JPS5894224A - Frequency stabilizing circuit and simple tuning displaying circuit of am receiver - Google Patents

Abstract

PURPOSE:To ensure the automatic frequency control for a frequency converting circuit, by applying the quadrature wave detection to the signal fed from the frequency converting circuit of an AM receiver, and displaying this signal to a tuning meter or feeding it back to a local oscillator of the AM receiver. CONSTITUTION:The output signal supplied from a frequency converting circuit 40 of an AM receiver is fed to an IF amplifier 12 of an FM receiver. The output signal of the amplifier 12 is connected to be fed a quadrature wave detector 13 and a quadrature limiter 15. The output of a phase shifter 16 for AM/FM waves is fed to the detector 13 and compared with the input signal given from the amplifier 12. A tuning coil 17 is connected to give an input/output to the detector 13. The output of the detector 13 is displayed in tuning to a tuning meter of a tuning meter circuit 18 via a tuning meter driving circuit 14. The other part of the output of the detector 13 is fed to a time constant circuit 20. The output of the circuit 20 is fed to a local oscillator 11 of the circuit 40. Then, an automatic frequency control is carried out so as to stabilize the frequency of the circuit 40 in accordance with the level of the signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AM wave frequency stabilization circuit and a simple tuning display circuit in which wave detection is applied to amplitude modulated waves.

Conventionally, quadrature detection is generally used for demodulating FM signals in FM receivers and the like. In the case of quadrature detection, ICs are being actively introduced, and are greatly contributing to eliminating the need for adjustment, improving performance, and reducing cost of FM receivers. In addition, by using quadrature detection to automatically control the frequency of FM waves and displaying the FM wave tuning on a tuning meter, we aim to improve the performance of FM receivers, etc.
Makes the receiver easy to use. However, AM receivers do not utilize such overdrive detection, do not automatically control the frequency of AM waves, and do not display tuning on a tuning meter. Although the performance of AM receivers has improved in recent years, no attention has been paid to this point. In fact, the local oscillators used in part of the frequency conversion circuit of AM receivers are affected by changes in temperature (4-,
As the characteristics of the elements used for this change change, the oscillation frequency fluctuates. Therefore, the frequency of the signal frequency-converted from the frequency conversion circuit was unstable. or,
The antenna used to indicate the tuning of AM receivers is a /gnal meter, which has the disadvantage of being difficult to tune.

The present invention has been made in order to eliminate the above-mentioned drawbacks in view of the above points, and includes an AM wave tuning coil and an AM wave phase shifter in a quadrature detection circuit used in FM receivers, etc. By providing this, a quadrature detection circuit that is also used for AM waves is configured. Using this quadrature detection circuit, the signal from the frequency conversion circuit of the AM receiver is quadrature-detected, and the detected signal is displayed on a tuning meter via the navigation/drive circuit, or is displayed on a tuning meter via the time constant circuit. An object of the present invention is to provide an AM receiver that automatically controls the frequency of a frequency conversion circuit by feeding back to a local oscillator of the AM receiver.

The present invention will now be described in detail with reference to the drawings.

FIG. 1 is a graph diagram of an embodiment of the present invention.

Pro7, which is represented by a double line in this Pro7 diagram, is an essential part of the present invention.

Roughly speaking, the upper half of FIG. 1 constitutes an FM receiver, and the lower half constitutes an AM receiver. / is an antenna for FM reception, and 3 is an antenna for AM reception. 3 is a tuning circuit for frequency selection, and 3 is an amplifier circuit. j is a mixing circuit which receives all the signals from the local oscillator // and performs frequency conversion from K. This mixing circuit S and local oscillator //
constitutes the frequency conversion circuit θ of the AM receiver. Note that the frequency conversion circuit θ is configured to receive a signal from the FM receiver and automatically control the oscillation frequency V. B is a ceramic, Kutsuilter, and 7 is an intermediate frequency amplification circuit. g is a tuning circuit, 9 is an intermediate frequency amplification circuit, /θ is a demodulation circuit, and a demodulated AM wave is outputted to a terminal T1. The output signal from the frequency conversion circuit DA θ of the AM receiver is passed through the ceramic filter 7 and the intermediate frequency amplifier 7.
The signal is then input to the intermediate frequency amplifier 7.2 of the FM receiver. Intermediate frequency amplifier/-? The output signal of is connected to the quadrature detector /3 and the quadrature detector /SK so as to be inputted thereto. /B is a phase shifter for AM waves and FM waves, which is switched by the switch sw of the switching circuit. When the SW is open, it is used for AM waves, and when it is closed, it is used as a phase shifter for FM waves.

