JPS5941604B2 - electronic tuning receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronically tuned receiver that does not cause erroneous station selection even when the search speed is increased.

FIG. 1 is a block diagram showing a conventional electronically tuned receiver.

In the figure, 1 is an antenna, 2 is a high frequency amplification circuit including a variable tuning circuit and a variable gain circuit, 3 is a mixing circuit with a local oscillation frequency for converting the high frequency into an intermediate frequency,
4 is an intermediate frequency amplification circuit including a tuning circuit, 5 is an audio frequency amplification circuit including a detection circuit, 6 is a speaker, 7 is a local oscillator whose oscillation frequency is variable, and 8 is the oscillation frequency of this local oscillator 1 or its oscillation frequency. 9, a signal detection circuit with steep selection characteristics; 10, a detection signal input from the signal detection circuit 9 performs a tuning operation; 11 is a gain control time constant (AG) including a detection circuit;
C loop filter) circuit. Incidentally, FIG. 2 is a diagram showing a frequency-gain curve when tuned to each frequency or each channel from point A to point B in FIG. 1.

Next, the operation of the electronically tuned receiver having the above configuration will be explained.

First, when the signal wave received by the antenna 1 matches the tuning frequency of the receiver, this signal wave is amplified by the high-frequency amplifier circuit 2, and then the local oscillator input from the local oscillator T is sent to the mixing circuit 3. It is mixed with the frequency and becomes an intermediate frequency. A part of the intermediate frequency input to the intermediate frequency amplifier circuit 4 is input to the signal detection circuit 9, performs an output detection operation, and is transmitted to the high frequency amplifier circuit 2 through the general control circuit 10 and the tuning frequency control circuit 8. and local oscillator 7
Fix the oscillation frequency. On the other hand, a part of the signal that has passed through the intermediate frequency amplification circuit 4 is input to the gain control time constant circuit 11, and the output signal operates the variable gain circuit of the high frequency amplification circuit 2, and the intermediate frequency amplification circuit 4 so as to keep the signal output level constant. In addition, the intermediate frequency amplification circuit 4
The remaining signal wave outputted by is transmitted to the speaker 6 through the audio frequency amplification circuit 5, and is output as audio. in this way,
When electronically tuned receivers automatically tune broadcast signal waves, they simultaneously raise or lower the local oscillation frequency and the tuning frequency of the high-frequency amplifier circuit, while searching for the point at which the signal detection circuit operates. , the local oscillation frequency and the tuning frequency are fixed at the frequency at which the output detection circuit is operated, and a broadcast reception state is entered. However, in conventional electronically tuned receivers, incorrect station selection occurs when the speed at which channels are sequentially switched, the so-called search speed, is increased. That is,
Assume that while performing an automatic tuning operation by sequentially changing the tuning point from channel 10 to channel 11, channel 12, etc., a strong signal wave hits channel 15. When the variable gain circuit AGC of the high frequency amplifier circuit 2 is in the maximum gain state, the 15 channel signal entering the point A from the antenna 1 changes the selection characteristics of the tuning circuit of the high frequency amplifier circuit 2 and the intermediate frequency amplifier circuit 4.
Due to the selection characteristics of the tuning circuit, the level that reaches point B, which is the output terminal of the intermediate frequency amplifier circuit 4, is almost zero level for the 10th, 11th, and 12th channels of tuning, as shown in Figure 2. , the 13th channel is Levely, and the 14th channel is Levello. Therefore, the speed at which channels are sequentially switched, the so-called search speed, is the gain control time constant (AGC loop filter).
If the time constant is faster than the time constant of the circuit 11, the gain control time constant (AGC loop filter) circuit The AGC control output voltage of No. 11 cannot rise sufficiently. At this time, if the output at point B saturates at level low or generates distortion close to it in the signal circuit from point A of antenna 1 to point B, which is the output end of intermediate frequency amplification circuit 4, Due to the third-order distortion of the audio signal component and the 15-channel carrier signal component included in the signal wave, 1
Even though the shin rock corresponding to 4 channels is generated inside the circuit and there is no 14 channel in the received signal wave,
The signal detection circuit works on channel 14, and the channel selection operation stops when channel 14 is received, so to speak, it has the disadvantage of causing incorrect channel selection. Note that if the time constant of the gain suppression time constant (AGC loop filter) circuit is made small, the output signal level will fluctuate due to the audio signal wave component, so it is usually necessary to make the time constant large.

