JPH0731638Y2 - Diversity circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a diversity circuit having a simple configuration for selecting an antenna output having a maximum electric field strength among a plurality of antennas.

[Prior Art] In the conventional space diversity system, as shown in FIG. 6, the outputs of the antennas A ₁ and A ₂ are converted to an intermediate frequency ω ₁ , and the output is E ₁ cos ω ₁ t, E ₂ It is assumed that cosω ₁ t and the magnitudes of E ₁ and E ₂ are compared by the amplitude comparison circuit and the larger antenna output is used. In FIG. 6, 1 is the output of the antenna A ₁ , 2 is the output of the antenna A ₂ , 3 is the local oscillator,
4 and 5 are frequency converters, 6 is an IF amplitude comparison circuit, 7 is a comparator output, 8 is an electronic switch, and 9 is an IF switching output.

The example shown in FIG. 6 is an example in which two antennas A ₁ and A ₂ are used, and the outputs 1 and 2 thereof are added to the frequency converters 4,5 together with the frequency ω ₀ of the local oscillator 3 and the IF stage Converted to frequency ω ₁ . The outputs are E ₁ cosω ₁ t and E ₂ cosω ₁ t. The amplitude comparison circuit 6 compares E ₁ and E _2, and if E ₁ > E _2, then the comparator circuit output 7 controls the electronic switch 8.
E ₁ cos ω ₁ t is selected, and if E ₁ <E _2, then E ₂ cos ω ₁ t is selected and added as an output 9 to an FM demodulator (not shown).

[Problems to be solved by the invention] However, in this method, the configuration of the amplitude comparison circuit for the carrier wave cosω ₁ t becomes complicated, and further, when the number of antennas is N, the amplitude comparison circuit becomes more complicated. Further, there is a drawback that the electronic switch 8 is required separately from this circuit.

It is an object of the present invention to provide a diversity circuit that can compare the amplitudes of the outputs of multiple antennas by using a high-frequency amplitude comparison circuit having a simple circuit configuration and enhance the spatial diversity effect.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the diversity circuit according to the present invention is configured such that signals from a plurality of antennas A ₁ and A ₂ are commonly connected to their output sides via diodes 12 and 13, respectively. Supply to the point,
A resistor is connected between the input of each diode and the reference potential point.
A bias voltage that determines the operating point is provided to each diode by interposing parallel resonant circuits 14 and 15 having a predetermined resonance frequency between the common connection point and the reference potential point. It is characterized in that the detection time constant circuits 16 and 17 to be applied are interposed between the resonance circuit and the reference potential point.

[Operation] In the diversity circuit of the present invention, the high frequency component of the received signal of each antenna is detected by the diodes 12 and 13. The respective detection outputs are combined at the common connection point, the operation of the diode is controlled by the resonance action of the resonance circuit according to the combination output, and the detection output having the maximum level is selected.

[Embodiment] An embodiment of the present invention shown in the drawings will be described below.

FIG. 1 shows an embodiment of the diversity circuit according to the present invention.
In order to select the highest level antenna output among the multiple IF stage outputs of the antenna output in the space diversity method, each output is combined with a diode that detects high frequency, and the detection output of the signal of almost the maximum output The bias is commonly applied, and the maximum level of the high frequency signal applied to the diode is automatically selected.

In the figure, reference numerals common to FIG. 6 are the same as or corresponding to those in FIG. 6, and 10 and 11 are resistors, 12 and 13 are diodes, and 14 and 15 are resonant circuits. Capacitor and inductance, 16
Reference numerals 17 and 17 represent capacitors and resistors forming a detection time constant circuit, and 18 represents an output.

FIG. 2 shows the detection characteristic of the IF signal due to the characteristic of the diode.

The outputs ₁ and ₂ of the antennas A ₁ and A ₂ are converted into IF signals by the frequency converters 4 and 5 to which the output of the local oscillator 3 is supplied, and added to the diodes 12 and 13. Diodes 12 and 13 detect the IF signal in parallel resonance circuits 14 and 15 and detection time constant circuit 16,
The detection is selectively performed by 17 as described below, and a detection output is generated.

The resistors 10 and 11 form a detection circuit with the diodes 12 and 13, and the anode side of each diode is set to the ground potential.
Further, the resonance frequency of the parallel resonance circuit is ω ₁ , and the resonance action increases the impedance with respect to the frequency of ω ₁ as viewed from the output 18, but becomes extremely low with respect to other frequencies.

