JPS6236368Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is an AM receiver, especially for various radio wave types.
Regarding an AM receiver capable of receiving AM waves.

Normally, AM waves have a carrier wave a as shown in Figure 1A.
A ₃ with lower sideband b and upper sideband c centered on
(DSB), A ₃ a including a carrier wave a and one of the sideband waves, for example, the upper sideband c, as shown in Figure 1B.
wave (residual carrier SSB), carrier wave a is _suppressed as shown in Fig.
SSB) etc.

For receiving _A3 waves and _A3A waves, for example, a device as shown in Fig. 2 has been proposed, while for receiving _A3j waves, for example, a device as shown in Fig. 3 has been proposed. ing.

First, in FIG. 2, a broadcast radio wave, that is, an AM wave, received by a receiving antenna 1 is supplied to a mixing circuit 2 through a high frequency amplification circuit (not shown). This AM wave is generally expressed as (1+mcospt)cosωt=cosωt+m/2cos(ω−p)t+m/2cos(ω+p′)t (1). In the above equation (1), m is the modulation degree,
p and p' are the angular frequencies of the lower sideband and upper sideband signals, respectively, and the first term on the right side of equation (1) above is the carrier signal, the second term is the lower sideband signal, and the third term is the upper sideband signal. Each represents a sideband signal, so in the case of A ₃ waves, it includes all the signals of the first to third terms,
In the case of A ₃ A waves, the signal includes the first term and the second or third term.

The high frequency signal supplied to the mixing circuit 2 is mixed with the local oscillation signal from the local oscillation circuit 3 and converted into an intermediate frequency signal, which is supplied to the multiplier 5 through the intermediate frequency amplifier circuit 4.

Further, the output signal of the intermediate frequency amplification circuit 4 is supplied to a carrier wave extraction circuit 6 consisting of, for example, a narrowband filter or a phase lock loop (hereinafter abbreviated as PLL) circuit, and the filter function of this extraction circuit 6 causes the carrier wave signal, i.e., the above (1) cosωt in the equation is derived on this output side.

A part of the output signal from extraction circuit 6, i.e., a signal in phase with the input carrier signal cosωt, is supplied to multiplier 5 and multiplied by the output signal from intermediate frequency amplifier circuit 4, and the output signal from multiplier 5 is further supplied to low-pass filter 7. As a result, an output signal expressed by the following equation (2) is obtained at the output side of low-pass filter 7.

m/4cospt+m/4cos(-p')t...(2) On the other hand, part of the output of the extraction circuit 6 is transferred to the 90° phase shifter 8.
Carrier signal cos (ωt-90°) that has a phase difference of 90° with respect to the input carrier signal that has been phase shifted by 90°
That is, the signal of sinωt is supplied to the multiplier 9 and multiplied by the output signal from the intermediate frequency amplifier circuit 4, and the output signal of this multiplier 9 is further supplied to the low frequency amplifier 10. As a result, an output signal expressed by the following equation (3) is obtained on the output side of the low frequency filter 10.

m/4sinpt+m/4sin(-p')t (3) These output signals are maintained by phase shift networks 11 and 12 in a relationship such that they have a phase difference of 90 degrees. That is, for example, the output signal of the low-frequency wave generator 10 is advanced by 90 degrees in phase with respect to the output signal of the low-frequency wave generator 7. As a result, the output signal of the low frequency converter 10 expressed by the above equation (3) becomes m/4 cospt - m/4 cosp't (4). Therefore, the next stage matrix circuit 13 is supplied with output signals as expressed by equations (2) and (4) above.

Then, in the matrix circuit 13, when the sum and difference of each output signal from the inputted phase shift circuit networks 11 and 12 is calculated, the following sum component and difference component are applied to the fixed contacts 14L and 14U of the changeover switch 14, respectively. The output signal of is extracted.

m/2cospt …(5) m/2cosp′t …(6) In other words, the above equation (5) is the sum component and represents the lower sideband signal, while the above equation (6) is the difference component and represents the upper sideband signal. represent

The lower sideband signal and upper sideband signal extracted in this way are selectively switched by the switch 14 and outputted to the output terminal 15, and sound is emitted via a low frequency amplifier circuit, a speaker, etc. (not shown). be done.

In addition, in FIG. 3, an oscillator 16 having a constant frequency, that is, an oscillation frequency equivalent to the intermediate frequency is provided in place of the extraction circuit 6 in FIG. 2, and if the oscillation frequency from this oscillator 16 and the intermediate frequency match, By the same operation as above, it becomes possible to receive A _3j waves.

By the way, in the case of the conventional AM receiver having the above-mentioned configuration, it is necessary to install a dedicated AM receiver for each different AM wave radio wave type, which is uneconomical and complicated to handle. There were some shortcomings.

In view of these points, the present invention provides an AM receiver that can receive AM waves in various radio wave formats with a single receiver and is inexpensive in terms of cost.

An embodiment of the present invention will be described in detail below with reference to FIG. In addition, in the same figure, Figures 2 and 3
Portions corresponding to those in the figures are given the same reference numerals, and detailed explanation thereof will be omitted.