In view of the above points, this invention was made to solve these problems and eliminate such drawbacks.The purpose of this invention is to prevent incorrect station selection even when the search speed of sequentially changing channels is fast. An object of the present invention is to provide an electronically tuned receiving device that can receive data reliably without any interference.

In order to achieve such an object, the present invention comprises a switch that is closed during the tuning operation of automatic tuning or manual tuning, and a resistor having a resistance value considerably lower than the equivalent resistance of a single tuning coil. and the above-mentioned resistor are connected in series, and then connected in parallel to the above-mentioned tuning coil alone to change the tuning circuit sharpness Q by closing the above-mentioned switch. During station or manual tuning operation, the tuning circuit sharpness Q including the intermediate frequency amplification circuit or the high frequency amplification circuit is made lower than the tuning circuit sharpness Q when listening to a signal. be.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 3 is a block diagram showing an embodiment of an electronically tuned receiver according to the present invention.

In FIG. 3, the same parts as in FIG. 1 are shown, and 12 is a high frequency amplifier circuit including a variable tuning circuit, a variable gain circuit, and a circuit that can vary the sharpness Q of the tuning circuit;
13 is a drive circuit for changing the tuning circuit sharpness Q of the high frequency amplifier circuit 12, and 14 is an intermediate frequency amplifier circuit including a tuning circuit and a circuit that can make the tuning circuit sharpness Q variable. Incidentally, FIG. 4 shows the frequency-gain selectivity characteristic when the tuning circuit sharpness Q from point A to point B in FIG. 3 is lowered.

Further, FIG. 5 is a circuit diagram showing a circuit that can change the sharpness Q of the tuning circuit. In the same figure, L1 and L
2 is a tuning coil, C1 and C2 are tuning capacitors, and R1 and R2 are to lower the tuning circuit sharpness Q.
Resistors SWl and SW2, which have a resistance value considerably lower than the equivalent resistance of coils L1 and L2 alone, are used during tuning operation.
Switches TR1 and TR2 for lowering the tuning circuit sharpness Q are an input transistor and an output transistor, respectively. Next, the operation of the electronically tuned receiver according to the above configuration will be explained. First, when the signal wave received by the antenna 1 matches the tuned frequency of the receiver, the tuning circuit sharpness of the high frequency amplifier circuit 12 Switch 8 and SW'2 of the circuit that can vary the Q are open.

After this signal wave is amplified by the high frequency amplifier circuit 12, it is mixed with the local oscillation frequency input from the local oscillator 7 in the mixing circuit 3 to become an intermediate frequency. and,
A part of the intermediate frequency input to the intermediate frequency amplifier circuit 14 is input to the signal detection circuit 9, performs an output detection operation, and changes the tuning frequency of the high frequency amplifier circuit 12 via the integrated control circuit 10 and the tuned frequency control circuit 8. and fixes the oscillation frequency of the local oscillator 7. On the other hand, a part of the signal that has passed through the intermediate frequency amplification circuit 14 is input to the gain controlled time constant circuit 11, and the output signal controls the variable gain circuit of the high frequency amplification circuit 12, and the intermediate frequency It operates to keep the signal output level of the amplifier circuit 14 constant. Further, the intermediate frequency amplification circuit 14
The remaining signal wave outputted by is input to the speaker 6 through the audio frequency amplification circuit 5, and is output as audio. Next, during a tuning operation in which broadcast signal waves are automatically tuned or manually tuned, the 1 drive circuit 13 operates, and the sharpness Q of the tuned circuit including the high frequency amplifier circuit 12 or the intermediate frequency amplifier 14 can be varied. of the circuit. Switches SWl and SW″2 are closed.