The output of the phase shifter/2 is input to a quadrature detector/3, and both signals are comparatively detected together with the signal input from the intermediate frequency amplifier/-2. /7 is a tuning coil connected to input/output to quadrature detector /3. The tuning coil /7 is constructed by connecting an AM wave tuning coil and an FM wave tuning coil in series. Quadrature detector/
The output of 3 passes through the tuning meter drive circuit/g of the DC amplifier, one is tuned and displayed on the tuning meter TM of the tuning meter circuit/g, and the other is the time constant circuit except for AC. has been entered. Time constant circuit 3
The output of θ is input to the local oscillator // constituting the frequency conversion circuit θ, and automatic frequency control is performed to stabilize the frequency of the frequency conversion circuit OG according to the magnitude of the input signal. In addition, in this pro-tsuk diagram,
Extraneous circuits other than those of the present invention are omitted. The demodulated FM wave is output to the terminal T2, the terminal T3 is a terminal for automatic frequency control, and the terminal T4 is a terminal for the cheating meter circuit/g.
This is a terminal that provides a reference voltage to be compared with.

The part surrounded by the dotted line is generally used for intermediate frequency amplification circuits.
c 3.2 is used. In this professional diagram, a circuit consisting of a local oscillator// and a mixing circuit S is used as the frequency conversion circuit θ, but a self-excited circuit that performs local oscillation and mixing simultaneously may also be used.

Fig. 2 is an example of a more detailed circuit of the pro-7 line diagram in Fig. 1, and since the frequency conversion circuit in Fig. 3 uses a self-excitation type circuit, the configuration is different from that in Fig. 1. is the same except for the frequency conversion circuit. ■CI and VC
2 is a triple variable capacitor for tuning, T1 is a transformer, RFA/
and RFA, 2 are amplifier circuits that amplify the tuned signals. The next stage is a variable capacitance diode VCD whose capacitance changes depending on the magnitude of the input signal and a capacitor c, -
c4 and double variable pull capacitor (varicon) ■
There is a frequency conversion circuit composed of C2, a transformer T2, and a converter circuit (C0NV). B is Cerami,
IFA/~IFA3 is an intermediate frequency amplifier, and one of the outputs of the intermediate frequency amplifier IFA/ is connected to the intermediate frequency amplifier/of the FM receiver via a resistor R3 and a capacitor C7.
, 2. The other output of IFA/ is
The AM signal is input to the demodulator DET via J, demodulated, and output to the terminal TI. 79 of the FM receiver is a front end 1.2/, 2j is a selection element that functions as a filter, and Tr is an amplification transistor, which constitutes an amplifier. /3 is a quadrature detector, /s is a quadrature detector. The inductances L] and L2 constitute a phase shifter/B, and when the switch SW of the switching circuit is open, the inductance is 10t.

Therefore, even in the ideal state, the phase of the AM wave is shifted by 2θ0. When SW is closed, the inductance becomes L2, and the phase of the FM wave is similarly shifted by 2θ°. Resistors R4, R5 and capacitor Cs,
c9 and inductance L3 constitute a tuning coil for FM waves, and inductance L4
It constitutes a tuning circuit for M waves.

These tuning coils are connected in series and input and output to the quadrature detector/3. The output of the quadrature detector /3 is connected via a tuning meter drive circuit /111 to a tuning meter circuit /g consisting of resistors R6 and R7, a capacitor C11, and a tuning meter TM. The terminal T4 is a terminal for supplying a DC voltage for comparison to the cheating meter circuit/g.

The other output of the tuning meter drive circuit is a time constant circuit consisting of resistors R1 and R2 and capacitors C5 and C6! It is connected to one end of a variable capacitance diode VCD and a capacitor C2 of the frequency conversion circuit via θ.

