JPH028446Y2 - - Google Patents

Description

[Detailed explanation of the invention] (a) Industrial application field The invention relates to an electronically tuned radio receiver.
In particular, the present invention relates to a radio receiver that can effectively eliminate whistle noise interference.

(b) Prior art When the receiving frequency is _r , the local oscillation frequency _p is, and the intermediate frequency is _i , the following formula m・_r ~ n・_p = _i (1) or the following formula _r = n・_i or _p = n・If _i (2) (where m and n are integers) is satisfied, beat interference (whistle noise interference) is likely to occur. For example, set the intermediate frequency to 450KHz and the receiving frequency to 900KHz.
Then, the received signal of 900KHz will be received at the tuner section.
After being lowered to 450KHz, it passes through the IF stage and is detected by a wave detector, but at that time, harmonic components of 450KHz are generated and returned to the antenna stage, which generates a beat with the receiving frequency and becomes the audio frequency. This causes deterioration of practical sensitivity and deterioration of S/N ratio at rated input.

(c) Problems that the invention aims to solve By the way, in conventional radio receivers, there is no means to effectively eliminate whistling noise interference, and the pattern of the printed circuit board was designed to prevent whistling noise interference at the design and manufacturing stages. This was done with consideration given to the design and parts placement. However, such conventional methods have the problem that the design is complicated and that the whistling noise interference cannot be completely removed.

Therefore, an object of the present invention is to provide a radio receiver that can effectively eliminate whistle noise interference.

Another object of the present invention is to provide a radio receiver that can determine the printed circuit board pattern and component placement without considering whistle noise interference.

(d) Means for solving the problem As shown in Figure 1, the radio receiver of the present invention has the following features:
tuner unit 11, intermediate frequency amplification circuit 12, detector 13, low frequency amplification circuit 14, and at least two intermediate frequency filters with different center frequencies provided between intermediate frequency amplification circuit 12 and detector 13; (IF filters) 15a and 15b, and a switching circuit 16 that inputs the output of the intermediate frequency amplifier circuit 12 to the detector 13 via a predetermined intermediate frequency filter,
It has a PLL circuit 17 and a control unit 18 that determines whether or not a whistle noise disturbance is occurring and causes the switching circuit 16 to select a predetermined intermediate frequency filter based on the determination result.
Note that in FIG. 1, AT is an antenna.

(e) Operation When a channel is selected by operating a channel selection switch (not shown) or when the power switch of the radio is turned on, the control unit 18 selects the station selected by the channel selection operation or the station selected when the power is turned on. Read the frequency (receiving frequency) _r from the table stored in the built-in memory in advance,
Using the received frequency _r , known intermediate frequency _i , and local oscillation frequency _p (= _r + _i ), equations (1) and (2)
Determine whether the expression holds true.

If both equations (1) and (2) do not hold true, whistle noise interference will not occur, so the intermediate frequency is _i (for example, 450KHz).
In other words, the control unit 18 is set so that the local oscillation frequency _p becomes ( _r + _i ).
is the digital frequency control data to the PLL circuit 17.
Enter FCD. Also, control unit 1
8 is a switching signal FCS which causes the switching circuit 16 to select the intermediate frequency filter 15a according to the intermediate frequency _i .
Enter.

The PLL circuit 17 executes well-known PLL control and controls the local oscillator of the tuner section 11 at a frequency _p (= _i + _r ).
to oscillate. The tuner unit 11 uses a built-in mixing circuit to output an intermediate frequency component of _p − _r (= _i = 450 KHz) to an intermediate frequency amplifier circuit 12, and the output of the intermediate frequency amplifier circuit 12 is sent to a wave detector via an intermediate frequency filter 15a. 13.

On the other hand, the control unit 18 uses the formula (1) or
If equation (2) holds true, whistling interference will occur, so the intermediate frequency will be _i ′ (for example, 468 KHz), in other words, the local oscillation frequency _p will be ( _r +
_i '), the control unit 18
Digital frequency control data in PLL circuit 17
Enter FCD. Also, control unit 1
8 is a switching signal that causes the switching circuit 16 to select the intermediate frequency filter 15b according to the intermediate frequency _i '.
Enter FCS.

The PLL circuit 17 executes PLL control as described above, and controls the local oscillator of the tuner section 11 at a frequency _p (=
_i ′+ _r ). The tuner unit 11 outputs the intermediate frequency component of _p − _r (= _i ′ = 468 KHz) to the intermediate frequency amplification circuit 12 using a built-in mixing circuit, and the output of the intermediate frequency amplification circuit 12 is sent to the intermediate frequency filter 1.
The signal is input to the detector 13 via 5b.

As above, at intermediate frequency _i, (1) or
If Equation (2) holds true and whistling noise is generated, changing the intermediate frequency from _i to _i ' will shift the harmonic at the detection stage to 2· _i ', resulting in a beat. Even if it is generated, it will be outside the audible frequency, and the generation of whistle noise interference will be prevented.

(f) Embodiment FIG. 2 is a block diagram of an embodiment of a radio receiver according to the present invention.

