JPS644702B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiver equipped with a diversity antenna.

Such a receiver is used mounted on a car, for example, and among multiple antennas,
When the level of an input signal from a certain antenna decreases, the signal from another antenna is switched to receive the signal, thereby enabling stable reception even in locations where the electric field strength of the wireless signal varies. In the prior art, the signal from each antenna is amplified by an amplifier circuit, and the amplified signal is switched by a changeover switch to be applied to a receiving circuit. In this case, especially when receiving an amplitude modulated signal in a strong electric field, the output of the amplifier circuit becomes saturated and distortion occurs.

An object of the present invention is to provide a receiver equipped with a diversity antenna that can receive an amplitude modulated signal without causing distortion when receiving the amplitude modulated signal in a strong electric field.

FIG. 1 is a block diagram of one embodiment of the present invention. This receiver is mounted on a car, and the rear window 1 of the car is equipped with an antenna 10 and an antenna 18, which will be described later with reference to FIG. The input signals from the antennas 10 and 18 are the first
The signal is applied via the amplifier circuit 81 and the second amplifier circuit 82 to the front end circuit 42 for amplitude modulation reception and frequency modulation reception via the changeover switch 41, respectively. The output from the front end circuit 42 is given to a circuit 43 that performs intermediate frequency amplification and detection. Intermediate frequency amplification detection circuit 43
The intermediate frequency signal from is applied from line 44 to multiplexer 47 via high-cut filter 45 and noise blanker 46 . When the input signal includes a 19KHz stereo pilot signal indicating stereo broadcasting, the multiplexer 47 detects the stereo pilot signal and sends the stereo audio signal to the amplification circuits 48 and 4.
9, and when there is no stereo pilot signal, a monaural signal is supplied to amplifier circuits 48 and 49. The audio signals from the amplifier circuits 48, 49 are sent to the speakers 50,
51.

The high-frequency cutoff filter 45 responds to the control signal from the line 52 and removes the stereo pilot signal and high-frequency components contained in the signal from the line 44 when the line 52 is at a high level. give to

The noise blanker 46 temporarily stops the reproduction of the desired signal when pulse noise with a relatively strong electric field is mixed in from the antennas 10 and 18, such as ignition noise when an internal combustion engine is ignited or noise when a wiper motor is activated. It serves as a pause, thereby improving clarity.

The intermediate frequency amplification and detection circuit 43 has a muting function and includes a muting control terminal A and a muting terminal B. Muting control terminal A delivers a high level voltage to line 53 when the level of the input signal from antennas 10, 18 is weak and therefore the reception detection level in its circuit 43 is low. This line 53
The signal from is input to muting terminal B. When a high level voltage is applied to the muting terminal B, muting, that is, inter-office noise is removed. When the level of the input signals from the antennas 10 and 18 is strong and the reception detection level is high, the voltage from the muting control terminal A is low and the muting operation is stopped.

Referring to FIG. 2, a graph illustrating the characteristics of the receiver shown in FIG. 1 is shown. FIG. 2 shows the relationship between the level of the input signal from the antennas 10 and 18 and the S/N ratio of the signal derived on line 44. When the level of the input signals from antennas 10 and 18 is small as shown by H1,
The S/N ratio is small, and as the input signal level from the antennas 10 and 18 reaches a high value H2, the S/N ratio decreases.
The ratio will improve. When the input signal level from the antennas 10 and 18 is sufficiently higher than H2, the S/N ratio is good and approximately constant.

FIG. 2 shows the relationship between the level of input signals from the antennas 10 and 18 and the output level from the muting control terminal A of the intermediate frequency amplification and detection circuit 43. As the level of the antenna input signal increases, the voltage from the muting control terminal A decreases. When the level of the input signal from antennas 10, 18 is at a low value H1, line 53
A high voltage V1 is derived at , and when the level of the antenna input signal goes to a high value H2, the voltage goes to a low value as indicated by reference V2.

Transfer switch 41 receives the output Q from toggle flip-flop 54 via lines 55 and 56. This changeover switch 41 provides the signal from the antenna 10 to the front end circuit 42 when the output terminal Q of the flip-flop 54 is at a high level, and sends the signal from the antenna 18 to the front end circuit when the other output is at a high level. to the end circuit 42. flipflop 5
4 alternately changes the level of the output Q, each time it receives a pulse from line 57.