The other end of the variable capacitance diode VCD is grounded, and the other end of the capacitor C2 is connected to the triple; recon C2 and capacitor C.
3 and C4. Series of Pariscon VC
The other ends of capacitor C3 and capacitor C3 are grounded, and one end of capacitor C3 is connected to one end of the seventh side of transformer T2 via capacitor C4. The other end of the seventh side of transformer T2 is grounded, and the converter circuit (CONV) is connected to the intermediate knob.
are connected via a capacitor C1. transformer T
The secondary side of 2 is connected to receive the output of the converter circuit (CONV) and output it to the ceramic filter B. Since the circuits to be described later are not essential parts of the present invention, an outline thereof will be described. , 23 are level detection circuits 1.
2G is a signal drive meter circuit, and 8M2 is an FM wave wave phase signal meter. 2j is an IF amplifier stop circuit whose terminal T5 is drawn out and connected to an automatic gain adjustment circuit or the like. 2 B is the inversion circuit 1.27 is the level detection circuit 1
．． 2g is a meet drive circuit which includes a meeting switch and the like, and is connected via 29 to an AF amplifier and a mute control circuit 3[theta]. Quadrature detector/3
In response to the output, the AF amplifier and mute control circuit 3θ output an FM demodulated wave to the terminal T2. The area surrounded by lines is generally used as IC3, 2 for intermediate frequency amplification circuits, and for example, RCA's cA3θg2 is used.

Next, the present invention will be explained in detail with reference to FIG. An AM wave signal received by an antenna 2 is tuned by a tuning circuit 3 to select a receiving frequency. The selected AM wave is amplified by an amplifier circuit and converted to a predetermined intermediate frequency by a frequency conversion circuit θ comprising a local oscillator// and a mixing circuit S. Here, the predetermined intermediate frequency is '133KHzf
I'll leave it as that.

The s5KH2OAM wave passes through a ceramic filter 4, removes other frequency noise components, and is input to an intermediate frequency amplification circuit 7. One of the signals amplified by the intermediate frequency amplification circuit 7 is output to the tuning circuit, through the intermediate frequency amplification circuit 2 and the demodulation circuit /θ, to the terminal T1 as a demodulated AM wave, that is, an audio signal. The other signal is sent to the FM receiver's intermediate frequency amplifier/,! is input. One of the signals amplified by the intermediate frequency amplifier/2 is applied as the first input of the quadrature detector/3, and the other signal is input to the quadrature limiter 15.

The signal input to the quadrature shifter/S is shaped into a square wave and input to the phase shifter/B. At this time switch S
W is open, and the input signal has a 2θ0 phase shift if its frequency is exactly 53 KHz. If the input signal is higher than '133KHz, there will be a phase shift greater than 2θ0, and if 'Is! ; When the frequency is lower than KHz, a phase shift smaller than 2θ0 occurs. The output from phase shifter/B is provided as the second input of quadrature detector/3.

Quadrature detector/3 performs comparative detection of two input signals given from intermediate frequency amplifier 7.2 and phase shifter/B.

Also, the signal from the quadrature detector/3 is sent to the tuning coil/7.
The signal is then applied as the third input of the quadrature detector/3 together with the signal from the phase shifter/B. The average value of the signal detected by quadrature detector/3 is
If the input signal is exactly '133KHz, it will be θ, and if the input signal is higher than 4t3;3KH1, it will be negative, and if the input signal is lower than l13;3KHz, it will be positive.

That is, the average value of the detected signal output from the quadrature detector/3 changes depending on the intermediate frequency applied from the AM receiver to the FM receiver through the frequency conversion circuit θ. The output of the quadrature detector/3 is given to the cheating meter drive circuit/g. Then, the average value of the signal is taken by a cheating meter drive circuit and DC amplified.

One of the outputs of the tuning meter drive circuit/q is a tuning meter circuit/g having a tuning meter TM.
(() is compared with the comparative upper pressure input from terminal T4 and displayed on the tuning meter TM. The output from the tuning meter drive circuit/IIL!
At the time, DaS! ; Since it is exactly in tune with KHz, it is only necessary to configure it so that the needle of the tuning meter TM shows that it is in tune at this time. Tuning meter drive circuit/
The other output from the DA is given to a time constant circuit 2θ, where the alternating current component is completely removed. The signal from which the alternating current component has been removed is applied to the local oscillator //. Here, the local oscillator // is configured so that its oscillation frequency changes depending on the input signal. When the input signal is θ, the output from the frequency conversion circuit qθ is exactly 'Is!
; KHz, so the frequency adjustment of the local oscillator // is not performed. When the input signal is a positive voltage, the output from the frequency conversion circuit da θ is lower than 13sKHz, so the oscillation frequency of the local oscillator // is increased. ;3KH
z. When the input signal is a negative voltage, the output from the frequency conversion circuit da θ is 1lt3sKHz
Therefore, the oscillation frequency of the local oscillator // is controlled to be lowered to 3 KHz.

