JPS5919650B2 - Noise blanker circuit for receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise blanker circuit for a radio receiver having a plurality of reception systems, in which the noise blanker circuit of one system is also used as a noise detection circuit necessary for the noise blanking operation of another system. This is intended to simplify the circuit.

Noise blanker circuits are usually used to remove pulse noise such as automobile ignition noise.
In principle, it is provided for each receiving system, but for example, F
If a radio receiver for M and AM reception is already equipped with a noise blanker circuit in the FM reception system, installing a new noise blanker circuit that can operate independently in the AM reception system is a shortcut for both. Considering that they have the same function and are not used at the same time, they are disadvantageous in terms of miniaturization and cost reduction of the receiver. Therefore, in the present invention, in a noise blanker circuit for a radio receiver equipped with a plurality of reception systems having a shared antenna or a plurality of adjacent antennas, one reception system is provided with a noise blanker circuit having a pulse noise detection function, The other reception system is provided with a noise blanker circuit that does not have a noise detection function and an antenna changeover switch that directly inputs the antenna output to the intermediate frequency circuit of the one reception system, and when the other reception system is activated, the antenna changeover switch is provided. to directly input the antenna output to the intermediate frequency circuit, and simultaneously operate at least the noise blanker circuit of the first receiving system to generate a pulsed noise detection signal detected by the noise blanker circuit of the first receiving system. The configuration of the noise blanker circuit for the receiver is simplified by applying the signal to the noise blanker circuit of the other receiving system, and the drawing will be described in detail below.

FIG. 1 shows one embodiment of the present invention, taking an AM-FM two-band radio receiver as an example.

In the same figure, ANT is connected to the first and second receiving systems A,
Although this is a shared antenna that is shared by A and B, in some cases, A and B may use dedicated antennas independently. 1st
The receiving system A is FM, and the front end 1, IF (
intermediate frequency) circuit 2, detection circuit 3, noise blanker circuit 4
The detection output (audio signal) SA that has passed through the noise blanker circuit 4 is provided to the audio amplifier 10 through the detection output changeover switch 9, and the amplified output drives the speaker 11. On the other hand, the second receiving system B is AM, and has a main path composed of a front end 6, an IF circuit 7, and a detection circuit 8.
The signal is input to the audio amplifier 10 through the input signal. These detection outputs SA and SB are selected by a switch 9. The state shown in the figure is when receiving AM. The noise blanker circuit 4 of the receiving system A is an existing one and has all functions that can be operated independently.

On the other hand, the noise blanker circuit 5 of the reception system B is a circuit with a simple configuration, which mainly has only a switch function for cutting off the signal from the front end 6, or at least has no noise detection function. Therefore, when receiving the signal from the receiving system B by switching the switch 9 to the B side, the receiving system A is also activated at the same time (normally, at this time, the receiving system A is turned off by an interlocking switch and is put into a non-operating state, but in this circuit, at least circuit 1
~ 4 do not turn off the power supply and keep these circuits in operation), noise detection signal D of noise blanker circuit 4
is led to the noise blanker circuit 5. In other words, receiving system B
Here, the noise blanker circuit 4 is used as a noise detection circuit, and the signal D is used as an operation trigger to act on the front end 6 to remove pulse noise mixed into the receiving system B. The positions of the noise blanker circuits 4 and 5 are not limited to the illustrated positions. In particular, the noise blanker circuit 5 can also be inserted in a portion after the IF stage. The only pulse noise is
Particularly in an AM receiving system with a relatively low frequency, the pulse width tends to widen as it goes downstream, so it is a good idea to process it upstream. Note that if the noise blanker circuit 5 is operated while receiving radio waves with high electric field strength, the S/N ratio will deteriorate due to the noise generated by intermittent cutting of the received signal. There is.
Therefore, in the circuit shown in FIG. 1, a noise blanker control circuit 12 is provided to control whether or not the noise blanker circuit 5 is in operation using a signal C indicating the received electric field strength such as the AGC voltage extracted from the IF circuit 7. That is, when the received human power level exceeds a certain value and the human power is large, the operation of the noise blanker circuit 5 is prohibited, and the circuit is operated only when the human power is medium or small. Also,
If the receiving system A is receiving a large power signal such as a nearby FM high-output broadcast wave while the receiving system B is in operation, noise detection in the noise blanker circuit 4 may become impossible.

Therefore, while the receiving system B is in operation, the frequency shifter 13 forcibly shifts the receiving frequency of the receiving system A to a band without strong electric field waves, such as outside the broadcast frequency. This frequency shifter 13 is composed of, for example, a capacitor inserted or removed in conjunction with the switch 9, and shifts the receiving station frequency of the front end 1. FIG. 2 shows another embodiment of the present invention in which the function of the frequency shifter 13 is realized by antenna input changeover switches 14 and 15.