The output from flip-flop 54 via line 56 is provided to a differentiator circuit 58. This differentiation circuit 58 consists of a capacitor 59 and a diode 6.
0,61, and the unipolar pulse is passed through the integrating circuit 6.
Give to 2. Integrating circuit 62 includes a capacitor 63 and a resistor 64 for discharging capacitor 63, and its integrated output is given to one input of comparator circuit 65. The other input of comparator circuit 65 receives a signal from muting control terminal A via line 53.

Comparison circuit 65 derives a high level signal when the output from integrator circuit 62 is below the level of the signal on line 53, and derives a low level signal when the output from integrator circuit 62 is above the level of the signal on line 53. Derive the level signal. The output from comparison circuit 65 is applied to one input of AND gate 66.

The signal from line 53 is also applied to one input of comparator circuit 67. A predetermined voltage V3 is applied to the other input of the comparison circuit 67. Comparison circuit 67 indicates that the voltage on line 53 is a predetermined voltage.
Derive a low level signal when it is less than V3,
A high level signal is derived when the voltage is V3 or higher. The signal from the comparison circuit 67 is sent to the AND gate 6
6 is applied to the other input of the AND gate 69, and also applied to one input of the AND gate 69 via the inversion circuit 68. The output from AND gates 66 and 69 is
It is applied to one input of an AND gate 71 via an OR gate 70. The other input of the AND gate 71 is supplied with a clock pulse from a clock generating circuit 72 having a frequency of, for example, about 100 KHz. The output from AND gate 71 is provided to flip-flop 54 via line 57.

Intermediate frequency amplification and detection circuit 43 via line 44
The signal from is given to a bandpass filter 73. This bandpass filter 73 selectively extracts the stereo pilot signal and sends it to the amplitude detection circuit 7.
Give to 4. The signal from the amplitude detection circuit 74 is given to another amplitude detection circuit 75 connected in cascade. The output from the amplitude detection circuit 75 is given to one input of the comparison circuit 76. Comparison circuit 76
A predetermined voltage V4 is applied to the other input of the . The output from comparison circuit 76 is applied via line 52 to high cutoff filter 45 and via line 77 to the other input of AND gate 69.

The input signals from antennas 10 and 18 are small,
Therefore, the signal from the muting control terminal A of the intermediate frequency amplification and detection circuit 43 has a predetermined voltage.
When the voltage is V3 or higher, the comparator circuit 67 derives a high level signal. In such a weak electric field strength, when the signal from the muting control terminal A via the line 53 exceeds the output of the integrating circuit 62, the comparison circuit 65 derives a high level signal. Therefore, the high level signal from the AND gate 66 is transmitted from the OR gate 70 to the AND gate 7.
1 is given. Clock generation circuit 72 derives the pulses shown in FIG. The high level signal from AND gate 66 is output to OR gate 7.
0 to AND gate 71 as described above, the pulse shown in FIG. 3 is derived from AND gate 71 on line 57. Therefore, flip-flop 54 is connected to line 57.
The stable state changes each time a pulse is received through the differential circuit 58, so that a unipolar differentiated pulse as shown in FIG. 3 is obtained from the differentiating circuit 58. The integrating circuit 62 integrates the pulses from the differentiating circuit 58 and provides an output having a waveform shown in FIG. 3 to the comparing circuit 65. As the flip-flop 54 repeatedly changes its stable state, the output of the integrator circuit 62 rises step by step until it exceeds the level 78 of the signal from the muting control terminal A via the line 53. Therefore, the output of the comparator circuit 65 becomes low level as shown in FIG. 3, and accordingly, the AND condition of the AND gate 71 no longer holds, and no pulse is applied to the flip-flop 54. In this way the voltage V1
When the switching operation of the changeover switch 41 is repeatedly performed in a weak electric field strength where the level of the input signal from the antennas 10 and 18 corresponding to the above is low, the repetition of the switching operation is stopped. Therefore, by continuing the switching operation of the changeover switch 41, the S/N ratio is prevented from being deteriorated any time soon. The output of the integrating circuit 62 will be reduced depending on the time constant determined by the capacitor 63 and the resistor 64. Therefore, the continuation of the switching operation of the changeover switch 41 is stopped for a period of time depending on the time constant.

