JPS6334359Y2 - - Google Patents

Description

[Detailed explanation of the invention] [Industrial application field] This invention focuses on the lower sideband (LSB) of the carrier wave.
The present invention relates to an AM receiver that extracts and receives a signal from one of the above-mentioned sidebands from a double sideband (DSB) signal having an upper sideband (USB) and an upper sideband (USB).

[Background technology and its problems]

Typically, AM waves include A _3a wave (DSB), which has a lower sideband and an upper sideband around the carrier, and A _3a wave (DSB), which includes a reduced carrier wave and one of the sidebands, e.g. There are carrier wave SSB), A _3j wave (carrier suppressed SSB), etc., in which the carrier wave is suppressed and includes only one of the sidebands, for example, the upper sideband.

A synchronous detection method using a phase-locked loop (PLL) circuit is generally known for single-side band reception of _A3 waves, reception of _A3A waves, or AM stereo reception, and Fig. 1 is an example of this. .

In FIG. 1, broadcast radio waves, that is, AM waves, received by receiving antenna A are transmitted to high frequency amplifier circuit 1.
is supplied to the mixing circuit 2 through. This AM wave is generally (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 lower sideband signal.
Each term represents an upper sideband signal. Therefore, in the case of A ₃ waves, all the signals of the first to third terms are included, and in the case of A _3a waves, the signals of the first term and the second or third term are included.

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 one input end of the multiplier 5 through the intermediate frequency amplifier circuit 4.

Further, the output signal of the intermediate frequency amplification circuit 4 is supplied to the PLL circuit 6, and the filter function of this PLL circuit 6 is used to generate the carrier wave signal, that is, in equation (1) above.
cosωt is derived on its output side.

The output signal of the PLL circuit 6, that is, a signal in phase with the input carrier signal cosωt, is supplied to the other input terminal of the multiplier 5, and multiplied by the output signal from the intermediate frequency amplifier circuit 4. Furthermore, the output signal of this multiplier 5 is supplied to a low pass filter 7. As a result, an output signal expressed by the following equation (2) is obtained on the output side of the low-pass filter 7.

m/4cospt+m/4cos(-p')t...(2) Also, the output signal of the PLL circuit 6 is transferred to the 90° phase shifter 8.
is supplied to The 90° phase shifter 8 outputs a carrier signal cos(ωt−90°), that is, a sinωt signal having a phase difference of 90° with respect to the input carrier signal,
The signal is supplied to a multiplier 9 and multiplied by the output signal from the intermediate frequency amplification circuit 4. Furthermore, the output signal of this multiplier 9 is supplied to a low pass filter 10. As a result, an output signal expressed by the following equation (3) is obtained on the output side of the low-pass filter 10.

m/4sinpt+m/4sin(-p')t (3) Further, these output signals are maintained in a relationship such that they have a phase difference of 90 degrees from each other by phase shift circuits 11 and 12. That is, for example, the output signal of the low-pass filter 10 is advanced by a phase difference of 90 degrees with respect to the output signal of the low-pass filter 7. As a result, the above-mentioned low-pass filter 10 expressed by the above equation (3)
The output signal is m/4cospt - m/4cosp't (4). Therefore, the matrix circuits 13 at the next stage are supplied with output signals as expressed by the above equations (2) and (4), respectively.

Then, in the matrix circuit 13, the sum and difference of each output signal from the input phase shift circuit networks 11 and 12 are determined, and the following sum component and difference component are input to terminals 14L and 14U of the changeover switch 14, respectively. An output signal is taken.

m/2cospt...(5) m/2cosp't...(6) In other words, equation (5) above is the sum component and represents the lower sideband signal, while equation (6) above is the difference component and represents the upper sideband signal. represents.

The lower sideband signal and upper sideband signal thus extracted are selectively switched by manually operating the switch 14 and output to the output terminal 15. Although not shown, the sound is emitted via a low frequency amplification circuit, a speaker, etc.

By the way, in the case of the conventional circuit having the configuration as shown in FIG. 1, the selection of the lower sideband signal or the upper sideband signal is done by manually switching the switch 14. Therefore, when selecting a channel, the tuning dial etc. A channel selection operation by operating the switch 14 and a switching operation by switching the switch 14 were required. That is, in the conventional example, the operation at the time of channel selection was extremely complicated.

