JPH06104788A - Superheterodyne receiver - Google Patents

Abstract

PURPOSE:To widen a reception band even in a single conversion type by separating the generating position of an intermediate frequency interference wave from a reception frequency band. CONSTITUTION:A PLL circuit 18 is used as a local oscillation circuit, and a station selection is operated by a synthesizer system. A CPU 22 divides the reception frequency band into an up-side frequency band and a low-side frequency band, and applies a frequency instruction to the PLL circuit(local oscillation circuit) 18 so that a local oscillation frequency lower than the reception frequency can be selected at the time of receiving (station-selecting) the up-side frequency band, and the local oscillation frequency higher than the reception frequency can be switched and selected at the time of receiving the low-side frequency band. Thus, the intermediate frequency jamming wave can be separated from the reception frequency band.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superheterodyne type receiver, and more particularly to control of a local oscillation signal of the receiver for selecting a channel by a synthesizer type.

[0002]

2. Description of the Related Art Conventionally, a superheterodyne receiver is used for receiving broadcast waves on radio and television. This superheterodyne method adds a local oscillation signal to a received input signal, By converting the input signal into an intermediate frequency signal and amplifying the intermediate frequency signal, characteristics such as sensitivity are improved. In this super heterodyne system, a synthesizer system is used for channel selection. This synthesizer system uses a PLL (Phase Locked Loo
p) circuit is used to oscillate a certain local oscillation frequency that is accurate and stable by this phase-locked loop, and mixes this with the broadcast wave. According to this, an excellent intermediate frequency signal corresponding to the reception frequency enables favorable tuning.

[0003]

However, in the above-mentioned super-heterodyne type receiver, since either the upper side or the lower side of the reception frequency is used as the above-mentioned local oscillation frequency, the reception frequency is centered. When an interfering wave that is generated symmetrically with the local oscillation frequency (hereinafter referred to as a local image wave) exists in or near the receiving frequency band, there is a problem that the receiving interfering characteristic deteriorates. For example, as shown in FIG. 4, when a single conversion type receiver receives a reception frequency band A of frequencies f1 to f2, a signal obtained from a high frequency selection band pass filter (RF / BPF) in the receiver. The attenuation amount of is as shown in the characteristic 1. Here, using the frequency below the reception frequency as the local oscillation frequency, the frequency f
When selecting the received signal of 1, local oscillation frequency fK1
The signal of (intermediate frequency IF = f1−fK1) is mixed with the broadcast reception wave, but in this case, at the same time, even the local image wave of frequency fB1 (fB1 = f1 + IF) above the reception frequency is generated. The received frequencies are mixed and interfere with each other.

That is, when the reception frequency is sequentially selected from the frequencies f1 to f2, the local oscillation signals of the frequencies fK1 to fK2 corresponding thereto are mixed with the broadcast reception signal. At this time, the frequencies fB1 to fB2. The local image waves up to (the local image wave region is 100) are sequentially generated. Since the local image wave 100 exists inside or in the vicinity of the reception frequency band A as shown in the figure, when an interfering wave having the same frequency as the local image wave exists, a beat phenomenon occurs, and as a result, The reception characteristics will deteriorate. Therefore, in the conventional single conversion type receiver, the frequency band in which the signal can be well received is limited, and the wide band reception cannot be performed.

The present invention has been made in view of the above problems, and an object of the present invention is to receive a super heterodyne system capable of widening a reception band even in a single conversion type by moving a position of an interfering wave away from a reception frequency band. To provide a machine.

[0006]

In order to achieve the above object, the present invention is a super-heterodyne type receiver for selecting a channel by a synthesizer system, in which the receiving frequency band is divided into an upper frequency band and a lower frequency band. Then, when receiving the upper frequency band, select the local oscillation frequency lower than the reception frequency, while when receiving the lower frequency band, select the local oscillation frequency higher than the reception frequency, It is characterized by switching control.

[0007]

According to the above configuration, when receiving the upper frequency band of the predetermined reception frequency band, the frequency setting is the down converter system, and when receiving the lower frequency band, the frequency setting is the up converter system. To the CPU
Etc. will be programmed. Therefore, in the reception of the upper frequency band, the interfering wave is generated in the upper side of the reception frequency band, and in the reception of the lower frequency band, the interfering wave is generated in the lower side.
It is possible to move the generation position of the interfering wave to a frequency position farther from the reception frequency band than before. As a result, wide band reception becomes possible.

[0008]

FIG. 1 shows a partial configuration of a super-heterodyne receiver according to an embodiment. This super-heterodyne receiver is connected to an antenna 10 to reduce the reception frequency band. A high frequency selection filter (pandpass filter) 12 for extracting broadcast waves is provided. A mixing circuit 14 that mixes a local oscillation signal with a received wave is connected to the high frequency selection filter 12, and an intermediate frequency filter (pandpass filter) 16 that forms an intermediate frequency amplifier circuit is connected to a stage subsequent to the mixing circuit 14. To be done. The mixing circuit 14 includes a PL that constitutes a local oscillation circuit.
An L (Phase Locked Loop) circuit 18 is connected to this P
In the LL circuit 18, a control loop is formed from a voltage controlled oscillator (VCO) 20 and a low pass filter (LPF), a phase comparator, a programmable counter that determines a selection frequency, and the like, which are not shown, and this phase comparator is formed. A frequency obtained by dividing the reference oscillation frequency by a prescaler or the like is supplied.

The PLL circuit 18 is provided with a CPU 22 for controlling the setting of the local oscillation frequency.
Reference numeral 2 supplies a local oscillation frequency instruction signal to the PLL circuit 18 in response to channel selection. In the PLL circuit 18, the instruction signal is input to, for example, a programmable counter, and the value of the programmable counter is conversion-controlled, whereby a predetermined local oscillation frequency can be obtained as an output of the voltage-controlled oscillator 20.

