capacitor C1 via a coil L1. The connection point between the cathode side of the pin diode D2 and the capacitor C2 is
The resistor R1 is grounded, and the capacitor C4, the resistor R4 and the pin diode D1 are grounded in series.

Anode side of pin diode D1 and resistance R
A control voltage generating circuit 7A is connected to a connection point with 4 via a coil L2. Each control voltage generation circuit 7A, 7
The operation of B is controlled by the CPU 8.

The control voltage generating circuit 7A supplies a high-level voltage and a low-level voltage to turn on / off the pin diode D1, respectively, and is composed of, for example, a transistor circuit. Control voltage generation circuit 7B
Is for supplying a current corresponding to the amount of attenuation to the pin diode D2, and is, for example, a D / A converter.

In the figure, L1 and L2 are RF signal blocking coils, and C1 and C2 are direct amount blocking capacitors.
In the attenuator circuit having such a configuration, when the attenuation amount is increased, the control voltage from the control voltage generation circuit 7B is lowered and the operating resistance value of the pin diode D2 is raised.
As a result, the amount of RF signal passing through the pin diode D2 is reduced.

At this time, the control voltage from the control voltage generating circuit 7A is set to the high level, the pin diode D1 is turned on, and the RF signal is drawn to the ground side through the capacitor C4, the resistor R4 and the pin diode D1. The impedance on the input side of 2A is lowered to a predetermined value (generally the on-resistance of R4 + D1).

As a result, the RF signal is transmitted to the capacitor C4,
The impedance on the input side of the attenuator circuit 2A is lowered because it is drawn to the ground side via the resistor R4 and the pin diode D1. Here, the resistance R4 is set to about 100Ω which does not hinder the antenna side.

FIG. 5 shows another embodiment in which the configuration of the attenuator circuit of FIG. 4 is changed. In the attenuator circuit 2B shown in the figure, the pin diodes D2 and D3 are
Are connected in series in the RF signal path in opposite directions with the anodes connected to each other.

A control voltage generating circuit 7B is connected to the cathode side of the pin diode D2 via a coil L3. A control voltage generating circuit 7C is connected to the cathode side of the pin diode D3 via a coil L1.

A power source + B is applied to the anode side of the pin diodes D2 and D3 via a resistor R7, and
It is grounded via a resistor R1. Pin diode D2
A series circuit of a capacitor C5 and a resistor R5 is connected in parallel with. A series circuit of a capacitor C6 and a resistor R6 is connected in parallel to the pin diode D3.

The connection point between the cathode side of the pin diode D2 and the capacitor C2 is grounded via the series circuit of the capacitor C4, the resistor R4 and the pin diode D1. A control voltage generating circuit 7A is connected to a connection point between the anode side of the pin diode D1 and the resistor R4 via a coil L2. Control voltage generation circuits 7A, 7B, 7C
Are controlled by the CPU 8, and each outputs a high level voltage or a low level voltage.

In the figure, L1, L2 and L3 are RF signal blocking coils, and C1, C2 and C3 are DC blocking capacitors. In the attenuator circuit with such a configuration,
When maximizing the amount of attenuation, the control voltage generation circuits 7B and 7C
When the output of is set to a high level and the pin diodes D2 and D3 are turned off, the RF signal is a capacitor C5, a resistor R5,
It flows through the resistor R6 and the capacitor C6 and is attenuated by these resistors R5 and R6.

To increase the amount of attenuation, the output of the control voltage generating circuit 7A is set to a high level, the pin diode D2 is turned on, and the RF signal is pulled to the ground side through the capacitor C4, the resistor R4 and the pin diode D1. The input impedance of the attenuator circuit 2B is lowered. In addition, the control voltage generation circuit 7B or 7
When the output of C becomes low level, the pin diode D2 or D3 is turned on, so that the resistor R5 or the resistor R6 is bypassed, and a predetermined amount of attenuation is obtained by the non-bypassed resistor.