Therefore, the frequency-gain selectivity characteristic from point A to point B in FIG. 3 is as shown in FIG. 4. From this figure, when the variable gain circuit has the maximum gain, a level corresponding to point A appears in the 11th channel, point B in the 12th channel, point C in the 13th channel, and point 2 in the 14th channel appears at the point B. Therefore, when the tuning changes from channel 11 to channel 12, for example, the level changes from point A to point A, and when it changes from channel 12 to channel 13, the level changes from point point A to point C, and 13. When changing from channel to channel 14, the level fluctuates from point C to two points, but since the level change at the moment the channel is switched is small, the gain control time constant (AGC loop filter) circuit 11 including the detection circuit The rise of the AGC voltage becomes faster. That is, the gain control time constant (AGC loop filter) circuit 11 including this detection circuit can follow, and it is possible to eliminate erroneous station selection due to saturation of the signal circuit. As explained in detail above, according to the electronically tuned receiving device according to the present invention, even when the search speed of sequentially switching channels is fast, erroneous station selection does not occur and reception can be ensured. effective.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional electronically tuned receiver; FIG. 2 is a diagram showing a frequency-gain curve when tuned to each frequency or channel from point A to point B in FIG. 1; FIG. 3 is a block diagram showing an embodiment of an electronically tuned receiver according to the present invention, and FIG. 4 is a block diagram showing the frequency range when tuned to each frequency or each channel from point A to point B in FIG. FIG. 5, which is a diagram showing a gain curve, is a circuit diagram showing a circuit that can change the sharpness Q of the tuning circuit. 1...Antenna, 2...High frequency amplification circuit, 3...Mixing circuit, 4...Intermediate frequency amplification circuit, 5...Audio Frequency amplification circuit, 6...
...Speaker, 7...Local oscillator, 8...
... Tuned frequency control circuit, 9 ... Signal detection circuit, 10 ...゛ ... Comprehensive control circuit, 11 ...
・Gain suppression time constant (AGC loop filter) circuit, 12
...High frequency amplification circuit, 13... Drive circuit, 14... Intermediate frequency amplification circuit, L1 and L2 ... Tuning coil, C1 and C2.・・・
...Tuning capacitor, R1 and R2...
Resistors, SWl and SW2.・・・． ．． ．． Switch, TR
l... Input side transistor, TR2...
・Output side transistor. Note that the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1 The received signal from the antenna is amplified by a high frequency amplifier circuit including a variable tuning circuit and a variable gain circuit, then added to a mixing circuit, mixed with the local oscillation frequency from a local oscillator, converted to an intermediate frequency signal, and the intermediate frequency signal is input to an intermediate frequency amplification circuit including a tuning circuit, and is also input to a signal detection circuit that performs an output detection operation, and the output of this signal detection circuit is transmitted to the high frequency amplifier circuit and the local section via a general control circuit and a tuning frequency control circuit. In addition to the oscillator, the tuning frequency of the high frequency amplifier circuit and the oscillation frequency of the local oscillator are controlled and fixed, and the output of the intermediate frequency amplifier circuit is input, and the gain of the high frequency amplifier circuit is variable by the output signal. In an electronically tuned receiving device such as an electronically tuned radio receiver or wireless device that is equipped with a gain control time constant circuit that controls the circuit, a switch that closes during automatic tuning or manual tuning operation and a single tuning coil. The switch and the resistor are connected in series, and then connected in parallel to the single tuning coil, and the tuning circuit is sharpened by closing the switch. A circuit for changing the sharpness Q of the tuned circuit including the intermediate frequency amplification circuit or the high frequency amplification circuit is provided on the output side of the general control circuit, and during automatic tuning or manual tuning operation, the sharpness Q of the tuned circuit including the intermediate frequency amplification circuit or the high frequency amplification circuit is changed by the signal. An electronically tuned receiving device characterized in that the tuning circuit has a sharpness Q lower than that when listening to or receiving.