The level of the input signals from antennas 10 and 18 is high, and the line 5 from muting control terminal A
When the level of the signal via V3 is less than the voltage V3, the output of the comparator circuit 67 is at a low level. Let us assume that a stereo broadcast is being received in such a so-called medium to strong electric field strength and that no multipath distortion occurs. At this time, from the band pass filter 73,
A stereo pilot signal with constant amplitude is derived as shown in . The amplitude detection circuit 74 derives a constant level signal shown in FIG. 42 having a level corresponding to the amplitude of the stereo pilot signal. Since the output from the amplitude detection circuit 74 is constant, the other amplitude detection circuit 75 derives a low level signal below the predetermined voltage V4 as shown in FIG. 4. Therefore, the output of the comparator circuit 76 is at a low level as shown in FIG.
6 to the multiplexer 47. Therefore, multiplexer 47 responds to the stereo pilot signal to derive an audio signal so that the stereo broadcast can be heard. Since the output from the comparison circuit 76 is at a low level, the output from the AND gate 69 remains at a low level, and the AND gate 76 remains at a low level.
The output of 1 is low level. In this way, a stable stereo broadcast reception state is maintained.

In the above-mentioned medium electric field strength to strong electric field strength where the input signals from the antennas 10 and 18 are high in level,
Assume that a stereo broadcast is being received and multipath distortion occurs in this state. When multipath distortion occurs, the amplitude of the stereo pilot signal derived from the bandpass filter 73 changes as shown in FIG. 5. The amplitude detection circuit 74 is shown in FIG.
A signal with a waveform shown is derived. Therefore, the amplitude detection circuit 75 derives the signal shown in FIG. 53 having a level higher than the voltage V4. Therefore, comparison circuit 7
6 supplies high level signals to lines 52 and 77 as shown in FIG. High frequency cutoff filter 45
In this case, the stereo pilot signal is set to noise blanker 4.
6 is prevented from being applied to the multiplexer 47, whereby the left and right separation operation of the multiplexer 47 is not performed, and a monaural signal is obtained. Therefore, the S/N ratio will be improved. Also, as the line 77 goes high, the AND gate 69 passes through the OR gate 70.
A high level signal is derived to the AND gate 71.
Therefore, flip-flop 54 is supplied with pulses from clock generation circuit 72 via AND gate 71 and line 57. In this way, the stable state of the flip-flop 54 is changed, and the switching operation of the changeover switch 41 is performed. When multipath distortion no longer occurs, the line 77 becomes low level and the switching operation of the changeover switch 41 is stopped.

Referring to FIG. 6, antennas 10 and 18 are buried in the rear window 1 of an automobile. This rear glass 1 is filled with filaments 2 and 3 that function as anti-fog heaters, from the bus bar 5, through the filament 2, from the bus bar 6, through the filament 3, to the bus bar 7.
A heating current is supplied to. A signal from the connection point 11 of the antenna 10 is given to the first amplification circuit 81, and is also sent from the antenna 18 via the connection point 12 to the second amplification circuit 81.
The signals are provided to the amplifier circuits 82, respectively. The carrier frequency of an amplitude modulated signal is on the order of about 1 MHz, whereas the carrier frequency of a frequency modulated signal is on the order of about 100 MHz. In the amplifier circuit 81, signals from the antenna 10 are applied to amplifier circuits 85 and 86 through a coil 83 and a capacitor 84, which have different impedances depending on the frequency. In this way, the amplitude modulation signal is amplified in the amplifier circuit 85, and the frequency modulation signal is amplified in the amplifier circuit 86.

In another second amplifier circuit 82, the amplitude modulated signal is derived without being amplified via a circuit consisting of coils 87, 88 and a capacitor 89. The frequency modulation signal is supplied from a capacitor 90 to an amplifier circuit 91 where it is amplified, and then a capacitor 92
It is derived through

In the switching circuit 41, the signal from the amplifier circuit 81 passes through a capacitor 93, a diode 94, and
The signal is applied from line 95 to front end circuit 42 via coupling capacitor 96. The signal from amplifier circuit 85 is routed to line 95 via capacitor 97 and diode 98. Line 95 is connected to ground via line 99 and resistor 100. Line 55 is connected forward through diode 101 and further through coil 102 to the anode of diode 94 . Line 56 is also connected from diode 103 to the anode of diode 98 via coil 104 . A signal from the amplifier circuit 81 via the capacitor 93 is applied to one input of the comparison circuit 106 via the detection circuit 105. A predetermined voltage Vr is applied to the other input of the comparison circuit 106. Comparator circuit 106 is powered via switch 107. This switch 107 is turned on when the front end circuit 42 receives the amplitude modulation signal, thereby activating the comparison circuit 106. The comparison circuit 106 detects that the level of the signal from the amplifier circuit 81 is high, so the detection circuit 105
When the output of Vr exceeds the voltage Vr, a high level signal is derived on line 108. Line 108 is connected to the cathode of diode 103 via diode 109. The cathode of the diode 101 is grounded via a transistor 110 and is supplied with a positive voltage via a resistor 111.
The base of transistor 110 is connected to line 108.
A signal from is applied via resistor 112.