Next, the operation shown in FIG. 2 will be explained. However, since the explanation of the operation other than the main part of the present invention is the same as the operation explanation of FIG. 1, it will be briefly explained or omitted. The AM wave signal received from the antenna 2 is tuned and selected by the double variable capacitors VCL and VC2 in the AM receiver, and is inputted to the converter (CONV) forming the frequency conversion circuit DA θ via the transformer T1 and the amplifier. Ru. Its output is a ceramic filter Otsu and an intermediate frequency amplifier IFA/, IFA,
2, further passes through resistor R3 and capacitor C7, and is input to intermediate frequency amplifier/2 of the FM receiver. Intermediate frequency amplifier 7
．． The output of 2 is given as the first input of quadrature detector /3 and also as the input of quadrature limiter /j. The phase of the signal shaped into a square wave by the quadrature millimeter 7.5 is shifted by inductances L, L2 as phase shifters.

When the switch SW is open, it is for AM waves, and in this state, due to the inductance L and L2, tyssKH
The inductances 1 and L2 are selected so that the phase of the signal of frequency 2 changes exactly 7θ0. Depending on whether the intermediate frequency is higher or lower than 1s3KHz, the phase also changes to be larger or smaller than θ0. This phase-shifted signal is applied as a second input to quadrature detector/3. Further, the signal from the quadrature detector/3 is tuned by a tuning circuit, and the AM wave phase is tuned by an inductance L4. However, since the inductance 73 of the tuning coil for FM waves is small, the AM waves pass through without being affected and are output by the quadrature detector along with the output of the phase shifter/B.
T;i is given as the third input to device/3. The quadrature detector /3 compares and detects the output signal of the intermediate frequency amplifier 7.2, which outputs the original signal with no phase shift, and the signal with a phase shift caused by the phase shifter /6. . The detected signal is output to a tuning meter drive circuit/gu, where the signal is averaged and amplified. One of these signals is simply tuned and displayed on the tuning meter TM by the tuning meter circuit/g. On the other hand, the alternating current component is removed in the time constant circuit 2θ, and the variable capacitance diode VCD of the local oscillator // of the frequency conversion circuit Gθ is removed.
Enter. When this input signal is θ, the output from the frequency conversion circuit qθ is exactly 11! ;Since it is 5KHz, the current state should be maintained, so the capacitance of the variable capacitance diode VCD is not changed. When the input signal is a positive voltage, the frequency of the output from the frequency conversion circuit θ is 'l
Since it is lower than 5 sKHz, the oscillation frequency of the local oscillator // of the frequency conversion circuit θ must be made high. Here, the variable capacitance diode VCD is connected in parallel with the local oscillator // tuning capacitor, and the variable capacitance diode VCD is connected in parallel with the tuning capacitor of the local oscillator //.
Since the CD is configured to decrease in response to a positive voltage input signal, the capacitance of the tuning capacitor of the local oscillator // decreases, thereby increasing the oscillation frequency. When the input signal is a negative voltage, the frequency of the output from the frequency conversion circuit θ is '13
Since it is higher than 3 KHz, the oscillation frequency of the local oscillator // must be lowered.

Here, since the capacitance of the variable capacitance diode VCD is configured to increase in accordance with a negative input signal, in this case, the capacitance of the tuning capacitor of the local oscillator // increases, so that the oscillation frequency becomes lower. In this way, the frequency of the output signal from the frequency conversion circuit θ is automatically controlled to be exactly 3 SKHz.

Also, if you want to use it as an FM receiver, just close the switch SW. At this time, in the circuit diagrams of FIGS. 1 and 2, the circuit having the configuration in the upper half from the antenna/ to the terminal T2 is used. Since the circuit of the FM receiver is well known, a description thereof will be omitted for the sake of brevity. Further, the present invention is not limited to this, and a simple tuning display is not necessarily required, and in that case, the tuning meter circuit/g may be removed. Furthermore, although quadrature detection has been described as being used in common with the FM receiver, it may also be used exclusively for the AM receiver.

At that time, the switch, switch, and FM switch used for FM waves.
Circuit including wave tuning coil and meeting switch,
29, the selection element, and the preceding circuit from 2.2 are unnecessary.

Also, at this time, the tun/g meter circuit/g is not necessarily required and may be removed.