In this embodiment, a phase comparator 21, a low frequency converter 22, and a voltage-controlled oscillator (hereinafter abbreviated as VCO) which constitute the PLL circuit 20 are provided, and the loop system of the PLL circuit 20 is opened and closed according to the power supply type. A switch circuit 24 is provided. The output signal of the intermediate frequency amplifier circuit 4 is supplied to one input terminal of the phase comparator 21, and the output signal of the VCO 23 is supplied to the other input terminal of the phase comparator 21. Moreover, the common terminal 24c of the switch circuit 24 is
The fixed contact 24a is connected to the input side of the VCO 23, and the fixed contact 24a is connected to the output side of the low frequency generator 22.
b is connected to the reference power source 25. The reference power supply 25 is
The voltage value is set in advance so that the VCO 23 oscillates at a constant frequency, that is, in this case, a frequency equivalent to the intermediate frequency.

Furthermore, the output signal of the VCO 23 is directly supplied to one input terminal of the multiplier 9 and also supplied to one input terminal of the multiplier 5 through the 90° phase shifter 8.

Now, when the switch circuit 24 is connected to the fixed contact 24a side, a loop system of the PLL circuit 20 is formed, and the phase comparator 21 compares the carrier wave component cosωt in the output signal of the intermediate frequency amplifier circuit 4 with this component. A phase comparison is made with the output signal sinωt from the orthogonal VCO 23, and the phase comparison error signal is converted into a DC voltage by the low frequency converter 22 and supplied as a control signal to the input side of the VCO 23. In this case, the PLL circuit 20 Performs carrier synchronous detection operation for A ₃ waves and A ₃ A waves.

The output signal of the VCO 23, ie, sinωt, is directly supplied to the multiplier 9, phase-shifted by 90° by the phase shifter 8, and supplied to the multiplier 5 as cosωt. As a result, switch 1 is activated by the same operation as described above.
The fixed contacts 14L and 14U of No. 4 take out the lower sideband signal and the upper sideband signal, respectively, and A ₃ waves or
A ₃ A wave reception becomes possible.

Furthermore, when the switch circuit 24 is switched to the fixed contact 24b side, the loop system of the PLL circuit 20 is opened.
The control signal of the VCO 23 is fixed to the voltage supplied from the reference power supply 25, so that the VCO 23 oscillates at a constant frequency, that is, an intermediate frequency.
The output signal of the VCO 23 is directly supplied to the multiplier 9 as described above, and is also phase-shifted by 90 degrees by the phase shifter 8 and supplied to the multiplier 5. Depending on which sideband is used to transmit this result information, switch 1
The lower sideband signal is taken out to the fixed contact 14L of No. 4, and the upper sideband signal is taken out to the fixed contact 14U. At this time, even if there is a phase difference between the signals supplied to the respective input terminals of the multipliers 5 and 9, the phase shift networks 11 and 12 maintain a relationship in which they have a phase difference of 90°. There is no problem as long as the intermediate frequencies in the VCO 23 match.

In this way, the switch circuit 24 is connected to the fixed contact 2.
By switching to the 4b side, A _3j waves can also be easily received.

Note that the switch circuit 24 may be switched manually, but the detection output of the detector 27, which detects the output signal of the intermediate wave amplifier circuit 4 and swings the meter 26, is used to detect, for example, the A ₃ wave or the A ₃ A wave. while receiving
When the electric field is so weak that the PLL circuit 20 does not lock, the detection output may be used to automatically switch the switch circuit 24 to the fixed contact 24b side, as shown by the broken line in FIG. This automatic switching is particularly effective when the electric field strength fluctuates due to fading or passing through tunnels during mobile reception, and can be widely used in receivers that use PLL circuits for detection, such as AM stereo receivers.

As mentioned above, according to the present invention, A ₃ waves, A ₃ a waves, A
It is extremely economical and easy to handle as it can handle reception of various radio wave types by simply changing the switch circuit to a single receiver without installing a dedicated receiver for each type of radio wave such as _3J wave. It is also extremely easy. Also, depending on the level of electric field strength,
Since it has a function of automatically switching the oscillator frequency of the VCO to a constant frequency, it is extremely useful especially when there are large fluctuations in electric field strength.

In the above embodiment, the oscillation frequency of the VCO 23 is fixed to an intermediate frequency, but it may be fixed to an arbitrary frequency depending on the frequency of the signal to be handled. Therefore, the reference power supply 25 can obtain an arbitrary voltage value. It can be made into a variable type so that it can be used.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining AM waves of various radio wave types, Figures 2 and 3 are block diagrams showing an example of a conventional AM receiver, and Figure 4 is an example of an embodiment of the present invention. FIG. 20 is a phase lock loop (PLL) circuit, 24 is a switch circuit, and 25 is a reference power source.

Claims (1)

[Scope of utility model registration request] An AM receiver that has a phase lock loop circuit and performs detection in synchronization with a carrier wave of an AM wave, comprising a switch circuit that switches a control signal for the phase lock loop circuit, and a reference power source that generates a predetermined voltage as the control signal. , when the AM wave has no carrier wave, a predetermined voltage from the reference power source is supplied to the oscillator of the phase lock loop circuit, and the AM reception is characterized in that the oscillator of the phase lock loop circuit is oscillated at a constant frequency corresponding to the predetermined voltage. Machine.