In the embodiment, the CPU 22 controls switching of the local oscillation frequency between the upper frequency band and the lower frequency band of the reception frequency band. That is, FIG. 2 shows the relationship between the local oscillation signal and the interfering wave when the lower frequency band is selected, and FIG. 3 shows the above relationship when the upper frequency band is selected. The reception frequency band is divided into an upper frequency band and a lower frequency band, and the lower local oscillation frequency is used for reception of the upper frequency band, and conversely, the upper local oscillation frequency is used for reception of the lower frequency band. Will be used.

In FIG. 2, the frequency band A is applied to the frequency band A of the reception frequencies f3 to f4 of the FM broadcast band (the high frequency selection filter 12 has the same characteristic 1 as in FIG. 4). In the reception of the lower frequency band B of the reception frequencies f3 to f5, which are substantially evenly divided into two, the CPU 22 outputs a frequency instruction so as to form the local oscillation frequencies fK3 to fK5 above the reception frequency. That is, when selecting the reception frequency f3, this frequency f3
Local oscillation frequency fK3
(FK3 = f3 + IF) is formed, and similarly, the frequency f
Up to 5, the local oscillation frequency is formed by adding the intermediate frequency to the selected frequency. Then, this local oscillation frequency is supplied from the voltage controlled oscillator 20 of FIG. 1 to the mixer 14, whereby an intermediate frequency signal is obtained, and this intermediate frequency signal is amplified by the latter stage via the intermediate frequency filter 16. It is amplified in the circuit and left for later processing.

At this time, with respect to the reception frequencies f3 to f5, the frequency fB3 (fB3 = f3-IF) corresponding to each frequency is obtained.
Although the local image wave 120 of up to fB5 (fB5 = f5-IF) exists, the local image wave existing in the conventional reception frequency band can be output to the outside as shown in the figure. As for the local image wave outside the reception frequency band, the local image wave 12 having the same frequency as the local image wave passing through the high frequency selection filter 12 as shown in FIG.
The level of 0 becomes smaller than before.

On the other hand, in FIG. 3, in the case of receiving the upper frequency band C of the reception frequency f6 (near f5) to f4 obtained by dividing the frequency band A into two, the local oscillation frequency fK6 to the lower side of the reception frequency fK6 to CPU2 to form fK4
2 outputs a frequency instruction. That is, when selecting the reception frequency f6, the intermediate frequency (IF) is calculated from this frequency f6.
To form a local oscillation frequency fK6 (fK6 = f6-IF), and similarly a local oscillation frequency having a value obtained by subtracting the intermediate frequency from the frequency selected up to the frequency f4 is formed. Therefore, at this time, the frequencies fB6 (fB6 = f6 + IF) to f corresponding to the reception frequencies f6 to f4, respectively.
A local image wave 140 of B4 (fB4 = f4 + IF) is generated, and in this case as well, it is smaller than the local image wave 100 in the conventional case of FIG.

In the conventional example of FIG. 4, the intermediate frequency (I
When F) is set under the condition of 1/2 <IF <reception frequency band, the interference wave exists within the reception frequency band A. However, according to the present invention, even if the above condition is satisfied, the interference wave Can be excluded outside the reception frequency band.

In the above embodiment, the high frequency selection filter 1 is used.
2 has described the characteristic 1 shown in FIG. 2 to FIG. 4, the same applies to filters having other characteristics, and the case where the reception frequency band is divided into two substantially equally has been described. However, the widths of the upper frequency band and the lower frequency band can be set to be different. For example, when the attenuation characteristic at the end of the reception frequency band of the high frequency selection filter 12 is different between the upper side and the lower side, the position of the local oscillation frequency that determines the position of the reception frequency that is the division point is set to the reception wave and the intermediate frequency. It should be set so that the passage of the interfering waves that are separated by a small amount is reduced.

[0016]

As described above, according to the present invention,
Divide the reception frequency band into the upper frequency band and the lower frequency band, select the local oscillation frequency lower than the reception frequency when receiving the upper frequency band, while receiving the lower frequency band when receiving the lower frequency band Since the switching control is performed so as to select the higher local oscillation frequency than the above, it is possible to improve the interference characteristic in the single conversion type receiver as compared with the conventional one and realize wideband reception. .

Moreover, the present invention has the advantage that the conventional circuit can be used as it is, and only the setting of the local oscillation frequency in the synthesizer system can be switched and controlled, and an economical superheterodyne system receiver can be obtained. .

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a configuration of a super-heterodyne receiver according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a local oscillation signal and an interfering wave when a lower frequency band is received in relation to the characteristics of the high frequency selection filter of the embodiment.

FIG. 3 is a diagram showing a relationship between a local oscillation signal and an interfering wave when an upper frequency band is received in relation to the characteristics of the high frequency selection filter of the embodiment.

FIG. 4 is a diagram showing a conventional generation state of an interference wave in relation to the characteristics of a high frequency selection filter.

[Explanation of symbols]

12 ... High frequency selection filter (band pass filter), 14 ... Mixer, 18 ... PLL circuit, 20 ... Voltage controlled oscillator, 22 ... CPU, f1 to f6 ... Receiving frequency, fK1 to fK6 ... Local oscillation frequency, fB1 to fB6 … Interference frequency.

Claims (1)

[Claims] 1. A super-heterodyne receiver for selecting a channel by a synthesizer system, wherein a reception frequency band is divided into an upper frequency band and a lower frequency band, and when the upper frequency band is received, it is lower than the reception frequency. The super-heterodyne receiver is characterized in that switching control is performed so that the local oscillation frequency is selected, and when the lower frequency band is received, the local oscillation frequency higher than the reception frequency is selected.