The tuner section 11 includes an antenna tuning circuit 11a.
, RF amplifier 11b, and high frequency tuning circuit 11c
, a local oscillator 11d, and a mixing circuit 11e, and the PLL circuit 17 is connected to a control unit 18.
A frequency division unit 17a that divides the output frequency of the local oscillator 11d based on reception frequency control data FCD output from the frequency division unit 17a, a crystal oscillator 17b that oscillates at a constant frequency, and an output signal from the frequency division unit 17a and the crystal oscillator 17a. It has a phase comparison unit 17c that compares the phases of the output signals from the oscillator 17b and outputs a phase difference signal PDS, and a low-pass filter 17d that smoothes the phase difference signal PDS into DC. The switching circuit 16 includes two switches 16a, 16
The switch 16a inputs the output of the intermediate frequency amplifier circuit 12 to the intermediate frequency filters (IF filters) 15a, 15b as appropriate based on the switching signal FCS from the control unit 18, and the switch 16b inputs the output of the intermediate frequency amplifier circuit 12 to the intermediate frequency filters 15a, 15b. 15b is similarly input to the detector 13 as appropriate based on commands from the control unit 18.

Next, the operation of the radio receiver of the present invention will be explained.

(a) When a channel is selected by operating a channel selection switch (not shown) or when the power switch of the radio is turned on, the control unit 18 controls the station selected by the channel selection operation or the station selected when the power is turned on. frequency (receiving frequency) _r
is read from a table stored in advance in the built-in memory 18a. Note that the memory 18a stores in advance a correspondence table of (1) station name, (2) reception frequency _i , and (3) reception frequency control data FCD input to the PLL circuit.

(b) The control unit 18 then selects the reception frequency _r and the known intermediate frequency _i (for example
450KHz) and the local oscillation frequency _p (= _r + _i ) to determine whether equations (1) and (2) hold.

(c) If both equations (1) and (2) do not hold true, no whistle noise will occur, so the intermediate frequency is _i (=450KHz)
In other words, the control unit 1 is set so that the local oscillation frequency _p becomes ( _r + _i ).
8 inputs digital reception frequency control data FCD to the PPL circuit 17. That is, the control unit 18 receives the received frequency control data using the selected station information and intermediate frequency _i as a key.
Obtain FCD from the table above, and PLL circuit 17
Enter.

Further, the control unit 18 is connected to the switching circuit 1.
6 is an intermediate frequency filter 1 corresponding to the intermediate frequency _i .
Input the switching signal FCS to select 5a,
Switches 16a and 16b are operated to select intermediate frequency filter 15a.

(d) The PLL circuit 17 executes well-known PLL control,
The local oscillator 11d of the tuner section 11 has a frequency _p
(= _i + _r ). The tuner section 11 uses the mixing circuit 11e to generate _p − _r (= _i = 450KHz)
The intermediate frequency component is outputted to the intermediate frequency amplification circuit 12, and the intermediate frequency amplification circuit 12 inputs its output to the detector 13 via the intermediate frequency filter 15a selected by the switching circuit 16.

(e) On the other hand, in the discrimination process in step (b)
If equation (1) or equation (2) holds true, whistle noise interference will occur, so the control unit 18 sets the intermediate frequency to _i ' (for example, 468 KHz).
In other words, digital reception frequency control data FCD is input to the PLL circuit 17 so that the local oscillation frequency _p becomes ( _r + _i '). In addition, the control unit 18 connects the switching circuit 16 to the intermediate frequency.
A switching signal FCS is input so as to select the intermediate frequency filter 15b according to _i '.

(f) The PLL circuit 17 executes PLL control as described above, and controls the local oscillator of the tuner section 11 at the frequency _p.
(= _i ′+ _r ). The mixing circuit 11e of the tuner section 11 outputs the intermediate frequency component of _p − _r (= _i ′=468 KHz) to the intermediate frequency amplifying circuit 12, and the intermediate frequency amplifying circuit 12 detects the output via the intermediate frequency filter 15b. input to the device 13.

In the above, when either equation (1) or equation (2) is satisfied, it is assumed that whistle noise interference occurs, but if the reception frequency _r is an integer multiple of the intermediate frequency _i ( _r =
n・_i ) It may be possible to monitor only whether or not the number has decreased, and only when the number has reached an integer multiple, it is assumed that a state in which whistle noise interference is generated is reached.

(g) Effect of the invention As explained in detail above, according to the _invention , (1) or
If equation (2) holds true and whistle noise is generated, the intermediate frequency can be changed from _i to _i ′ (for example, 468KHz).
By changing the harmonics at the detection stage to 2.
_i ', even if a beat occurs, it will be outside the audible frequency range, and the occurrence of whistling noise interference will be prevented.
Further, according to the present invention, since the occurrence of whistling noise interference can be prevented, the printed circuit board pattern and component arrangement can be designed without considering the whistling noise interference.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a radio receiver according to the present invention, and FIG. 2 is a block diagram of an embodiment of the radio receiver according to the present invention. 11...Tuner, 12...Intermediate frequency amplifier circuit, 13...Detector, 15a, 15b...Intermediate frequency filter, 16...Switching circuit, 17...PLL
Circuit, 18...control unit.

Claims (1)

[Claims for Utility Model Registration] In an electronically tuned radio receiver having a tuner section, an intermediate frequency amplification circuit, and a wave detector, the center frequencies provided between the intermediate frequency amplification circuit and the wave detector are different. Two intermediate frequency filters, a switching circuit that inputs the output of the intermediate frequency amplification circuit to the detector via a predetermined intermediate frequency filter, and a receiving frequency
Either _r is an integer multiple of the intermediate frequency _i , or the local oscillation frequency _p is an integer multiple of the intermediate frequency _i , or the following formula m・_r〜o・_p = _i (m, n are integers) is satisfied. Based on whether this is true, it is determined whether or not the whistling noise interference is occurring, and if the whistling noise interference is occurring, the intermediate frequency is changed, and the intermediate frequency is changed.
A radio receiver comprising: a control unit that causes the switching circuit to select a predetermined intermediate frequency filter according to an intermediate frequency.