When front end circuit 42 is ready to receive a frequency modulated signal, switch 107 is shut off. When line 55 is at a high level, diodes 101 and 94 are conductive, and the frequency modulated signal amplified by amplifier circuit 86 in amplifier circuit 81 is provided to front end circuit 42 . Furthermore, when line 56 is at a high level, diodes 103 and 98 are conductive, thereby causing amplifier circuit 82
The frequency modulated signal amplified by the amplifier circuit 91 in is given to the front end circuit 42.

When the front end circuit 42 is receiving an amplitude modulated signal, the switch 107 is conductive. When the electric field strength of the amplitude modulation signal is a weak electric field to a medium electric field, the output of the detection circuit 105 is a voltage
less than Vr. Line 108 therefore remains low and transistor 110 is cut off. Therefore, a switching operation similar to that when receiving a frequency modulation signal is performed depending on the levels of lines 55 and 56.

In the strong electric field of the amplitude modulated signal, the detection circuit 105
the output of exceeds the voltage Vr and therefore line 10
8 is a high level. Therefore diode 10
9 conducts, and diode 98 conducts regardless of the level of line 56. Therefore antenna 1
The signal from coil 8 in amplifier circuit 82
7 and 88, and is applied to the front end circuit 42. At the same time, transistor 11
0 is conductive, the anode of the diode 94 is grounded, and therefore the signal from the amplifier circuit 81 is not provided to the front end circuit 42. In this way, a signal distorted by saturation of the amplifier circuit 85 in a strong electric field is not applied to the front end circuit 42, and a good reception condition can be achieved.

In the embodiment described above, two antennas 10, 18
Although only one antenna is provided, in other embodiments of the invention, more antennas may be sequentially switched and provided to the front end circuit 42. In this case, the first amplifier circuit 81 is interposed between at least one of the plurality of antennas and the changeover switch 41, and the other second amplifier circuit 82 is interposed between at least one of the remaining antennas and the changeover switch 41. 41.

As described above, according to the present invention, when receiving an amplitude modulated signal, the signal that is not amplified by the amplifier circuit in the strong electric field is switched and given to the front end circuit. It becomes possible to eliminate distortion in a strong electric field.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
This figure is a graph for explaining the operation of the receiving circuit shown in FIG. 1, and FIG. 3 is a graph for explaining the operation of the embodiment of FIG. 1 when the level of the input signals from the antennas 10 and 18 is small. 4 and 5 are waveform diagrams for explaining the operation when multipath distortion occurs, and FIG. 6 is a waveform diagram of the amplifier circuit 8.
1 and 82 and a specific electric circuit diagram of the changeover switch 41. 10, 18... Antenna, 41... Changeover switch, 42... Front end circuit, 43... Intermediate frequency amplification/detection circuit, 45... High frequency cutoff filter, 46... Noise blanker, 47... Multiplexer, 48, 49...Amplification circuit, 50, 51...
...Speaker, 54...Flip-flop, 58...
...Differential circuit, 62...Integrator circuit, 65, 67, 7
6... Comparison circuit, 72... Clock generation circuit, 7
3... Band pass filter, 74, 75... Amplitude detection circuit, 81... First amplifier circuit, 82... Second
Amplification circuit.

Claims (1)

[Claims] 1. A plurality of antennas, a receiving circuit that receives an amplitude modulated signal and a frequency modulated signal, a changeover switch that switches the input signals from the plurality of antennas and provides them to the receiving circuit, and a switch that changes the level of the input signal to the receiving circuit. A level detection circuit to be detected; in response to the output from the level detection circuit, when the level of the input signal to the reception circuit is less than a predetermined value, a changeover switch is set so that the input signal from another antenna is given to the reception circuit. a control circuit that performs switching control; a first amplifier circuit that is interposed between at least one of the plurality of antennas and the changeover switch and amplifies the amplitude modulated signal and the frequency modulated signal; and at least one of the remaining antennas. a second amplification circuit that is interposed between the switch and the changeover switch and amplifies the frequency modulation signal without amplifying the amplitude modulation signal; A receiver equipped with a diversity antenna, characterized in that when the output from the first amplifier circuit exceeds a predetermined value, the output from the second amplifier circuit is forced to be given to the receiver circuit.