A switch 14 is connected between the ANT and the input terminal of the IF circuit 2, and a switch 15 is connected between the ANT and the front end 1, and these operate in reverse in conjunction.
That is, if the switch 9 is on the A side (when receiving FM), the switch 15 is closed and the ANT input is guided to the front end 1. In response, the switch 9 switches to the B side (
When receiving AM), switch 15 is open and switch 14 is open.
is closed. Therefore, the receiving system A becomes a receiving system that receives 10.7 MHz intermediate frequency radio waves using the IF circuit 2 as the first stage amplifier, and receives the 1F band component of the pulse noise input to the antenna ANT. This band includes FM
Since there are no broadcast waves, noise detection will not be impossible due to interference from strong broadcast waves, and the same effect as the frequency shifter described above can be expected. FIG. 3 is a block diagram showing the main parts of FIG. 1 in more detail. The noise blanker circuit 4 of the receiving system A is a low pass filter (LPF) 4L.
It includes an FM signal reception system consisting of a delay circuit 42 and a gate circuit 43, and a noise detection system consisting of a high pass filter (HPF) 44, a noise detection circuit 45, and a pulse shaping circuit 46. Since the output of the detection circuit 3 also contains 10.7 MHz, it is passed through a low-pass filter 41 to convert it into a low-frequency signal component, while the high-frequency component is determined to be noise and is extracted by a high-pass filter 44. The noise detection circuit 45 treats the noise that exceeds a certain threshold as pulse noise, which is shaped by a pulse shaping circuit 46 such as a one-shot multi-type pulse generator, and outputted as a noise detection signal D. This signal D is guided to the gate circuit 43, and after passing through the LPE 4l, the low frequency signal, which is delayed in consideration of noise detection processing time, is passed through the gate circuit 43 if it contains noise. The noise is removed. For example, this gate circuit 43 consists of a switch that opens and closes a signal circuit and a capacitor connected to the output side of the switch, and when the noise detection signal D is applied, the switch opens, cuts off the input signal, and charges the capacitor instead. The current signal level is output, and the pulse noise is cut and removed at the signal level. When receiving system B is activated, receiving system A
Although this operation is not necessary, at least the common pulse shaping circuit 46 is kept in an operating state so that the noise detection signal D is generated.

This signal D is then guided to the noise blanker circuit 5 of the receiving system B. The noise blanking power circuit 5 includes a delay circuit 5L and a pulse width adjustment circuit 52, which in this example controls on/off the transistor Trl that drops the signal to ground. The secondary side of the output stage transformer T in the front end 6 is the line L.
1 to the input stage of the IF circuit 7, and the transistor Trl is connected between this L1 and the ground via a capacitor C1. The delay circuit 51 delays the noise detection signal D detected in the FM system so as to match the timing with the operation in the AM system, and the pulse width adjustment circuit 52 similarly adjusts the pulse width of the delayed detection signal D. A.M.
The width is adjusted to an appropriate width for noise removal in the system. However, these circuits 51 and 52 are provided as necessary, and basically it is sufficient to have C, Trl that ground the line L] at high frequency during blanking. A control circuit 12 is connected to the base of the transistor Trl via a resistor R1.
Then, when the AGC voltage is applied, and the received electric field is sufficiently high, the base potential is deeply biased in the negative direction, and even if the detection signal D is generated, Trl cannot be turned on. In other words, blanking operation is prohibited. With the above-described noise blanker circuit for a receiver according to the present invention, in a radio receiver having a plurality of receiving systems, if one system has a noise blanker circuit having a noise detection function, the other systems have a noise detection function. Since the noise blanking operation can be performed simply by adding a noise blanker with a simple configuration that does not have any functions, it is advantageous for downsizing and cost reduction.

In particular, it is effective to use the noise blanker circuit of the FM reception system as a noise detection circuit for noise blanking of the AM reception system. In other words, if AM system noise blanking is performed using the noise detection signal of the FM reception system, which operates in a high frequency range and is easy to detect noise, noise blanking can be easily and reliably performed at an early stage on the upstream side of the AM system. It is possible and advantageous.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the present invention, Fig. 2 is a block diagram showing the main part of another embodiment of the invention, and Fig. 3 is a block diagram showing the main part of Fig. 1 in detail. be. ANT...shared antenna, A...one receiving system, B...other receiving system, 4...
... Noise blanker circuit of system A, 5 ... Noise blanker circuit of system B, 12 ... Noise blanker control circuit, 13 ... Frequency shifter, 14,
15...Antenna input selection switch.

Claims (1)

[Claims] 1. In a noise blanker circuit for a radio receiver equipped with a plurality of reception systems having a shared antenna or a plurality of adjacent antennas, a noise blanker circuit having a pulse noise detection function in one reception system and the one reception system An antenna changeover switch is provided to directly input the antenna output to the intermediate frequency circuit of the antenna, and a noise blanker circuit having no noise detection function is provided in the other reception system, and the antenna changeover switch is activated when the other reception system is activated. The antenna output is directly input to the intermediate frequency circuit, and at least the noise blanker circuit of the first receiving system is also operated at the same time, so that the pulsed noise detection signal detected by the noise blanker circuit of the first receiving system is transmitted to the other. A noise blanker circuit for a receiver, characterized in that the noise blanker circuit is applied to a noise blanker circuit of a receiving system of the receiver.