The operation of each pin diode D1, D2, D3 when the attenuation amount is 0 dB to 20 dB is shown in FIG.
Shown in. That is, when the attenuation amount is 0 dB, the pin diodes D2 and D3 are turned on. When the attenuation amount is 10 dB, only the pin diode D3 is turned on.
If the attenuation is 15 dB, the pin diode D1
, D2 are turned on. When the attenuation amount is 20 dB, only the pin diode D1 is turned on.

FIG. 7 shows an example of actual measurement of IM characteristics in this case. As can be seen from the comparison with the IM characteristic of FIG. 3, the allowable level of the interfering wave is improved, especially in the characteristic of the attenuation amount of 20 dB, and the IM improvement of about 20 dB is obtained.

As described above, in each of the above embodiments, when the pin diodes D2 and / or D3 inserted in series in the RF signal path are turned on, the impedance of the input side of the attenuator circuit is lowered to make the signal jump. At the same time, the influence of noise and return is reduced, and at the same time, the impedance variation of the attenuator circuit 2B viewed from the antenna 1 side is reduced, so that impedance mismatch is eliminated and RF signal reflection is reduced.

As a result, even if the electric field level is particularly strong, the amount of attenuation can be increased without deteriorating the IM. Furthermore, when lowering the input impedance, the resistance value is only reduced to a predetermined value without short-circuiting. Therefore, for example, even when the antenna 1 is shared with other receivers (co-listening antenna). There is no attenuation of the RF signal to the other receiver side.

In FIGS. 4 and 5, the impedance of the pin diode D1 may be controlled in an analog manner, and in that case, the resistor R4 may be omitted. The directions of the pin diodes D2 and D3 in FIG. 5 may be reversed if the logics of the control voltage generating circuits 7B and 7C are inverted.

Furthermore, in each of the above embodiments, the case where the pin diode is used for the attenuation of the RF signal and the control of the input impedance has been described, but other semiconductor elements having good high frequency characteristics, such as a relay, may be used. Furthermore, the control of the amount of attenuation may be performed by the CPU reading a manual switch that is appropriately operated by the user, or by a method that does not use the CPU. Further, the control of the attenuation amount may be automatically performed according to the AGC voltage or the detection result of the multipath. Moreover, the broadcast frequency band is not limited.

[0038]

As described above, according to the attenuator circuit of the present invention, when the electric field strength of the input signal is extremely high, the attenuation amount of the input signal can be increased without deteriorating the IM. Moreover, even when a co-listening antenna is used, it is possible to reduce adverse effects on other receivers.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a radio receiver using a conventional attenuator circuit.

FIG. 2 is a block diagram showing another example of a radio receiver using a conventional attenuator circuit.

FIG. 3 is a diagram showing IM characteristics in the radio receiver of FIG.

FIG. 4 is a block diagram showing an embodiment of a radio receiver using the attenuator circuit of the present invention.

5 is a block diagram showing another embodiment in which the configuration of the attenuator circuit of FIG. 4 is changed.

6 is a diagram showing an operating state of a pin diode corresponding to an attenuation amount in the attenuator circuit of FIG.

FIG. 7 is a diagram showing IM characteristics of the attenuator circuit of FIG.

[Explanation of symbols]

 1 antenna 2A, 2B attenuator circuit 3 antenna circuit 4 high frequency amplification circuit 5 MIX circuit 6 local oscillator circuit 7A, 7B, 7C control voltage generation circuit 8 CPU D1, D2, D3 pin diode

Claims (1)

[Claims] 1. An attenuator circuit for attenuating a level of an input signal input to a radio receiver by a predetermined amount, and a signal passing amount control means for controlling a passing amount of the input signal according to a first control signal, Impedance control means for lowering the impedance at the input side of the signal passage amount control means to a predetermined value in response to the second control signal when the passage amount of the input signal is reduced by the signal passage amount control means. Characteristic attenuator circuit.