According to the present invention, quadrature detection can be applied to an AM receiver by virtue of the structure and operation described above, thereby stabilizing the frequency of the frequency conversion circuit of the AM receiver. If the frequency is stable, the frequency deviation from the tuned point will be reduced. or,
Using a tuning meter makes it easier to tune, which greatly contributes to the ease of use of the AM receiver. Furthermore, if it is used in common with an FM receiver, the quadrature detection circuit can be used in common with the AM receiver, and the cheating meter can also be used in common.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing one embodiment of the present invention;
The figure is a detailed circuit diagram showing one embodiment of the present invention. S;Mixed circuit//;Local oscillator/,! ; Intermediate frequency amplifier/3; Quadrature detector/ri; Nauni/gmeter drive circuit/, S; Quadrature detector/ri; Phase shifter/7; Tuning coil 7g; Tuning meter circuit βθ; ;Frequency conversion circuit

Claims (1)

[Scope of Claims] (1) An AM wave phase shifter is connected to the intermediate frequency amplifier circuit, which includes an intermediate frequency amplifier, a quadrature detector, and a quadrature limiter, to the quadrature limiter and the quadrature detector. an AM wave tuning coil is connected to input and output the quadrature detector to form an AM quadrature detection circuit, and the output from the frequency conversion circuit of the AM receiver is input to the intermediate frequency amplification circuit. The signal is detected by the AM quadrature detection circuit, and the detected signal is connected to be input to the local oscillator of the frequency conversion circuit of the AM receiver via the time constant circuit. . A frequency stabilization circuit for an AM receiver, wherein the frequency conversion circuit performs automatic frequency adjustment. (2) F consisting of an intermediate frequency amplifier, a quadrature detector, a quadrature limiter, a phase shifter, and a tuning coil
An FM receiver equipped with an M detection circuit is provided with an AM wave phaser via a switching circuit in the phase shifter of the FM detection circuit, and an AM wave tuning coil is provided in series with the tuning coil. configuring an AM dual-use FM detection circuit, inputting a signal from the frequency conversion circuit of the AM receiver to the intermediate frequency amplifier, switching the phase shifter to an AM wave phase shifter using the switching circuit, and The AM wave is quadrature-detected in the AM/FM detection circuit, and the detected signal is input to the local oscillator that constitutes the frequency conversion circuit of the AM receiver via the time constant circuit, and the frequency conversion circuit converts the frequency according to the input signal. AM characterized by automatic frequency adjustment
Receiver AM frequency stabilization circuit. ] 3) An AM wave phase shifter is added to an intermediate frequency amplifier circuit including an intermediate frequency amplifier, a quadrature detector, a quadrature limiter, a tuning meter drive circuit, and a tuning meter circuit. The AM quadrature detection circuit is configured by connecting input and output, and the output of the frequency conversion circuit of the AM receiver is input to the intermediate frequency amplifier, and the detected wave is detected by the AM quadrature detection circuit. The signal is passed through a tuning meter drive circuit, compared with a reference voltage in a tuning meter circuit having a tuning meter, and displayed on a tuning meter, and the detected signal is sent to an AM receiver via a time constant circuit. An AM receiver having a frequency stabilization circuit and a simple display circuit configured to be input to a local oscillator of the frequency conversion circuit, and wherein the frequency conversion circuit is automatically frequency controlled according to the input signal. . (4) FM equipped with an FMM detection circuit consisting of an intermediate frequency amplifier, a quadrature detector, a quadrature limiter, a phase shifter, and a tuning coil, a tuning meter drive circuit, and a tuning meter circuit having a tuning meter. In the receiver, an AM wave phase shifter is provided through a switching circuit to the phase shifter of the FM detection circuit, and an AM wave tuning coil is provided in series with the tuning coil to form an AM/FM detection circuit. The output from the frequency conversion circuit of the AM receiver is input to the intermediate frequency amplifier, and the
The AM wave is quadrature-detected by the M-combined FM detection circuit,
The detected signal is passed through the tuning meter drive circuit and compared with a reference voltage in the tuning meter circuit to be displayed in tune on the tuning meter, and the detected signal is sent to the AM receiver via a time constant circuit. An AM receiver having a frequency stabilization circuit and a simple display circuit, characterized in that the frequency conversion circuit is automatically frequency-controlled in accordance with the input signal to a local oscillator of the frequency conversion circuit.