[Purpose of invention]

In view of the above-mentioned points, the present invention aims to improve operability when selecting a channel by making it possible to automatically select a lower sideband signal or an upper sideband signal in conjunction with the channel selection operation. The purpose is to provide an AM receiver with

[Summary of the idea]

That is, in order to achieve the above-mentioned purpose, the present invention receives a double sideband (DSB) signal having a lower sideband (LSB) and an upper sideband (USB) around a carrier wave, and connects it to a phase lock loop. In the AM receiver, the above-mentioned The signal level of the oscillation control signal supplied to the voltage controlled oscillator (VCO) constituting the PLL circuit is compared with a preset reference signal level, and the lower sideband (LSB) ) or the upper sideband (USB), and the signal from either of the above sidebands is automatically switched and extracted in conjunction with the channel selection operation. It is said that

〔Example〕

Hereinafter, the second preferred embodiment of the present invention will be explained.
This will be explained with reference to the figures. In this figure, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 2, the output signal from the intermediate frequency amplification circuit 4 is output from a phase lock loop circuit, i.e.
The signal is supplied to the PLL circuit 6. The above PLL circuit 6 is
It is composed of a phase comparator 61, a low pass filter 62, and a voltage controlled oscillator (VCO) 63. The output signal from the intermediate frequency amplification circuit 4 is first supplied to a phase comparator 61, and the output signal from the phase comparator 61 is supplied to a voltage controlled oscillator 63 via a low pass filter 62. Furthermore, the output signal from the voltage controlled oscillator 63 is fed back to the phase comparator 61. That is, the phase comparator 61 compares the phases of the output signal from the intermediate frequency amplification circuit 4 and the output signal from the oscillator 63, and outputs a difference signal voltage according to the phase difference between these signals. Further, the difference signal voltage becomes a control voltage that controls the voltage controlled oscillator 63 via the low-pass filter 62.

Here, the PLL circuit 6 is designed to be in a phase-locked state within a range of approximately ±2KHz centering on the intermediate frequency, and the control voltage is V [v].
It is assumed that an oscillation output locked to the intermediate frequency can be obtained from the voltage controlled oscillator 63 when . Also,
The phase comparator 61 outputs a control voltage lower than V[v] if the frequency of the input signal is lower than the intermediate frequency, and outputs a control voltage lower than V[v] if the frequency of the input signal is higher than the intermediate frequency. Output higher control voltage. In this embodiment, the control voltage is used to switch between the lower sideband signal and the upper sideband signal.

The control voltage is supplied to a voltage comparator 17 of a sideband selection circuit 16 that switches between the lower sideband signal and the upper sideband signal. The voltage comparator 17
compares the control voltage with a reference voltage determined by resistors 18 and 19, and uses its output to control switch 14 for switching between the lower sideband signal and the upper sideband signal. Note that the reference voltage determined by the resistors 18 and 19 is set to a voltage V [v] at which the voltage controlled oscillator 63 oscillates at an intermediate frequency.

Further, the voltage comparator 17 outputs a positive voltage when the input voltage, that is, the control voltage, is lower than the reference voltage. At that time, the switch 14 is connected to the terminal 14L side, and the lower side wave A band signal is extracted. Further, when the input voltage of the voltage comparator 17 is higher than the reference voltage, the voltage comparator 17 outputs a negative voltage, and at that time, the switch 14 is connected to the terminal 14U side, and the upper side Waveband signals are now being extracted. Although not shown, the voltage comparator 1
By using the output voltage of 7, it is possible to display whether the signal being extracted is a lower sideband signal or an upper sideband signal.

Next, when performing the tuning operation, start from the lower frequency side of the desired station frequency, that is, turn the tuning dial from the lower frequency side until you reach the desired station frequency. As a result, the frequency of the signal output from the intermediate frequency amplification circuit 4 approaches the intermediate frequency from the lower frequency side as the channel selection operation is performed.
Therefore, the control voltage output from the phase comparator 61 becomes V[v] due to the channel selection operation.
The voltage approaches V [v] from a lower voltage.

The control voltage is determined by the voltage comparator 17.
It is compared with the reference voltage, but the reference voltage V [v]
Therefore, the control voltage is lower than the reference voltage. Therefore, as described above, the voltage comparator 17 outputs a positive voltage, and the output connects the switch 14 to the terminal 14L side, and the lower sideband signal is taken out.

In the same way, if you select the desired station from the higher frequency side,
When the tuning dial is turned from the high frequency side and tuned to the frequency of the desired station, the frequency of the signal output from the intermediate frequency amplification circuit 4 will change from the high frequency side with respect to the intermediate frequency due to the above tuning operation. It will get closer. Therefore, the control voltage output from the phase comparator 61 approaches V[v] from a voltage higher than V[v] as the channel selection operation is performed.