However, in terms of direct current, the resistance 10, the diode 12, the L of the resonance circuit
(15), the loop of the resistor 17 and the resistor 11, the diode 13, the L (15) of the resonance circuit, and the loop of the resistor 17 are in a conductive state.

Therefore, the IF signals output from the frequency converters 4 and 5 are respectively E ₁ c
At osω ₁ t and E ₂ cos ω ₁ t, E ₁ > E _{2 as} shown in FIG.
Then, E ₁ cos ω ₁ t and E ₂ cos ω ₁ t are diodes 12, 13
As is clear from the figure, the diode 12 is first turned on and the rectified current I ₁ (low frequency component close to direct current) mainly determined by E ₁ and the diode characteristic is applied to the parallel resonant circuit L ( 15) and the resistor 17, and the voltage I ₁ R ₁ appearing at the resistor 17 is applied to the bias voltage M (−I
₁ R ₁ ) is applied. Therefore, the operating points of the diodes 12 and 13 are the points M in FIG. 2, and the diode 12 is in the operating state and E ₁ cosω ₁ t is detected and appears at the output 18, but the diode 13 is almost in the off state. E ₂ cos ω ₁ t is hardly detected. Therefore, the output 18 has a large output level E ₁
Only the detection output of cosω ₁ t appears.

Since the impedance of the parallel resonant circuit is low for frequency components other than ω ₁ , I ₁ becomes large and a large bias is applied to each diode, and the component is not detected.

In FIG. 6, the function for selecting the detection output is obtained by the amplitude comparison circuit 6 and the electronic switch 8, but it can be seen that the configuration for obtaining such a function in FIG. 1 is much simpler.

FIG. 3 shows four examples of antennas A _{1 to} A ₄ , and the number of diodes increases to 12, 13, 12 ', 13', but the circuit does not become so complicated. FIG. 4 is an example of using four directional antennas with spatial diversity. Antennas A _{1 to} A ₄ are separated by a cross reflector 19 in FIG.
The direction is as unidirectional as possible as shown in FIG. When the circuit of FIG. 3 is combined with the antenna system of FIG. ₄ , the IF signal with the maximum output from A _{1 to} A ₄ can always be supplied to the FM demodulation circuit.

As shown in FIG. 5, when the high frequency resonant circuits 20 and 21 are provided in the antenna output stage, the antenna output stage may have the same configuration as that in FIG. 20, 21 are resonant circuits at high frequency.

According to this embodiment, it is possible to automatically select an antenna output having a large high-frequency output among the desired channels.

[Advantage of the Invention] As described above, according to the present invention, the output with the largest antenna output can be automatically selected without using the amplitude comparison circuit and an electronic switch separate from the amplitude comparison circuit. The advantage that the diversity effect can be obtained with the circuit configuration is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of a diversity circuit according to the present invention, and FIG. 2 is a diagram explaining an operating point of a diode,
FIG. 3 is a block diagram showing a configuration of a diversity circuit when four antennas are used, FIG. 4 is a diagram showing an example of a directional antenna, and FIG. 5 is a diversity circuit according to still another embodiment. FIG. 6 is a block diagram showing the configuration of FIG. 6, and FIG. 6 is a block diagram showing the configuration of a conventional diversity circuit. 1 ... Output of antenna A ₁ 2 ... Output of antenna A ₂ 3
...... Local oscillator, 4,5 …… Frequency converter, 12,13 …… Diode, 14,15 …… Resonance circuit capacitors, inductance, 16,17 …… Detection time constant circuit capacitors, resistors , 18 …… Output.

Claims (1)

[Scope of utility model registration request] _1. Signals from a plurality of antennas A ₁ and A ₂ are supplied to a common connection point on the output side thereof via diodes (12) and (13), respectively, and an input of each diode and a reference potential point are supplied. Resistors (10) and (11) are respectively interposed between the two, and parallel resonance circuits (14) and (15) having a predetermined resonance frequency are interposed between the common connection point and the reference potential point. A diversity circuit, wherein detection time constant circuits (16) and (17) for applying a bias voltage that determines an operating point to each diode are interposed between the resonance circuit and a reference potential point.