The control voltage is determined by the voltage comparator 17.
compared to a reference voltage. In this case, since the control voltage is higher than the reference voltage, as described above, the voltage comparator 17 outputs a negative voltage, and the output causes the switch 14 to
It is connected to the 4U side and the upper sideband signal is extracted.

That is, in conjunction with the channel selection operation, either the lower sideband signal or the upper sideband signal can be automatically extracted.

Here, in the above embodiment, when performing the tuning operation from the low frequency side, the lower sideband signal is extracted, and when performing the tuning operation from the high frequency side,
I tried to extract the upper sideband signal, but this is
This is due to the following reasons. In FIG. 3, when selecting a desired station with frequency c, it is assumed that the frequency of the local oscillation signal output from the local oscillation circuit 3 should be adjusted to soc. At this time, if the frequency of the local oscillation signal is approached from the lower frequency side, that is, if soc ₁ in the figure is brought closer to soc than in the A direction, the frequency _M1 of the signal converted by the mixing circuit 2 will be lower than in the A' direction in the figure. The intermediate frequency approaches ₀ .
Therefore, at this time, it is necessary to extract the lower sideband signal.

On the other hand, if the frequency of the above local oscillation signal is approached from the higher frequency side, that is, if soc ₂ in the figure is brought closer to soc than in the B direction, the frequency _M2 of the signal converted by the mixing circuit 2 will be intermediate from the B' direction in the figure. Frequency approaches ₀ . Therefore, at this time, the upper sideband signal must be extracted.

By the way, the voltage comparator 17 has a hysteresis characteristic, and for example, when performing a tuning operation from the low frequency side, the control voltage output from the phase comparator 61 is a voltage lower than V [v]. The switch 14 approaches V [v] from
Immediately after the above control voltage reaches V [v], terminal 1
It does not switch from 4L to terminal 14U,
In this case, the switch 14 is not switched to the terminal 14U unless the control voltage becomes higher than V [v] to some extent. Similarly,
When performing a channel selection operation from the higher frequency side, the control voltage output from the phase comparator 61 is V [v]
The voltage approaches V[v] from a higher voltage, but even in this case, unless the control voltage becomes lower than V[v] to some extent, the switch 14 will close the terminal 14U.
It does not switch from to terminal 14L.

Therefore, for example, if you perform a tuning operation from the lower frequency side, the extracted signal will switch from the lower sideband signal to the upper sideband signal, but after the above switching, the upper sideband signal will be switched from the lower sideband signal to the upper sideband signal. It becomes difficult to switch from the band signal to the lower sideband signal, and therefore the above-mentioned respective sideband signals can be stably switched.

[Effect of idea]

As is clear from the above explanation, the present invention
According to the AM receiver, it has an extremely simple configuration by controlling the selection of a lower sideband signal or an upper sideband signal based on a signal formed by a PLL circuit for extracting a carrier wave from a received signal. The selection of the lower sideband signal or the upper sideband signal can be performed automatically in conjunction with the channel selection operation, and the operation at the time of channel selection can be simplified and the operability can be improved.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a conventional AM receiver, Fig. 2 is a circuit diagram showing an embodiment of this invention, and Fig. 3 is a frequency distribution diagram showing the signal state during channel selection operation. It is. 6...PLL circuit, 14...Switch, 14L,
14U... terminal, 16... sideband selection circuit, 17
...Voltage comparator, 18, 19...Resistor, 61...
Phase comparator, 62...Low pass filter, 63...
...voltage controlled oscillator.

Claims (1)

[Claim for Utility Model Registration] Receiving a double sideband (DSB) signal having a lower sideband (LSB) and an upper sideband (USB) centered around a carrier wave, and receiving it in a phase lock loop (PLL) circuit. The above using the carrier extracted from the signal
In an AM receiver that performs synchronous detection of a DSB signal and selectively extracts and demodulates a signal from one of the above-mentioned sidebands, oscillation control is supplied to a voltage-controlled oscillator (VCO) that constitutes the above-mentioned PLL circuit. The signal level of the signal is compared with a previously set reference signal level, and the lower sideband (LSB) is adjusted according to the comparison output.
Alternatively, a sideband selection circuit for selecting the upper sideband (USB) is provided, and the signal of one of the above-mentioned sidebands is automatically switched and extracted in conjunction with the channel selection operation. AM receiver.